COMPREHENSIVE

SELF – STUDY MATERIAL

FOR

NEET - BIOLOGY - XI

Content Page
Module 4 .............................................................................................................................. 2

(1) Photosynthesis in Higher Plants ............................................................................ 3

(2) Respiration in Plants ........................................................................................... 44
(3) Plant Growth and Development .......................................................................... 75
(4) Digestion and Absorption ................................................................................. 106
(5) Breathing and Exchange of Gases .................................................................... 161
COMPREHENSIVE
SELF - STUDY MATERIAL
FOR
NEET & AIIMS

BIOLOGY

Module - 4

n Photosynthesis in Higher Plants

o Respiration in Plants
p Plant Growth and Development
[ Digestion and Absorption
\ Breathing and Exchange of Gases

2
 CHAPTER
12
PHOTOSYNTHESIS IN
HIGHER PLANTS
“Will is nothing more than a particular case of the general doctrine of
association of ideas, and therefore a perfectly mechanical thing”.

“JOSEPH PRIESTLEY ( 1733-1804)”

INTRODUCTION

T
he process in which green parts of the manufacture or synthesize complex organic
food substances using carbon dioxide and water in the presence of sunlight and
release oxygen as a by-product. In this process, energy from the sun is converted
into chemical energy. It is endergonic, anabolic and oxido-reduction process.
Photosynthesis is important due to two reasons: it is the primary source of all food
on earth . It is also responsible for the release of oxygen into the atmosphere by
green plants.

A simple equation reperesening the process is:

6CO2 + 12 H2O 
o C6 H12 O6 + 6 H2O + 6O2

3
BIOLOGY FOR NEET & AIIMS

History of Photosynthesis
z Aristotle and Theophrastus (320 BC) :– Stated that plants absorb all food matter from soil (Humus theory).
z Van Helmont (1648) :– By weighing the Willow plant, concluded that plant take up their food mostly from soil water.
z J. Woodbard (1699) :– Besides water, soil also increases the weight of plants.
z Stephen Hales (1727) :– Recognised the importance of air (CO2) and light for photosynthesis (nourishment) in
plants. He is considered as discoverer of photosynthesis and "Father of plant physiology".
z J. Priestley (1772) :– He carried out very interesting experiment on Bell jar, Rat, Pudina & Candle. He came to
conclude that plants purify air (burning of candles) and gaseous exchange occurs during photosynthesis.

z Jan Ingenhousz (1779) :– He explained the importance of light and green colour and also suggested the O2
releases in the presence of light by green parts.
z Senebier (1782) :– Green plants absorb CO2 from atmosphere and when the concentration of CO2 increases the rate
of O2 evolution also increases.
z N. De–Saussure (1804) :– Clarified that released O2 is equal to the absorbed CO2. He realised the significance of
H2O in this process. De–Saussure stated that O2 comes from CO2 during photosynthesis. (Later on it was disproved
by Van Niel)
z Pallatier & Caventou (1818) :– They named green pigment as 'Chlorophyll' and isolated the chlorphyll with the
help of alcohol.
z Englemann (1888) :– Described action spectrum of photosynthesis with the help of Spirogyra/Cladophora and
aerobic bacteria experiment.
z Mayer (1845) :– Green plants convert solar energy into chemical (potential) energy in the form of organic sub-
stance. He gave law of conservation of energy. Formation of organic matter recognised by Mayer.
z Liebig (1845) :– Organic matter are derived from CO2 and H2O, during the process of photosynthesis.
z J. V. Sachs (1862) :– Recognised the relation among photosynthesis, chloroplast and starch. First visible product
of photosynthesis is starch. Founder of modern concept of photosynthesis. Some people consider Sachs as father
of plant physiology. Three cardinal point concept wal also given by him.
z Willstater, Stall Fisher :– Chemistry, structure and properties of Chl–a, and nobel prize winner.
z F. F. Blackman (1905) :– Dark reaction associated with light reaction in photosynthesis and law of limiting
factors.
z Warburg (1920) :– Intermittent or flash light experiment on Chlorella and proved that dark reaction exists in
photosynthesis.
z Emerson and Arnold (1932) :– Concept of two pigment system (photosystem) in light reaction. Red drop &
Emerson enhancement effect.
z Van Niel :– O2 releases from water and O2 of glucose comes from CO2.

6CO2 + 12H2S   o C6H12O6 + 12S + 6H2O

Bacteria

z Robert Hill & Bendal (1937) :– Detailed study of light reaction in isolated chloroplast of stellaria.
Photolysis of H2O is the chief role of chloroplast and evolution of O2 only in the presence of suitable e– acceptor,
from water in photosynthesis. (Hill–reaction)
z Ruben, Hassid & Kamen (1941) :– Used O18 to experimentally show that O2 in photosynthesis released from water.

4
 PHOTOSYNTHESIS IN HIGHER PLANTS

Light
6CO162 + 12H2O18   o C6H12O166 + 6H2O + 6O218
Chlorophyll
Arnon :– ATP formation in presence of light (photophosphorylation) and cyclic and non–cyclic electron transport
system.
z M. Calvin and Benson (1954) :– Biochemical cyclic pathway of dark reaction and recognised PGA is Ist stable
product in dark reaction. (It is formed from unstable 6C Keto Acid)
z C3 – cycle or Calvin – Benson – cycle discovered.
z Chromatography and Radioisotopy (C14) techniques used in Chlorella and Scenedesmus algae. (Nobel
Prize 1960).
z Arnon, Allen & Whitley (1954) :– CO2 fixation demonstrated in isolated chloroplast by C14O2 isotope.
z Hatch & Slack (1967) :– C4 pathway dicarboxylic acid cycle (DCA cycle) in sugarcane and maize. Ist stable product
is oxaloacetic acid (OAA 4C).
z Moll :– CO2 is essential for photosynthesis by half leaf experiment.
z Govindji & Rabinowitch :– Studied ultrastructure of pigment system in detail.
z Kok & Clayton :– Chl–a, P–700 discovered

O2
z Bussingault :– Photosynthetic Quotient (PQ) or Assimillatory coefficient = =1
CO2
z Park & Biggins :– Photosynthetic units as Quantasome in chloroplast.
z Huber Michel and Dissenhofer :– Crystalization & X–ray crystallography of reaction center in Rhodobacter.
(Nobel–1988)

INTRODUCTION
"Photosynthesis is a photo–biochemical process (anabolic & endergonic) in which organic compounds
(carbohydrates) are synthesised from the inorganic raw material (H2O & CO2) in presence of light & pigments. O2
is evolved as a by product".
Light energy is conserved into chemical energy by photosynthesis.

6CO2 + 12H2O   o C H O + 6O - + 6H O
Pigment
light 6 12 6 2 2

90% of total photosynthesis is carried out by aquatic plants (85% algae) & 10% by land plants.
First true & oxygenic photosynthesis started in cyanobacteria. (BGA)
In the Cuscuta & fungi photosynthesis is absent. Euglena is photosynthetic organism & is link between animal &
plants.
Roots of Tinospora & Trapa are assimilatory or photosynthetic.
Absorption spectrum of photosynthesis is blue & red light. (maximum absorbed part of spectrum)
Action spectrum of photosynthesis is red & blue light. (most effective in reaction)
Rate of photosynthesis is higher in red wavelength of light, but highest in white light (Full spectrum), than
monochromatic light.

IMPORTANT SCIENTIFIC CONTRIBUTION :

According to Van Niel, oxygen comes from water in photosynthesis.
6CO2 + 12H2S o C6H12O6 + 12S + 6H2O

5
BIOLOGY FOR NEET & AIIMS

z Ruben, Hassid and Kamen (1941) :– Used O18 to show experimentally that O2 in photosynthesis comes from
water.

Light
6CO162 + 12H2O18   o C6H12O166 + 6H2O + 6O218
Chlorophyll
Existence of two steps in Photosynthesis
z Blackman discovered dark reaction (By study of Q10 value or temperature coefficient).
z Calvin and Benson gave cyclic pathway for this, thus dark reaction is called as Calvin cycle OR C3–cycle.
Q 10 (Tempereture coefficient) for light reaction is one, while Q 10 for dark reaction is between
2-3. (By Vont Hoff).
Q10 means the doubling of rate of reaction, which involves chemicals, on 10°C rise in temperature in it's optimum
range.
Experimental evidences for Blackman findings were given by Warburg 1920. He carried out intermittent light
experiment on Chlorella. (by using flash light)
The product of photosynthesis has been found greater in intermittent light (i.e., light given after intervals of dark
periods) than in continuous light.
This is due to the fact that light reactions are faster than the dark reaction.
In continuous light product of light reactions (ATP and NADPH2) are not consumed at the same rate as in subsequent
dark reaction. Thus dark reaction is rate limiting step of photosynthesis.
Photosynthesis – (i) Light reactn/Hill reactn (ii) Dark reaction/Blackman reactn.
z Hill Reaction – Experiment on isolated chloroplast (Stelaria plant) study of light reaction, which is called as Hill
Reaction.
O2 gas liberated from photolysis of H2O, only in the presence of suitable e– acceptor. (DCPIP (Dichlorophenol
Indophenol- a dye), ferricyanide, NADP+ – Hill reagents)

1
O + NADP o NADPH2
2 2
z Emerson & Arnold – worked on Chlorella and gave the concept of two photosystem or two pigment systems.
When they gave only monochromatic light, longer than 680 nm wavelength, then quantum yield is suddenly
dropped down, this event is called as red drop.
When Emerson gave light, shorter and greater than 680 nm (combined light) then photosynthetic, activity increases,
this is called as Emerson effect or enhancement effect.
(i) 680 nm- r PS – I (cyclic process) red drop appears.
(ii) 680 nm¯ + 680- nm (Mixed light) rBoth cyclic & non cyclic operates. (Emerson effect)
Quantum requirement –
The number of light Quanta or photons required for the evolution of 1 mol. of O2 in photosynthesis = 8
Quantum Yield –
The number of oxygen molecule evolved by one quantum of light in photosynthesis is called as Quantum yield.
Emerson calculated that the quantum requirement is 8. Hence the quantum yield is 0.125 or 12.5%)
Arnon's experiment (Chlorella) –
light
Discovered cyclic and non–cyclic photophosphorylation (ADP + iP  o ATP.).
Chl.

E.T.S. in photosynthesis was proposed by Arnon.

6
 PHOTOSYNTHESIS IN HIGHER PLANTS
CHLOROPLASTAND PIGMENTS

ds-Circular DNA

Outer membrane
Inner membrane
Quantasomes
(230 pig. mol.) Stroma or matrix

Granum thylakoid Granum

888
70s Ribosomes
Fret channel or Rubisco (Most abundant enz.)
stroma thylakoid

Chloroplast

Photosynthetic pigments

Non-Appressed part
(Exposed surface)
Appressed part
(Associated thylakoids)

Stroma thylakoids
Grana thylakoids

Many pigment present in photosynthetic cells. PSU (Photosynthetic units) presents on thylakoid membranes, are made
up of 230-400 molecules of various pigments, called Quantasomes by Park & Biggins.
The PS II is located in the appressed region of granal thylakoids and PS I in non appressed region of grana and stroma
thylakoids.
PS I located - on both granum & intergranum (Stroma thylakoid), (P-700, 680 nm-, Cyclic ETS).
PS II located - on only granum, (P-680, 680 nm¯, non cyclic ETS).
Chlorophyll – a C55H72O5N4Mg o CH3 grp. at IIIrd C of IInd pyrrole ring.
Chlorophyll – b C55H70O6N4Mg o CHO group at IIIrd C of IInd pyrrole.
Chlorophylls are magnesium porphyrin compounds. Porphyrin ring consists of four–pyrrole rings (Tetrapyrrole).
Chlorophyll molecule has a Mg–porphyrin head and alcoholic phytol tail. Head is hydrophilic and phytol tail is lipophilic
(hydrophobic).
Phytol tail is alcoholic with one double bond. Phytol part embeded in lipid layer.
Chl–a and carotenes are universal pigment, which are found in all O2 liberating cells.
Chlorophylls are soluble only in organic solvents like ketons, ethers etc.
z Stroma lamellae/stroma thylakoids lack PS II and enzyme NADP reductase .
z In paper chromatography/chromatogram –
Chlorophyll 'a' appears bright or blue-green.
Chlorophyll 'b' as — yellow green/grass green.
Xanthophyll as — yellow
Carotenoids as — Yellow to yellow - orange

7
BIOLOGY FOR NEET & AIIMS

Chlorophyll synthesis :

Succinyl CoA + GlycineoProtochlorophyll (Protochlorophyllide)   o Chlorophyll.

Light
2H

Light for chlorophyll synthesis is required only in angiosperms, (exception Nelumbium and Citrus)

MECHANISM OF PHOTOSYNTHESIS

CHLOROPHYLL STRUCTURE x* –CH3 in Chlorophyll A, –CHO in Chlorophyll 'b'

8
 PHOTOSYNTHESIS IN HIGHER PLANTS

DISTRIBUTION & LIGHT ABSORPTION OF PIGMENTS

Pigments Formula Distribution Absorption (mm)

Chlorophylls o
Chl. – a C55H72O5N4Mg All green plants. 435, 670, 680
(Several forms)
Chl. – b C55H70O6N4Mg All green plants (except BGA 453, 480, 650
Red, brown and diatoms algae)
Chl. – c C35H32O5N4Mg Brown algae and diatoms 645
Chl. – d C54H70O6N4Mg Red Algae (Rhodophyceae) 740
Chl. – e Xanthophyta (Tribonema &
Vaucheria Zoospores)
Bacterio Chl. – a C55H74O6N4Mg Purple & green bacteria 800, 850, 890
Bacterio Chl. – b C55H74O6N4Mg Purple bacteria 1017
(Rhodopseudomonas)
Bacterioviridin Green bacteria (Chlorobium) 750, 760
(Chlorobium
chlorophyll)
Carotenoids o
Carotenes o
a–carotene C40H56 Red, green algae & 450, 470
All green plants
b–carotene C40H56 In all green plants 450, 480
g–carotene Green bacteria
X a nt h o p h y l l s  C a r o te n o ls o
Luteole C40H56O2 Red, green algae, all plants 425, 475
Violaxanthin C40H56O2 Green leaves 425, 450, 475
Fucoxanthin C40H56O3 In Brown algae
Phycobilins o
Phycocyanin BGA (mainly), red algae 618
Phycoerythrin Red algae (mainly), BGA 490, 576
Allophycocyanin

400 – 700 nm light is used in photosynthesis also known as PAR (Photosynthetic active radiation)

9
BIOLOGY FOR NEET & AIIMS

[A] Light reaction/Hill reaction/Photochemical reaction/Generation of assimilatory powers (NADPH2 + ATPs)/

photophase.
Antenna or accessory pigments receive radient energy and transfer it among themselves. This transfer of energy is
known as resonance transfer. Then antenna molecules excited and transfer their energy to the chlorophyll 'a' molecules
of reaction centre.
It is known as inductive resonance. Finally chl. 'a' of leaf center molecules converts the light energy into electrical
energy by bringing about electric charge separation.
Light Light
Photosystem (LHC)

hQ hQ

Antenna

Resonance transfer
Inductive resonance
Reaction centre

Conversion of light into electrical energy. Accessory

pigment molecules absorb light and funnel it to the

(I) Cyclic ETS and Photophosphorylation

In cyclic ETS, only PS–I (LHC–I) works, which consists of Chl–'a' Fd
670, Chl–a–683, Chl–'a'–695, carotenoids, some molecules of chl–
'b' & reaction centre–Chl–'a'–700/P–700. e–
ADP
Cyclic ETS OR PS–I is activated by wavelength of light greater
than 680 nm.
ATP
It occurs at grana thylakoids and stroma thylakoids. e– Cyto b6
During Cyclic ETS the electron ejected from reaction centre of ADP + ip e–
PS-I, returns back to its reaction centre.
In cyclic ETS, no oxygen evolution occurs, because photolysis of ATP Cyto f
FRS e–
water is absent.
Cyclic
NADPH2 (reducing power) is not formed in cyclic process. e–
ETS
Plastocyanin (PC) is Cu–containing blue coloured protein in cyclic e–
ETS.
PC
According to modern researches, first e– acceptor is FRS
e–
(Ferredoxin Reducing Substance), which is a Fe-S containing
P–700
Protein. Earlier fd (Ferredoxin) was considerd as first e– acceptor.
Pigment S. –I
Phosphorylation takes place at two places, thus two ATP LHC–I
generates in each cyclic ETS.

Quantasome

Light/Solar Energy 680 nmn

CYCLIC PHOTOPHOSPHORYLATION

10
 PHOTOSYNTHESIS IN HIGHER PLANTS
Stroma 2H+
-
e- e e
-
Fe- S/FRS Fd Cyt b6 PQ

P700 Cyt f
e-

ADP+Pi
PC
+
H
H+
+
H+
H
+
H +
+
H
+
H H
+
3H
+
H
+
H PMF
LUMEN CF0 CF1

ATP
THYLAKOID MEMBRANE

CYCLIC - PHOTOPHOSPHORYLATION

(II) Z-Scheme/Non-cyclic ETS and Photophosphorylation-

Both PS–I and PS–II involved in non cyclic ETS.
PS–II (P–680) consists of Chl–a–660, Chl–a–673, Chl–a–680, Chl–a–690, Chl–b, or Chl–c or Chl–d, carotenoids &
phycobilins. Phycobilins present only in PS II
It occurs at grana thylakoids only.
The e– ejected from PS–II never back to chl–a–680 (reaction centre) & finally gained by NADP. Thus gap of e– in PS–II
is filled by photolysis of water as a result, oxygen evolution occurs in Z–scheme.
Each turn of non cyclic ETS produces 1 ATP and 2NADPH2 (4 mol. of water is photolysed and 1 O2 released)

NADP-Reductase
+
+
H NADP NADPH2
2H
e–
e
–
e –
Fd
Q PQ FeS e
–

e–
Pheophytin Cyt f Fe S/FRS
e– –
e
PC
ADP+Pi

–
e
P680 P700

e- +
H H
+ + H
4 H2O O2
H+
H+ H+ H+ 3H+
H + +
H H + H+
LUMEN
CF0 CF1
ATP

THYLAKOID MEMBRANE

NON-CYCLIC - PHOTOPHOSPHORYLATION

11
BIOLOGY FOR NEET & AIIMS

Non cyclic Photophosphorylation/Z-scheme

2NADP
4e– 4e– 4H+
Fd fd–NADP-reductase

2NADPH2
PQ
e– 4H+
e–
Non-cyclic ETS
FRS e– Cyto b6
Z–Scheme
Q
e–
ADP + pi
Pheo
e– Cyto f ATP

e– 4e–

Pigment S.–I
P-700 PC
1O2
LHC–I e– 2H 2 O

Mn++
4H2O Cl– Ca++
4 H+ + 4 (OH–)
Pigment S–II
Quantasome (O.E.C.) +0.8E°
–
4e P- 680
Photolysis
LHC–II
Reaction center

AAAAA Accessory/
Light/Solar Energy
680 Nmn
4 H+ AAAA A AAA antenna
A pigments

680 Nmp
Light Photon/
Excitation

12 NADPH2 + 18 ATP are required as assimilatory power to produce one molecule of Glucose in dark reaction, thus 6
turns of Z–scheme are necessary for the production of one glucose molecule by calvin cycle.
Additional 12 ATP come from 6 turn of cyclic ETS. (over all 54 ATP equivalents)
Primary e– acceptor in non–cyclic reaction is PQ or plastoquinone. Recently pheophytin (structure like chl. a without Mg)
is considered as Ist e– acceptor in Z–scheme.
Plastocyanin (PC) is link between PS–I and PS–II in non cyclic ETS. (Some scientists–cyto-f)
Final e– acceptor in Z–scheme is NADP+ (Hill reagent)
During Non-Cyclic ETS energy flow takes place from PS II to PS I.

12
 PHOTOSYNTHESIS IN HIGHER PLANTS
Photophosphorylation :
Chemiosmotic theory : Proposed by Peter Mitchell. During ETC of photosynthesis concentration of H+ gradually
increases in thylakoid lumen. During cyclic photphosphrylation PQ leads to shifting of H+ from stroma to thylakoid
lumen. On the other hand during non cyclic photophoshorylation there are three causes of differential H+ ion concentration.
(i) Photolysis of H2O produces H+
(ii) PQ shifting of H+ ion from stroma to lumen.
(iii) NADP redutase mediated utilisation of H+ from stroma.
This differential H+ ion concentration leads to development of proton gradient and electrical potential across thylakoid
memberane. Both proton gradient and electrical potential collectively called proton motive force (PMF)
PMF do not allow stay of H+ ions in lumen so H+ start to move towards stroma through CF0 particle selectively. The
passage of 3H+ ions leads to activation of ATP synthase and forms ATP from ADP and Pi.
Some physiologist beleive that synthesis of one ATP is required passage of 2H+ ions.

[B] Dark Reaction/Blackman Reaction/Calvin cycle/C3–Cycle/Biochemical phase/Carbon assimilation/photosynthetic

carbon reduction cycle (PCR-Cycle)/Reductive pentose phosphates pathway –
Blackman reaction is called as dark reaction, because no direct light is required for this. Calvin presented these reactions
in cyclic manner & thus called as Calvin cycle.
Ist stable compound of Calvin cycle is 3C–PGA (Phosphoglyceric acid) thus Calvin cycle is called as C3–cycle. (First
compound is unstable, 6C keto acid)
Study by Calvin was on Chlorella & Scenedesmus. During his experiment he used chromatography & radioisotopy
(C14) techniques for detecting reactions of C3–cycle.
Rubisco (Ribulose bis-phosphate carboxylase-oxygenase) is main enzyme in C3–cycle, which is present in stroma & it
makes 16% protein of chloroplast. Rubisco is most abundant enzyme.
CO2–acceptor in Calvin cycle is RuBp. This carboxylation reaction is catalysed by Rubisco.
C3, C4, C5, C6 and C7 monosaccharides are intermediates of calvin Cycle.
C3=Phosphoglyceraldehyde and DHAP, C4=Erythrose, C5=Xylulose, Ribose, C7 = Sedoheptulose.
The largest monosaccharide in livings are 7C–Sedoheptulose–P (Ketose)
Warburg effect – Inhibitory effect of high conc. of O2 on photosynthesis is called as Warburg effect (It is due to
Photorespiration).
6 turns of Calvin cycle are required for the formation
- of one glucose.
Biochemical reactions of Calvin cycle are as follows :
Carboxylation o
Rubisco
  o 6C unstable comp.o12,3–PGA (3C)
(1) 6, RuBp (RuDp) + 6,CO2 (HCO3–) (Carboxydismutase )

Glycolytic reversal o

(2) 12 Mol. 3 – PGA + 12ATP  

Triokinase
o 12, 1,3–BiPGA
(3 C )

(3) 12, 1,3–BiPGA 12, 3–PGAL (Triose phosphate) + 12H3PO4

(4) 5 Molecules of PGAL isomerise in to DHAP (Dihydroxy acetone phosphate).

Aldolase
3, PGAL + 3 mol. DHAP  o 3, Fructose-1,6-Biphosphate
9C (3C × 3) (9C) (3C × 3) (18C) (6C × 3)
Isomerase
[1 mol. fructose   o C 6 H1 2 O 6 Glucose oSucrose/Starch]

13
BIOLOGY FOR NEET & AIIMS
Regeneration of ribulose 1,5 biphosphate o
Transketolase
(5) 2, fructose–P + 2, PGAL   o 2 Mol, Erythrose–P + 2 Mol. Xylulose–P
(12C) (6C) (8C) (10C)

Aldolase
(6) 2, Erythrose–P + 2, DHAP  o 2, Sedoheptulose-1,7-BiP
(8C) (6C) (14C)
Trans Ketolase
(7) 2, Sedoheptulose–P + 2 PGAL  
o 2, Xylulose–P + 2, Ribose–P
(14C) (6C) (10C) (10C)
Epim erase
(8) 2 + 2, Xylulose–P  
o 4, Ribulose–5P
(20C)
Isomerase
(9) 2 , Ribose–5P  o 2 Ribulose–5P
(10C)
Kinase
(10) 6, Ribulose–5P + 6ATP  
o 6, Ribulose-1, 5-BiP (CO2 acceptor) + 6 ADP

Calvin Cycle/ C3 –Cycle / Reductive Pentose Phosphate Pathway, in chloroplast stroma

12 pi
Dehydrogenase

1,3-bis - PGA 12NADPH2 12NADP

(12 Mol.) (12 Mol.)
3-Phosphoglyceraldehyde
12 ADP Mol.
e 2 5 3 2
las
Triokinase

Calvin Cycle to Isomerase

ske
C - Cycle
an 2 DHAP 3
Tr
3

12 ATP Stroma
Aldolase

3-PGA (12 mol.) Ribose 5–P

Sedoheptulose 7P
2mol. (2Mol.)
o
sc
Corboxydis

bi
Ru
mutase

Sedoheptulose bis
(2mol.) Fructose bis-P
6CO2 (3 mol.)
e

RubP-1,5 (6 mol.)
ras
me

Aldolase ip
Iso

6 ADP Fructose 6P
Kinase

Erythrose 4P
(3mole)
2(Mol.)
6 ATP

Ribulose-5P (6 Mol.) Glucose

xylulose 5,P (2mol.)

Transketolase
Epim
erase Xylulose -5P
2 mol.

14
 PHOTOSYNTHESIS IN HIGHER PLANTS
DIVERSITY IN DARK REACTIONS

CO2 concentrating mechanism/Co-operative photosynthesis/Dicarboxylic acid cycle (DCA cycle) /C4 cycle/Hatch &
Slack Pathway
z Kortschak and Hartt first observed that 4C, OAA (Oxaloacetic Acid) is formed during dark reaction in sugarcane
leaves.
First stable product of this reaction is OAA. Which is 4C, DCA (Dicarboxylic Acid), thus Hatch & Slack pathway is
called as C4 cycle or DCA cycle.
z Hatch & Slack Australia (1967). Studied in detail and proposed pathway for dark reactions in sugarcane & maize
leaves.
C4–cycle occurs in 1500 species of 19 families of angiosperm, but most of the plants are monocots, which belong to
Graminae & Cyperaceae (Sugarcane, Maize, Sorghum, Oat, Chloris, Sedges, Bajra, Panicum, Alloteropsis etc.)
Rice species.
Dicots with C4–cycle are Euphorbia sps., Amaranthus, Chenopodium, Boerhavia, Atriplex rosea, Portulaca, Tribulus.
Atriplex hastata & A. patula are temperatespecies. which are C3–plants.
Wheat and barley (monocot) are C3 species. rice species devlopes as C4 plants by plant breeding scientists.
z Kranz (Wreath) anatomy – Present in leaves of C4 plants.
(i) Green bundle sheath cells (BS cells) present around the vascular
bundles.
(ii) Dimorphic chloroplasts present in leaf cells. Chloroplast of B.S.
cells or Kranz cells are larger and without grana. Mesophyll
chloroplast are small and with grana.
Rubisco present in BS cells, while PEPCase in mesophyll cells.
In the C4–Plant, C3–cycle occurs in bundle sheath cells, while
C4–cycle occurs in mesophylls.
Thus operation of Hatch and Slack pathway require cooperation
of both photosynthetic cell i.e. mesophyll cells and BS cells.
Primary CO2 acceptor in C4 mesophyll is PEP (Phosphoenol

Pyruvate). (3C–compound), while RuBp in bundle sheath cells.

Photosynthetically C4 plants are more efficient as there is no Warburg effect or photorespiration, Because at the site of
Rubisco (BS cells) no O2 is release & (mesophyll cells pumps more CO2 for C3 cycle).
C4–plants found in tropical habitats and adapted themselves, with high temperature, low water availability and intense
light.
If concentration of O2 increases artificially, then photorespiration may be started in C4 plants.
First carboxylation in C4–cycle occurs by PEPCase in mesophyll cytoplsam, while second carboxylation or final CO2
fixation by C3 cycle occurs in bundle sheath cells.
12 NADPH2 & 30 ATP needed for production of 1 Hexose (Glucose) in C4–plants.
Pyruvate phosphate dikinase (PPDK) (ATP o AMP) is a temperature sensitive enzyme of C4 and CAM plants due to
this C4 plants better photosynthesizes at high temperature.
C4 plant evolve by Anatomical, physiological & genetical modified.

15
BIOLOGY FOR NEET & AIIMS

C4 – Cycle/ Hatch & Slack Cycle

MESOPHYLL CELLS BUNDLE SHEATH CELLS
Oxaloacetate > aspartate Sugars C 6 H 12 O 6
(4C) C4,C5,C6,C7
NADPH2
Atm.
CO2 C4- Cycle
NADP RuBp
PEP C3- Cycle
(3C)
ip + AMP PGA
Pyruvate phosphate Malic Acid CO2
dikinase (PPDK) Pyruvic acid Malic Acid
ATP

NADPH2 NADP
– Granal chloroplast. – Agranal chloroplast.
– Syn. of NADPH2 & ATP, evolutions of O2 – Absence of Z-scheme or PS-II, no evolution of O2
– Absence of Calvin cycle & Enzyme Rubisco – NADPH2, from mesophyll chloroplast, C3 cycle occur

KEY PO INTS
Special features of C4 plants :
(1) The productivity (fertility) in C4 plants, does not increase when CO2 concentration is increases. because :
(a) Mesophyll cells pump more CO2 for Calvin cycle.
(b) Thus concentration of CO2 is high around the site of Rubisco in C4 plants, thus little or no chance of
photorespiration.
(2) C4 plants posses low CO2 compensation points. (8-10 ppm.
(3) C4 plants are more efficient plants at present CO2 concentration.
(4) Present level of atmospheric CO2 is generally not limiting factor for C4 plants.

CAM–Plants / Crassulacean acid metabolism / Dark CO2 fixation / Dark acidification

Oleary and Rouhani discovered CAM–process in members of Crassulaceae family. Succulent xerophytie plants.
Eg. are .– Kalanchoe, Bryophyllum, Sedum, Kleinia, Opuntia, Crassula,Agave,Aloe, Euphorbiasps, Pineapple, Welwitschia
(Gymnosperm) etc.
CAM plants exhibits ecophysiological adaptation with xeric habits.
In CAM plants 30 ATP and 12 NADPH2 are required as assimilatory power for 1 glucose synthesis.
In CAM plants stomata are of scotoactive type, so initial CO2 fixation is found in night but light reactions operates at day
time. Final CO2 fixation (C3 cycle) occurs in day time. PEPcase induces carboxylation reaction in night.
Primary acceptor of CO2 is PEP (Phosphoenol pyruvate) and oxaloacetic acid is the first product of carboxylation
reaction.
PEP carboxylase & Rubisco present in mesophyll cells. (No Kranz–anatomy)

16
 PHOTOSYNTHESIS IN HIGHER PLANTS

Night (Stomata open) Day (Stomata closed)

Photosynthetic carbon oxidation cycle/C2 Cycle/Photorespiration/Glycolate–Metabolism

1. Term was given by ‘Krotkov’

2. First of all Krotkov et. al indicated that more CO2 evolves during day time in C3 plants.
3. The light dependent uptake of O2 & release of CO2 in C3 photosynthetic cell is called photo–respiration.
4. Decker & Tio discovered photorespiration and clarified that C2–cycle or glycolate pathway operates during day
time in C3–plants & Rubisco acts as oxygenase at higher concentration of O2 and low CO2 concentration in the C3
– green cells.
5. Photorespiration is not linked with ATP generation (in place ATP are consumed) as ordinary dark respiration, thus
it is harmful or wasteful process linked with C3 cycle.
6. It occurs in chloroplast, peroxisomes & mitochondria (three cell organalle reaction).
RuBP + CO2   o 2PGA
Rubisco

RuBP  Oxygenase
RuBP + O2   n
o 1 PGA + 1 Phosphoglycolate.
Low CO2, High O 2 con , High temp.

(3C) (2C)
7. During photorespiration, 75 percent of the carbon lost by the
oxygenation of RUBP is recovered. Because two molecules
of glycine (2C + 2C = 4C) form one molecule of serine (3C).
During this one carbon releases in form of CO 2 in
mitochondria thus 25 percent carbon is lost.
8. H2O2 (Peroxisome) and NH3 (Mitochondria) produced in
photorespiration.
9. Glycine (Peroxisome) and serine (mitochondria) are also
formed in photorespiration.
10. This serine molecule changes into PGA via different
reactions of C2 cycle.
11. Scientists are trying to change C3 spe. into C4 sps.
12. It is assumed that in C3 plants, if photorespiration does not
occur, then increases O 2 conc. which may oxidise Photorespiration/Photosynthetic
(Photooxidation or Solarization) the different protoplasmic
parts of photosynthetic cell at high light intensity.

17
BIOLOGY FOR NEET & AIIMS
FACTORS AFFECTING PHOTOSYNTHESIS
(1) CO2 (0.03%/314 ppm)
An increase in CO2 concn. upto 1% rate of photosynthesis is increased. Higher CO2 concentration. is toxic to plant
& also closes stomata.
C4–Plants can photosynthesize at low CO2 concn (upto 10 ppm). “CO2 concn at which CO2 fixation in photosynthesis
is equal to volume of CO2 released in respiration is "CO2compensation point”, when plant saturated with full light.
CO2 compensation point for C4 plants is 8-10 ppm, while for C3 plants it is 40-100 ppm.
(2) Light
(a) Light Quality or wavelength oMaxm photosynthesis takes place in red light than in Blue light. But rate of
photosynthesis is highest in white light. Minimum in green light.
(b) Light Intensity – Rate of photosynthesis is greater in intense light than diffused light. But at higher light intensity
photooxidation (solarization) occurs and photosynthetic apparatus may get destroyed.
P/R (Photosynthesis : Respiration) Ratio at mid day is 10 : 1; but can reach upto 20 : 1 ratio. At the time of evening
& morning rate of photosynthesis equals to respiration, this situation called as light compensation point.
Intensity of light, at which rate of photosynthesis, becomes equal (or compensate) with the rate of respiration in
plants is known as light compensation point. (Net photosynthesis or net primary productivity at this
point is zero.)
Plants which are adapted to grow in high intensity of light is called heliophytes & plants which are adapted to grow
in shade is sciophytes.
(c) Duration of Light – On the basis of effect of light on plants may be LDP & SDP.
Product of photosynthesis is greater in intermittent light than continuous light – Warburg.
(3) Temperature
Optimum temp. for photosynthesis is 20–35°C
At high temp. rate of photosynthesis decreases due to denaturation of enzymes.
Conifers & lichens can perform photosynthesis at –35°C, while thermal algae Oscillatoria at
70–80°C..
Generally different habitat plants show, different response to photosynthesis on a given temperature.

C4 plants (High light)

Use of CO2

C3 plants (High light)

0 10 50 100 200 300 360 400 450 500

S.P. S.P.
CO2 in ppm (S.P. = Saturation point)

18
 PHOTOSYNTHESIS IN HIGHER PLANTS
(4) Water –
Less availability of water reduces the rate of photosynthesis (stomata get closed)
(5) O2 –
High O2 concn. reduces photosynthesis due to photorespiration.
(6) Leaf –
Various leaf factors like leaf age and leaf orientation effect the rate of photosynthesis.
In young & mature leaves photosynthesis is more than old (senescent) leaves.
(7) Inhibitors –
DCMU (Diuron/Dichlorophenyl Dimethyl Urea)CMU (Monuron), PAN,Atrazine, Simazime, Bromocil, Isocil– inhibit
the photosynthesis by blocking PS–II. They stop electron flow between P-680 & PQ.
In cyclic ETS diquat, paraquat (Viologen dyes) inhibit electron flow between P-700 & Fd.
All these chemicals are used as herbicides, which mostly block ETS.
(8) Chlorophyll–
The amount of CO2 in grams absorbed by 1 gm. of chlorophyll in 1 hour is called as photosynthetic number or
assimilatory number (Willstatter & Stoll).
(9) Product –
Rate of photosynthesis decreases, when sugar accumulates in mesophyll cells.

(10) Minerals :- Mg and Nitrogen are essential for structure of chlorophyll and enzymes. Thus reduction in N2 and Mg
supply to plants effects adversely the rate of photosynthesis.
Rubisco alone accounts for more than half of total leaf nitrogen.
Generally all essential element affect the rate of photosynthesis.
concept of three cardinal points (Von Sachs) :- The effect of the various external factors on the rate of biological
processes were centered around the attempts to establish minimum, optimum and maximum values known as cardinal
points.
Law of minimum (Liebig) :- According to it, when a process is governed by a number of separate factors, then the rate
of process is controlled by that factor present in minimum amount.
Law of limiting factors – (Blackman) :- It is the modification of Law of minimum by Liebig. "When a process is
conditioned to its rapidity by a number of factors, then rate of process is limited by the pace of the slowest factor" (CO 2,
light, chlorophyll, water, temp.)
CO2 becoming limiting in clear sky, but light limiting in cloudy days.
Atmospheric CO2 is not limiting factor for C4 plants & submerged hydrophytes.

BACTERIAL PHOTOSYNTHESIS
Certain bacteria are capable for photosynthesis Eg :- Chlorobium (Green Sulphur), Chromatium (Purple Sulphur),
Rhodospirillum, Rhodopseudomonas (Purple non sulphur).
Cyclic photophosphorylation is an important method in bacterial photosynthesis.
Absorption of Infra red spectrum takes place during bacterial photosynthesis thus no red drop.
Pigment system of bacteria denoted by – B–890 or 870
Evolution of O2 is not related to bacterial photosynthesis, because water is not electron donor and PS II is absent.
Only one ATP is produced in each turn of cyclic photophosphorylation, in bacteria.
z Olson 1970 gave a non cyclic scheme in bacterial photosynthesis.
IR light
z 6CO2 + 12 H2S 
Pigments in chromotophores
o C6H12O6 + 6H2O + 12S.
z Bacteria has only one pigment system, PS I.

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BIOLOGY FOR NEET & AIIMS

Cyclic ETS

Non Cyclic ETS

ADP+ip

HETEROTROPHIC PLANTS NUTRITION

Heterotrophs – Heterorophic plants are of following types –
[A] Parasites –
(1) Total stem parasites – Cuscuta or dodar (totally depend)
(2) Partial stem parasites – Loranthus, Viscum (depend on host for H2O & minerals)
(3) Total root parasites – Members of Rafflesiaceae, Balanophoraceae & Orobanchaceae (totally depends
on host)
(4) Partial root parasites – Santalum album & Striga.
[B] Insectivorous plants –
These are green plants but of insectivorous habits which develop, due to deficiency of nitrogen, because they grow on
N2–deficient places (Swampy places).
(1) Nepenthes or pitcher plant – Found in north eastern parts of
India (Endangerd).
(2) Utricularia or bladderwort – hydrophyte and pollution
Indicator.
(3) Drosera or Sundew
(4) Pinguicula or butterwort.
(5) Dionaea or venus fly trap.
(6) Saracenia or pitcher plant with symbiotic
bacteria.
(7) Aldrovanda (Water flea trap)
Parasitic plants-Orobanche
(8) Genlisea (Lobster pot trap) (A) A flowering plant growing on the root of bringal
[C] Saprophytes – (B) Viscum-Plant attached to the host stem
Non green plants, which depend on dead organic matter –
Monotrapa (Indian Pipe) Neottia (Birds eye nest)
(Dischidia is a pitcher plant but not insectivorous).

20
 PHOTOSYNTHESIS IN HIGHER PLANTS

Insectivorous plant - Nepenthes (Pitcher

plant)

Insectivorous plant - Utricularia - (Bladderwort) (A) Complete plant

(B) One bladder (C) Part of leaf with several bladders

Saprophytic Plants (A) Neottia (Birds nest

Insectivorous plant - Drosera (A) Complete plant (b) One leaf

Insectivorous plant Dionaea : Different stages in the

Insectivorous plant - Dionaea (Venus fly trap)

21
BIOLOGY FOR NEET & AIIMS

KEY PO INTS
"Photosynthesis is a photo–biochemical process, in which organic compounds are synthesized from the inorganic
raw materials (H2O & CO2) in presence of light energy and pigments (chl.) gas–oxygen evolved as byproduct."
First true & oxygenic photosynthesis started in cyanobacteria (BGA).
Roots of Tinospora and Trapa are photosynthetic.
Modern view about photosynthesis is conversion of light/radiant energy into biochemical or potential energy.
Absorption spectrum for photosynthesis in visible light is blue & red wavelength.
Action spectrum is red & blue light in which rate of photosynthesis is higher.
(But rate of photosynthesis is highest in white light than monochromatic light).
Function of accessory pigment carotene is –
1. Converts elementary or nasent oxygen to molecular/gaseous O2.
O + O (elementary oxygen) + Carotene o Epoxide complex   Deepoxidase
o O2 + Carotene.
2. Protects photooxidation (photodamaging) of pigment system.
3. Precursor of vit.–A.
4. Oxidation to form ABA hormone in guard cells.
Chlorophyll pigment soluble in organic solvents like acetone, ether etc. (anthocyanin is non photosynthetic water
soluble pigment, which present in vacuole).
Chloroplast in bundle sheath of Burmuda grass is also granal type.
Photolysis of water occurs at +0.8 E°
In cyanobacteria (BGA), photosynthesis occurs on chlorosomes or lamellisome or carboxysome.
PS–I is strong reductant as PS–I has good ability to reduce NADP+, while PS-II is a strong oxidant, because it has
extreme power of oxidation & photolysis of water molecule.
264 gm. CO2 and 216 gm. water produced, 108 gm. water, 192 gm. O2 and 180 gm. glucose.
Annual production of photosynthesis is 170 billion tones of carbohydrate.
Wilmott’s bubbler apparatus proves that oxygen is evolved during photosynthesis.
Cytochromes are Iron – porphyrin protein discoverd by MacMunn (termed by Keilin).
Pigments except chlorophyll, presents in Quantasomes are called as accessory or antenna pigment of light harvesting
complex (LHC).
Electroosmotic theory - By Spanner and Jones for translocation of sugars.
Chollet and Ogren (1975) - Recognised 3 categories of C4 plants.
(i) Maize and Sugarcane type : In this category malate transported to bundle sheath cells and its decarboxylation
gives CO2 for C3 cycle.
(ii) Panicum and Chloris type :- In this category malate transported into bundle sheath cells, but this changes into
oxaloacetate, which gives CO2 for C3 cycle.
(iii) Atriplex type :- In this category the aspartate transported into bundle sheath cells, where it changes into
malate, which provides CO2 for C3 cycle.
Mg++ required for Rubisco & PEPcase
Ist formed unstable 6-C compound during Calvin cycle is carboxy ketoribitol biphosphate.
Significance of photosynthesis –
Photosynthesis is vital process for life on planet earth as it is the only process, that links the physical and biological
world by conversation of solar energy into organic matter, which make bulk of the dry matter of any organism.
Presence of O2 in the atmosphere is also an outcome of photosynthesis. This oxygen is helpful to living organisms in
two ways :
1. Oxidative break down of organic food matter (respiration)
2. Making ozone (O3), in outer layer of atmosphere, which helps in stopping the highly destructive U.V. rays.
Efficiency of photosynthesis –
One quantum of red light = 47.6 Kcal (One red photon or quantum = 47.6 Kcal)
One glucose = 686 Kcal. (1 CH2O = 114.3 Kcal)
8 Quantum × 47.6 Kcal = 381 Kcal energy require for fixation of one CO2

22
 PHOTOSYNTHESIS IN HIGHER PLANTS

114.3
Thus × 100 = 30%
381
DIFFERENCES
Photorespiration Dark Respiration
(i) Occurs in chloroplast, peroxisome (i) Occurs in cytoplasm,
and mitochondria. mitochondria.
(ii) Wasteful process. (ii) Useful process.
(iii) NH3 & CO2, H2O2 are produced (iii) CO2, H2O & ATP generated.
(iv) In green cells of C3–plants. (iv) In all living cells.
(v) Occurs during day time only. (v) All time

Cyclic photophosphorylation Non–cyclic photophosphorylation

(1) Only PS–I involved in cyclic process. (1) Both PS–II & PS–I works in non–
cyclic process.
(2) The electron expelled from chl–700 is (2) The electron expelled from reaction center
cycled back. is not cycled back. Its loss is
compensated by electron from H2O.
(3) Phosphorylation at two place. (3) Phosphorylation at one site.
(4) Photolysis of water and evolution (4) Photolysis of water and evolution of
of O2 does not take place. O2 takes place.
(5) NADP is not reduced.
+
(5) NADP+ is reduced to NADPH.

C3–pathway C4–pathway CAM- pathway

(1) Ist stable compound (1) Ist stable compound (1) First formed compound
is 3–C PGA is 4C O.A.A. is O.A.A.
(2) 18 ATP & 12 (2) 30 ATP & 12 (2) 30 ATP and 12
NADPH2 used for 1 NADPH2 used for 1 NADPH2 used for
glucose formation glucose formation Production of 1 glucose
(3) Kranz anatomy absent (3) Kranz anatomy present (3) Kranz anatomy absent
(4) Presence of (4) Absence of (4) photorespiration
photorespiration photorespiration may present
(5) One type of (5) Two type of (5) Two type of
carboxylase enzyme, carboxylase enzyme carboxylase enzyme
Rubisco only Rubisco & PEPcase Rubisco & PEPcase
(6) CO2 acceptor - RUBP (6) Primary CO2 acceptor - (6) Primary CO2 acceptor -
PEP & RUBP is PEP & RUBP
is secondary acceptor is secondary acceptor
(7) Exhibits high CO2 Low CO2 compensation (7) High CO2 compensation
compensation point point (8-10 PPM) point (40–100 PPM)
(40–100 PPM)
(8) Transpiration ratio (TR) (8) TR - 200-300 (8) TR - 50-100
500-1000

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BIOLOGY FOR NEET & AIIMS

o It is an physicochemical process .
o Half leaf experiment showed that CO2 is required for photosynthesis .
o Joseph Priestley -Proposed the Concept of gaseous exchange by plants with the help of bell jar experiment.
o Jan Ingenhousz -Showed the importance of Sunlight and Green colour in photosynthesis by using a similar setup
as the one used by Priestley.
o Julius von Sachs -Provided evidence for production of glucose and its storage as starch.
o T.W. Engelmann -Proposed action spectrum of photosynthesis i.e. Red -blue. Experiment on green filamentous alga
Cladophora.
o Cornelius Van Niel -Suggested that O2 evolved during photosynthesis comes from H2O, not from CO2 . Experiments
on purple and green sulphur bacteria.

o There is a clear division of labour (distribution of work) within the chloroplast i.e. membrane system (grana thyla-
koids and stroma lamellae) is responsible for light reaction and stroma for dark reaction.
o In the chromatogram, chlorophyll 'a' shows bright or blue green colour, chloropyll 'b' shows yellow green colour,
xanthophyll - yellow & carotenes - yellow - orange.
o Absorption spectrum of photosynthesis - blue red.
o Action spectrum of photosynthesis - red blue.

o Accessory pigments (chlorophylls other than reaction centre, xanthophylls and carotenoids) absorb light and
transfer the energy to chlorophyll a (reaction centre) thus enhance the efficiency and range of absorption for
photosynthesis. oThese pigments also protect chlorophyll a from photo-oxiation.
o One molecule of chlorophyll a (reaction centre) + Antennae molecules (LHC = Light Harvesting Complex) = Photo-
system.
PS-I - Reaction centre (Chi 'a' 700 or P700)
PS-II - Reaction centre (Chi 'a' 680 or P 680)
P = Peak of absorption

o Noncyclic photophosphorylation is called the Z scheme (due to characteristic shape on a redox potential scale)
Water splitting (Photolysis of water) occurs on the inner side (lumen side) of the thylakoid membrane . Products of
noncyclic photophosphorylation - ATP, NADPH + H+ and O2 .
o Product of cyclic photophosphorylation - ATP .
o Products of light reaction which are utilised in dark reaction - ATP & NADPH + H+ .
o In grana thylakoid - both noncyclic & cyclic process occurs .
o In stroma thylakoid - only cyclic process occurs because stroma thylakoid / lamellae lack PS-II as well as NADP
reductase enzyme.
o Primary electron acceptor from PS-I : - Fe-S protein (FRS)
o Primary electron acceptor from PS-II : - Pheophytin .
o The chemiosmotic hypothesis has been put forward by Peter Mitchell to explain the mechanism of ATP synthesis
in chloroplast (Photophosphorylation) and Mitochondria (oxidative phosphorylation). According to this hypoth-
esis, ATP synthesis is linked to development of a proton gradient across a membrane (Thylakoid membrane in
chloroplast and Inner membrane in mitochondria).

24
 PHOTOSYNTHESIS IN HIGHER PLANTS
o Creation of proton gradient in chloroplast - Low pH in thylakoid lumen (More H+) . Chemiosmosis requires - a
membrane, a proton pump, a proton gradient and ATPase
(Two parts - F0 / transmembrane channel and F1).
o Melvin Calvin used 14C radioisotope to workout the complete pathway of Hexose (glucose or fructose) formation
from CO2 i.e. Calvin Cycle.
o In C3 pathway first product of biosynthetic phase or dark reaction - PGA (3C)
o In C4 pathway first product of biosynthetic phase - OM (4C)
o In C3 plants primary acceptor of CO2 = Ribulose bisphasphate (RuBP) - 5 Carbon Ketose sugar
o In C4 and CAM primary acceptor of CO2 = Phosphoenolpyruvate (PEP) - 3 Carbons .
o Calvin Cycle occurs in all photosynthetic plants (C3, C4 and CAM plants)
o Calvin Cycle can be described under three stages - Carboxylation, reduction and regeneration . Carboxylation is the
most crucial step of the Calvin Cycle .
o Reduction step involve utilisation of 2 ATP and 2 NADPH + H+ for 1 CO2 molecule. Regeneration Step require 1 ATP.
Hence for each CO2' 2NADPH2 and 3 ATP are required in Calvin Cycle.
o To make one molecule of hexose (glucose or fructose), 6 turns of the calvin cycle are required. (18 ATP and 12
NADPH2)
o C4 plants are adapted to dry tropical regions. These plants have Kranz anatomy in their leaves . Bundle sheath cells
or Kranz cells are characterised by having a large number of chloroplasts, thick walls impervious to gaseous
exchange and no intercellular spaces.
o In C4 plants, PEPcase is found in mesophyll cells and RubisCO in bundle sheath cells .
o In C4 plants, CO2 transported in the form of malic acid (4C) or aspartic acid (4C) from measophyll cell to bundle
sheath cell.

o RubisCO can bind to both CO2 and O2. In C3 plants some O2 does bind to RubisCO (Photorespiration) . In photores-
piration 1, RuBP (SC)
1 PGA (3C) (Phosphoglycerate) + 1, Phosphoglycolate (2C).
o Photorespiration is wasteful process. (Neither synthesis of sugar nor of ATP and NADPH 2) .
o In C4 plants, photorespiration does not occur because they increase the concentration of CO2 in bundle sheath cells
(site of RuBisCO enzyme) by pumping it in the form of C4 acid. (malic acid or aspartic acid).
o Law of limiting factor - proposed by Blackman .
o CO2 is the major limiting factor for photosynthesis .
o CO2 saturation for C4 plants - at about 360 μeL-1 /PPM concentration of CO2 .
o CO2 saturation for C3 plants - at beyond 450 μ.eL-1 /PPM concentration of CO2 .
o Current availability of CO2 levels is limiting to the C3 plants not for C4 plants .
o C3 plants respond to higher CO2 concentration by showing increase rate of photosynthesis (experiments on green
house crops such as tomatoes and bell pepper.)
o For plants in shade or in dense forest, light may be the limiting factor .
o The dark reactions being enzymatic, are temperature controlled, light reactions are less temperature sensitive.

25
BIOLOGY FOR NEET & AIIMS

SOLVED EXAMPLE
Ex.1 The law of limiting factor for photosynthesis was Ex.6 Manganese and Chlorine is required in
enunciated by
(A) Blackman (B) Hill (A) Nucleic acid synthesis
(C) Ruben (D) Kalmen (B) Plant cell wall formation
Sol. (A) : Blackman propounded the law of limiting (C) Photolysis of water during photosynthesis
factors. He also proposed the occurrence of the dark (D) Chlorophyll synthesis
phase in photosynthesis.
Sol. (C) : The splitting of water during photosynthesis
Ex.2 Emerson's enhancement effect and Red drop have is called photolysis. Mn and Cl plays important role
been instrumental in the discovery of in photosynthesis specially light reaction of
(A) Photophosphorylation and non-cyclic electron photosynthesis in splitting of water.
transport
(B) Two photosystems operating simultaneously Ex.7 Stroma in the chloroplasts of higher plant contains
(C) Photophosphorylation and cyclic electron
transport (A) Light-independent reaction enzymes
(D) Oxidative phosphorylation (B) Light-dependent reaction enzymes
Sol. (B) (C) Ribosomes
(D) Chlorophyll
Ex.3 Isotopes popularly known to have been used in the
study of photosynthesis are Sol. (A)
Or
Which of the following isotope of carbon was used Ex.8 Consider the following statements with respect to
by Calvin to trace the path of carbon in photosynthesis
photosynthesis
A. The first carbon dioxide acceptor in C4 cycle is
(A) C14 and O18 (B) C11 and C32
PGA
(C) C and N
16 15
(D) P32 and C15
Sol. (A) : C isotope used for knowing carbon path and
14 B. In C 3 plants, the first stable product of
O 18 used for verified that source of O 2 in photosynthesis during dark reaction is RuBP
photosynthesis is H2O, not CO2 C. Cyclic photophosphorylation results in the
Ex.4 The first event in photosynthesis is formation of ATP
(A) Synthesis of ATP D. Oxygen which is liberated during photosynthesis
(B) Photoexcitation of chlorophyll and ejection of comes from water
electron
Of the above statements
(C) Photolysis of water
(D) Release of oxygen (A) A and B alone are correct
Sol. (B) : When photon of light energy falls on (B) A and C alone are correct
chlorophyll molecule, one of the electrons pair from (C) C and D alone are correct
ground or single state passes into higher energy (D) B and C alone are correct
level called excited single state.
(E) B and D alone are correct
Ex.5 The synthesis of ATP in photosynthesis and
respiration is essentially an oxidation-reduction Sol. (C)
process involving removal of energy from
Ex.9 Excitation of chlorophyll due to light is a
Or
Which one is always transferred in redox reaction (A) Photooxidation reaction
(A) Oxygen (B) Phytochrome (B) Endergonic reaction
(C) Cytochrome (D) Electrons (C) Thermochemical reaction
Sol. (D) (D) Photochemical reaction
Sol. (A)

26
 PHOTOSYNTHESIS IN HIGHER PLANT
Ex.10 Which one of the following is not true about the Ex.15 The Calvin cycle proceeds in three stages
light reactions of photosynthesis 1. Reductions, during which carbohydrate is formed
at the expense of the photochemically made
(A) Light energy provides energy for the photolysis
ATP and NADPH.
of water through excitation of the reaction
2. Regeneration, during which the carbon dioxide
centre of PS II acceptor ribulose - 1, 5-biphosphate is formed
(B) The flow of electrons from water to NADP in 3. Carboxylation, during which carbon dioxide
non-cyclic electron transport produces one ATP combines with ribulose-1, 5-biphosphate
(C) Reactions of the two photosystems are needed Identify the correct sequence
for the reduction of NADP (A) 3 - 1 - 2 (B) 3 - 2
(D) P680 and P700 are the reaction centres of PS I and (C) 1 -2 - 3 (D) 2 - 1 - 3
PS II respectively (E) 1 - 3 - 2
(E) NADPH is not produced in cyclic transport in Sol. (A)
light reactions Ex.16 PGA as the first CO2 fixation product was discovered
Sol. (D) in photosynthesis of
(A) Alga (B) Bryophyte
Ex.11 Which one of the following statements about the (C) Gymnosperm (D) Angiosperm
events of noncyclic photophosphorylation is not Sol. (A)
correct
(A) Only one photosystem participates Ex.17 The enzyme responsible for primary carboxylation
in C3 plants is
(B) ATP and NADPH are produced
(A) Hexokinase
(C) Photolysis of water takes place
(B) Succinic dehydrogenase
(D) O2 is released
(C) Pyruvate carboxylase
Sol. (A) (D) RuBP carboxylase oxygenase
(E) PEP carboxylase
Ex.12 Pigment systme - I conducts
Sol. (D)
(A) Cyclic photophosphorylation
(B) Non-cyclic photophosphorylation Ex.18 In a condensed schematic represntation of dark
reaction of photosynthesis given below, steps are
(C) Both (A) and (B) indicated by alphabets. Select the option where the
(D) None of the above alphabets are correctly identified.
Sol. (A)

Ex.13 The reaction centre for PS-I and PS-II are

(A) P700 and P680 respectively
(B) P680 and P700 respectively
(C) P580 and P700 respectively
(D) P700 and P580 respectively
Sol. (A) : The reaction centres of PS-I and PS-II can be
denoted as P700+ and P680+ respectively. Positively (A) A = CO 2 fixation, B = Reduction,
charged reaction centres act as attractants for C = Phosphorylation, D = Regeneration
electrons (B) A = Regeneration, B = CO 2 fixation,
C = Reduction, D = Phosphorylation
Ex.14 Photo-oxidation of water results in the formation of (C) A = CO 2 fixation, B = Phosphorylation,
(A) H+, O2 and ATP (B) H+, O2, e– and ATP C = Reduction, D = Regeneration
(D) A = CO 2 fixation, B = Phosphorylation,
(C) H+, O2 and e– (D) None of these
C = Regeneration, D = Reduction
Sol. (C) Sol. (C)

27
BIOLOGY FOR NEET & AIIMS
Ex.19 If bundlesheath cells of the C4 plants are infected a Ex.24 ............... are CAM plant
by an organism, which utilize CO2 efficiently then
(A) Maize, papaya (B) Pineapple, agave
which process will affected very first
(C) Onion, mango (D) Pea, sugarcane
(A) PGAL o RUBP
(B) PGAL + PGA o Glucose Sol. (B)
(C) PGA o PGAL
Ex.25 Which one of the following is a CAM plant
(D) RUBP o PGA
(A) Maize (B) Kalanchoe
Sol. (D) : Dark reaction takes place in bundle sheath
(beacuse RuBISCO present in stroma of chloroplast (C) Sugarcane (D) Jowar
of bundle sheath). Sol. (B)

Ex.20 During Calvin cycle the total number of CO2, ATP Ex.26 Photorespiration takes place is
and NADPH molecules utilized and glucose, ADP
and NADP molecules generated is (A) Chloroplast, mitochondria
(A) 31 (B) 36 (B) Mitochondria, peroxysome
(C) 61 (D) 67 (C) Chloroplasts, peroxysome, mitochondria
Sol. (D) (D) Chloroplasts, cytoplasm, mitochondria
Sol. (C)
Ex.21 Which of the following statements with regard to
photosynthesis is/are correct
Ex.27 Bacteria that uses chemical energy to fix CO2 are
A. In C4 plants, the primary CO2 acceptor is PEP
known as
B. In the photosynthetic process PS II absorbs
energy at or just below 680 nm (A) Chemoautotroph (B) Photoautotroph
C. The pigment that is present in the pigment system (C) Heterotroph (D) None of these
I is P683 Sol. (A)
(A) B and C only (B) A only
(C) C only (D) A and B only Ex.28 Which of the following inhibits O2 release in light
phase
(E) A and C only
Sol. (D) (A) PMA (B) Zeatin
(C) DCMU (D) None of these
Ex.22 The C4 plants are photosynthetically more efficient
than C3 plants because
(A) The CO2 efflux is not prevented Sol. (C) : During light reaction of photosynthesis O2
release as a result of photolysis of water. DCMU is
(B) They have more chloroplasts
a photosynthetic inhibitor which inactivates the PS
(C) The CO2 compensation point is more
- II and inhibit the Hill reaction.
(D) CO2 generated during photorespiration is trapped
and recycled through PEP carboxylase Ex.29 The most effective wavelength of visible light in
Sol. (B) photosynthesis is in the region of
Ex.23 In C4 plants, the bundle sheath cells (A) Violet (B) Green
(A) Have thin walls of facilitate the gaseous exchange (C) Yellow (D) Red
(B) Have large intercellular spaces Sol. (D) : Blue and red regions of the light specturm are
(C) Are rich in PEP carboxylase the most effective in photosynthesis. Blue
(D) Have a high density of chloroplasts and rich in wavelengths of light carry more energy while red
RuBisCo wavelengths have lesser energy. Therefore, the most
Sol. (D) efficient wavelengths of light effective in
photosynthesis are those of light.

28
 PHOTOSYNTHESIS IN HIGHER PLANT
Ex.30 RuBisCo is an enzyme that acts both as a (C) Point D represents the optimum point and gives
carboxylase and oxygenase. Why do you think the light intensity at which the
RuBisCo carries out more carboxylation in C4 plants? maximum photosynthesis is recorded. The rate of
Sol. The enzyme RuBisCo is absent from the mesophyll photosynthesis remains constant after this point,
cells of C4 plants. It is present in the bundle-sheath even though the intensity of light
cells surrounding the vascular bundles. In C4 plants,
the Calvin cycle occurs in the bundle-sheath cells.
The primary CO2 acceptor in the mesophyll cells is
phosphoenol pyruvate – a three-carbon compound.
It is converted into the four-carbon compound
oxaloacetic acid (OAA). OAA is further converted
into malic acid. Malic acid is transported to the
bundle-sheath cells, where it undergoes
decarboxylation and CO2 fixation occurs by the
Calvin cycle. This prevents the enzyme RuBisCo
from acting as an oxygenase.

Ex.31 Figure shows the effect of light on the rate of

photosynthesis. Based on the graph, answer the
following questions:
(A) At which point/s (A, B or C) in the curve is
light a limiting factor?
(B) What could be the limiting factor/s in region
A?
(C) What do C and D represent on the curve?

Sol. (A) Generally, light is not a limiting factor. It becomes

a limiting factor for plants growing in shade or under
tree canopies. In the given graph, light is a limiting
factor at the point where photosynthesis is the
minimum. The least value for photosynthesis is in
region A. Hence, light is a limiting factor in this
region.
(B) Light is a limiting factor in region A. Water,
temperature, and the concentration of carbon
dioxide could also be limiting factors in this region.

29
 PHOTOSYNTHESIS IN HIGHER PLANT

Exercise PART - 1 PREVIOUS YEAR (NEET/AIPMT)

(D) Phosphoglyceraldehyde
1. Which element is located at the centre of the por-
phyrin ring in chlorophyll : -[CBSE AIPMT 2003] 8. Photosynthesis in C4 plants is relatively lesslimited
(A) Manganese (B) Calcium by atmospheric CO2 levels because :
(C) Magnesium (D) Potassium [CBSE AIPMT 2005]
(A) Effective pumping of CO2 into bundle sheath
2. Which one of the following is wrong in relation to cells
photorespiration : - [CBSE AIPMT 2003]
(B) RuBisCO in C4 -plants has higher affinity for
(A) It is a characteristic of C3 - plants
CO2
(B) It occurs in chloroplasts
(C) Four carbon acids are the primary initial CO2
(C) It occurs in daytime only fixation products
(D) It is a characteristic of C4 -plants (D) The primary fixation of CO2 is mediated via PEP
carboxylase
3. In sugarcane plant 14CO2 is fixed in malic acid, in
which the enzyme that fixes CO2 is :-
9. As compared to a C3-plant, how many additional
[CBSE AIPMT 2003]
molecules of ATP are needed for net production of
(A) Fructose phosphatase one molecule of hexose sugar by C4-plants -
(B) Ribulose biphosphate carboxylase [CBSE AIPMT 2005]
(C) Phosphoenol pyruvic acid carboxylase (A) 2 (B) 6
(D) Ribulose phosphate kinase (C) 12 (D) Zero

4. Which fractions of the visible spectrum of solar ra- 10. During photorespiration the oxygen consuming re-
diations are primarily absorbed by carotenoids of action (s) occur in- [CBSE AIPMT 2006]
the higher plants : - [CBSE AIPMT 2003] (A) Stroma of chloroplasts and peroxisomes
(A) Violet and blue (B) Blue and green (B) Grana of chloroplasts and peroxisomes
(C) Green and red (D) Red and violet
(C) Stroma of chloroplasts
5. Chlorophyll in chloroplasts is located in :- (D) Stroma of chloroplasts and mitochondria
[CBSE AIPMT 2004]
(A) Outer membrane (B) Inner membrane 11. In photosystem-I, the first electron acceptor is-
(C) Thylakoids (D) Stroma [CBSE AIPMT 2006]
(A) Cytochrome
6. Plants adapted to low light intensity have :-
(B) Plastocyanin
[CBSE AIPMT 2004]
(C) An iron sulphur protein
(A) Larger photosynthetic unit size than the sun
plants (D) Ferredoxin
(B) Higher rate of CO2 fixation than the sun plants
12. The first acceptor of electrons from an excited chlo-
(C) More extended root system rophyll molecule of photosystem II is:
(D) Leaves modified to spines [CBSE AIPMT 2007]
7. In C3 -plants, the first stable product of photosyn- (A) Cytochrome
thesis during the dark reaction is :- (B) Iron-sulphur protein
[CBSE AIPMT 2004] (C) Ferredoxin.
(A) Malic acid (D) Quinone
(B) Oxaloacetic acid
(C) 3-phosphoglyceric acid

30
BIOLOGY FOR NEET & AIIMS
13. In the leaves of C4 plants, malic acid formation dur- 20. Of the total incident solar radiation the proportion
ing CO2 fixation occurs in the cells of: of PAR is [CBSE AIPMT 2011]
[CBSE AIPMT 2007] (A) About 60% (B) Less than 50%
(C) More than 80% (D) About 70%
(A) Mesophyll (B) Bundle Sheath
(C) Phloem (D) Epidermis 21. CAM helps the plants in [CBSE AIPMT 2011]
14. Carbohydrates are commonly found as starch in (A) Secondary growth (B) Disease resistance
plant storage organs. Which of the following five (C) Reproduction (D) Conserv-
(1-5) properties of starch make it useful as a storage ing water
material? [CBSE AIPMT 2008]
22. The correct sequence of cell organelles during pho-
A. Easily translocated torespiration is [CBSE AIPMT 2012]
B. Chemically non-reactive (A) Chloroplast, - Golgiboidies - mitochondria
C. Easily digested by animals (B) Chloroplast, Rough Endoplasmic reticulum-
D. Osmotically inactive Dictyosomes
E. Synthesized during photosynthesis (C) Chloroplast, mitochondria, peroxisome
(A) B and C (B) (B) and (D) (D) Chloroplast, - vacuole - peroxisome
(C) A, C and E (D) A and E
23. A process that makes important difference between
15. Cyclic photophosphorylation results in the forma- C3 and C4 plants is [CBSE AIPMT 2012]
tion of : [CBSE AIPMT 2009] (A) Transpiration (B) Glycolysis
(A) NADPH (B) ATP and NADPH (C) Photosynthesis (D) Photorespiration
(C) ATP, NADPH and O2 (D) ATP
24. Anoxygenic photosynthesis is characteristic of
16. Oxygenic photosynthesis occurs in : [CBSE AIPMT 2014]
[CBSE AIPMT 2009] (A) Rhodospirillum (B) Spirogyra
(A) Chromatium (B) Oscillatoria (C) Chlamydomonas (D) Ulva
(C) Rhodospirillum (D) Chlorobium
25. In photosynthesis, the light-independent reactions
17. Stroma in the chloroplast of higher plant contains : take place at : [CBSE AIPMT 2015]
[CBSE AIPMT 2009] (A) Thylakoid lumen (B) Photosystem - I
(A) Light-independent reaction enzymes (C) Photosystem-II (D) Stromal matrix
(B) Light-dependent reaction enzymes
26. The process which makes major difference between
(C) Ribosomes C3 and C4 plants is [NEET 2016]
(D) Chlorophyll (A) glycolysis (B) Calvin cycle
(C) photorespiration (D) respiration
18. C4 plants are more efficient in photosynthesis than
C3 plants due to ? [CBSE AIPMT 2010] 27. The oxygen evolved during photosynthesis comes
(A) Higher leaf area from water molecules. Which one of the following
(B) Presence of large number of chloroplasts in the pairs of elements involved in this reaction ?
leaf cells [NEET 2016]
(C) Presence of thin cuticle (A) Manganese and chlorine
(D) Lower rate of photorespiration (B) Manganese and potassium
(C) Magnesium amd molybdenum
19. PGA as the first CO2 fixation product was discov- (D) Magnesium and chlorine
ered in photosynthesis of ?[CBSE AIPMT 2010]
(A) Bryophyte (B) Gymnosperm 28. In a chloroplast the highest number of protons are
(C) Angiosperm (D) Algae found in [NEET 2016]
(A) Lumen of thylakoids
(B) Inter membrane space
(C) Antennae complex

31
 PHOTOSYNTHESIS IN HIGHER PLANT
(D) Stroma 32. Phosphonol pyruvate (PEP) is the primary CO2 ac-
ceptor in:
29. Emerson’s enhancement effect and Red drop have
been instrumental in the discovery of [NEET 2016] (A) C3 - plants (B) C4 - plants
(A) Two photosystems operating simultaneously (C) C2 - plants (D) C3 and C4 -plants
(B) Photophosphorylation and cyclic electron trans- 33. Oxygen is not produced during photosynthesis by
port (A) Cycas (B) Nostoc
(C) Oxidative phosphorylation (C) Green sulphur bacteria(D) Chara
(D) Photophosphorylation and non-cyclic electron
transport 34. Stomatal movement is not affected by
30. A plant in your garden avoids photorespiratory [NEET 2018]
losses, has improved water use efficiency, shows (A) O2 concentration (B) Light
high rates of photosynthesis at high temperatures (C) Temperature (D) CO2 concentration
and has improved efficiency of nitrogen utilization.
In which of the following physiological groups 35. Stomata in grass leaf are [NEET 2018]
would you assign this plant? [NEET 2016] (A) Rectangular (B) Kidney shaped
(A) C4 (B) CAM (C) Dumb-bell shaped (D) Barrel shaped
(C) Nitrogen fixer (D) C3
36. Which of the following is not a product of light
31. With reference to factors affecting the rate of pho- reaction of photosynthesis? [NEET 2018]
tosynthesis, which of the following statements is (A) NADPH (B) NADH
not correct? (C) ATP (D) Oxygen
(A) Light saturation for CO2 fixation occurs at 10%
of full sunlight
(B) Increasing atmospheric CO2 concentration upto
0.05% can enhance CO2 - fixation rate
(C) C3 plants responds to higher temperatures with
enhanced photosynthesis while C4 -plants have
much lower temperature optimum
(D) Tomato is a greenhouse crop which can be
grown in CO2 enriched atmosphere for higher
yield

32
BIOLOGY FOR NEET & AIIMS

Exercise PART - 2 PREVIOUS YEAR (AIIMS)

9. Photorespiration shows formatio of [2012]

1. Photorespiration in C3 plants starts from [2003] (A) sugar but not ATP
(A) phosphoglycerate (B) phosphoglycolate (B) ATP but not sugar
(C) glycerate (D) glycine. (C) both ATP and sugar
2. Hill reaction occurs in [2003] (D) neither ATP nor sugar
(A) high altitude plants
10. [2012]
(B) total darkness A
(C) absence of water B
C ---
(D) presence of ferricyanide e acceptor
ADP + Pi NADPH
3. What is PAR range ? [2007] Light Electron ATP

(A) 200 nm - 800 nm (B) 400 nm - 700 nm transport NADP

system
(C) 350 nm - 550 nm (D) 600 nm - 100 nm
D
4. Which of the following is the characteristic of PS-I?
LHC
[2009] H2O 2e + 2H+ + [O]
(A) It is active only upto 680 nm of light. Which of the following is correctly labelled for the
(B) The reaction centre of PS-I is P680. given figure ?
(C) PS-I is reduced by the electrons released in pho- (A) A : PS II ; B : PS I ; C : e– acceptor; D : LHC
tolysis of water. (B) A : LHC; B : e– acceptor; C : PS I; D : PS II
(D) PS-I is involved in non-cyclic photophos- (C) A : PS I ; B : PS II ; C : e– acceptor; D : LHC
phorylation.
(D) A : e– acceptor; B : LHC; C : PS II; D : PS I
5. Cyclic photophosphorylation involves [2010]
(A) PS I (B) PS II
11. Kranz anatomy is usually associated with [2012]
(C) PS I and PS II (D) P 680.
(A) C3 plants
6. The first stable product of Calvin cycle is [2010] (B) C4 plants
(A) 3-phosphoglycerate (C) CAM plants
(B) 1, 3 biphosphoglycerate (D) C3 – C4 intermediate plants.
(C) glyceraldehyde - 3 phosphat
12. C4 plants have better productivity because [2013]
(D) ribulose - 5 - phosphate. (A) C4 plants absorb more light
7. PS-II occurs only in [2011] (B) C4 plants absord more CO2
(A) stroma (B) granal thylakoids (C) C4 plants does not carry photorespiration
(C) stromal lamella (D) matrix (D) C4 plants have more amount of RuBisCO.

13. The first carbon dioxide fixation product of C4 plants

8. Which of the following statements is correct ?
is
[2011] [2015]
(A)Photorespiration is useful process. (A) oxaloacetic acid
(B) C4 plants are more efficient than C3 plants. (B) ribulose biphosphate
(C) C3 plants are more efficient than C4 plants. (C) phosphoenol pyruvate
(D) Photorespiration is absent in C3 plants but (D) phosphoglyceric acid.
present in C4 plants.

33
 PHOTOSYNTHESIS IN HIGHER PLANT
14. Carbon dioxide is necessary for photosynthesis. The 17. Assertion : Photomodulation of flowering is a phy-
chemical used to remove this gas most effectively tochrome - regulated process. [2004]
from entering a control apparatus is [2015] Reason : Active form of phytochrome (Pfr) directly
(A) calcium oxide induces floral induction in shoot buds.
(B) distilled water 18. Assertion : Photomodulation of flowering is a phy-
(C) potassium hydroxide solution tochrome - regulated process. [2004]
(D) sodium carbonate. Reason : Active form of phytochrome (Pfr) directly
induces floral induction in shoot buds.
15. Photosynthesis in C4 plants is relatively less limited
19. Assertion : Cyclic pathway of photosynthesis first
by atmospheric CO2 levels because [2016]
appeared in some eubacterial species. [2004]
(A) there is effective pumping of CO2 into bundle Reason : Oxygen started accumulating in the atmo-
sheath cells sphere after the non-cyclic pathway of photosyn-
(B) RuBisCO in C4 plants has higher affinity for CO2 thesis evolved.
(C) six carbon acids are the primary initial CO2 fixa-
tion products 20. Assertion : C4 photosynthetic pathway is more effi-
cient than the C3 pathway. [2005]
(D) the primary fixation of CO2 is mediated via PEP
Reason : Photorespiration is suppressed in C4
carboxylase.
plants.
16. The chemiosmotic coupling hypothesis of oxida-
21. Assertion : the atmospheric concentration of CO2
tive phosphorylation proposes that adenosine triph- at which photosynthesis just compensates for res-
osphate (ATP) is formed because [2016] piration is referred to as CO2 compensation point.
(A) a proton gradient forms across the inner mito- [2005]
chondrial membrane
Reason : The CO2 compensation point is reached
(B) there is a change in the permeability of the inner when the amount of CO2 uptake is less than that
mitochondrial membrane towards adenosine generated through respiration because the level of
diphos phate (ADP) CO2 in the atmosphere is more than that required for
(C) high energy bonds are formed in mitochondrial achieving CO2 compensation point.
proteins
22. Assertion : When the ambient temperature is high
(D) ADP is pumped out of the matrix into the and soil contains excess of water, the plants tend to
intermembrane space. lose water in the form of droplets from lenticels.
[2006]
ASSERTION AND REASON Reason : Root pressure regulates the rate of loss of
Statement based question : - water form lenticels.
Each of the questions given below consist of
23. Assertion : Under conditions of high light intensity
Assertion and Reason. Use the following Key
and limited CO2 supply, photorespiration has auseful
to choose the appropriate answer.
role in protecting the plants from photo-oxidative
(A) If both Assertion and Reason are correct, damage. [2006]
and Reason is the correct explanation of Reason : If enough CO2 is not available to utilize
Assertion. light energy for carboxylation to proceed. the ex-
(B) If both Assertion and Reason are correct cess energy may not caus damage to plants.
but Reason is not the correct explanation
of Assertion. 24. Assertion : Photosynthetically C4 plants are less
(C) If Assertion is correct but Reason is efficient than C3 plants. [2006]
incorrect. Reason : The operation of C4 pathway requires the
(D) If Assertion is false but Reason is correct. involvement of only bundle-sheath cells.
25. Assertion : Dark reaction is purely enzymatic reac-
tion. [2007]
Reason : it occurs only in absence of light.

34
BIOLOGY FOR NEET & AIIMS
26. Assertion : Dark reaction occurs only at night in 30. Assertion : In light reaction of photosynthesis, light
the stroma of chloroplast. [2009] is required for the functioning of PS I and PS II, and
Reason : CO2 fixation occurs only during C3 cycle. production of NADPH and ATP. [2015]
Reason : Dark reaction does not occur in light.
27. Assertion : Protons or hydrogen ions produced by
photolysis of water accumulate in the lumen of thy- 31. Assertion : CAM plants lack structural
lakoids. [2011] compartmentation of leaf as found in C4 plants.
Reason : Photolysis of water takes place in inner [2016]
membrane of thylakoid. Reason : Stomata of CAM plants are open during
28. Assertion : The efficiency of C4 plant is more than the day.
those of C3 plant.
Reason : C4 plants are more efficient in picking CO2.

29. Assertion : Photorespiration interferes with the suc-

cessful functioning of Calvin cycle.
Reason : Photorespiration oxidises ribulose - 1,5
biphosphate which is an acceptor of CO2 in Calvin
cycle.

35
 PHOTOSYNTHESIS IN HIGHER PLANT

ANSWER KEY

EXERCISE : PART - 1
1. C 2. D 3. C 4. A 5. C 6. A 7. C 8. D 9. C 10. A 11. C 12. D 13. A
14. C 15. D 16. B 17. A 18. B 19. D 20. B 21. D 22. C 23. D 24. A 25. D 26. C
27. A 28. A 29. A 30. A 31. C 32. B 33. C 34. A 35. C 36. B
PART - 2
1. B 2. D 3. B 4. D 5. A 6. A 7. B 8. B 9. D 10. C 11. B 12. C 13. A
14. C 15. D 16. A 17. B 18. C 19. B 20. A 21. C 22. D 23. C 24. D 25. C 26. D
27. B 28. A 29. A 30. C 31. C

36
BIOLOGY FOR NEET & AIIMS

HINTS & SOLUTIONS

EXERCISE 7. (C) In C3 - plants the first stable product formed
P-1 (NEET/AIPMT) during dark reaction is 3-phosphoglyceric acid.
Since, it is a 3 carbon compound hence, the path-
1. (C) Magnesium is at the centre of the porphyrin
way is referred as C3-pathway. Oxalo Acetic Acid
ring in chlorophyll. the general structure of chloro-
(OAA) is the first stable compound in C4 - plants. It
phyll was elucidated by Hand Fischer in 1940.
is a 4C compound.
2. (D) Dicker and Tio (1959) discovered photorespira-
8. (D) The fixation of CO2 in C4 - plants takes place two
tion i tobacco plant. It is a light dependent process
places and by two different organic compounds.
of oxygenation of Ribulose Bisphosphate (RuBP).
Phosphoenol Pyruvate (PEP) is found in mesophyll
During this process CO2 is liberated and O2 is con-
cells which primarily fixes atmospheric CO2 into
sumed. C4 - plants avoid photorespiration by fol-
oxalo acetic acid (4C). RuBisCO is present in bundle
lowing hatch Slack pathway.
sheath cells where final fixation of CO2 on hexose
sugars takes place. CO2 is primarily fixed by PEP
3. (C) In C4 - plants, CO2 is taken up by Phosphoenol-
carboxylase because this enzyme has greater affin-
Pyrfuvate (PEP) and the reaction being catalysed
ity to CO2 than RuBisCO.
by PEP carboxylase.
9. (C) In C4 - plants every CO2 molecule has to be fixed
PEP carboxylase twice, so these plants are needed more energy for
CO2 + PEP Oxalo acetic acid the synthesis of hexose sugar molecules than C3 -
(Mesophyll cells of C4 - plants )
plants in which CO2 has to be fixed only once. 18
ATP molecules are required by C3 - plants for the
Dehydro NADPH synthesis of one molecule of hexose sugar while 30
genase
ATP molecules are needed by the C4 - plants for the
same. Thus, C4 - plants have a need of 12 ATP mol-
Metalic acid ecules extra than C3 - plants for the synthesis of
+ one molecule of hexose sugar.
+
NADP
10. (A) The first reaction pof photorespiration occurs
4. (A) Carotenoids are a group of yellow, red and or- in stroma of chloroplast. In this reaction the RuBP
ange pigments which function as accessory pig- (Ribulose 1-5 biphosphate) consumes one oxygen
ments and protect chlorophyll molecules from de- molecule in presence of enzyme RuBisCO.
struction by intensive light rays. Carotenoids have In peroxisome the glycolate transferred from chlo-
three absorption peaks in the blue-violet range of roplast takes up O2 and formed the glyoxylate
the spectrum. wjereas, the H2O2 released as byproduct.

5. (C) The thylakoids of chloroplast are flattened 11. (C) In photosystem-I, the primary electron accep-
vesicles arranged as a membranous network within tor is probably a Fe-S protein. The reduced primary
the storma. 50% of chloroplast proteins and vari- acceptor transfers the electrons to secondary elec-
ous components involved (namely chlorophyll, tron acceptor (most probably P430). The sequence
carotenoids and plastoquinone) on photosynthe- of electron transfer is as follows
sis are present in thylakoid membranes.   
P700 eo A1 eo A2 eo A3
6. (A) Shade tolerant plants have lower photosynthetic (Chl–a+) (Phyloquinone) (Fe - S (P430)
rates and hence, lower growth rates. On the other protein)
hand, these plants have larger photosynthetic unit The reduced P430 passes its electrons to ferredoxin
size than the sun plants. (Fd) present at outer surface of thylakoid membrane.

37
BIOLOGY FOR NEET & AIIMS
12. (D) Plastoquinone is the first acceptor of electrons rium, also a non-oxygenic photosynthetic.
from an excited chlorophyll molecule of photosys-
tem-II 17. (A) In higher plants, enzymes for light indepen-
dent reactions (dark reactions) are present in the
13. (A) The oxalic acid is reduced to malic acid in me- stroma of chloroplasts.
sophyll cells, from chloroplast of mesophyll cells Light dependent reaction occurs in grana of chlo-
the malic acid is transferred to the chloroplast of roplast.
bundle sheath cells where, it is decarboxylated to
Ribosomes are necessary for protein synthesis.
form CO2 and pyruvic acid.
Chlorophyll is green photosynthetic pigment found
14. (C) Option (C) is correct. As starch is a high mo- in chloroplasts.
lecular weight polyrner of D-glucose in D 1o 4 link-
18. (B) C4 -plants are more efficient in photosynthesis
age. It is synthesised in chloroplasts as one of the
than C3-plants but use more energy. They possess
stable end products of photosynthesis. It is most
the larger number of chloroplasts in the leaf cells. In
abundant and common storage polysaccharide in
the leaves of C4 -plants, the vascular bundles are
plants hence, most staple food for man and herbi-
sunounded by bundle sheath cells which in turn
vores. It is a mixture of two types of glucose
are surrounded by mesophyll cells. Chloroplast in
homopolysaccharide viz, amylose and amylopec-
bundle sheath cells are larger and always contain
tin. During day time the starch synthesis in chloro-
grana, whereas chloroplasts in mesophyil cells are
plast is coordinated with sucrose synthesis in
smaller.
cylosol. Typically about 90% of total solute carried
in phloem is the carbohydrate sucrose, a disaccha- 19. (D) The use of radioactive 14 C by Melvin Calvin in
ride. algal (Chlorella) photosynthesis studies led to the
discovery that the first CO2 fixation product was a
This is relatively inactive and highly soluble sugar
3-carbon organic acid. The first product identified
playing little direct role in metabolism and so, mak-
was 3-phosphoglyceric acid (PGA)
ing an ideal transport sugar.
20. (B) PAR (Photosynthetically Active Radiation) des-
15. (D) Cyclic-photophosphorylation involves only ignates the spectral range of sorar radiation from
pigment system-I and resuits in the formation of 400-700 nm that photosynthetic organisms are able
ATP only. When the photons activate PS-I, a pair to use in the process of photosynthesis. Of the
of electrons are raised to a higher energy level. They total incident solar radiation the proporfion of PAR
are captured by primary acceptor which passes is less than 50%
them on to ferredoxin, plastoquinone, cytochrome
21. (D) CAM plants are mostly succulent xerophytes.
complex, plastocyanin and finally back to reaction
The stomata in these plants remain closed during
centre of PS-I, i.e., P700.
the day. This helps to check the transpiration. In
At each step of electron transfer, the electrons lose this way, water is conserved.
potential energy. Their trip down hill is caused by
22. (C) None of the option is correct. Photorespiration
the transport chain to pump H+ across the thyla-
required three cell organelles in sequence of chlo-
koid membrane. The proton gradient thus estab-
roplast, peroxisome and mitochondria. Option (C)
lished is responsible for forming ATP (2 molecules).
may be correct if be read as said sequence.
No reduction of NADP to NADPH + H+.
23. (D) Photorespiration is a light dependent process
16. (B) Oscillatoria is a photosynthetic which occurs in C3 -plants. It is opposite to photo-
cyanobacterium. In this cyanobacteria during pho- synthesis because during this process, uptake of
tosynthesis water is electron donor and oxygen is a O2 and release of CO2 take place. Due to the pres-
byproduct, i.e., oxygenic photosynthesis occurs. ence of Kranz anatomy, C4 plants do not show pho-
Rhodospirillum and Chlorobium are non-oxygenic torespiration.
photosynthetic, purple non-sulphur and green sul-
phur bacteria. Chromatium is purple sulphur bacte-

38
 PHOTOSYNTHESIS IN HIGHER PLANT
24. (A) Anoxygenic photosynthesis (in which O2 is 31. (C) In C4 -plants, the initial fxation of CO2 occurs in
not released) is seen in Rhodospirillum which is a mesophyll cells. The primary acceptor of CO2 is
purple non-sulphur bacteria. It helps an organism Phosphoenol pyruvate (PEP). It combines with CO2
to trap tight energy and store it as chemical energy. in the presence of enzyme PEP carboxylase to form
Other than this anoxygenic photosynthesis com- the first stable product, i.e. Oxalo Acetic Acid
monly occurs in purple non_sulphur bacteria, green (OAA). Where as C3 -plants lack PEPcarboxylase en-
sulphur/non-sulphur baiteria, and heliobacteria, etc. zyme . They possess RuBisCO enzyrne. This en-
zyme can work as both carboxylase (fixation of
25. (D) The light-independent reactions (or dark reac-
CO2)and oxygenase (fixation of.O2). RuBisCO has a
tions) take prace in the stromal matrix of the chloro-
much greater affinity for CO2 than for O2 and the
plasts.
binding is competitive. At higher temperature, its
In light independent reactions, carbon dioxide is
affinity for CO2 decrease and it works as oxyge-
reduced to glucose (carbohydrate) by the hydro-
nase.
gen in NADPH by using the chemical energy stored
Therefore, at higher temperature photosynthesis
in ATP. This reaction takes place in the presence of
decrease in C3 -plants, while in C4 - plants it in-
a substance called RuDp.
creases.
26. (C) Photorespiration is thg process which makes a 32. (B) Phosphoenol pyruvate (PEP) is found in rhe
difference berween the C3 and C4 - plants. In this mesophyll cell, which accepts the atmospheric CO2
process there is a continuous loss of carbon fixed in C4 -plants and converts it to to oxalo acetate -a C4
in the form of CO2. compound. It is the first stable compound of C4 -
It occurs due to the high O2 content, high tempera- plants.
ture conditions in which RuBp carboxylase starts Concept Enhancer C4 -plants possess special the
working as RuBP oxygenate and normal photosyn- adaptation anatomy in their leaves to cope up the
thesis does not occur. photorespiratory losses. There are dimorphic chlo-
27. (A) Photolysis of water during photosynthesis roplast present in them - agranal bundle sheath cells
evolve nascent oxygen in the presence of manga- and granal in mesophyll cells.
nese, calcium and chloride ions. 33. (C) Green sulphur bacteria undergoes anoxygenic
photosynthesis.
28. (A) Proton concentration is higher in the lumen of
34. (A) Stomatal movement is greatly affected by light,
thylakoid due to photolysis of water, H+ pumping
temperature, and CO2 concentration.
and NADP reductase activity which occurs in
35. (C) In dicots, guard cells are kidney bean shaped,
stroma of the chloroplast.
whereas in monocots like grasses, they are Dumbell
29. (A) Emerson performed photosynthetic experiment shaped.
on Chlorella. He provided monochromatic light of 36. (B) NADH are produced in Respiration
more than 680 nm and observed decrease in rate of
photosynthesis known as red drop.
Later, he provided synchronised light of 680 nm
and 700 nm and observed increas in rate of
plotosynthesis, known as enhancement effect.
This experiment led to discovery of two photosys-
tems – PS-I and PS –II operating in photosynthe-
sis.
30. (A) This plant is a C4 -plant as these group of plants
shows little photorespiration, efficient in bilding to
CO2 even at low concentrations, better utilisation
of water as well as high rates of photosynthesis
even at high temperatures, i.e. tropical region. Be-
sides, they can also tolerate excess of salts due to
presence of organic acids.

39
BIOLOGY FOR NEET & AIIMS
EXERCISE
does not pass on NADP+ but is cycled back to the
P-2 (AIIMS) PS I complex through the electron transport chain.
The cyclic flow hence, results only in the synthesis
1. (B) In the process of photorespiration oxygen of ATP, but not of NADPH + H+.
combines with RUBP (Ribulose-biphosphate) in
chloroplast as following
6. (A) Calvin pathway occurs in all photosynthetic
O2 + RUBP 
Rubisco
o 3-Phosphoglycerate + 2-
plants which is CO2 fixation cycle. Carbon dioxide
Phosphoglycolate 
o CO2
combines with ribulose-1, 5-biphosphate to produce
Phosphoglycolate enters in peroxisomers and is a transient intermediate compound. The intermediate
finally congverted to CO2. compound splits up immediately in the presence of
water to form the two molecules of 3-
2. (D) Hill reaction is the light phase or photochemical phosphoglycerate or PGA. It is the first stable
phase of photosynthesis which consists of light product of photosynthesis.
driven splitting of water or photolysis, evolution of
7. (B) Photosystem II mostly occurs in the appressed
oxygen and synthesis of assimilatry power (ATP
regions of granal thylakoids.
and NADPH). An enzyme complex, Mn, Cl and
ferricyanides are required for this reaction. 8. (B) C4 plants are more efficient than C3 plants
because they have little photorespiration while in
3. (B) Light is the visible part of electromagnetic
C3 plants more than half of photosynthetic carbon
radiations. Sunlight or solar radiations reaching the
get losst in photorespiration. C4 plants are more
earth have wavelength between 300 nm to 2600 nm.
efficient in picking up CO2, even in low CO2
Part of the spectrum used in photosynthesis has a
concentration because of high affinity of CO2 with
wavelength between 400-700 nm. It is called
PEP (phosphoenol pyruvic acid).
photosynthetically active radiations (PAR).
9. (D) Photorespiration is the light dependent process
4. (D) Photosystem I is located in the nonappressed
of oxygenation of ribulose biphosphate (RuBP) and
part of grana thylakoids as well as stroma thylakoids.
release of carbon dioxide by the photosynthetic
In this photosystem chlorophyll : carotenoid
organs of a plant. Normally photosynthetic organs
content is high. Its photocentre is P700 . Pigment
do the reverse in the light, i.e., uptake of CO2 and
molecules of PS I absorb at or below 700 nm
release of O2. At high temperature, RuBP carboxylase
wavelength of light. It receives electrons from
functions as oxygenase and instead of fixing carbon
photosystem II. Photosystem I is involved in both
dioxide (C 3 cycle), oxidises ribulose 1,
cyclic and non cyclic photophosphorylation. It is
50biphosphate to produce a 3-carbon
not connected with photolysis of water. Usually it
phosphoglyceric acid and a 2-carbon
hands over its electron to NADP+ .
phosphoglycolate.
5. (A) Cyclic photophosphorylation is a process of Photorespiration does not produce energy or
photophosphorylation in which an electron reducing power. Rather, it consumes energy, Further,
expelled by the excited photocentre is returned to it it undoes the work of photosynthesis. There is 25%
after passing through a series of electron carries. loss of fixed CO2. Therefore, photorespiration is a
Cyclic photophosphorylation is performed by highly wasteful process. This happens only in case
photosystem I only. The electron is circulated within of C3 plants. C4 plants have overcome the problem
the photosystem and the phosphorylation occurs of photorespiration.
due to cyclic flow of electron. The excited electron
10. (C) A - Photosystem I (PS I)
B - Photosystem II (PS II)

40
 PHOTOSYNTHESIS IN HIGHER PLANT
C - e– acceptor across the mitochondrial membrane. ATP synthase,
D - LHC (Light Harvesting Complex). required for ATP synthesis is located in F1 particles
present in the inner mitochondrial membrane and
11. (B) The C4 plants are adapted to dry tropical regions becomes active only when there is high
and have greater productivity of biomass. They concentration of proton on F0 side as compared to
have special type of leaf anatomy known as Kranz F1 side. The flow of proton through F0 channel
anatomy. In this type of anatomy the bundle sheath induces F1 particle to function as ATP synthase
cells form several layers around the vascular and the energy of proton gradient produces ATP
bundles; they are characterized by having a large by attaching a phosphate radical to ADP.
number of chloroplasts, thick walls impervious to ASSERTION AND REASON
gaseous exchange and no intercellular spaces.

12. (C) Presence of photorespiration is considered as a

17. (B) The apoplast is the system of adjacent cell walls
wasteful and energy consuming process in crop
which is continuous through the plant. As water
plants which ultimately leads to reduction in final
evaporates from the mesophyll cell walls into the
yield of crops. It is estimated that during C 3
intercellular air spaces, tension develops in the
photosynthesis, upto 50% of the CO2 fixed may have
continuous stream of water in the apoplast, and
to pass through photorespiratory process, thereby
water is drawn through the walls in a mass flow by
resulting in considerable decrease in photosynthetic
the cohesion of water molecules.
productivity. In C 3 plants, there is loss of
When water moving through spaces in the cell wall
photosynthetic activity on account of
reaches the endodermis, it’s progress is stopped
photorespiration which is absent in C4 plants and
by a waterproof substance called suberin which is
hecne they have better productivity.
deposited in cell walls in the form of bands called
13. (A) In C4 plants, initial fixation of carbon dioxide casparian strips. Therefore water and solutes must
occurs in mesophyll cells. The primary acceptor of pass through the cell surface membrane and into
CO2 i.e., phosphoenol pyruvate (PEP) combines with the cytoplasm of the cells of the endodermis.
CO2 in the presence of PEP carboxylase or PEPcase
18. (C) Flowering is a phytochrome regulated process.
to form oxaloacetic acid, which is the first stable
Phytotchrome is a blue protein pigment with a
carbon dioxide fixation product in C4 pathway.
molecular mass of about 125 k Da (kilodaltons).
14. (C) Like other alkali metals, potassium hydroxide Phytochrome occurs in two interconvertyible form
combines with CO2 as such : P1 (which absorbs red light) and Pfr (which absorbs
far red light). The studies with mutants of
2KOH + CO2 o K2CO3 + H2O
Arabidopsis support and prove that the Pfr is the
15. (D) CO 2 acceptor molecule in C 4 plants is active form of phytochrome. When Pr molecules
phosphoenol pyruvate (PEP). C4 plants are more are exposed to red light, most of them absorb it and
efficient in picking up CO2 even when it is found in converted to Pfr. This causes floral induction in the
low concentration because of high affinity of PEP. shoot. A night interruption inhibits flowring of
PEP carboxylase (PEPcase (is the key enzyme which short-day plants and promotes flowering of long-
catalyses the primary fixation of CO2. day plants. Red light is more effective with short-
day plants and a mixture of red and far-red with
16. (A) The chemiosmotic coupling hypothesis of long-day plants.
oxidative phosphorylation proposed by Mitcheli,
explains the process of ATP formation and states 19. (B) Cyclic pathway of photosynthesis is appeared
that it is linked to development of a proton gradient first in some eubacterial species. It is supposed to
be the first evidence of production of ATP in the

41
BIOLOGY FOR NEET & AIIMS
presence of light. During non-cyclic form phosphoglycollate thus utilizing the excess
photophosphorylation photolysis of water takes energy.
place. Under the influence of light energy and the
catalytic action of chlorophyll, water, a substance 24. (D)
of low energy value, is split up into oxygen and
25. (C) Photosynthesis is actually oxidation reduction
hydrogen. Oxygen is used in the chloroplast. Non-
process in which water is oxidised and CO2 is
cyclic photophosphorylation is the only natural
reduced to carbohydrates. Assimilatory power ATP
process which adds molecular oxygen to the
and NADPH2 are required for reduction of CO2. But
atomosphere.
this reduction is independent of light i.e. occurs in
20. (A) presence or absence of light but production of
assimilatory power is light dependent. This reaction
21. (C) At very low CO2 concentration photosynthesis
is called light reaction of Hill’s reaction and the light
is strongly limited by the low CO2 while respiratory
independent phase is an enzymatic reaction called
rates are unaffected. As a result there is a negative
dark reaction. It occurs is stroma of chloroplast and
balance between CO2 fixed by photosynthesis and
is enzyme radiated one.
CO2 produced by respiration and a net efflux of CO2
from the plant.
By increasing the atmospheric concentration of CO2 26. (D) Dark reaction is also known as light-independent
at which photosynthesis just compensate for phase. Unlike, light reaction, it does not require light
respiration is referred to as CO2 compensation point. as an essential factor. thus can takes place both in
the presence or absence of light. The term dark
reaction does not mean that it takes place only in
22. (D) When the ambient temperature is high and soil dark period or at night. CO2 fixation occurs in both
contains excess water, the rate of transpiration is C3 and C4 cycle. In C3 cycle, CO2 is added by the
increased i.e., loss of waster takes place from leaves enzyme, RuBisCO to a 5 carbon compound RuBP
through stomata. Lenticular transpiration is only that is convertyed to 2 molecules of 3-carbon PGA.
0.1% of the total transpiration. It however continues In C4 cycle the first product of CO2 fixation (takes
day and night because lenticels have no mechanism place in mesophyll) is a 4-carbon compound,
of closure. The lenticels connect the atmospheric oxaloacetic acid. It is seen in some tropical plants.
air with the cortical tissue of stem through
27. (B) The first step in photosynthesis is the
intercellular spaces present amongst the
lightdriven oxidation (splitting or photolysis) of
complementary cells. Root pressure regulates the
water. It provides the electrons for the
rate of loss of wate from the the stomata in some
photosynthetic electron transport chains as well as
plants.
protons for the establishment of a proton gradient.
23. (C) Photorespiration protects the plants from It occurs on the lumenal side of the thylakoid
photoxidative damage by dissipating excess of membrane. During photolysis, water is oxidised to
excitation energy. When the CO 2 supply is oxygen, protons and electrons. Protons accumulate
limitedand under high light intensity in the lumen.
photorespiration takes place thus protecting the
28. (A) The efficiency of C4 plants is more than those of
plants. If enough CO2 is not available to utilize light
C3 plants because (i) C4 plants are more efficient in
energy for carboxylation to proceed, the excess
picking up CO2 even when it is found in low
energy will cause photoxidative damage to the
concentration because of the high affinity of PEP,
plants. The energy liberated should be used in
(ii) concentric arrangement of mesophyll cells
photophosphorylation in presence of CO2. If CO2 is
less then in C3 plants O2 combines with RuBP to

42
 PHOTOSYNTHESIS IN HIGHER PLANT
produces a smaller area in relation to volume for
better utilization of available water and reduce the
intensity of solar radiations, (iii) they can tolerate
excess salts because of the presence of organic
acids, (iv) normal oxygen concentration is not
inhibitory for the growth in contrast to C3 plants,
(v) they are adapted to high temperature and intense
radiation of tropics.

29. (A)

30. (C) Light reactions of photosynthesis take place in

the presence of light. These involve photolysis of
water and production of assimilatory power
(NADPH + ATP) through PS I and PS II.
Dark reactions of photosynthesis catalyse
assimilation of CO2 to carbohydrates. Dark reactions
are light independent reactions, hence can take
place both in the light as well as in the dark.

31. (C) CAM plants do not exhibit the structural

compartmentation as shown by C4 plants which
exhibit kranz anatomy. CAM plants fix CO2 at night
because their stomata are open at night and remain
closed during the day.

43
 CHAPTER
13
RESPIRATION IN PLANTS

“Biochemistry has an important bearing on the progress of medicine.

But because of this, it must itself remain a pure science, whose initiates
are inspired by a craving for understanding and by nothing else.”

“ OTTO FRITZ MEYERHOF ( 1884-1951)”

INTRODUCTION

W
hy is breathing so essential for life? What happens when we breathe? When it comes
to life, respiration is considered as one of the basic freatures which helps the organism
to survive. Respiration provides energy for carrying out daily life activities, be it
absorption, transport, movement, reproduction or even breathing.
The process of breathing is very much connected to the process of release of energy
from food. All the enrggy required for ‘life process’ is obtained by oxidation of some
macromolecules that w call as ‘food’. The gaseous exchange i..e., intake of oxygen
and release of carbon dioxide is calld breathing while respiration includes biological
oxidation of organic molecules i.e. breaking of C-C bonds by using enzymes and
results in the release of energy in the form of ATP. The oxidation of macromolecules
that takes place inside the body us called as “FOOD”. Only green plants prepare
their own food through photosynthesis but only those cells which conain chloroplast
show photosynthesis. In eukarytoes, photosynthesis takes place in chloroplast and
respiration in cytoplasm and mitochondria. The compounds subjected to biologiccal
oxidation is called Respiratory substrate. These may be carbohydrates, fats, protiens
or organic acids.

44
BIOLOGY FOR NEET & AIIMS

z Respiration is an enzymatic process, which is also known as internal respiration / tissue respiration/dark
respiration / cellular respiration / mitochondrial respiration.
z Respiration is a Amphibolic & exergonic cellular process.
z An important feature of respiration is liberation of metabolic energy as ATP.
Respiratory substrate :
(Carbohydrates o Fats o Protein o others)
When respiratory substrates are carbohydrates like glycogen, starch, sucrose, hexose or fats, then respiration is
known as floating respiration.
When protein is oxidised in respiration, then respiration is Known as protoplasmic respiration protoplasmic
components or cellular proteins may oxidised at the time of starvation & disease.
Exceptionally oxidation of proteins in legume seeds is called floating respiration.
Types of respiration :
(A) Aerobic respiration :- The complete oxidation of food with the use of oxygen and when entire carbon released, as
CO2 is called as aerobic respiration.

C6H12O6 + 6O2 + 6H2O   o

Enzyme
6CO2- + 12H2O + 686 Kcal E (38/36 ATP)
cyto. & mito

(B) Anaerobic respiration :- During it most of the energy is lost in form of heat. It occurs in cytoplasm and only 2ATP
are produced.
This is an incomplete oxidation.When food is oxidized into alcohol or organic acids without use of oxygen.

C6H12O6  
Enzymes
o 2C2H5OH + 2CO2+ 21 KCal
cytoplasm
(2ATP)

Anaerobic respiraton was first reported by Kostytchev.

Anaerobic respiration may takes place in bacteria, some lower parasitic animals (Ascaris, Taenia) plants, R.BCs. &
muscles of human body. When oxygen is not available, then food is incompletely oxidised in to some organic compounds
like ethanol, acetic acid, lactic acid.
In muscle cells & some bacteria, the energy is produced by breaking of glucose into lactic acid inside the cells.
The amount of energy released in anaerobic respiration is much less than aerobic respiration.
Fermentation is performed by only some fungi & some bacteria (only by microbes) and is an extracellular process.
No ATP is produced. If occure inside the cell then 2ATP forms.

C6H12O6  
Yeast
o 2C H OH + 2CO + Heat
Bact . 2 5 2

In energy generating processes either inorganic or organic compounds function as electron acceptors. The terms
aerobic respiration, anaerobic respiration and fermentation are often used on energy generating processes.
In aerobic respiration the final electron acceptor is free O2.
In anaerobic respiration the final electron acceptors is organic compound or inorganic compounds (nitrates) other
than free O2
In fermentation, the final electron acceptor is organic intermediates of the process, no external substance.
Both anaerobic respiration and fermentation are incomplete oxidations.
Inhibitory effect on respiration high concentration. of oxygen is called Pasteur effect.

45
 RESPIRATION IN PLANTS
STEPS OF AEROBIC RESPIRATION
(1) Glycolysis – Occurs in cytosol/cytoplasm
(2) Formation of Acetyl COA – (Link Reaction) Perimitochondrial space (outer chamber)
(3) TCA cycle or Kreb's cycle – Matrix of mitochondria & cytosol in bacteria
(4) ETS – Occurs in cristae or inner memberane of mitochondria and Oxidative phosphorylation –Occrus in
Oxysome head (F1 particle)
(1) Glycolysis – EMP – (Embden, Meyerhof, parnas) pathway.
The glycolysis is common phase for aerobic & anaerobic respirations both.
Glycolysis involves a series of ten biochemical reactions in cytoplasm.
In glycolysis, neither consumption of oxygen nor liberation of CO2 take place.
In glycolysis, 1 glucose, produces 2mol. of pyruvic acids (3C)
2NADH2 & 2ATP are generated in glycolysis, which are equal to 8 ATP.
Substrate level phosphorylation forms 4 ATP :- [When the substrate releases energy for phosphorylation of ADP
OR formation of ATP, without ETS then called as substrate level phosphorylation]
Glycolysis is also known as oxidative anabolism or catabolic resynthesis, because it links with anabolism of fats
and amino acids. An intermediate PGAL is used for the synthesis of glycerol later forms fats or lipid. PGA is used
for synthesis of Serine, Glycine, Cystine. Alanine forms from pyruvate.
1, 3, 10 are irreversible reactions in EMP pathway.
Biochemical reactions of Glycolysis
Hexo Kinase
1. Glucose ++ Glucose - 6P
Mg
ATP ADP

2. Glucose-6P Isomerase Fructose - 6P

Phosphofructokinase
3. Fructose-6P Fructose -1,6-BiP
Mg++
ATP ADP

PGAL
Aldolase Isomerase
4. Fructose-1,6-BiP
DHAP
Non enzymatic
5. 2 PGAL + 2 ip
1,3 Bi PGAL(2mol.)
(Phosphoglyceraldehyde)
3c
Starting of energy conserving phase :
dehydrogenase
6. 2,1,3 BiPGAL 1,3 Bi PGA (2mol.)
2NAD 2NADH2 (Iodoacetate inhibits this reaction)
Transphosphorylase
7. 2,1,3 BiPGA (kinase) 3 – PGA (2mol.)
2ADP + ip 2ATP

8. 2,3–PGA Phosphoglyceromutase 2-PGA

Enolase
9. 2, 2–PGA Mg++
2, 2–PEP
Pyruvate kinase
10. 2-PEP 2, Pyruvic Acid
+ ++
K , mg
2ADP + ip 2ATP (3C)

46
BIOLOGY FOR NEET & AIIMS

Hexokinase

Investment phase
Mg++
Activation or
(Robinson's ester)

Isomerase

(Newberg's ester)

Phosphofructokinase, Mg++

(Herden and young's ester)

Aldolase
2, Pyuvic Acid + 2ATP + 2NADH2

2,
2H3PO4 (ip)

2,

Dehydrogenase

2,

Transphosphorylase
Glucose + 2ADP + 2 ip + 2NAD+

2,

Mutase
Payoff - phase

2,

Enolase

2,

Pyruvic acid kinase

Mg++, K+

GLYCOLYSIS / EMP PATHWAY

47
 RESPIRATION IN PLANTS
Phosphofructokinase is an allosteric enzyme. The phosphorylation of fructose 6 phosphate is the most important
regulation point of glycolysis.
Phosphofructokinase has multiple allosteric modulator. It's activity is inhibited by ATP
(–ve modulator) and stimulated by ADP & AMP (+ve modulator). Most of the biochemical reactions catalysed by
allosteric enzymes are irreversible type and these are control point of glycolysis.
(2) Formation of Acetyl-Co-A :- (Link/Gateway reaction)
When respiration is aerobic, then pyruvic acid is oxidised to form 2C compound – Acetyl Co-A. It occurs in presence
of O2 and CO2 is released first time during it.
Acetyl Co-A is a connecting link between glycolysis & Krebs-cycle. Decarboxylation and dehydrogenation
(Oxidative decarboxylation) take place during formation of acetyl Co-A.
Acetyl Co-A is formed in perimitochondrial space by enzyme pyruvate dehydrogenase complex. (Mg++, LA (Lipoic
Acid), TPP(Thiamine pyrophosphate), NAD, CoA)

2Pyruvic Acid + 2Co–A 2Acetyl Co-A + 2CO2

Acetyl Co-A is also common intermediate between fat & carbohydrate metabolism.
(3) Kreb cycle / TCA (Tricarboxylic acid) Cycle / Citric acid cycle :-
This cycle was discovered by H.A. Kreb. (Nobel prize)
TCA cycle occurs in mitochondrial matrix or power house of cell.
Kreb cycle begins by formation of citric acid [TCA(Tri carboxylic acid)] & O.A.A. is the acceptor molecule of
Acetyl CoA in Kreb's cycle.
A number of Krebs cycle intermediates are used in synthetic (anabolic) pathways, thus TCA cycle is also called
amphibolic pathway or anaplerotic pathway.
Succinyl CO–A is important for synthesis of porphyrin ring compounds like Chlorophylls, Phytochromes,
Cytochromes, Haemoglobin etc.
a-ketoglutaric acid (5c) involves in Amino Acid formation (Nitrogen-metabolism)
Oxidation occurs at 4 sites in Kreb cycle.
3NADH2, 1FADH2 & 1GTP (ATP) produced by each turn of TCA cycle.(=12 ATP)
All the enzymes of TCA cycle, except marker enzyme Succinic dehydrogenase (in inner mitochondrial membrane)
present in matrix.
Bio Chemical reactions in Krebs Cycle Þ
Acetyl Co–A + OAA m o
Citrate
1. Synthase Citric Acid + Co–A
(2C) (4C) (TCA)

2. Citric Acid m


o
Aconitase
Cis Aconitic Acid ¾o Isocitrate
Fe
(6C)
3. Isocitrate + NAD+ m
oIsocitric
Dehydrogenase Oxalosuccinic Acid + NADH2
(6C)

4. Oxalosuccinic Acid m
Mn
Decarboxylase

o a Ketoglutarate + Co2

(6C) (5C)

48
 2 Acetyl Co-A + 6NAD+ + 2 FAD+ + 2 GDP or ADP + 2ip 4CO2 + 6NADH2 + 2FADH2 + 2GTP or ATP + Co-A
(2C + 2C)
BIOLOGY FOR NEET & AIIMS

49
/
Citrogenase
Kreb's Cycle/ TCA Cycle/ Citric Acid Cycle
 RESPIRATION IN PLANTS
Dehydrogenase comp.
5. a Ketoglutaric Acid TPP, LA,
Succinyl Co A + Co2
Mg++, CoA
(5C) NAD NADH2 (4C)
(This reaction similar to link reaction)
Thiokinase
6. Succinyl Co A Succinic Acid + Co A
(4C) GDP + ip (4C)
GTP

[Energy of thioester bond is released, which used in formation of GTP]

Nucleoside
(GTP + ADP   o
diphosphokinase
GDP + ATP)

The GTP formed in reaction 6, reacts with ADP to form ATP and GDP, as GTP and ATP have approximatly same
energy.
Succinic dehydrogenase
7. Succinic Acid Fumaric Acid
(4C) FAD (4C)FADH2

8. Fumaric Acid Fumarase Malic Acid

(4C) (4C)

dehydrogenase

9. Malate OAA (Acceptor of Acetyl CoA)

NAD FADH2
(4C) (4C)

Glutamate
a – Ketoglutaric acid + NH4+ + NAD (P)H  o Glutamate + H O + NADP+
dehydrogenase 2

This is known as reductive amination .

The first formed amino acid (in plants) is glutamic acid, which forms other types of amino acids by the process of
transamination.
Ex. Glutamic acid + Pyruvic acid l a–Ketoglutarate + alanine.

(4) ETS & Oxidative phosphorylation : (Terminal oxidation of NADH2 & FADH2)
ETS (Respiratory chain) consists of four components
(i) FP (FMN), (ii) Fe–S Protein, (iii) Co-Q (UQ) & (iv) Cytochromes.
Cytochromes are cyto.-b, cyto. – C1 & cyto. – C, cyto-a & cyto a3.
Now components of ETS are categorise as follows :
Name of complexes Components of ETS Inhibitors
Complex-I FMN-NADH2 dehydrogenase Rotenone & amytal
Complex-II CoQ/UQ-FADH2 dehydrogenase
/Succinate dehydrogenase
Complex-III Cytochrome b-Cyto c1 antimycin
Complex-IV Cyto. a and Cyto. a3 cyanide, CO
Complex-V ATP synthetase/ATPase

50
BIOLOGY FOR NEET & AIIMS
UQ and Cyto. c are mobile e– carriers in mitochondrial ETS. (PQ and PC is mobile in z-scheme)
Cytochrome a3 is last cytochrome in respiratory chain or electron transport chain (ETC).
O2 is last e– acceptor in oxidative phosphorylation & due to this metabolic water is formed.
DNP (Dinitrophenol) and oligomycin both are called uncouplers.
Enzyme Cytochrome oxidase is responsible for oxidation of cyto. a3 & reduction of O2.
Enzyme Cytochrome oxidase has cyto. a & a3 as its components. (Cu present in cyto a and cyto. a3)
Cytosolic or extra mitochondrial or glycolytic 2NADH2 comes at ETS by two type of shuttles (Only in eukaryotes) :
(i) Glycerol phosphate shuttle :- In brain/muscle cells.

GLYCEROL-PHOSPHATE SHUTTLE SYSTEM

Cytoplasm OM PMS IM Matrix

NAD
NADH2

ETS
FADH 2 FAD

DHAP
Glycerol PO4 Glycerol PO4
DHAP

? 2NADH2 o2FADH2 = 4ATP 1 Glucose = 36 ATP,

(ii) Malate aspartate shuttle :-
MALATE - ASPARTATE SHUTTLE SYSTEM

Cytoplasm OM PMS IM Matrix

NAD
NADH2 NADH2 NAD
ETS

OAA
MALATE MALATE
OAA

ASPARTIC ASPARTIC
ACID ACID

? 2NADH2 = 6ATP 1 Glucose = 38 ATP

In prokaryotes, shuttle mechanism is absent. They always get 38 ATP from aerobic respiration of 1 glucose mol.
Cyanide inhibits the activity of cytochrome oxidase & inhibits the oxidation of cyto-a3.
In mitochondria, of some plants alternative oxidase system is present, in which ETS continues even in presence of
cyanides. This type of respiration is known as cyanide resistance respiration or Alternate electron pathway.
Ex. Spinacea, Pisum.

51
 RESPIRATION IN PLANTS

IMM MATRIX
PMS

FMN NADH2

NAD
FMNH2
2H+
Fe-S
2H+
FADH2
CoQ
+ FAD
2H
+ Cyt b
+
+
+
+
Fe-S
+
2H
+
2H
Cyt C1

ADP+Pi
Cyt C
Cyt a
2H+
Cyt a3 H2O
ATP

1
2 O2

ETC
Oxidative phosphorylation
Chemiosmotic theory / Coupling theory :
During ETC of respiration CoQ & FMN can releases H+ ions in perimitochondrial space and leads to differential H+
ion concetration across inner mitochondrial membrane. This differential H+ ion concentration across inner
mitochondrial membrane leads to creation of proton gradiant (PH gradient) and Electrical potential (difference of
charge). Both are collectively known as Proton motive force (PMF).
PMF do not allow stay of H+ ions in Perimitochondrial space (PMS) so they return towards the matrix through F0
particales selectively.
The passage of 3H+ ions activate ATP synthase and gives rise to 1ATP from ADP & Pi.
Some physiologist beleive that passage of 2H+ ions through F0 particle or coupling factor or proton channel leads
to synthesis of 1 ATP.
ª º
« 10NADH 2 30 ATP »
« »
1Glucose « 2FADH 2 4 ATP »
« 34 ATP »
« »
¬ ¼

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BIOLOGY FOR NEET & AIIMS

Bioenergetics of respiration – (1 mol. of glucose)

(1) EMP-Pathway
(i) ATP formed at substrate level phosphorylation Ÿ 4.ATP
(ii) ATP produced via ETS (2NADH2) Ÿ 6 ATP
(iii) ATP consumed in glycolysis Ÿ 2 ATP

10 ATP – 2 ATP = 8 ATP

Gross – Expenditure = Net or Total gain

Direct Gain = 2 ATP
(2) Link reaction or Gateway reaction –

2NADH2 = 6 ATP (via ETS)

(3) Kreb's Cycle –

(i) ATP produced at substrate level phosphorylation = 2 GTP/2ATP

ª 6NADH2 o 18 ATP
(ii) ATP produced via ETS «
¬ 2FADH2 o 4 ATP

24 ATP

Total o 38 ATP
1 Sucrose = 80 ATP
1 Fructose 1,6–Bisphosphate = 40 ATP
1 Pyurvic acid = 15 ATP
1 Acetyl Co-A or 1 TCA cycle = 12 ATP
Pentose phosphate pathway (PPP) / HMP (Hexose mono phosphate) Shunt / Warburg-Dickens pathways

PPP is also called as Warburg - Dickens

pathway/HMP shunt/Phospho gluconola
ctone pathway/Carbohydrate degradation
without mitochondria/Cytosolic oxidative
decarboxylation/Horecker -Racker
Pathway
Glycolysis & TCA cycle is the main route
of carbohydrate oxidation, but Warburg
& Dickens (1935) discovered an
alternative route of carbohydrate break
down, existing in plants, some animal
tissues (Mammary glands, adipose, liver
& microbes).
HMP/PPP occurs when

53
 RESPIRATION IN PLANTS
(i) NADPH2 requirement of cell increases during biosynthetic processes.
(ii) When EMP pathway blocked by iodoacetate, fluorides, arsenates.
(iii) When mitochondria is busy in other pathways.
Most of the intermediates are similar to Calvin cycle, but PPP is amphibolic and oxidative process.
One ATP is utilised in phosphorylation of glucose, so net gain equals to 35 ATP. (12 NADPH2)

Significance of HMP shunt :-

(1) An intermediate erythrose-P (4C) of this pathway is precursor of shikimic acid, which goes to synthesis of
aromatic compounds and amino acids.
(2) This cycle provides pentose sugars Ribose-p for synthesis of nucleotides, nucleosides, ATP and GTP.
(3) A five carbon intermediate Ribulose-5-phosphate may used as CO2 acceptor in green cells.
(4) This pathway produces reducing power NADPH2 for the various biosynthetic pathways, other than
photosynthesis like fats synthesis, starch synthesis, hormone synthesis and chlorophyll synthesis.
(5) Intermediates like PGAL and fructose-6-phosphate of this pathway may link with glycolytic reactions.

E -Oxidation of Fatty acids

b-oxidation takes place mainly in perimitochondrial space but also in glyoxisome, peroxisome, cytosol.
Liberation of 2C segments from the fatty acid mol. in the form of acetyl Co-A is known as b-oxidation. These acetyl-
CoA provides ATP after oxidation in kreb cycle.
Acetyl CoA is oxidised in TCA cycle to CO2 & H2O with the production of 12 ATP molecules.

Enzymes
16C palmitic acid
NADH2 FADH2 Acetyl Co-A
( = 5 ATP) (2C) oxidised in Krebs cycle

5 ATP × 7 times = 35 ATP

12 ATP × 8 Acetyl CoA = 96 ATP

131 ATP
(1 stearic acid = 146 ATP) – 2 ATP consumed

1 palmitic acid = 129 ATP

Glyoxylate Cycle
Discovered by Kornberg & Krebs,during germination of fatty seeds.
This cycle converts fats into sugars so it is an example of gluconeogenesis in plants.
Glyoxylate cycle occurs in glyoxisome, cytosol, & mitochondria.

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BIOLOGY FOR NEET & AIIMS

Fermentation
Cruick Shank & Pasteur (1898).
Fermentation is much similar to anaerobic respiration, but this is an extracellular process & substrate is present
outside the cell. Energy released as heat, no ATP generated.
Buchner discovered the enzyme zymase complex, which is responsible for alcoholic fermentation.

Types of Fermentation :-
(i) When the one type of product formed in fermentation then it is called homofermentation.
(ii) When the products of fermentation process are more than one type, then process is heterofermentation.
(1) Alcoholic fermentation :
This is the oldest & the best known type of fermentation performed by yeast & some bacteria.
Zymase (Bact .)
C6H12O6  
yeast
o 2C H OH + 2CO + Energy..
2 5 2

Decarboxylase
Glucose




2 Pyruvic Acid








2 Acetaldehyde + 2CO2




2C2 H5 OH
Dehydrogenase _
2NADH2 e
+
2NAD
Alcoholic fermentation

(2) Lactic acid fermentation :-

It occurs during curd formation.
Lactobacillus
Lactose o Hexose / C6H12O6   o 2C3H6O3
Lactate de hydrogenase
L. Acid

(3) Acetic acid fermentation

This is aerobic fermentation
C2H5OH + O2   o CH3COOH + H2O
Acetobacter sp.
Acetic acid

(4) Butyric acid fermentation :-

In rancid butter, butyric acid fermentation takes place. Also in jute fiber.
C6H12O6   o C4H8O2 + 2CO2+ 2H2
C. butyricum

Other eg. are curring of tea, tanning of leather, retting of fibers, processing of Tobacco

Respiratory quotient (R.Q.)

The ratio of the volume of CO2 released to the volume of O2 taken in respiration is called R.Q.

vol. of CO 2 liberated
R.Q.
vol. of O 2 consumed

Value of R.Q. depends upon the type of respiratory substrate used & measured by Ganong's respirometer.

55
 RESPIRATION IN PLANTS
(1) Carbohydrates :- R.Q. = 1
C6H12O6 + 6O2 + 6H2O o 6CO2 + 12 H2O + E
(2) Fat / Oil o R.Q. = 0.70 or R.Q. < 1
2C51 H98O6 + 145O2 o 102 CO2 + 98 H2O +E
Fatty seeds germination-castor, R.Q. < 1
At the time of formation of fatty seeds, (maturing fatty seed) R.Q. is more than 1 because more CO2 is released
than O2 consumed.
(3) Organic acids :- (In succulent xerophytes at day time)

Malic acid :- R.Q. = 1.33

C4H6O5+ 3O2 o 4CO2 + 3H2O + Energy

Oxalic acid R.Q. = 4
Citric acid R.Q. = 1.3
(4) Incomplete oxidation of carbohydrates :-

In CAM plants during night :- R.Q. = 0

2C6H12O6+ 3O2 o 3C4H6O5 + 3H2O + Energy

(5) Protein :- R.Q. = 0.8 or 0.9 or < 1

2CO 2
(6) Anaerobic respiration :- RQ = ¥ Anaerobic respiration f (Infinite)
0O 2

FACTORS EFFECTING CELL RESPIRATION

(1) Temperature :-
Optimum temperature for respiration is between 20-35°C. Maximum temperature is around 45°C.
At low temp respiration is low due to inactivation of enzymes (Freeze preserve the food) while at very high
temperature decrease, as enzyme denatured. Q10 = 2 to 3 for respiration.
Production of potato crop is high on the hill areas due to low temperature throughout year.
CPRI (Central potato Research Institute is situated at Kufri-Shimla (H.P.)
(2) Oxygen :-
The inhibition of anaerobic respiration by O2 concentration is called as Pasteur's effect.
The minimum amount of oxygen, at which aerobic respiration takes place & anaerobic respiration become
extinct is called as extinction point.
Oxygen concentration at which both aerobic & anaerobic respiration take place simultaneously is called as
transition point.
(3) CO2 :-
If CO2 concentration increases, then rate of respiration decreases in plants, (because stomata get closed).
(4) Salts :-
If a plant is transferrered from water to salt solution, it's respiration increases, this is known as salt respiration.
Because absorption of ions requires metabolic energy.

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BIOLOGY FOR NEET & AIIMS
(5) Hormones :-
IAA, GA & cytokinin increase the respiration rate.
The rapid increase in rate of respiration during ripening of fruits and senescence of leaves and plant organs is
called as "Climacteric respiration". This rate is decrease after sometime.
It is due to production of ethylene hormone.
(6) Light :-
Rate of respiration increases with increase in light intensity.
Light controls the stomatal opening & influence on temperature and also produce respiratory substrates.
(7) Injury, disease & wounds :-
The respiration increases due to injury wounding & infection.
(8) Inhibitors :
CN, azides, DNP (Dinitrophenol), CO, rotenone, antimycin, amytal. etc inhibit the respiration.
(9) Age :
Rate of respiration is more in young cells. Rate of respiration at meristem apex is high.
(10) Water : Seeds are slow respiring part of plants, because dry seeds are deficient of H2O.

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 RESPIRATION IN PLANTS

Enzymes are proteinaceous, biocatalysts.

Term enzyme was given by Kuhne.
First of all isolated & discovered by Buchner
Zymase (from yeast) was the first discovered enzyme. (Buchner)
The first purified and crystalized enzyme was urease (by J.B.Sumner) from Canavalia/Jack Bean (Lobia plant).
Proteinaceous nature of enzyme was suggested by Northrop and Sumner.

DEFINITION
Enzymes are biocatalysts made up of proteins (except ribozyme), which increases the rate of bio-chemical reactions
by lowering down the activation energy.
First discovered ribozyme was L19 RNAase by T.Cech from rRNA of a protozoan Tetrahymena thermophila and
RNAase P or Ribonuclease P by Altman in prokaryotic cell (Nobel prize).
CHARACTERISTICS OF ENZYMES
1. All enzymes are proteins, but all proteins are not enzymes.
2. Enzymes accelerate the rate of reaction, without undergoing any change in themselves.
3. Molecular weight of enzymes ranges from 6000 (bacterial fd) to 46 lakh (Pyruvate dehydrogenase comp.)
4. Enzymes are colloidal substances, which are very sensitive to pH & temperature. Optimum temperature for
enzymes is 20-35°C.
5. Most of enzymes are active at neutral pH, hydrolytic enzymes of lysosomes are active on acidic pH (5).
6. All enzymes are tertiary & globular proteins (Isoenzymes quarternary protein)
7. Enzymes lower down the activation energy of substrate or reactions.
8. Enzymes are required in very minute amount for bio-chemical reactions. Their catalytic power is represented by
Michaelis Menten constant or Km constant and turn over number.
"The number of substrate molecules converted into products per unit time by one molecule of the enzyme in
favourable conditions is called turn over number." The maximum turn over number is of Carbonic anhydrase, is
360 lakh, for Catalase is 50 lakh, for flavoprotein is 50 & for lysozyme is 30 per minute.
9. Enzymes are very specific to their substrate or reactions.

10. Enzymes are macromolecules of amino acids, which are synthesized on ribosomes under the control of genes.
Transition state
Potential energy

Substrate

Progess of reaction
Concept of activation energy

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BIOLOGY FOR NEET & AIIMS
STRUCTURE OF ENZYME
(1) Simple enzymesoThey are made up of only proteins. eg. pepsin, trypsin, papain.
(2) Conjugated enzymes o They are made up of a protein part & non protein part (cofactor).
(i) Co-enzymes – Co-enzymes are non-protein organic groups, which are loosely attached to apoenzymes. They
are generally made up of vitamins.
(ii) Prosthetic group – When non-protein part is tightly or firmly attached to apoenzyme.
(iii) Metal activators/metallic factor :- Loosely attached inorganic co-factor.
eg. Mn,Fe,Co,Zn,Ca,Mg,Cu
Active site :- Specific part of amino acid chain in enzyme structure at which specific substrate is to be binded
and catalysed, known as active site. Active site of enzyme is made up of very specific sequence of amino acids,
determined by genetic codes.
Allosteric site :- Besides the active site's, some enzymes posess additional sites, at which chemicals other than
substrate (allosteric modulators) are bind. These sites are known as allosteric sites and enzyme with allosteric sites
are called as allosteric enzymes. e.g. hexokinase, phosphofructokinase.

Enzyme

Simple enzyme Conjugated enzymes (holoenzyme)

made up of only proteins.

Protein part Non-protein part

Co-enzyme Metal activators Prosthetic group

Loosely attached, organic Loosely attached Tightly attached organic,
part of enzyme. inorganic or metallic ions may inorganic part, can
Ex. Vitamins, AMP, ADP,
NAD, NADP, FMN, FAD,

TERMINOLOGY
Endoenzymes – Enzymes which are functional only inside the cells.
Exoenzymes – Enzymes catalysed the reactions outside the cell Eg:- enzymes of digestion, some enzymes of
insectivorous plants, Zymase complex of fermentation.
Proenzyme/Zymogen – These are precursors of enzymes or inactive forms of enzymes.
eg. Pepsinogen, Trypsinogen etc.
Iso-enzymes – Enzymes having similar action, but little difference in their molecular configuration are called isoenzymes.
16 forms of a-amylase of wheat & 5 forms of LDH (Lactate dehydrogenase) are known. These all forms are
synthesised by different genes.
Inducible enzymes – When formation of enzyme is induced by substrate availability.
eg. Lactase, Nitrogenase, b-galactosidase,
Extremozymes – Enzymes, which may also function at extremely adverse conditions e.g Taq polymerase
Abzymes – When the monoclonal antibodies are used as enzymes or reagents.
Biodetergents – Enzymes used in washing powders are known as bio-detergents eg. – amylase, lipase, proteolytic
enzymes.
House keeping / constitutive enzymes – Which are always present in constant amount & are also essential to cell.

59
 RESPIRATION IN PLANTS
NOMENCLATURE AND CLASSIFICATION
Enzyme commission of IUB-1961 divides all enzymes into 6 major classes and also proposed an international code
of 4 digits for each enzyme.
(I) Ligases (Synthases) :- Covalent bonding of two substrates to form a large molecule. e.g. Citrate synthetase,
Ligase
(II) Lyases :- Split the substrate molecule without water. These Enzymes splits the specific covalent bonds without
hydrolysis or H2 O addition.
e.g. Aldolase.
(III) Transferases :- These Enzymes transfer specific group from one substrate to another.
e.g.- Transaminase, Hexokinase.
(IV) Oxido-reductases :-These enzymes involve in oxidation-reduction reactions.
It involves 3 sub classes (i) Oxidase (ii) dehydrogenase (iii) reductase
e.g.- Cytochrome oxidase.
(V) Hydrolases :- These Enzymes involve in hydrolysis reactions with help of H2O.
e.g. Proteases, Lipases, Carbohydrases.
(VI) Isomerases :- Rearrangement of molecular structure to form isomers.

MODE OF ACTION OF ENZYME

(1) Lock & Key theory or template theory :-
Given by Emil Fischer
According to this theory active sites of enzymes serve as a lock into, which the reactant/substrate fits like a key.
Supported by competitive inhibition.
(2) Enzyme - substrate complex theory :-
– Given by Henry explained by Michaelis & Menten
E+S o ESC o EPC o E+P
(3) Induced fit theory
z Given by D.E. Koshland (1973-74)
z According to this theory active site is not static, but it undergoes a conformational change which is induced
by specific substrate. The active site has two groups, (1) Buttressing (supporting) group & (2) Catalytic
group
z Buttressing group is meant for supporting the substrate, while the catalytic group break the substrate into
product.
FACTORS
(1) pH – Enzymes very sensitive to pH.
(2) Temperature – High temp inactivates enzyme causing their denaturation . They also get inactive at lower temp.
Generally all enzymes better perform at body temperature of organism.
(3) Enzyme concentration – Increase in concentration of enzymes will increase the rate of enzymatic reaction till
enough the substrate.
(4) Substrate concn – Increase in substrate concn increases the activity of enzymes until all the active sites of enzyme
are saturated.
Rxn.
Rate of

conc.

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BIOLOGY FOR NEET & AIIMS
(5) Inhibitors/Enzyme inhibition :-
(i) Competitive inhibitors or competetive inhibition and reversible type :-
z These are substrate analogues, which bind to the active site of enzymes & enzymes get inhibited, such
inhibition is called as competitive inhibition.
Eg. Succinic dehydrogenase is inhibited by its competitor malonate.
z This is reversible inhibition. Malonate is known as substrate analogue of succinate.
Similarly sulpha drugs are substrate analogue of p-amino benzoic acid (PABA) used in folic acid synthesis in
bacterical cells. Hence these drugs are used to kill bacterial cells.
(ii) Non-competitive inhibitors or non competitive inhibition and irreversible type :-
In this type of inhibition, inhibitor substance can bind simultaneously to an enzyme, other than it's active site
and destroy the sulfhydryl (S – H) group of enzyme.
Example :- Toxic metals, CO, CN poisoning of cytochrome oxidase.
Such inhibition are irreversible inhibition.
(iii) Non competitive & reversible type :- When inhibitor binds at allosteric site reversibly.
When product of biochemical reaction inhibits the enzyme action, it is known as product inhibition or
retro inhibition or feed back inhibition.
The product may binds at allosteric site of allosteric enzyme then it is non-competitive, reversible,
allosteric inhibition. Example : inhibition of hexokinase by glucose 6P.
Jacob & Monad. First discovered L-threonine dehydratase, inhibited by its product isoleucine.
In the allosteric modulation, chemical or products fits in allosteric sites & bring a change in shape of active
site of enzyme.
Chemicals which bind at allosteric site of allosteric enzymes are known as allosteric modulators.
If allosteric modulator positively change the configuration of active site, then called positive allosteric
modulation and if negatively change then called negative allosteric modulation respectively by +ve
modulator (activators) and –ve modulator (inhibitors).
Ex. Phosphofructokinase inhibited by ATP, activated by AMP, ADP and Glucose 2, 6 BisP.
Ex. hexokinase inhibited by glucose - 6P and exhibits feed back inhibition but not Glucokinase.
All allosteric modulation are not feed-back inhibition.

KM CONSTANT (MICHAELIS & MENTEN CONSTANT)

"Km constant of an enzyme, is the concentration of substrate at which rate of reaction of that enzyme attains half of
its maximum velocity". It is given by Michaelis & Menten. The value of Km should be lower for an enzyme.
Km exhibits catalytic activity of an enzyme.
Vmax
velocity of

1
V
2 max.

Substrate conc.

Ki constant (Enzyme inhibitor complex dissociation constant) indicates the dissociation of enzyme inhibitor complex
(EIC). of reversible inhibitors.
Km and Ki constant of an enzyme should be low.
1. If competitive inhibitor is present, then, km – - and Vmax. – No change.
2. If Non competitive inhibitor is present, then, Km – No change, Vmax. – Decrease
3. Competitive inhibition is overcome by increase in concentration of substrate.
4. Allosteric enzyme donot obey Km thus no Km is changes.

61
 RESPIRATION IN PLANTS

Maximal reaction

Rate of reaction
Rate of reaction

Maximal reaction

Competitive inhibitor non competitive inhibitor

Substrate concentration Substrate concentration

SPECIAL POINTS OF RESPIRATION & ENZYMES

NAD = Nicotinamide Adenine Dinucleotide
DPN = Diphospho Pyridine Nucleotide
NADP = Nicotinamide Adenine Dinucleotide Phosphate
TPN = Triphospho Pyridine Nucleotide
FAD = Flavin Adenine Dinucleotide
FMN = Flavin Mono Nucleotide
Co-A = Adenosine Triphospho Panto Thenylthio Ethanol Acetyl Amine
ATP discovered by Lohman, while importance of ATP in metabolism by Lipman.
1 gram of fat equals to 9.8 K.Cal.
Proteins = 4.8 K. Cal
Carbohydrate = 4.4 K. Cal (Old 3.8 K. Cal)
(Fat is energy rich respiratory substrate)
Almost all enzymatic reactions are reversible type.
Cytochromes are Iron - porphyrin protein discoverd by MacMunn (Termed by Keilin)
Entener - Doudoroff pathway, Occurs only in bacteria (Pseudomonas and Azotobacter for Carbohydrate - oxidation.
(Bacterial respiration)
1 ATP = 7.6 K.Cal. (now 1 ATP = 8.9 K. Cal.)
Imp. Coenzymes are
Co - I (NAD) / DPN.......................... Niacin
Co - II (NADP) / TPN .......................Niacin
FAD ....................................................... Riboflavin
FMN....................................................... Riboflavin
TPP ....................................................... Thiamine
CO - Q .................................................. Ubiquinone
CO-R ..................................................... Biotine
CO - A ................................................... Pantothenic Acid

Important Co-factor :-
Fe++ = Cytochrome oxidase, catalase, peroxidase, aconitase
Mg ++
= Hexokinase, glucokinase, pyruvate kinase, pepcase, Rubisco.
K +
= Pyruvate kinase
Cu++ = Cytochrome oxidase, tyrosinase

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BIOLOGY FOR NEET & AIIMS
Zn++ = Carbonic anhydrase, alcohol dehydrogenase
Mn ++
= arginase, ribonucleotide reductase, decarboxylase.
Mo = Nitrogenase complex, Nitrate reductase.
Se = Glutathione peroxidase
When respiratory substrate is fats or proteins, then level of Hg rises in Ganong's respirometer, because more O 2
absorbed than CO2 released.
In bacteria site of ETS is mesosome.
Respiration efficiency :
288 Kcal
1 glucose = 686 Kcal. 38 ATP × 7.6 Kcal. = u 1 00 = 42%
686
Thus efficiency of aerobic respiration is 42% +.
For the complete oxidation of one glucose if, in option 38 or 36 ATP are not given, then the answer goes to
32 or 30 ATP.
Significance of respiration
1. The energy released during respiration is used for the various metabolic processes.
2. Various chemical substances are formed in this process which are important for cellular componants.
3. CO2 released in this process maintains a balance in the atmosphere.
4. Complex insoluble food materials are converted into simple soluble molecules by this process.
5. It converts the stored (static)energy into more useful (kinetic) form.

63
 RESPIRATION IN PLANTS

o In cellular respiration, carbohydrates are primary respiratory substrates. Others are Fats, organic acids and proteins.
Organic acids are used in CAM plants.
o Cellular respiration is an multistep process so that energy released in some steps can be used for ATP synthesis. If
it occurs in single step, all the energy may released as heat.
o ATP - energy currency of the cell .
o Reasons behind absence of specialised respiratory organs in plants -

o Very little transport of gases required as each plant part takes care of its own gas exchange needs.
o Plants have slow respiration rate.
o In plants, most of the living cells located quite close to the surface of the plants.

1. Glycolysis - Greek words Glycos = Sugar, Lysis = Splitting.

o Also called EMP pathway (E = Embden, M = Meyerhof, P = Parnas)
o Common in both aerobic and anaerobic respiration.
o Occurs in cytoplasm and it is the partial oxidation of hexose (glucose or fructose) into two molecules of
pyruvic acid.
o No use of O2 and no release of CO2.
o Net or total ATP gain - 6 ATP or 8 ATP (2 NADH2 = 4 or 6 ATP + 2 ATP by SLP = Substrate level
o Direct gain of ATP = 2 ATP (by SLP) [Not count the ATP from NADH2]
o In glycolysis during anaerobic respiration, net or total or direct gain of ATP= 2 ATP [as NADH 2 not enter
into the ETS]
Conversion of pyruvic acid to Acetyl CoA (Link reaction) is an oxidative decarboxylation catalysed by pyruvic
dehydrogenase. (Occurs in the matrix of the mitochondria)
2. Krebs Cycle -
o Also called TCA (Tri Carboxylic Acid) Cycle or CA (Citric Acid) Cycle.
o Occurs in the matrix of the mitochondria.
o Involve 4 dehydrogenations (3 NADH2 and 1 FADH2) and 2 decarboxylations (2 CO2).
o Net or total ATP gain - 12 ATP (3 NADH2 = 9 ATP+ 1 FADH2 = 2 ATP+ 1 GTP = 1 ATP).
[If Question is asked for 1 glucose or fructose - in above point no. - (iii) and (iv) calculation will be double
as Krebs cycle occurs two times during complete oxidation of 1 molecule of glucose or fructose.]
o Cycle has single 5 carbon compound - oc-ketoglutaric acid.

3. Electron transport system (ETS) and oxidative phosphorylation -

o ETS is present in the inner mitochondrial membrane.
o Five complexes - NADH dehydrogenase (I), FADH2 (II), Cytochrome bc1 (III), Cytochrome a, a3 & 2 C
centres (IV) and ATP synthase (V).
o In respiration the energy of oxidation - reduction utilised in production of proton gradient t synthesis ATP
(Oxidative phosp!iorylation).
o Molecular Oxygen (O2) act as the final/ ultimate hydrogen (electron) acceptor and it get reduce, to water.
o Mobile electron carrier - Cytochrome C and ubiquinone (UQ) / CoQ.

In aerobic respiration, net or total gain of ATP from one glucose or fructose - 36 ATP or 38 ATP.
In aerobic respiration in prokaryotes - 38 ATP.
Respolaration is an amphibolic pathway (involved in both anabolism and catabolism).

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BIOLOGY FOR NEET & AIIMS
4. Fermentation :-
o Incomplete oxidation of respiratory substrate.
o Usually anaerobic, may be aerobic.
o Alcoholic fermentation - in yeast, Enzymes - pyruvic acid decarboxylase and Alcohol dehydrogenase.
o Lactic acid fermentation - In some bacteria and in muscles, Enzyme - Lactate dehydrogenase.
o Net or Total or direct gain of ATP = 2ATP.
o Naturally fermented beverages (alcoholic drinks) have about 13 percent alcohol concentration as yeast
poison themselves at this concentration.

5. Respiratory Quotient (R.Q.) -

o R. Q. = CO2 evolved / O2 consumed
o Depend upon the type of respiratory substrate.
o Carbohydrates (complete oxidation) = 1, Fat = 0.7, Protein = 0.9
o All enzymes are proteins (More correct - almost all enzymes are protein as some nucleic acids also behave like
enzymes and called ribozymes).
o Enzymes have primary, secondary and tertiary structure like proteins (mainly tertiary structure).
o Inorganic catalysts work efficiently at high temperatures while enzymes (biocatalysed) get damaged at high tem-
peratures.
o Enzymes increase the rate of any biochemical process by lower down the activation energy (energy difference
between substrate and transition state).
o Enzymes generally function in a narrow range of temperature and pH.
o Michaelis and Menten constant (Km) = Concentration of substrate at which enzymatic reaction attain Vmax/2.

o Competitive inhibitors are used in the control of bacterial pathogens. (Sulpha drugs are competitive inhibitors of
para-amino benzoic acid (PABA) which is required by bacteria to produce folic acid for their growth).
o According to modern classification enzymes are classified into 6 classes and each class has 4 - 13 subclass.
o According to this classification each enzyme has specific four digit number which indicate the position of enzyme
in classification e.g. - Hexokinase has 2.7.1.1 number.
o 6 Classes are - Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases.
o Cofactors are non protein constituents those bound to the enzyme to make the enzyme catalytically active.
o Cofactors are of 3 types -
(i) Prosthetic group - tightly bound organic compound e.g - haem group.
(ii) Coenzyme - Loosely bound organic compound (usually vitamins). e.g. - NAO and NADP. (Vitamin niacin).
(iii) Metal ions - loosely bound and inorganic, form coordination bonds. e.g. - Zn for enzyme carboxypepti
dase.

65
 RESPIRATION IN PLANT

SOLVED EXAMPLE
Ex.1 The energy releasing process in which the substrate Ex.8 Which of the option is correct for photorespiration
is oxidised without an external electron acceptor is (A) In chloroplast, glycerate forms glycine
called (B) In peroxisome, glycerate forms phosphoglycolate
(A) Aerobic respiration (B) Glycolysis (C) In mitochondria, glycine forms serine
(C) Fermentation (D) Photorespiration (D) In bundle sheath, serine form glycine
Sol. (C) Sol. (C) : Two molecules of glycine form a molecule of
serine, CO2 and NH3 in mitochondria.
Ex.2. How many ATP molecules are obtained from
fermentation of 1 molecule of glucose Ex.9 The three boxes in this diagram represent the three
(A) 2 (B) 4 major biosynthetic pathway in aerobic respiration.
Arrows represent net reactants or products.
(C) 3 (D) 5
Sol. (A)

Ex.3 During cellulose fermentation by anaerobic bacteria

in remen and reticulum, cellulose is majority
converted into Arrow numbered 4, 8 and 12 can all be
(A) Lactic acid (B) Ethyl alcohol (A) FAD+ or FADH2 (B) Unused
(C) Volatile fatty acids (D) CO2 (C) ATP (D) H2O
Sol. (C)
Sol. (C)
Ex.10 How many ATP are formed from NADPH+ to NAD+
Ex.4 Aerobic respiratory pathway is appropriately termed
(A) 2 ATP (B) 3 ATP
(A) Catabolic (B) Parabolic
(C) 6 ATP (D) 4 ATP
(C) Amphibolic (D) Anabolic
Sol. (B)
Sol. (C)
Ex.11 The net gain of energy from one gram molecule of
Ex.5 How many ATP molecules will be generated in a glucose when oxidized is
plant system during complete oxidation of 40 moles (A) 2 ATP (B) 36 ATP
of glucose ? (C) 38 ATP (D) 15 ATP
(A) 190 (B) 380 Sol. (C)
(C) 1520 (D) 3040
Ex.12 Choose the correct combination of labelling the
Sol. (C) molecules involved in the pathway of anaerobic
respiration in yeast
Ex.6 How much of the energy released during aerobic
respiration is approximately conserved in the form
of ATP
(A) 20 % (B) 40 %
(C) 60 % (D) 100 %
Sol. (B)

Ex.7 Chemiosmotic theory of ATP synthesis in the

chloroplasts and mitochondria is based on
(A) Proton gradient (A) A - EthanolB - CO2 C - Acetaldehyde
(B) Accumulation of K ions (B) A - CO2B - Ethanol C - Acetaldehyde
(C) Accumulation of Na ions (C) A - CO2B - Acetaldehyde C - Ethanol
(D) Membrane potential (D) A - AcetaldehydeB - CO2C - Ethanol
Sol. (A) (E) A - EthanolB - Acetaldehyde C - CO2
Sol. (E)

66
BIOLOGY FOR NEET & AIIMS
Ex.16 In glycolysis, the end product is
Ex.13 In which of the following reaction of glycolysis, a
(A) Protein is converted to glucose
molecule of water is removed from the substrate
(B) Glucose is converted into fructose
(A) Fructose - 6 - phosphate o fructose 1, 6 -
(C) Starch is converted into glucose
bisphosphate
(D) Glucose is converted into pyruvic acid
(B) 3 - phosphate glyceraldehyde o 1, 3 -
bisphosphoglyceric acid Sol. (D)

(C) PEP o Pyruvic acid

Ex.17 Glycolysis (EMP Pathway) takes place in
(D) 2 - Phosphoglycerate o PEP
Or
(E) Glucose o glucose 6 - phosphate
Anaerobic respiration takes place in the
Sol. (D)
(A) Mitochondria
(B) Cytoplasm
Ex.14 Which process does the following equation
represent (C) Both mitochondria and cytoplasm
(D) Vacuole
C6H12O6 + 2NAD + 2ADP + 2Pi o 2CH3 - CO - COOH
(B) : Glycolysis takes place in the cytoplasm and
+ 2NADH2 + 2ATP
does not use Oxygen. In anaerobic respiration only
(A) Complete glycolysis glycolysis is found, in which there is no need of
(B) Complete aerobic respiration mitochondria.
(C) Complete anaerobic respiration
(D) Complete fermentation Ex.18 What is oxidative phosphorylation?
Sol. Oxidative phosphorylation is a process in which
Sol. (A)
electrons are transferred from electron donors to
oxygen, which acts as electron acceptor. The
Ex.15 Consider the following statements with respect to
oxidation-reduction reactions are involved in the
respiration
formation of proton gradient. The main role in
A. Glycolysis occurs in the cytoplasm of the cell oxidative phosphorylation is played by the enzyme
B. Aerobic respiration takes place within the ATP synthase (complex V). This enzyme complex
mitochondria consists of F0 and F1 components. The F1 headpiece
is a peripheral membrane protein complex and
C. Electron transport system is present in the outer
contains the site for ATP synthesis from ADP and
mitochondria membrane inorganic phosphate. F0 component is a part of
D. C51H98O5 is the chemical formula of Tripalmitin, a membrane protein complex, which acts as a channel
fatty acid for crossing of the protons from inner mitochondrial
E. Respiratory quotient membrane to the mitochondrial matrix. For every two
protons passing through F0 – F1 complex, synthesis
Volume of O 2 evolved of one ATP molecule takes place.
= Volume of CO consumed
2

Of the above statements

(A) A, B and D alone are correct
(B) B, C and D alone are correct
(C) C, D and E alone are correct
(D) B, D and E alone are correct
(E) A, C and E alone are correct
Sol. (A)

67
BIOLOGY FOR NEET & AIIMS

Exercise PART - 1 PREVIOUS YEAR (NEET/AIPMT)

1. In which one of the following do the two names 7. How many ATP molecules could maximally be gen-
refer to one and the same thing : - erated from one molecule of glucose, if the complete
[CBSE AIPMT 2003] oxidation of one mole of glucose to CO2 and H2O
yields 686 kcal and the useful chemical energy avail-
(A) Tricarboxylic acid cycle and urea cycle
able in the high energy phosphate bond of one
(B) Kreb’s cycle and Calvin cycle mole of ATP is 12 kcal ? [CBSE AIPMT 2006]
(C) Tricarboxylic acid cycle and citric acid cycle (A) 30 (B) 57
(D) Citric acid cycle and Calvin cycle (C) 1 (D) 2

2. Which one of the following concerns photophos- 8. All enzymes of TCA cycle are located in the mito-
phorylation : - [CBSE AIPMT 2003] chondrial matrix except one which is located in inner
mitochondrial membranes in eukaryotes and in cy-
(A) AMP + Inorganic PO4 o
Light energy ATP
tosol in prokaryotes. This enzyme is:
(B) ADP + AMP o
Light energy ATP [CBSE AIPMT 2007]
(C) ADP + Inorganic PO4 o
Light energy ATP (A) lactate dehydrogenase
(B) isocitrate dehydrogenase
(D) ADP + Inorganic PO4 o ATP
(C) malate dehydrogenase
3. In alcoholic fermentation : - (D) succinate dehydrogenase
[CBSE AIPMT 2003]
(A) Oxygen is the electron acceptor 9. The overall goal of glycolysis, Krebs cycle and the
electron transport system is the formation of:
(B) Triose phosphate is the electron donor while
[CBSE AIPMT 2007]
acetaldehyde is the electron acceptor
(A) ATP is small stepwise units
(C) Triose phosphate is the electron donor while
pyruvic acid is the electron acceptor (B) ATP in one large oxidation reaction
(D) There is no electron donor (C) Sugars
(D) Nucleic acids
4. In glycolysis, during oxidation electrons are re-
moved by - [CBSE AIPMT 2004] 10. The chemiosmotic coupling hypothesis of oxida-
(A) ATP tive phosphorylation proposes that Adenosine Tri-
(B) Glyceraldehyde-3-phosphate Phosphate (ATP) is formed because:
(C) NAD+ [CBSE AIPMT 2008]
(D) Molecular oxygen (A) High energy bonds are formed in mitochondrial
proteins
5. Chemiosmotic theory of ATP synthesis in the chlo- (B) ADP is pumped out of the matrix into the inter-
roplasts and mitochondria is based on membrane space
[CBSE AIPMT 2005] (C) A proton gradient forms across the inner mem-
(A) Membrane potential brane
(B) Accumulation of Na+ ions (D) There is a change in the permeability of the in-
ner mitochondrial membrane toward Adenos-
(C) Accumulation of K+ ions
ine Di-Phosphate (ADP)
(D) Proton gradient
11. Aerobic respiratory pathway is appropriately termed
6. During which stage in the complete oxidation of :- [CBSE AIPMT 2009]
glucose are the greatest number of ATP molecules
formed from ADP - [CBSE AIPMT 2005] (A) Catabolic (B) Parabolic
(C) Amphibolic (D) Anabolic
(A) Glycolysis
(B) Krebs cycle
(C) Conversion of pyruvic acid to acetyl Co - A
(D) Electron transport chain

68
 RESPIRATION IN PLANT
12. The energy-releasing metabolic process in which 17. Which of the following biomolecules is common to
substrate is oxidised without an external electron respiration-mediated breakdown of fats, carbohy-
acceptor is called ? [CBSE AIPMT 2010, 08] drates and proteins? [NEET 2016]
(A) Glycolysis (B) Fermentation (A) Glucose-6-phosphate
(C) Aerobic respiration (D) Photorespiration (B) Fructose 1,6-bisphosphate
(C) Pyruvic acid
13. Which of the metabolites is common to
respirationmediated breakdown of fats, carbohy- (D) Acetyl CoA
drates and proteins ? [NEET 2013]
18. Which statement is wrong for Krebs’ cycle?
(A) Glucose–6–phosphate [NEET 2017]
(B) Fructose1,6–bisphosphate
(A) There are three points in the cycle where NAD+
(C) Pyruvic acid is reduced to NADH + H+
(D) Acetyl Co-A (B) There is one point in the cycle where FAD+ is
reduced to FADH2
14. The three boxes in this diagram represent the three
major biosynthetic pathways in aerobic respiration. (C) During conversion of succinyl Co-A to succinic
Arrows represent net reactants or products. acid, a molecule of GTP is synthesised
[NEET 2013] (D) The cycle starts with condensation of acetyl
group (acetyl Co-A) with pyruvic acid to yield
9 10
1 5
citric acid
Glucose Pathway A 2 Pathway B 6 Pathway C 11 19. What is the role of NAD+ in cellular respiration ?
7
4 8 12
[NEET 2018]
(A) It is a nucleotide source for ATP synthesis
3 (B) It functions as an electron carrier
Arrow numberd 4, 8 and 12 can all be : (C)It functions as an enzyme
(D)It is the final electron acceptor for anaerobic
(A) NADH (B) ATP
respiration
(C) H2O (D) FAD+ or FADH2
20. Which of these statements is incorrect ?
15. In which one of the following processes CO2 is not
released? [CBSE AIPMT 2014] [NEET 2018]
(A) Glycolysis operates as long as it is supplied
(A) Aerobic respiration in plants
with NAD that can pick up hydrogen atoms
(B) Aerobic respiration in animals (B) Glycolysis occurs in cytosol
(C) Alcoholic fermentation (C) Enzymes of TCA cycle are present in
(D) Lactate fermentation mitochondrial matrix
(D) Oxidative phosphorylation takes place in
16. Oxidative phosphorylation is NEET 2016] outer mitochondrial membrance
(A) Formation of ATP by transfer of phosphate
group from a substrate to ADP.
(B) Oxidation of phosphate group in ATP
(C) Addition of phosphate group to ATP
(D) Formation of ATP by energy released from elec-
trons removed during substrate oxidation

69
BIOLOGY FOR NEET & AIIMS

Exercise PART - 2 PREVIOUS YEAR (AIIMS)

9. In alcoholic fermentation, NAD+ is produced dur-
1. Which of the following is the connecting link be- ing the [2017]
tween glycolysis and Krebs cycle? [2007] (A) reduction of acetyldehyde to ethanol.
(A) acetyl Co-A (B) oxalosuccinic acid (B) oxidation of glucose.
(C) pyruvic acid (D) citric acid (C) oxidation of pyruvate to acetyl coA.
(D) hydrolysis of ATP to ADP.
2. Cut surfaces of fruit and vegetables often become
10. Glycolysis is [2018]
dark because [2008]
(A) Anaerobic (B) Aerobic
(A) dirty knife makes it dark (C) Anaerobic Aerobic both(D) None
(B) oxidation of tannic acid in the presence of trace Statement based question : -
of iron from the knife makes it dark
(C) dust of the air makes it dark Each of the questions given below consist
(D) none of the above. of Assertion and Reason. Use the following
Key to choose the appropriate answer.
3. The enzyme decarboxylase catalyses the following
step [2009] (A) If both Assertion and Reason are correct,
(A) conversion of citric acid to cis aconitic acid and Reason is the correct explanation of
(B) fumaric acid to malic acid Assertion.
(C) oxalosuccinic acid to D-ketoglutaric acid (B) If both Assertion and Reason are correct
(D) malic acid to oxaloacetic acid but Reason is not the correct explanation
4. Which of the following it true regarding the given of Assertion.
electron transport chain ? [2009] (C) If Assertion is correct but Reason is
CoQ o Cyt c o Cyt aa3 o O2 incorrect.
(A) CoQ o Cyt c is H+ absorbing site
(D) If Assertion is false but Reason is correct.
(B) aa3 o O2, H+ yielding site
ASSERTION AND REASON
(C) CoQ o Cyt c is H+ yielding site and aa3 o O2 is
11. Assertion : F1 particles are present in the inner mi-
H+ absorbing site tochondrial membrane. [2008]
(B) No H+ is absorbed or released Reason : An electron gradient formed on the inner
5. After glycolysis, fate of glucose in mitochondrial mitochondrial membrane, forms ATP. [2009]
matrix is [2011]
12. Assertion : Glycolysis is the first step of respiration
(A) carboxylation in which glucose completely breaks into CO2 and
(B) reduction H2O.
(C) oxidative decarboxylation 13. Assertion : Glucose is the favoured respiratory sub-
strate. [2014]
(D) hydrolysis
Reason : When glucose is used as respiratory sub-
6. In aerobic respiration, total number of ATP mol- strate it is completely oxidised, and RQ is 1.
ecules formed from 1 glucose molecule is [2012] 14. Assertion : Hybrid is formed by cross between two
(A) 28 (B) 32 (C) 36 (D) 30 organisms that are different in one, or more than
one traits [2018]
7. Which enzyme helps in transfer of phosphate group Reason : Mendel crossed two plants differing in
from ATP to a carbohydrate ? [2015] one trait to obtain F1 plants which is monohybrid
cross
(A) Phosphatase (B) ATPase
15. Assertion : Photorespiration is found in all plants
(C) Phosphorylase (D) Catalase [2018]
8. Refer the given equation and answer the question. Reason : In C4 plants, first CO2 fixation product is
2(C51H98O6) +145O2 o 102CO2 + 98H2O Energy formed in bundle sheath cells
16. Assertion : Fermentation is incomplete oxidation of
The R.Q of above reaction is [2017] glucose [2018]
(A) 1 (B) 0.7 (C) 1.45 (D) 1.62 Reason : Pyruvic acid decarboxylase, Alcoholic de-
hydrogenase catalyze the reaction

70
 RESPIRATION IN PLANT

ANSWER KEY

EXERCISE : PART - 1
1. C 2. C 3. B 4. C 5. D 6. D 7. B 8. D 9. A 10. C 11. C 12. B 13. D
14. B 15. D 16. A 17. D 18. D 19. B 20. D

PART - 2
1. A 2. B 3. C 4. C 5. C 6. C 7. C 8. B 9. A 10. A 11. C 12. D 13. A
14. B 15. D 16. A

71
BIOLOGY FOR NEET & AIIMS

HINTS & SOLUTIONS

EXERCISE
P-1 (NEET/AIPMT)
1. (C) Tricarboxylic acid cycle is also known as citric 6. (D) The last step of aerobic respiration is the oxida-
acid cycle. This is an aerobic process, that takes tion of reduced coenzyrnes, i.e., NADH2 and FADH2
place in the matix of mitochondria. Kreb that dis- by molecular oxygen through FAD, ubiquinone, cyt.-
covered this cycle in 1937. So, this is also known as b, cyt -c, cyt-c1, cyt-a and cyt.-a3. By oxidation of 1
Krebs’ cycle. molecule of NADH2, 3 ATP molecules are produced
and by oxidation of 1 molecule of FADH2 2ATP
2. (C) Phosphorylation refers to the process in which molecules are produced . In glycolysis 2 ATP mol-
ATP is made when energy is used to bind another ecules are produced from ADP.
phosphate to ADP. Photophosphorylation reactions Further 2NADH2 produced, give 2 × 3 = 6 ATP, on
are part of both respiration and photosynthesis. oxidative phosphorylation. Similarly in Krebs’ cycle
2 ATP molecules are produced. So the greatest num-
3. (B) In alcoholic fermentation, ber of ATP molecules are produced in the electron
(A) NADH (formed during conversion of triose-3 transport chain.
phosphate to 3 phosphoglycerate) is oxidised to
NAD+ 7. (B) One mole of ATP liberates 12 kcal of energy, so
(B) Electrons are accepted by acetaldehyde formed 686 kcal will be liberated by 686 / 12 = 57.1 ATP
by decarboxylation of Pyruvate. molecules.
8. (D) Succinate dehydrogenase enzyme is present
4. (C) When 3-phosphoglyceraldehyde is converted on inner membrane of mitochondria and catalyses
into 1,3 diphosphoglyceric acid, two electrons and the oxidation of succinate to fumarate.
two protons are released which are utilised to
convert NAD+ to NADH and one H+. 9. (A) Glycolysis, Krebs’ cycle and electron transport
system are meant for ATP synthesis in different
NAD+ + 2H+ + 2e– o NADH + H+
steps. ATP is the energy curency of cell.
5. (D) Chemiosmotic hypothesis for oxidative phos-
phorylation (ATP synthesis) was proposed by Pe-
ter Mitchell in 1961, for this he was awarded Nobel
Prize in 1978. This theory is based on proton gradi-
ent.

72
BIOLOGY FOR NEET & AIIMS
10. (C) The production of ATP with the help of energy
liberated during oxidation of reduced coenzymes 15. (D)
and terminal oxidation is called oxidative phospho- 2 lactate
Glucose
rylation. Peter Mitcheli (1961) gave a hypothesis
known as chemiosmotic hypothesis for ATP syn- P+ + ADP + 2P NAD
thesis. According to this when electrons flow from
Glycolisis
dual proton, electron carrier to a non-hydrogen car- 2NADH
+

rier the H+ are released and expelled into the inter- ATP + PPP +
+2H
membrane space and thus creates a proton gradi- 2 pyruvate
ent with higher concentration of H+ in the inter
membranous space than the matrix. Lactic acid fermentation is process by which glu-
cose, fructose and sucrose are converted into en-
Due to the proton motive force the protons flow
ergy and the metabolite lactate. It is an anaerobic
back and energy liberated during this back flow of fermentation reaction that occurs in some bacteria
protons activate ATPase present in F1 head to syn- and animal cells and allows glycolysis to continue
thesize ATP. by ensuring that NADH is returned to its oxidised
11. (C) An amphibolic pathway is a biochemical path- state (NAD+ )
way that serves both anabolic and catabolic pro- 16. (A) Oxidative phosphorylation is the process of
cesses. An important example of an amphibolic path- formation of ATP from ADP and inorganic phos-
way is the Krebs’ cycle, which involves both the phate (Pi ) in the presence of oxygen. It occurs
catabolism of carbohydrates and fatty acid and the mainly in the Electron Transport Chain (ETC) of
synthesis of anabolic precursors for amino acid cellular respiration.
synthesis, eg, D-ketogluturate and oxalo acetate. 17. (D) Carbohydrates, fats and proteins, all can be
12. (B) Fermentation takes place in the lack of oxygen used as a substrate in celiuiar respiration. All of
(when the electron transport chain is unusable) and them first get converted to acetyl Co-A to enter into
becomes the cell’s primary means of ATP (energy) Krebs’ cycle of aerobic cellular respiration. Thus, it
production. It turns NADH and pyruvate in the gly- is the common factor of respiration entering Krebs’
colysis into NAD+ and various small molecules de- cycle after breakdown of carbohydrates, fats and
pending on the type of fermentation. In the pres- proteins.
ence of O2, NADH and pyruvate are used to gener- 18. (D) Option (D) is incorrect, which can be conected
ate ATP in respiration. It is called oxidative respira- as Krebs’ cycle starts with the condensation of
tion. acetyl group with oxaloacetic acid and water to yield
citric acid.
13. (D) Acetyl Co-A is common to respiration medi-
ated breakdown of fats, carbohydrates and proteins. During conversion reduced to fumaric acid FAD+ is
Glucose and fructose are phosphorylated to give reduced to FADH2. During conversion of pyruvic
rise to glucose-6-phosphate by the activity of the acid to acetyl Co - A, isocitrate to oxalosuccinic
enzyme hexokinase. Glucose-6-phosphate is then acid and D - ketoglutaric acid to succinyl Co-A
converted into fructose-6-phosphate and further to NAD+ is reduced to NADPH + H+.
fructose 1-6-bisphosphate. Pyruvic acid is the end 19. (B) NAD+ Function as an electron carrier in cellular
product of glycolysis. respiration. It is a co-enzyme and not an enzyme.
14. (B) Pathway A is glycolysis, pathway B is the Krebs’
cycle and pathway C is oxidative phosphorylation 20. (D) Oxidative phosphorylation takes place in inner
Arrow 1 – ADP or NAD+ mitochondiral membrane.
Arrow 2 – Pyruvate
Arrow 3 – NADH
Arrow 4 – ATP
Arrow 5 – ADP, NAD+ or FAD
Arrow 6 and 7 – FADH2 and NADH (ei
ther one can be 6 or 7)
Arrow 8 – ATP or CO2
Arrow 9 and 10 – O2 and ADP (either one
can be 9 or 10)
Arrow 11 and 12 – H2O and ATP (either
one can be 11or 12)

73
 RESPIRATION IN PLANT
EXERCISE
Reason is not the correct explanation of the Asser-
tion.
P-2 (AIIMS) (c) If Assertion is true but Reason is false.
1. (A) During glycolysis 1 molecule of glucose is con- (d) If both Assertion and Reason are false.
verted to 2 molecules of pyruvic acid in the cyto- 9. (A) Alcoholic fermentation is a process in which
plasm. These two molecules of pyruvic acid is then molecules such as glucose etc. are
converted to acetyl CoA by decarboxylation. This converted into cellular energy and thereby
acetyl CoA is the connecting link between glycoly- 10. (A)
sis and Krebs cycle. Acetyl CoA thus formed par- 11. (C) Oxysomes of F0 – F1 particles are present on the
ticipates in Krebs cycle and combines with oxalo- inner mitochondrial membrane. The F1 head-piece
acetic acid to form citric acid. of oxysome functions as ATP-synthetase which
2. (B) synthesises ATP from ADP and ip (inorganic phos-
3. (C) Oxalosuccinate is decarboxylated to form D-ke- phate) using energy from proton gradient or ATP
toglutarate through the enzyme decarboxylase. It is synthetase becomes active in ATP formation ony
one of the step involved in Kreb’s cycle. It releases when there is a proton gradient having high con-
on molecule Of CO2. centration of protons on F0 side (base) as compared
Oxalosuccinate
Decarboxylase
D-ketoglutarate + CO2 to F1 side (head piece) F0 – F1 particles or oxysomes.
Mg2+ 12. (D) Glycolysis is the process of breakdown of glu-
4. (C) In electron transport chain electrons transport cose or similar hexose sugar into two molecules of
through a series of carriers. H+ of NADH+ (received pyruvic acid through a series of enzyme mediated
from Krebs cycle) is accepted by FAD as a result of reactions, releasing energy (ATP) and reducing
which FAD is reduced to FADH+ and NADH+ is power (NADH2). It is the first step of respiration,
oxidised to NAD. Reduced FADH+ is oxidised by which occurs inside the cytoplasm and is indepen-
CoQ, with tghe formation of CoQH+. H+ ions then dent of O2. In glycolysis, two molecules of ATP are
move to Cyt b, then Cyt c, Cyt a and Cyt aa3. Ulti- consumed during double phosphorylation of glu-
mately these H+ are accepted by O2 and H2O is cose to form fructose 1, 6 diphosphate. Four mol-
formed. ecules of ATP are produced in the conversion of 1,
5. (C) Pyruvic acid formed as a result of glycolysis, 3-diphosphoglycerate to 3-phosphoglycerate and
enters mitochondria and undergoes oxidative de- phosphenol pyruvate to pyruvate whereas, two
carboxylation to form acetyl CoA, NADH and molecules of NADH2 are formed during oxidation
evolve CO2. The reaction occurs in the presence of of glyceraldehyde 3-phosphate to
enzyme complex pyruvate dehydrogenase. Acetyl 1, 3-diphosphoglycerate. Since, each NADH is
CoA then undergoes oxidation to form CO2 and H2O equivalent to 3 ATP, so net gain in glycolysis is 8
through Kreb’s cycle in mitochondrial matrix. ATP.
6. (C) The net gain from complete oxidation of a glu- 13. (A) The ratio of the volume of CO2 evolved to the
cose molecule in aerobic respiration is 36 ATP mol- volume of O2 consumed in respiration is called the
ecules. 10 molecules of NADH2 (2 from Glycolysis respiratory quotient (RQ) or respiratory ratio.
+ 8 from Kreb’s cycle) yield = 10 × 3 = 30 ATP, 2 Volume of CO 2 evolved
RQ
molecules of FADH2 yield = 2 × 2 = 4 ATP and gly- Volume of O 2 consumed
colysis also yields 2 ATP. Therefore, total release of The respiratory quotient depends upon the type of
ATP per hexose will be = 30 + 4 + 2 = 36 ATP. respiratory substrate used during respiration. When
7. (C) Transfer of phosphate group from ATP to a car- carbohydrates are used as substrate and are com-
bohydrate is referred to as phosphorylation and is pletely oxidised, the RQ will be 1, because equal
carried out in the presence of phosphorylase en- amounts of CO2 and O2 are evolved and consumed.
zymes. E.g., glucose (a carbohydrate) is phospho- C6H12O6 + 6O2 o 6CO2 + 6H2O + Energy
rylated to glucose-6-phosphate by ATP in the pres- 6CO 2
ence of enzyme hexokinase or glucokinase and Mg2+. RQ 1
8. (B) The ratio of the volume of CO2 liberated to 6O 2
the volume of oxygen absorbed per
molecule during respiration is called
RespiratoryQuotient (RQ). The value of RQ
indicates the types of respiratory substrate. 14. (B)
Volume of CO 2 evolved 15. (D)
102 16. (A)
RQ = Volume of O consumed ŸRQ = = 0.7
2 145
In the following questions, a statement of Asser-
tion is followed by a statement of Reason.
(a) If both Assertion and Reason are true and the
Reason is the correct explanation of the Assertion.
(b) If both Assertion and Reason are true but the

74
PLANT GROWTH AND
CHAPTER
14
DEVELOPMENT
“The true laboratory is the mind, where behind illusions we uncover
the laws of truth..”

“J.C. BOSE ( 1858-1937)”

INTRODUCTION

G
rowth is a characteristic feature of all living organisms. It is also a vital process,
which brings about permanent and irreversible change in any plants or its part.
Development is the sum of two processes: growth and differentiation. To begin with,
it is essential and sufficient to know that a mature plant develops from a single-celled
zygote which divides and differentiates to form various types of cell.
The structures like flowers, leaves or fruits show limited growth and dimensions due
to which these appear and fall periodically whereas other strutures like roots and
stem remain intact and show unlimited growth. This chapter will let you know about
the various factors involve in govern and control of development processes.

75
BIOLOGY FOR NEET & AIIMS

INTRODUCTION :
z Growth is a characteristic feature of all living organisms.
z Growth is a vital process, which brings about permanent and irreversible change in any plant or its part.
z Growth in plants means increase in shape, size, weight and volume of a plant or plant part.
z Growth leads to increase in fresh weight, dry weight, length, area, volume and cell number. All these are controlled
externally (by environmental factors) and internally (by Genetics).
z Growth is diffused in animals, but in plants growth is localised & irregular (nail in plant stem, occupies same
height till several years of growth).
z Seed germination is the first step of plant growth. Almost all the plants face a period of suspended growth.
z If the suspension of growth is due to exogenously controlled factors (environmental factors) then it is called
quiescence. Development is a part of growth.
z When the suspension of growth is due to the endogenously controlled factors (hormonal, genetic) then it is termed
as dormancy.
z Weight increased during growth but exceptions are potato & seed germination, where weight decrease.

PHASES OF GROWTH
(1) Phase of cell division or cell formation :- Number of cells is increases by cell division.
(2) Phase of cell enlargement or cell elongation :- Size of cells increases due to vacuolization & TP (turgor pressure).
(3) Cell maturation or differentiation phase :- (Also called as morphogenetic, organogenic phase) Development or
qualitative change is important feature of this phase.
Pattern or course of plant growth : (growth curve)
z The pioneering work on growth was done by Von Sachs.
z He plotted a growth curve between time & growth, which is known as sigmoid curve or S–curve or GP (Grand
period)–curve.
z Growth pattern of cell, organisms is uniform under favourable conditions. Thus following phases of growth are
recognized.
(1) Lag phase :- In lag period the growth is slow.

(2) Log phase :- Also called as exponential phase. During this phase growth is maximum & most rapid.
(3) Steady or stationary phase :-
Time taken in growth phases (mainly log phase) is called as "grand period of growth".

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Measurement of growth :
(1) By direct observation
(2) By horizontal microscope
(3) By Crescograph (J.C. Bose) :- It magnifies growth as 10,000 times
(4) By Auxanometers :-
(i) Arc - auxanometer
(ii) Pfeffer's auxanometer/pully auxanometer (Permanent graph on smoke paper)
(iii) Micrometer screw - auxanometer
Factors affecting plant growth :
(1) Light :- Light involves in photosynthesis and determine the direction of shoot and root growth. Light controlled
morphogenesis of plant is called photomorphogenesis.
Light is not essential during the initial stage of growth or seed germination. In absence of light plant exhibit
etiolation.
(2) Temperature :- Optimum temperature for growth is 20 - 35°C. temperature above 45°C damages the protoplasm and
growth can be retarded.
Effect of low temperature on flowering is called vernalization.
(3) Water :- Water maintains the turgidity of cell, which is essential for growth. (TP is important for growth.) in order to
cell to grow \ Z must not be allowed to reach zero.
Water is essential for the enzyme activity in protoplasm.
(4) Oxygen :- Necessory for cell respiration.
(5) Mineral nutrients :- All essential elements are compulsory for growth and metabolism.
(6) Genetic factors :- Genotype & Phenotype.

PLANT HORMONES
First of all idea of plant hormones was given by Von Sachs "organ forming substance"
Ist Plant hormone discovered by F.W.Went was auxin but term hormone was given by starling & phytohormone by
Thieman.
Chemicals, which act as natural phytohormones are called as synthetic growth hormones. Synthetic auxins – a & b–
NAA, 2,4-D, 2,4,5-T, IPA, PAA, IBA, Maleic hydrazide (MH).
NAA – Napthalene acetic acid.
2,4–D – 2, 4-Dichlorophenoxy acetic acid.
2,4,5–T – 2, 4, 5-Trichloro phenoxy acetic acid.
IPA – Indole Propeonic/Pyruvic acid
PAA – Phenyl/phenoxy acetic acid

Hormones
(a) Growth Promoters
Factors
Growth (IAA, GA, CK)
Regulators
(b) Growth retardants or Inhibitors
Substances (ABA, C2H4)

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AUXINS
History –
First of all Charles Darwin & F. Darwin (1880) was studying phototropism. They observed coleoptile bending in Canary
grass (Phalaris). Wrote, Book "Power of movements in plants" term - “Stimulus” By Darwin
Boysen & Jensen 1910 :- Experiments on oat (Avena sativa) Plant.
In the first experiment, he removed the coleoptile tip and then replaced it on stump. On providing unilateral light the
coleoptile tip gave positive curvature.
They observed, that if gelatin inserted between the tip & cut stump, then coleoptile bends towards the unilateral light.
If mica inserted then coleoptile fail to show phototropism. Material substance term for growth hormone was given by
him.
Paal :- Demonstrated that, when the cut tip was replaced on cut end (stump) eccentrically (asymmetrically) it causes
bending even in dark.
If coca butter or platinum foil inserted-there is no curvature observed.
Idea of unequal distribution of growth substance was given by Paal. large amount of substance found on shaded side.
F.W. Went (1928):- Went isolated the growing tip of Avena sativa on agar plate & performed Agar–block experiment.
He gave name “auxin” to growth substance, thus credit of auxin discovery goes to F. W. Went
He also found that the curvature (bending) in Avena coleoptile is proportional , with in limits to the amount of auxin in
Agar - block. This test was named as Avena curvature-test (Bioassay of Auxin).
Went found that 27% auxin present on illuminated side & 57 % on the dark side. (About 16% auxin lost on illuminated
side & rest transferred to base)
Transport of natural auxin is basipetal & polar type. (Synthetic ® auxin = apolar transport)
Kogl & Haagen Smit (1931) :- Isolated an active substance from urine of pellagra patient, which was called as auxin -
A or chemically auxenotriolic acid (C18 H32O5)
Later a similar substance was isolated from corn grain oil and was named as auxin-B or auxenolonic acid. (C18H30O4)
Again Kogl, Erxleben & Haagen Smit 1934 - Isolated another substance from human urine and named as heteroauxin
(IAA - C10H9O2N) by Thimann.
Auxin from Rhizopus was obtained by Thimann.
Auxin biosynthesis occurs by tryptophan amino acid in the presence of Zn++ ion.
Enzymatic (by IAA oxidase)

ª
Degradation or oxidation of auxin «
¬
Photooxidation
Now IBA (Indole butyric acid) has been also isolated from plants (natural auxin) but IAA, is most widely found auxin in
plants.
The compounds, which can be converted into auxin are called as auxin precursor, whereas the compound, which inhibit
the activity of auxin are called as antiauxins.
The auxin, which can be easily extracted in agar are called free auxins, while auxins, which are not easily extracted
practically are called bound auxins. A dynamic equilibrium is exists between these two forms (free and bound auxins).
Physiological effects and applications of auxin

(1) Apical dominance :- The phenomenon, in which apical bud dominates over the growth of lateral buds is called
apical dominance. Prunning in gardens promotes densing of hedge.

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(2) Cell division & cell enlargement/Callus formation :- Auxin is important in tissue culture & grafting. It stimulates
division of intrafascicular cambium. Also in healing of wounds.
(3) Shortening of internodes :- a-NAA induces the formation of dwarf shoot or spurs in apple, pear etc., thus number
of fruits increases.
(4) Prevention of lodging :- Auxin spray prevents lodging of crops, immature leaves & fruits.
(5) Root initiation :- Rooting on stem cuttings is promoted by IBA & NAA (Root growth inhibited by auxin)
(6) Potato dormancy :- MH (Maleic-Hydrazide), a-NAA, induces dormancy of lateral buds in potato tubers & potato
can stored for long duration.
(7) Prevention of abscission :- IAA, NAA prevents premature abscission of plant organs.
(8) Flower initiation :- Auxin is inhibitor of flowering but it promotes uniform flowering in pine apple & litchi plants.
(9) Parthenocarpy :- Seed less fruits can be produced by spray of IAA. (By Gusteffson)

(10) Selective weed killer :- Dicot broad leave weeds can be eradicated by 2,4-D & 2,4-5-T
Agent orange

Agent orange is used in biowar. It was used by USA against Vietnam (1966-70)
(11) Femaleness :- Feminising effect in some plants.
(12) Flower & fruit thinning :- Certain trees like mango form less number of fruits in alternate years. But auxins can
produced normal fruit crops every year. This is known as fruit thinning.
(13) When antiauxin (TIBA-Tri-Iodo Benzoic Acid) are sprayed on mature cotton field then cotton balls can picked
easily.
Bio-assay
Bioassay means the testing of substance for it's activity in causing a growth response in a living plant or it's parts.
(i) Avena curvature test
(ii) Root growth inhibition test, are bioassays for examining auxin activity.
GIBBERELLINS
First of all Japanese farmers observed peculiar symptoms in rice seedlings & called the bakanae disease (foolish
seedling disease)
Rice plants become thin, tall & pale due to infection of Gibberella (Ascomycetes) or Fusarium (Duteromycetes)
confirmed by Kurosawa & Swada.
Yabuta and Sumiki 1938 were the first to extract a crystaline substance from the Gibberella fungus , which they named
as Gibberellin.
Gibberellin, is an acidic & posses a gibben ring structure, are able to overcome genetic dwarfism in plants.

100 type of Gibberellins (GA1, GA2 GA3 ............ GA100) are known. GA3 [C19H26O6] is representative of all gibberellins.

GA found in all groups of plants (algae, to angiosperms, but as a flowering hormone acts only in angiosperms.
Biosynthesis of gibberellin takes place by mevalonic acid pathway (Kaurene o GA)

Physiological effects and applications

(1) Stem/internode elongation :- GA induces internode elongation, leaf expansion & used in sugarcane cultivation.
Gibberellins induce stem elongation in rosette plants (Cabbage) this phenomenon known as bolting effect. (Elimination
of rossete habit in some plants by gibberellins action is bolting)
(2) Elongation of genetic dwarf plants :- When gibberellin are applied to dwarf maize, pisum & vicia faba, then they
become tall. The rosset plant of sugarbeet indicate an extreme dwarfism, this habit can be eliminate by GA.

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(3) Flowering in LDP, in short light duration :- (Shortning of life cycle)
(4) Parthenocarpy :- Like auxin, exogenous use of GA also induces the formation of seedless fruits.
(5) Substitution of cold treatment or vernalisation :- The biennials plants form their vegetative body in the
I st year. Then they pass through a winter season & produce flower & fruits in II nd year. GA induces flower
in first year.
(6) Breaking of dormancy :- GA breaks the dormancy of seeds, buds and tubers
(7) Seed germination :- Gibberellin induce the synthesis of hydrolysing enzymes like a-amylse, lipases, & proteases
(8) Sex expression :- GA induces maleness in Cucumis, Cannabis.
(9) Germination of photoblastic seeds :- Gibberellin treated light sensitive seeds can germinates in dark. Ex. Lettuce,
Tobacco.
(10) Fruit & flower enlarger :- Size of grape fruits & bunch & Geranium flowers increased by GA
Pomalin Ÿ GA (GA4 & GA7) + CK (6-Benzyladenine) – acts as an apple enlarger..
(11) In fermentation :- More growth of yeast cells by GA.
(12) Increase height of Sugarcene plant :- (More sugar contents by IAA )

Bio–assay :– (1) a-amylase activity test in barley endosperm

(2) Dwarf pea & maize test

CYTOKININS (CK)

Cytokinin was discovered by Miller when he was working (in lab. of prof. Skoog) on tobacco pith culture. He added the
contents of an old DNA-bottle (Herring fish sperms DNA) to the culture medium & observed that the tobacco pith
callus could grow for longer period.
Miller isolated an active substance from autoclaved DNA from Herring sperm, which stimulated cell division. He named
this substance as kinetin
Term cytokinin By Letham, Phytokinin by Osborne and Kinin by Skoog.
The first natural cytokinin was identified & crystalized from immature corn grains by Letham & named as Zeatin.
The most common cytokinin in plants are isopentenyl adenine zeatin .
BAP (Benzylamino purine), diphenylurea and thidiazuron are synthetic cytokinins.
Cytokinin is a derivative of adenine base.
Root tips are major site of synthesis of CK (by mevalonic acid pathway).
Movement of cytokinin is polar & basipetal.
Coconut milk factor also performed activity like cytokinin, thus used in tissue culture.
Zachau obtained cytokinins from serine-t-RNA of yeast.

Physiological effects and applications

(1) Cell division & Cell enlargement :- One of the most important biological effect of CK (cytokinin) on plants is
induction of cell division. In tissue culture also.
(2) Formation of interfascicular cambium and induce secondary growth.
(3) Morphogenesis :- Morphogenetic changes induced by CK in presence of IAA.
High auxin + low CK - Root formation

Low CK Hight CK
( Hight Auxin Ratio oroot) ( Ratio o shoot differentiation)
Low Auxin

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(4) Counteraction of apical dominance :- promotes growth of lateral buds.

(5) Breaking the dormancy of seeds :- Like GA the dormancy of certain seeds can be broken by CK.
(6) Seed germination :- Seeds of parasite plant (Striga) can germinate in the absence of host by CK treatment.
(7) Delay in senescence :- (Richmond Lang Effect) The ageing process of leaves usually accompanies with loss of
chlorophyll & rapid catabolism. This is called as senescence. senescence postponed by CK. (increase short life of
plant parts)
(8) Lignin biosynthesis.
(9) Parthenocarpy in some fruits.
(10) Pro-plastids modification.
(11) Phloem conduction (nutrients mobilisation)
(12) Femaleness.
(13) Flowering in SDP (also in long days).
(14) Induce stomatal opening :-
Bio–assay :– (1) Tobacco pith cell division test
(2) Chlorophyll preservation (retension) test (delay in senescence test)
(3) Soyabean and radish cotyledon cell division test.

ABSCISIC ACID (ABA C15H20O4)

First indication of growth inhibitors was given by Osborne.
First growth inhibitor was identified by Bennet-Clark and Kefford (1953) from dormant potato tuber and called it b-
inhibitor.
Addicott & Okhuma (1963) obtained from mature cotton fruits and named as Abscisin II.(C15H20O4)
Waring & Robinson – Isolated a growth inhibitor from old Betula leaves & called as dormin.
Later establised that b-inhibitor, Abscisin-II and dormin are same and called as Abscisic acid.
ABA is the most wide spread growth inhibitor in plants.
ABA synthesized by Mevalonic acid pathway & oxidation of carotenes in chloroplasts.
ABA also known as stress hormone, because it protects plants from adverse conditions like water stress. ABA increases
tolerance of plants to various type of stresses.

Physiological effects and applications

(1) Induce abscission – ABA causes ageing and abscission of leaves & fruits (antiauxin) (cellulase & pectinase genes
induced by ABA)
(2) Induce bud & seed dormancy – ABA regulates (anti–GA) bud & seed dormancy.
ABA plays a major role in seed maturation enabling seeds to become dormant.
(3) Induce senescence – ABA accelerates senescence of leaves.
(4) Inhibition of cell division & cell elongation – anti CK.
(5) Stomatal closing – ABA causing the stomatal closing under the water stress conditions. Increases resistance to
frost injury. (anti transpirant & stress hormone)
(6) Delaying of flowering in LDP.
(7) Tuberisation in potato.
(8) Inhibitor of a–amylase synthesis – Inhibition of seeds germination.
(9) Geotropism in roots.

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ETHYLENE
H.H Cousin first suggested, that ripened oranges are responsible for ripening of unripen bananas.
Ethylene is a gaseous pollutant hydrocarbon, but Burg reported it as a fruit ripening hormone.
Pratt Goeschl – Recognized ethylene as a natural plant growth regulator.
Biosynthesis of ethylene takes place by methionine amino acid. Ethylene is synthesized in large quantity by ripening
fruits and senescent organs.
Ethylene also formed in roots in water logged condition.

Physiological effects and applications

(1) Post harvest ripening of fruits – Citrus, oranges, banana, apple, tomato. today ethephon/CEPA (Chloroethyl
Phosphonic acid) used at commercial level.
(2) Stimulation of senescence & abscission of leaves. Ethylene is synthesized in large quantity by ripening fruits and
senescent organs.
(3) Flowering in pineapple.
(4) Triple response on stem :- (i) Inhibition of stem elongation
(ii) Stimulation of radial swelling of stem
(iii) Horizontal growth of stem (ageotropism)
(5) Inhibits root growth :- Ethylene is inhibitor of root growth but stimulates the formation of root hairs.
(6) Epinasty of leaves.
(7) Femaleness (Feminising effect) Pineapple (Bromeliaceae).
(8) Tightening of hooks of epicotyl and hypocotyl.
(9) Inhibits the polar movement of auxin.

Other growth regulating substances

Wound hormone Traumatic Acid :- Induce callus formation on injured parts (healing of wounds) Chemically traumatins
are auxin like substance.
Calines (Formative hormones)
(i) Rhizocalines :- Produced by leaves & induce formation of roots.
(ii) Caulocalines :- Produced by roots & induce formation of stem.
(iii) Phyllocalines :- (Self forming hormone) produced in cotyledons & leaves, induce division of leaf
mesophylls.
Morphactins or (HFCA) These are, synthetic growth inhibitors, which are polyvalent (wide range) in action
(i) Inhibition of internode elongation
(ii) Reduction of apical dominance & promotion of lateral branching
(iii) Reduces the laminar area of leaf.
(iv) Abolition of phototropism
Chlormequat (CCC or Cycocel):- Growth inhibitor, which is used in bonsai.
Alar - 85 (B-Nine):- in floriculture
Agent orange :- Mixure of 2,4-D & 2,4,5-T used in bio–war. (Used by U.S.A. in Vieatnam war)
Amo - 1618 :- in biowar.
Phosphon-D, Cycocel, Amo-1618, Alar-85, Ancymidol (A-REST) are antigibberellins and cause inhibition to stem
growth.

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PHOTOPERIODISM

The relative length of day & night is called as photoperiod.

The response of plants to the photoperiod, expressed in the form of flowering is called as photoperiodism.
“Effect or requirement of relative length of day (photoperiod) & night (dark phase) on flowering of plants is called as
photoperiodism”
The phenomenon of photoperiodism was first discovered by Garner & Allard on Maryland mammoth (a mutant variety
of tobacco) and biloxy soyabean.
Garner & Allard classified the plants in following groups.
(1) SDP (Short Day Plants) :- “These plants give flowers on exposure to photoperiod equal or shorter than their
critical day length”.
They need a continuous (uninterrupted) dark period for flowering. Thus SDP also called as LNP (Long Night
Plants).
Ex. of SDP :- Tobacco, Soyabean , Viola, Xanthium (Cocklebur), Chrysanthemum, Cannabis, Coleus, Chenopodium,
Mustard, Dahlia, Sugarcane , Strawberry, Cosmos, Rice etc.
In SDP the dark period is critical and must be continuous. If this dark period is breaks by a brief exposure to red
light, then SDP will not flowers.
Maximum inhibition of flowering with red light occur at about the middle of critical dark period.
Prolongation of the continuous dark period, initiates early & good flowering in SDP.
(2) LDP (Long Day Plants) :- These plants flowers only when they exposed to critical photoperiod or photoperiod
longer than their critical day length”.
The light period is critical for LDP.
Ex. :- Henbane (Hyoscyamus) Spinach, Sugarbeets, Radish, Carrot, Wheat, Larkspur, Barley, Avena, Potato.
A brief exposure in the dark period stimulates flowering in LDP
(3) DNP (Day Neutral Plants) or Intermediate plants :- These plants do not need specific light period for the flowering.
Ex. Zea, Cotton, Tomato, Sunflower, Cucumber
L-SDP :- These are SDP but must be exposed to long days during early stage of their growth. Ex. Bryophyllum
S-LDP :- These are LDP but must be exposed to short photoperiod during early stage of growth. Ex. Wheat & Rye
sps.
Cajlachjan :- Reported that stimulation of critical photoperiod is percepted by leaves.
Chailakhyan :– Discovered “Florigen”, it has been not isolated, thus called as hypothetical hormone.

PHYTOCHROME

Borthwick & Hendricks :- Discovered a light sensitive pigment responsible for flowering
Butler :- Give term “phytochrome” for this pigment & isolated it.
Pigment phytochrome is a chromophore billiprotein, which is an open tetrapyrrolic related to phycobilin.
Phytochrome mainly located on cell membrane of all type of plants.
Phytochrome :- exists in two different forms
Pr (Phytochrome red). – Red light absorbing form, induce flowering in SDP.
Absorption range- 630-670 nm. absorption peak-667 nm.

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Pfr (Phytochrome far red) – This is far -red light absorbing form, induce flowering in LDP.
Absorption range - 720-740 nm. absorption peak-735 nm.
Both forms of phytochromes are photobiochemically inter-convertible into each other and are stable.
The Pfr (Yellowish) form, gradually changed in to Pr (bluish) form in dark.

DARKNESS
During the day the Pfr form is accumulated in the plants, which is inhibited to flowering in SDP but stimulates in LDP.
Phytochrome - Pfr (P730) is active form, which controls many photophysiological processes in plants.
Control of morphogenesis by light & phytochrome is called photomorphogenesis.
Now phytochrome is considered as universal distribution in plant kingdom.
Photomorphogenesis in higher plants appear to be under control of one of three photoreceptors.
(a) Phytochrome – which absorbs red and far red region of light.
(b) Cryptochrome – which absorbs blue and UV-A (380 nm) light.
(c) UV-B-Receptors – which absorb UV-B (290 nm) light.

VERNALISATION

Effect of low temperature on the initiation and development of flower, was first realised by Klippart 1857 (Exp. on winter
& Spring wheat)
Detail study and term – ‘‘Vernalisation’’ by Lysenko (Credit of discovery).
Chourad defined as 'acceleration of ability to produce flower by chilling treatment is called vernalisation'.
Mainly embryo tip, shoot apex & leaves perceps induction of low temperature on plants.
Concept of hormone ‘vernalin’ in vernalisation was given by Melcher et. al. This is a hypothetical plant hormone,
because not has been isolated till today.
Vernalisation of seeds or plant propagule in laboratory can be induced at 1°C to 10°C in presence of O2 & H2O.
If vernalized plant prapagules are kept in high temperature, just after the low temp. treatment then effect of vernalisation
is reverse, this effect is called as devernalization.
Significance :–
(i) Better & early flowering.
(ii) Vernalisation increases the resistance to fungal diseases.

PLANT SENESCENCE
Period from complete maturity to degredative changes during the death of an organ or plant is known as senescence.
During senescence a gradual destruction occurs in protoplasm, cell, tissue, organ or plant and functioning of the plant
and plant parts.
During the senescence, higher rate of catabolism starts, under the control of growth hormones like ABA, ethylene.
Senescence occurs as a result of ageing and leads to death of plant parts or whole plant. (Senescence and ageing -
studied in phyto-gerontology)
Senescence may be of following types :-

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(a) Whole plant senescence : ex. Tomato, Wheat, Mustard, Rice, Beans.
(b) Organ senescence : When plant part above ground dies (shoot) each year and root & rhizome system
alive. Ex. Alfa-alfa, Sugarcane, Banana, Ginger.
(c) Sequential or progressive senescence : Evergreen perennials show progressive or sequential senescence
of older leaves, lateral organs, branches, flowers, fruits and shoot.
Ex. Eucalyptus, Mango.
(d) Simultaneous or Synchronous leaf senescence : In perennial deciduous plants, all the leaves undergo
senescence and abscission sp.
Ex. Dalbergia sisso, Azadirachta indica, Ficus religeosa.

ABSCISSION

Detachment of senescent or mature plant organs like leaves, fruits, flowers due to change in hormonal activity.
There is a separation layer (abscission layer) is formed within the region of attatchment of these parts. Cell wall layers
and middle lamella are dissolved by the activity of cellulase and pectinases (Polysaccharide hydrolysing enzymes)
during the abscission.
Hormone ABA is main controllar of abscission process.

PLANT - MOVEMENTS

(A) Movement of locomotion :- When the whole plant, plant part or organs of plant move from one place to another place.
(I) Autonomous :- (by internal stimulus )
(1) Amoeboid :- Ex : Gametes of Spirogyra
(2) Ciliary movement :- Ex : Chlamydomonas, Euglena, Zoospores
(3) Cyclosis :-
(i) Rotation :- Whole protoplasm moves around the one central vacuole, in one direction.
Ex : Hydrilla, Vallisneria cells.
(ii) Circulation :- Protoplasm moves, around the different vacuoles in different directions.
Ex : Stamenal hairs of Tradescantia.
(II) Induced/paratonic/tactic movement :- (Due to external stimulus)
(i) Phototactic :- Due to stimulus of light . Ex : Algae - by (Eye spot/Stigma).
(ii) Chemotactic :- Due to stimulus of chemicals. Ex : Male gametes of lower plants (antherozoids). By
Chemical gradient sensing mechanism.
(iii) Thermotactic :- Due to stimulus of temperature. Ex : Chlamydomonas , Euglena
(B) Movement of curvature :- Movement of plant organs only.
(I) Autonomous :- Movement of variation - Dance movement by Desmodium. (Indian telegraph plant) due to turgor
pressure change.
Epinasty & hyponasty, the growth movements in flower & leaves.
(II) Induced/Paratonic movement :- (By external stimulus, but directional)
(i) Tropic movement :- Definite direction towards stimulus.

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+ve ex : Stem

ª
(a) Phototropism «
¬
–ve ex : Root
Definite direction in relation to light
+ve Ex : Root

ª
(b) Geotropism « (Root cap percept stimulus)
¬
–ve Ex : Stem & Mangrove plant roots.
Definite direction in relation to gravity, (root cap percept stimulus).
(c) Chemotropism :- Ex.Pollen tubes & fungal hyphae
Definite direction in relation to chemicals.
(d) Thigmotropism (haptotropism) :- Ex : Tendrils, haustoria of Cuscuta.
Definite direction in response to contact or support.
(e) Hydrotropism :- Ex : Roots of seedlings
(ii) Nastic movement (External stimulus but diffused type or nondirectional) :-
(a) Nyctinasty :- Ex : Flowers, leaves, stomata, daily movement (Sleep movements)
Due to rhythemicity of day and night.
(b) Thigmonasty or haptonasty :- Tentacles of insectivorous plants
(c) Chemonasty :- Ex : Tentacles of insectivorous plants
(d) Seismonasty :- Ex : Mimosa (touch me not plant) turgor change in pulvinus leaf base
K+ ion also involved in this movement.

KEY PO INTS

Many plant parts specially leaves exhibits nastic movement and involves differential growth, this type of movement is
known as movement of growth. This movement, is caused due to unequal growth in plant organs.
Ex : Epinasty, hyponasty, Nutation.
Epinasty & hyponasty :- Ex : Leaves, flower (petal) opening & closing respectively.
Epinasty - More growth on upper surface of plant parts.
Hyponasty - More growth on lower surface of plant parts.
Both epinasty & hyponasty are example of autonomic growth movements.
Nutation :- Zig zag growth of plant organ mainly shoot, is called as nutation
Circumnutation :- Spiral growth of plants in tendrils
Portulaca is known as compas plant.
Rhizomes diageotropic (90° to gravitation force)
Clinostat :- used for nullifying geotropism
Xerochasy :- Due to loss of water

ª
Hygroscopic movement « Ex :- Dehiscence of legume fruits
¬

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 PLANT GROWTH & DEVELOPMENT
(Mechanical movement) Hydrochasy :- By excess of water
Ex :- Ruellia fruit dehiscence
Traumatropism :- Injury induced plant movement
Plageotropism :- Shown by stem & root branches growing at an angle of 45° from axis of plant.
Climacteric fruits (Banana, Apple, Avocados):- Fruits, in which rate of respiration increases (climacteric respiration)
during their ripening (ethylene). Citrus is non climacteric fruits.
The flower stalk of the poppy is +vely geotropic but after the opening of flower, this stalk change as negative geotropic.
Formation of nodule is a combined activity of cytokinin (By bacteria) and auxin.(By leguminous plant)
Blue light has more effects on most of physiological and growth processess in plants except photosynthesis and
photoperiodism.
Arabidopsis thaliana (Brassicaceae) is the most widely used plant tool for the studies of developmental genetics and
growth physiology of plants.
Betacyanin or Betalains :- Pigment mainly found in vacuole of beet roots and flower of Bougainvellia are differ from
anthocyanin due to the presence of nitrogen (N). These pigments do not show reversibility of colour change due to pH
change.
Anthocyanin is water soluble vacuolar pigment, which does not involve in photosynthesis.
Anthocyanin exhibits different colour like purple, pink, blue, scarlet etc.
The colour of anthocyanin is sensitive to pH change for Ex. colour of anthocyanin changes from Red (acidic pH) to violet
(neutral pH) to blue (in alkaline pH).
Turgorin-a newly discovered hormone found in pulvinous leaf base regulates turgor pressure changing movements.
Growth rate : Increased growth per unit time.

Plants growth is of two types :

(a) Arithmetec growth : From dividing cell to new cells are formed (by mitotic division) out of them one daughter cell
continues to divide while other differentiate and mature (stop dividing).
(b) Geometric / Exponential growth : From dividing cell (by
Z Steady
Size/wt. of forgan

Log

Lag
Time
mitotic division) both daughter cells retains the ability to divide and continue to do so.
(c) Absolute and relative growth rates : Absolute growth rate : Measurement and the comparision of total growth per
unit time in plant or plant parts.
or
Total growth occurs in unit time in plant or plant parts.
Relative growth Rate : The growth of the given system per unit time expressed on a common basis i.e. per unit initial
parameter in plant parts.
or
Total growth occurs in unit time in comparision to initial growth in plant or plant parts. Relative growth rate is
generally high in young developing plant parts.

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BIOLOGY FOR NEET & AIIMS

o Development is the sum of two processes -Growth and differentiation

o Growth is irreversible permanent increase in size of an organ or it's parts or even of an individual cell.
o Growth is accompanied by metabolic processes-both catabolic and anabolic, that occur at the expense of energy. o
Plants show open form of growth -new cells are always being added to the plant body
o Apical meristem -contribute primary growths
o Lateral meristem (vascular cambium and cork cambium) contribute lateral growth and causes increase in girth.
o Growth at cellular level is principally a consequence of increase in the amount of protoplasm.
o Growth is measured by a variety of parameters like -increase in fresh weight, dry weight, lengths, areas, volume and
cell number
o Period of growth is generally divided into three phases -“Meristematic“Elongation“Maturation“Cells in meristem-
atic phase are rich in protoplasm, possess large conspicuous nuclii.“Their cell walls are primary“Phase of elonga-
tion charaterised by increased vacuolation, cell enlargement and new cell wall deposition
o Cell of maturation phase attain theirs maximal size in terms of wall thickening & protoplasmic modification.
o The increased growth per unit time is termed as growth rate.
o The growth rate shows an increase that may be arithmetic or geometrical.
o In Arithmetic growth only one daughter cell continuous to divide while other differentiate and matures. Root
elongation at constant rate is the expression of arithmetic growth
o It proved linear growth and can be expressed as Lt = Lo + rt
o In Geometrical growth -both daughter cells continuously divide. It attain sigmoid curve if space and food is limited.
trees with seasonal activities show sigmoids curve.
o Exponential growth (log phase of sigmoid curve) can be expressed as -
o Here r is referred as efficiency index
o Quantitative comparisons between the growth of living system cans also be made in two ways -
(1) Absolute growth rate o measurement and comparision of total growth per units time
(2) Relative growths rate o per unit initial parameter. increase/initial parameter × 100
o Water, oxygen and nutrients are essential for growth
o Plant growth and furthers development is intimately linked to the water status of plant
o Water helps in -Turgidity, enzyme activation
o Oxygen o helps in releasing metabolic energy
o Nutrients o helps in synthesis of protoplasm and act as source of energy.
o Optimum temperature range and environmental signals such as light and gravity also affect growth.
o Plant growth is open - can be determinate (Plant organs) or Indeterminate (Shoot & root apices).
o Plant differentiation is also open - Same meristem have differents structures at maturity
o Final structure at maturity of cell/tissue is also determined by location of cell within.
o Development includes all changes from seed germination to senescence.
o Plant follow different pathway in response to environment or phases of life to form different kinds of structure, this
ability called Plasticity
o Heterophylly in Butter cup, cotton, coriander and larkspur is an examples of plasticity
o Development in plants is under control of extrinsic (light, Temperature, water, oxygens & nutrition) and Intrinsic
(Intracellular - genetic/intercellular - PGR) factors
o Plant growth regulators are small, simple molecules of diverse chemical composition

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 PLANT GROWTH & DEVELOPMENT
o Auxins - indole compounds
o Cytokinins - adenine derivatives
o Gibberellins - terpenes
o Abscisic acid - Carotenoids
o Ethylene - gases
o Growth proming activities of PGR - Cell division, cell enlargement, pattern formation, tropic growth, flowering,
fruiting & seed formation
o Plant growth promoters -+ Auxin, Gibberellin, cytokinin,
o Growth inhibiting activities of PGR - dormancy, Abscission, response to wound & stress.“Plant-growth inhibitor -
Abscisic and
o Ethylene - is both promoter & inhibitor but it is largly an inhibitor
o Auxin - was isolated by F. W. Went from coleoptile of oat seedling
o Bakane (foolish seedling) disease caused by Gibberella fujikuroi
o E.Kurosawa - indentified & discovered. gibberellic acid. Plant growth is open - can be determinate (Plant organs) or
Indeterminate (Shoot & root apices).
o Plant differentiation is also open - Same meristem have diff erents structures at maturity
o Final structure at maturity of cell/tissue is also determined by location of cell within.
o Development includes all changes from seed germination to senescence.
o Plant follow different pathway in response to environment or phases of life to form different kinds of structure, this
ability called Plasticity
o Heterophylly in Butter cup, cotton, coriander and larkspur is an examples of plasticity
o Development in plants is under control of extrinsic (light, Temperature, water, oxygens & nutrition) and Intrinsic
(Intracellular - genetic/intercellular - PGR) factors
o Plant growth regulators are small, simple molecules of diverse chemical composition
o Auxins - indole compounds
o Cytokinins - adenine derivatives
o Gibberellins - terpenes
o Abscisic acid - Carotenoids
o Ethylene - gases
o Growth proming activities of PGR - Cell division, cell enlargement, pattern formation, tropic growth, flowering,
fruiting & seed formation
o Plant growth promoters o Auxin, Gibberellin, cytokinin,
o Growth inhibiting activities of PGR - dormancy, Abscission, response to wound & stress.“Plant-growth inhibitor -
Abscisic and
o Ethylene - is both promoter & inhibitor but it is largly an inhibitor
o Auxin - was isolated by F. W. Went from coleoptile of oat seedling
o Bakane (foolish seedling) disease caused by Gibberella fujikuroi
o E.Kurosawa - indentified & discovered. gibberellic acid.
o Skoog & Miller - identification & crystallisation of cytokinin
o Natural source of cytokinin o extract of vascular tissues. Yeast extracted, coconut milk or DNA
o Abscisic acid o inhibitor - B, Abscission-II and dormin .
o Cousins o reported volatile subtances froms ripened oranges .
o First isolation of Auxin - from human urine
o Synthesis - at growing apices of stem mainly & slight on root apicess
o Natural Auxin - IAA, IBA
o Synthetic auxin - NAA, 2, 4-D
o Auxin functions o Root initiation on stem cuttings

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BIOLOGY FOR NEET & AIIMS
o Promotion of flowering in pineapple
o Prevents early stage fruits & leaf drop but promote abscission of older mature leaves & fruits.
o Promotion of Apical dominance that is why decapitation usually results in to profused branching which is
used in tea plantation & hedge making.
o Induce parthenocarpy - in tomatoes
o Used as herbicides e.g. 2, 4-D destroy Dicot weed
o Xylem differentiation & cell division promotion.

Gibberellins
o More than 100 gibberellins reported from different organisms.
o GA3 is first gibberellins to be discovered and most extensively studied.
o Elongate and improve shape of fruits like apple
o Delay in Senescence, thus fruit-can be left on the tree longer so as to extend the market period.
o Increase yield of sugarcane as much as 20 tonnes per acre.
o Speed up malting process for breving industries.
o Early maturing in conifer so leading to early seed production.
o Promote bolting (internodal elongation) in beet, cabbages and other rosette plants.

Cytokinins
o Kinetin - Synthetic cytokinin - modified form of adenine obtain from autoclaved herring sperm DNA
o Zeatin - Natural cytokinin, isolation from corn-Kernels and coconut milk.
o Natural cytokinin synthesised in regions where rapid cell division occurs-like Root apices, developing shoot buds,
young fruits etc.

o Promote - new leaves, Chloroplast in leaves, lateral shoot growth, Adventitions shoot formation
o Overcome apical dominance
o Promote nutrient mobilisation so helps in delay in leaf senescence.

ETHYLENE Gaseous PGR (Plant Growth Regulator)

o Synthesised largely by tissues under going senescence and ripening fruits.
o Ethylene leads to
o horizontal growth of dicot seedling
o Swelling of axis
o apical hook formation.
o Promotion of senescene and abscission of plant organs especially leaves and flowers
o Highly effective in fruit ripening
o Enhance rate of respiration during fruit repering (climatic rise in Respiration)
o Break seed & Bud dormancy initiates germination of peanut seeds & sprouting of Potato tubers.

o Rapid internode/petiole elongation in deep water rice.

o Root growth (especially adventitious) & Root hair formation.
o Initiation and synchronisation of fruit setting in pineapples.
o Induce flowering in Mango

o Most widely used PGR in agriculture because it regulate so many physiological processes.
o Most widely used form of Ethylene is - ETHEPHON
o It hasten (acceleration) fruit ripening in tomatoes and apples
o Accelerate abscission in flower & fruits (thinning of cotton, cherry & walnut).
o Promote female flower formation in cucumber to increases their yield.

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 PLANT GROWTH & DEVELOPMENT
ABSCISIC ACID
o General plant growth inhibitor and inhibitor of plant metabolism.
o Inhibit seed germination
o Stimulate closure of stomata
o Increase stress tolerance so called Stress hormone
o Induce seed dormancy
o ABA helps seeds to withstand desiccation and other unfavourable growth factors.
o ABA act as an antagonist of GA
o Role of PGR could be complimentary or antagonistic
o Role of PGR could be individualistic or synergistic
o Events where more than one PGR interact to affect the event.
o Dormancy in seeds/Buds
o Abscission
o Senescence
o Apical dominance
o PGR play inter cellular intrinsic control
o Several External factors like temperature and light, control growth and development via PGR.
PHOTOPERIODISM :
o Influence of relative duration of light & dark on flowering.
o LDP -needs light exposure more than critical light period.
o SDP -needs light exposure less than critical light period.
o DNP -No correlation between exposure of light durations & induction of flower.
o Duration of light & dark are equally important
o Site of perception of light & dark duration are leaves.
o Hypothetically -any hormonal substance move from leaves to shoot apex to induce flowering.
VERNALISATION :
o Qualitative or quantitative dependance of flowering on low temperature exposure
o It prevent precocious reproductive development late in growing season.
o It enables the plant to have sufficient time to reach maturity
o Vernalisation applicable on winter varieties of wheat, rye & barley as well as biennials such as sugarbeet,
cabbages & carrots

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SOLVED EXAMPLE
Ex.1 Maximum growth in roots occurs Ex.6 To induce formation of organs in a callus it is
(A) At apex (B) In presence of light necessary to provide
(C) Behind the apex (D) In presence of soil (A) Growth hormones (B) Water
Sol. (C) : Apex portion of root is made up of protective
(C) Soil (D) Antibiotics
tissue 'root cap' and region of cell division is situated
below the root cap. Sol. (A)

Ex.2 The rate of growth of any organism follows Ex.7 Dr. F. Went noted that if coleoptile tips were removed
Or and placed on agar for one hour, the agar would
Typical growth curves in plants is produce a bending when placed on one side of
(A) Hyperbola curve (B) J-shaped curve freshly cut coleoptile stumps. Of what significant is
(C) Sigmoid curve (D) Parabola curve this experiment
Sol. (C) : The growth of an organism/organ passes (A) It supports the hypothesis that IAA is auxin
through different phases. If the growth rate of a (B) It demonstrate polar movement of auxins
plant part is plotted against time on a graph paper, a
(C) It made possible the isolation and exact
sigmoid/S-shaped growth curve is obtained.
identification of auxin
Ex.3 Exponential growth occurs in (D) It is the basis for quantitative determination of
(A) Yeast small amounts of growth-promoting substances
(B) Asexual reproduction Sol. (C) : F.W. went isolated auxin from Avena coleoptile
(C) Bacterial tip.
(D) All of these
Sol. (B) Ex.8 Which one of the following plants function is not
generally governed or controlled by auxin
Ex.4 Given below is a graph drawn on the parameterrs of
growth versus time A, B, C respectively represent (A) Apical dominance (B) Phototropism
(A) Exponential phase, log phase and steady state (C) Photosynthesis (D) Growth
phase Sol. (C) : Because photosynthesis is enzymatic reaction
(B) Steady state phase, log phase and lag phase and it is anabolic process
(C) Slow growing phase, lag phase and Steady state
phase Ex.9 One of the synthetic auxin is
(D) Lag phase, steady state phase and logarithmic Or
phase Flowering in pineapple is promoted by
(E) Lag phase, steady state phase and logarithmic (A) NAA (B) IAA
phase
(C) GA (D) IBA
Sol. (B)
Sol. (A)
Ex.5 The instrument by which the rate of growth of stem
is accurately measured is Ex.10 Both is callus and suspension cultures commonly
(A) Hydrometer (B) Auxanometer used auxin is
(C) Osmometer (D) Potometer (A) NAA
Sol. (B) : Auxanometer can register total, rate of growth (B) IBA
at specific time and overall pattern of growth. In arc (C) 2, 4-D
auxanometer actual growth in length of a plant is
(D) 2, 4, 5-Trichlorophenoxy acetic acid
measured as Actual growth =
(E) Abscisic acid
distance travelled by pointer u radius of pulley Sol. (C)
Length of pointer from centre of pulley

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 PLANT GROWTH AND DEVELOPMENT
Ex.11 One of the commonly used plant growth hormone Ex.17 Which of the following is a coconut milk factor
in tea (A) Auxin (B) Cytokinins
(A) Ethylene (B) Abscisic acid (C) Morphactin (D) None of the above
(C) Zeatin (D) Indole-3-acetic acid Sol. (B) : In liquid endosperm of coconut kinetin
Sol. (D) : Auxins are commonly use in hedge making (cytokinins) are present.

Ex.18 The ripening of fruits can be hastened by treatment

Ex.12 Bioassay for auxins is
with
(A) Avena curvature test (B) Green leaf test
(A) Gibberellic acid (B) Indole acetic acid
(C) Dwarf maize test (D) Cell division test (C) Florigen (D) Ethylene gas
Sol. (A) Sol. (D) : Ethylene is a gaseous plant hormone and it is
responsible for fruit ripening.
Ex.13 Cell elongation in internodal region takes place due
to Ex.19 Root development is promoted by
(A) Gibberellins (B) Ethylene (A) Abscisic acid (B) Auxin
(C) Cytokinins (D) Indole acetic acid (C) Gibberellin (D) Ehtylene
Sol. (A) : The gibberellin induce elongation of the Sol. (D) : Root development and root hair formation C2H4.
internodes. The elongation of stem results due to Ex.20 Which one of the following generally acts as an
rapid cell division and cell elongation induced by antagonist to gibberellins
gibberellin. (A) Zeatin (B) Ehtylene
Ex.14 Gibberellins can promote seed germination because (C) ABA (D) IAA
of their influence on Sol. (C) : Gibberellins and ABA are antagonistic with
each other.
(A) Rate of cell division
(B) Production of hydrolyzing enzymes Ex.21 Importance of day length (Photoperiodism) in
(C) Synthesis of abscisic acid flowering of plants was first shown in
(D) Absorption of water through hard seed coat (A) Cotton
Sol. (B) : Aleurone layer of endosperm releases a-amylase (B) Petunia
and protease hydrolytic enzyme which promotes (C) Lemna (Photoperiodism)
seed germination. (D) Tobacco
Sol. (D)
Ex.15 Richmond Lang effect can be observed in plants by
the treatment of Ex.12 Vernalisation stimulates flowering in
(A) Zamikand (B) Turmeric
(A) Cytoplasm (B) Ethylene
(C) Carrot (D) Ginger
(C) Abscisic acid (D) Gibberellins
Sol. (C)
Sol. (A) : Cytokinins delay the senescence of leaves and
other organs by controlling protein synthesis and Ex.23 Biological clock in plants is controlled by
mobilization. Reported by "Richmond and Lang" in (A) Phytochrome (B) Cryptochrome
1957 working on "Xanthium leaves" (C) Both (A) and (B) (D) Gibberellin
Sol. (C)
Ex.16 The cut flowers and vegetables can be kept fresh a
long period by this plant hormone Ex.24 The term "photoperiodism" was proposed by or The
(A) Gibberellins (B) Cytokinins phenomenon of photoperiodism in plants was
discovered by
(C) Auxins (D) Ethylene
(A) Lysenko and Thimman
(E) 2, 4-dichlorophenoxy acetic acid
(B) Blackman and Skoog
Sol. (B) : Cytokinins increase shelf life of vegetables
(C) Garner and Allard
and cut flowers and keep them fresh for longer time
(D) Chailakhyan and Borthwick
by preventing deterioration of protein chlorophyll.

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BIOLOGY FOR NEET & AIIMS
Sol. (C) : The effect of photoperiod on flowering was
discovered by Garners and Allard at USA in 1920 in
case of Maryland mammoth variety of Tobacco
which is an SDP.

Ex.25 A few normal seedings of tomato were kept in a dark

room. After a few days they were found to have
become white-coloured like albinos. Which of the
following terms will you use to describe them
Exponential growth can be expressed as:
(A) Etiolated (B) Defoliated
W1 = W0ert
(C) Mutated (D) Embolised
Where,
Sol. (A) : Etiolation in depigmentation in leaf when plant
W1 = Final size
is placed in dark for more than 36 hrs. Plants get
etiolated in dark, because chlorophyll is not W0 = Initial size
synthesized in darkness. r = Growth rate
t = Time of growth
Ex.26 Describe briefly:
e = Base of natural logarithms
(A) Arithmetic growth
(D) Absolute and relative growth rates
(B) Geometric growth
Absolute growth rate refers to the measurement and
(C) Sigmoid growth curve
comparison of total growth per unit time.
(D) Absolute and relative growth rates
Relative growth rate refers to the growth of a
Sol. (A ) Arithmetic growth
particular system per unit time, expressed on a
In arithmetic growth, one of the daughter cells
common basis.
continues to divide, while the other
differentiates into maturity. The elongation of Ex.27 List five main groups of natural plant growth
roots at a constant rate is an example of regulators. Write a note on discovery, physiological
arithmetic growth. functions and agricultural/horticultural applications
(B) Geometric growth of any one of them.
Geometric growth is characterised by a slow
Sol. Plant growth regulators are the chemical molecules
growth in the initial stages and a rapid growth
during the later stages. The daughter cells secreted by plants affecting the physiological

derived from mitosis retain the ability to divide, attributes of a plant. There are five main plant growth
but slow down because of a limited nutrient regulators. These are:
supply. (i) Auxins
(C) Sigmoid growth curve (ii) Gibberellic acid
The growth of living organisms in their (iii) Cytokinins
natural environment is characterised by an S (iv) Ethylene
shaped curve called sigmoid growth curve. This (v) Abscisic acid
curve is divided into three phases – lag phase,
log phase or exponential phase of rapid growth, Sol. (i) Auxins
and stationary phase. Discovery:

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 PLANT GROWTH AND DEVELOPMENT
The first observations regarding the effects of It increases the length of grape stalks.
auxins were made by Charles Darwin and Francis It improves the shape of apple.
Darwin wherein they saw the coleoptiles of canary It delays senescence.
gross bending toward a unilateral source of light. It hastens maturity and induces seed-production in
It was concluded after a series of experiments that juvenile conifers.
some substance produced at the tip of coleoptiles (iii) Cytokinins Discovery:
was responsible for the bending. Finally, this
Through their experimental observations, F. Skoog
substance was extracted as auxins from the tips of
and his co-workers found that the tobacco callus
coleoptiles in oat seedlings.
differentiated when extracts of vascular tissues,
Physiological functions: yeast extract, coconut milk, or DNA were added to
They control plant cell-growth. the culture medium. This led to the discovery of
They cause the phenomenon of apical dominance. cytokinins.
They control division in the vascular cambium and Physiological functions:
xylem differentiation. They promote the growth of lateral branches by
They induce parthenocarpy and prevent abscission inhibiting apical dominance.
of leaves and fruits. They help in the production of new leaves,
Horticultural applications: chloroplasts, and adventitious shoots.
They are used as the rooting hormones in stem They help in delaying senescence by promoting
cuttings. nutrient mobilisation.
2-4 D is used weedicide to kill broadleaf, Horticultural applications:
dicotyledonous weeds. They are used for preventing apical dominance.
They induce parthenocarpy in tomatoes. They are used for delaying senescence in leaves.
They promote flowering in pineapple and litchi. (iv) Ethylene
(ii) Gibberellic acid Discovery: Discovery:
Bakane or the “foolish rice seedling” disease was It was observed that unripe bananas ripened faster
first observed by Japanese farmers. In this disease, when stored with ripe bananas.
rice seedlings appear to grow taller than natural Later, the substance promoting the ripening was
plants, and become slender and pale green. Later, found to be ethylene.
after several experiments, it was found that this
Physiological functions:
condition was caused by the infection from a certain
It helps in breaking seed and bud dormancy.
fungus Gibberella fujikuroi. The active substance
It promotes rapid internode-elongation in deep-water
was isolated and identified as gibberellic acid.
rice plants.
Physiological functions:
It promotes root-growth and formation of root hairs.
It causes elongation of internodes.
It promotes senescence and abscission of leaves
It promotes bolting in rosette plants.
and flowers.
It helps in inducing seed germination by breaking
It hastens the respiration rate in fruits and enhances
seed dormancy and initiating the synthesis of
fruit ripening.
hydrolases enzymes for digesting reserve food.
Horticultural applications:
Horticultural applications:
It is used to initiate flowering and synchronising
It helps in increasing the sugar content in sugarcane
the fruit set in pineapples.
by increasing the length of the internodes.

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BIOLOGY FOR NEET & AIIMS
It induces flowering in mango. Sol. (A) Induce rooting in a twig –Auxins
Ethephon is used to ripen the fruits in tomatoes and (B) Quickly ripen a fruit – Ethylene
apples, and accelerate the abscission of flowers and (C) Delay leaf senescence – Cytokinins
leaves in cotton, cherry, and walnut. (D) Induce growth in axillary buds – Cytokinins
It promotes the number of female flowers in (E) ‘Bolt’ a rosette plant – Gibberellic acid
cucumbers. (F) Induce immediate stomatal closure in leaves
– Abscisic acid
(v) Abscisic acid Discovery:
During the mid-1960s, inhibitor-B, abscission II, and 29. What would be expected to happen if:
dormin were discovered by three independent (A) GA3 is applied to rice seedlings
researchers. These were later on found to be (B) Dividing cells stop differentiating
chemically similar and were thereafter called ABA (C) A rotten fruit gets mixed with unripe fruits
(Abscisic acid). (D) You forget to add cytokinin to the culture
medium.
Physiological functions:
It acts as an inhibitor to plant metabolism. Sol. (A) If GA3 is applied to rice seedlings, then the rice
It stimulates stomatal closure during water stress. seedlings will exhibit internodeelongation and
increase in height.
It induces seed dormancy.
(B) If dividing cells stop differentiating, then the
It induces abscission of leaves, fruits, and flowers.
plant organs such as leaves and stem will not be
Horticultural application: formed. The mass of undifferentiated cell is called
It induces seed dormancy in stored seeds. callus.

Ex.28 Which one of the plant growth regulators would

you use if you are asked to:
(A) Induce rooting in a twig
(B) Quickly ripen a fruit
(C) Delay leaf senescence
(D) Induce growth in axillary buds
(E) ‘Bolt’ a rosette plant
(F) Induce immediate stomatal closure in leaves.

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 PLANT GROWTH AND DEVELOPMENT

Exercise PART - 1 PREVIOUS YEAR (NEET/AIPMT)

(B) Gibberellic Acid – Leaf fall
1. Differentiation of shoot is controlled by : - (C) Cytokinin – Cell division
[CBSE AIPMT 2003] (D) IAA – Cell wall elongation
(A) High gibberellin : cytokinin ratio 9. ‘Foolish Seedling’ disease of rice led to the discov-
(B) High auxin : cytokinin ratio ery of : [CBSE AIPMT 2007]
(C) High cytokinin : auxin ratio (A) GA (B) ABA
(D) High gibberellin : auxin ratio (C) 2, 4 D (D) IAA
2. One set of a plant was grown at 12 hours day and 10. The wavelength of light absorbed by Pr form of phy-
tochrome is: [CBSE AIPMT 2007]
12 hours night period cycles and it flowered while in
(A) 640 nm (B) 680 nm
the other set night phase was interrupted by flash
(C) 720 nm (D) 620 nm
of light and it did not produce flower. Under which
one of the following categories will you place this 11. Opening of floral buds into flowers, is type of :
plant ? [CBSE AIPMT 2004] [CBSE AIPMT 2007]
(A) Long day (B) Darkness neutral (A) Autonomic movement of locomotion
(C) Day neutral (D) Short day (B) Autonomic movement of variation
(C) Paratonic movement of growth.
3. Anthesis is a phenomenon which refers to - (D) Autonomic movement of growth
[CBSE AIPMT 2004]
(A) Reception of pollen by stigma 12. Importance of day length in flowering of plants was
first shown in: [CBSE AIPMT 2008]
(B) Formation of pollen
(A) Lemna (B) Tobacco
(C) Development of anther (C) Cotton (D) Petunia
(D) Opening of flower bud
13. Senescence as an active developmental cellular pro-
4. Cell elongation in internodal regions of the green cess in the growth and functioning of a flowering
plants takes place due to :- [CBSE AIPMT 2004] plant, is indicated in: [CBSE AIPMT 2008]
(A) Indole acetic acid (B) Cytokinins (A)Vessels and tracheid differentiation
(C) Gibberellins (D) Ethylene (B)Leaf abscission
(C) Annual plants
5. Treatment of seed at low temperature under moist (D) Floral parts
conditions to break its dormancy is called -
14. Which one of the following acids is a derivative
[CBSE AIPMT 2006]
of carotenoids ? [CBSE AIPMT 2009]
(A) Vernalisation (B) Chelation (A) Indole butyric acid
(C) Stratification (D) Scarification (B) Indole-3-acetic acid
6. An enzyme that can stimulate germination of barley (C) Gibberellic acid
seeds is- [CBSE AIPMT 2006] (D) Abscisic acid
(A) Lipase (B) Protease 15. One of the synthetic auxin is :
(C) Invertase (D) D- amylase [CBSE AIPMT 2009]
(A) NAA (B) IAA
7. How does pruning help in making the hedge dense (C) GA (D) IBA
? [CBSE AIPMT 2006]
(A)It frees axillary buds from apical dominance 16. Coiling of garden pea tendrils around any
(B) The apical shoot grows faster after pruning support is an example of ?
(A) Thigmotaxis (B) Thigmonasty
(C) It released wound hormones
(C) Thigmotropism (D) Thermotaxis
(D) It induces the differentiation of new shoots from
the rootstock 17. Phototropic curvature is the result of uneven dis-
tribution of ? [CBSE AIPMT 2009]
8. Which one of the following pairs, is not correctly (A) Gibberellin (B) Phytochrome
matched? [CBSE AIPMT 2007] (C) Cytokinins (D) Auxin
(A) Abscissic Acid – Stomatal closure

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BIOLOGY FOR NEET & AIIMS
18. During seed germination its stored food is mobi- 23. You are given a tissue with its potential for differen-
lized by : [NEET 2013] tiation in an artificial culture. Which of the follow-
(A) Ethylene (B) Cytokinin ing pairs of hormones would you add to the medium
(C) ABA (D) Gibberellin to secure shoots as well as roots? [NEET 2016]
19. A few normal seedlings of tomato were kept in a (A) IAA and gibberellin
dark room. After a few days they were found to (B) Auxin and cytokinin
have become white-coloured like albinos. Which of (C) Auxin and abscisic acid
the following terms will you use to describe them ? (D) Gibberellin and abscisic acid
[CBSE AIPMT 2014]
(A) Mutated (B) Embolised 24. Phytochrome is a [NEET 2016]
(C) Etiolated (D) Defoliated (A) flavoprotein (B) glycoprotein
20. Which one of the following growth regulators is (C) lipoprotein (D) chromoprotein
known as ‘stress hormone’ ?
[CBSE AIPMT 2014,1993 ] 25. The avena curvature is used for bioassay of
[NEET 2016]
(A) Abscisic acid (B) Ethylene
(C) GA3 (D) Indole acetic acid (A) GA3 (B) IAA
(C) Ethylene (D) ABA
21. Dr. F. Went noted that if coleoptile tips were re-
moved and placed on agar for one hour, the agar 26. Fruit and leaf drop at early stages can be prevented
would produce a bending when placed on one side by the application of [NEET 2017]
of freshly cut coleoptile stumps. Of what signifi- (A) Cytokinins (B) Ethylene
cance is this experiment? [CBSE AIPMT 2014] (C) Auxins (D) Gibberellic acid
(A) It made possible the isolation and exact identifi-
cation of auxin
(B) It is the basis for quantitative determination of
small amounts of growth-promoting substances
(C) It supports the hypothesis that IAA is auxin
(D) It demonstrated polar movement of auxins

22. Auxin can be bioassayed by :[CBSE AIPMT 2015]

(A) Avena coleoptile curvature
(B) Hydroponics
(C) Potometer
(D) Lettuce hypocotyl elongation

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 PLANT GROWTH AND DEVELOPMENT

Exercise PART - 2 PREVIOUS YEAR (AIIMS)

4. Which of the following plant growth regulators
1. Phytohormones are [2008] (PGRs) promotes root initiation, flowering and in-
(A) hormones regulating growth from seed to adult- duced parthenocarpy ? [2013]
hood (A) Gibberellin (B) Auxin
(B) growth regulators synthesised by plants and (C) Cytokinin (D) Ethylene
influencing physiological process
5. Vernalisation is subjected to plants growing in
(C) hormones regulating flowering
[2014]
(D) hormones regulating secondary growth
(A) tropical areas
2. Refer the given figures on photoperiodism and se- (B) sub tropical areas
lect the correct option. [2010] (C) temperate areas
(D) hot areas/arctic region.

6. Gibberellins can promote seed germination because

of their influence on [2015]
(A) rate of cell division
(B) production of hydrolysing enzymes
(C) synthesis of abscisic acid
(D) absorption of water through hard seed coat.
A B C
7. One hormone hastens maturity period in juvenile
(A) no correleation long light-
conifers, a second hormone controls xylem differ-
short light - between exposureexposure
entiation, while the third hormone increases the tol-
light period period periodand flower erance of plants to various stresses. They are re-
ing spectively [2016]
(B) long light - no correlation short light - (A) Gibberellin, Auxin, Ethylene
exposure between exposure
(B) Auxin, Gibberellin, Cytokinin
period light period exposure
(C) Gibberellin, Auxin, ABA
period light period period and
(D) Auxin, Gibberellin, ABA.
flowering
(C) short light- long light - no correlation 8. Cytokinin involves [2018]
exposure exposure between (A) kinetin, zeatin, BAP
period period light period (B) GA3, IBA Kinetin
and flowering (C) Zeatin, GA3, BAP
(D) no correlation short light - long light - (D) IAA, Zeatin, kinetin
between exposure exposure
light period period exposure and 9. Auxin was first isolated from [2018]
flowering (A) Human urine (B) Callus
(C) Coconut milk (D) None
3. Abscisic acid is known as the stress hormone be-
cause it [2012] 10. Which of the following statement is wrong about
(A) sugar but not ATP Abscisic acid : [2018]
(B) ATP but not sugar (A) It helps in general plant metabolism
(B) It is antagonistic to GAE
(C) both ATP and sugar
(C) It helps in seed maturation & dormancy
(D) neither ATP nor sugar.
(D) Morphogenesis

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BIOLOGY FOR NEET & AIIMS

15. Assertion : Plant growth as whole is indefinite.

ASSERTION AND REASON
[2011]
Statement based question : -
Reason : Plants retain the capacity of continuous
Each of the questions given below consist of growth throughout their life.
Assertion and Reason. Use the following Key to
choose the appropriate answer. 16. Assertion : Plant growth regulators (PGRs) are very
(A) If both Assertion and Reason are correct, and important for plant growth and development.
Reason is the correct explanation of Assertion. [2015]
(B) If both Assertion and Reason are correct but Reason Reason : Auxins do not induce flowering in gymno-
is not the correct explanation of Assertion. sperms.
(C) If Assertion is correct but Reason is incorrect.
17. Assertion : Storage of seeds at low temperature is
(D) If Assertion is false but Reason is correct.
possible. [2016]
Reason : Respiration and enzymatic activity of seeds
11. Assertion : A correct concentration of auxin and are very high low temperature.
cytokinin is required for the development of root
and shoot in a callus. [1996, 2015]
Reason : When the ratio of kinetin to auxin is high,
then only shoots develop. But when the ratio is low
then only roots develop.

12. Assertion : Rhoeo leaves contain anthocyanin pig-

ments in epidermal cells. [2003]
Reason : Anthocyanins are accessory photosyn-
thetic pigments.

13. Assertion : Vernalization is acceleration of

subsquent flowering by low temperature treatment.
[2007]
Reason : Site of vernalization is apical meristem.

14. Assertion : Cytokinins increases shelf life of fruits

and vegetables. [2009]
Reason : Cytokinins induce cell division.

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 PLANT GROWTH AND DEVELOPMENT

ANSWER KEY

EXERCISE : PART - 1
1. C 2. D 3. D 4. C 5. C 6. D 7. A 8. B 9. A 10. B 11. D 12. B 13. B
14. D 15. A 16. C 17. D 18. D 19. C 20. A 21. B 22. A 23. B 24. D 25. B 26. C

PART - 2
1. B 2. C 3. D 4. B 5. C 6. B 7. C 8. C 9. C 10. A 11. A 12. C 13. B
14. B 15. A 16. B 17. C

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BIOLOGY FOR NEET & AIIMS

HINTS & SOLUTIONS

EXERCISE through pruning, the axillary buds grow and the
P-1 (NEET/AIPMT) hedge becomes dense.

1. (C) Ratio of cytokinins to auxins controls differen-

tiation. If both of these are present in equal quanti- 8. (B) Gibberellins help in cell growth of stem, leaves
ties, the.cells divide but fall to differentiate. If there and other aerial parts.
is more cytokinin than auxin, shoot buds develop.
If there is more auxin than cytokinin, roots develop.
9. (A) Gibberellins (GA) were first observed from the
2. (D) The condition shows that the plant require fungus Gibberella fujikuroi, the causal organism of
photo-period shorter than the critical day length. foolish seedling disease of rice plants in Japan by
This plant needs uninterrupted dark period for flow- Kurasawa in 1926.
ering. Therefore, it is a short-day plant and these
do not flower if the dark period is interrupted with 10. (B) When P, absorbs red light (650-670 nm) it is
flashes of light. converled into Pfr form and when Pfr absorbs far red
light (730-735 nm) it is converted back into Pr form.
3. (D) Anthesis is the opening of floral buds. Recep-
tion of pollen by stigma is called pollination. For- 11. (D) Opening of floral buds into flower is a type of
mation of pollen is called microsporogenesis. autonomic movernen! of growth (nastic movement).
This is non-directional movement in which the re-
4. (C) Gibberellin (GA3 ) promotes intemodal elonga- sponse is determined by the structure of the re-
tion in a wide range of species. This intemodal elon- sponsive organ and not to the direction of stimu-
gation phenomenon is known as bolting. lus. Greater growth on one side oauses the organ to
Gibberellin is a plant growth hormone which was bend to the opposite side
first time obtained from a fungus Gibberella fujikuroi
12. (B) Photoperiodism was first discovered by Gar-
(Fusarium moniliformi)
ner and Allard (1920, 1922). They observed, that
5. (C) Stratification involves the treatment of seed at
maryland mammoth variety of tobacco could be
low temperature (5-10°C) under sufficiently moist
made to flower only by reducing the light hours
conditions to break its dormancy and to induce
with artificial darkning.
germination.
On the basis of photoperiodic response to flower-
Scarification involves any damage or breakage of
ing plants have been divided into short day plants
seed coat by physical methods, (e.g. use of scalpel,
(tobacco), long day plant (e.g. wheat, hanbane),
wooden hammer, etc.) or chemical methods (use of
short long day plants. (e.g. Campanula), long short
mild acids) to break seed dormancy.
day plants (e.g. Bryophyllum) intermediate plants
Vernalisation and Chelation are the chill treatment
(e.g. wild kidney bean) and day neutral plants (e.g.
of plant in its early stages of life history to stimulate
cotton).
or induce early flowering.

6. (D) Barley seeds are rich in carbohydrate (starch). 13. (B) Abscission is natural shedding of leaves, foli-
The starch is hydrolysed by D-amylase to monosac- age branches, fruits, floral parts, etc. According to
charides unit at the time of germination of seeds. Leopold (1967) abscission is a senescence phenom-
enon. Senescence is known as ‘the sum of deterio-
7. (A) Pruning helps in making the hedge dense as it
rative processes which naturally, terminate the func-
frees the axillary buds from apical dominance. In
tional life of an organism.
fact, the apices of the plant axis, (e.g. shoot apex)
Senescence is not confined only to whole plant, it
has the highest concentration of auxin which sup-
may be limited to a particular plant organ such as
presses the axillary buds while promotes the growth
leaf and flower or cells such as phloem and xylem.
of apical bud. When the shoot apex is cut down
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BIOLOGY FOR NEET & AIIMS
Senescence as an active developmental cellular pro- 18. (D) Gibberellin induces aleurone cells to secrete
cess in the growth and functioning of a flowering enzyme that break stored food in seed. Cytokinines
plant, is indicated in leaf abscission. promote nutrient mobilisation which helps in the
Whole plant senescence also knownas all senes- delay of leaf senescence. ABA plays an important
cence occurs in annuals, (e.g., rice, wheat, gram, role in seed development, maturation and dormancy.
mustard), biennials (e.g. henbane) or perennials. Ethylene induces fruit ripening, breaks seed dor-
mancy.
14. (D) Abscisic acid is a terpenoid, which is a deriva-
tive of steroid (carotenoid). 19. (C) Etiolation is a process in which flowering plants
Indole butyric acid and indole-3-acetic acid are aux- are grown in partial or complete absence of light.
ins which are weak organic acids. Etiolation is mainly characterised by long and weak
Gibberellic acid (gibberellin) is a terpene. stem and smaller, sparse pale yellow colour of leaves
due to the longer internodes. Thus due to this to-
mato seeding became white coloured
15. (A) NAA (Naphthalene Acetic Acid) and 2,4-D (2,4-
20. (A) Abscisic Acid (ABA) is also known as ‘stress
dichlorophenoxy acetic acid) are synthetic auxins.
hormone’ or dormin because it is produced in much
The term auxin is applied to the indole-3-acetic acid
higher amounts, when plants are subjected to vari-
(IAA) and to other natural and synthetic com-
ous kinds of stresses
pounds having certain growth regulating proper-
It often gives plant organs a signai that they are
ties.
undergoing physiological stresses such as lack of
IAA and IBA (Indole Butyric Acid) have been iso-
water, saline, soil, cold temperature and frost. ABA
lated from plants. All these auxins have been used
often cause responses that help plants and protect
extensively in agricultural and horticultural prac-
against these stresses.
tices.
21. (B) Dr. F Went isolated auxin ftom Avenacoleoptile
16. (C) Thigmotropism movements are due to the con-
tip. His experiment demonstrated the polar move-
tact with a foreign body. In twiners and lianas, there
ment of auxins, i.e. it showed that the plants grow
is less growth on the idea of contact and more
towards light in response to a signal generated in
growth on the side of branch away from the con-
the tip of coleoptile by a piant hormone auxin.
tact. Coiling of garden pea tendrils arround any
support is an example of thigmotropism. 22. (A) Auxin is a phytohormone that is often bioas-
sayed by Avena coleoptile curvature test. The angle
17. (D) Darwin and his son Francis used germinating
of curvature of a decapitated oat coleoptile is mea-
oat (Avena sativa) and canary grass (Phalaris
sured after placing an agar block containing auxin
canariensis) seedling in their experiments and
on one side. The ability of auxin to stimulate shoot
hypothesised that when shoots were illuminated
growth is then measured.
from one side, they bent forward the light in re-
sponse to an ‘influence’, that was transmitted down- 23. (B)When a tissue with a potential of differentiation
ward from its source at the tip of the shoot. Paal is grown in an artificial medium containing auxin
concluded that the tip secretes a substance which and cytokinin in a specific ratio, it starts differenti-
promotes the growth of part below it. ating.
In 1926. F Went discovered that some unidentified Thus, root and shoot differentiation occurs. Auxin
compound probably caused curvature of oat co- initiate root formation while cytokinin starts shoot
leoptile towards light, i.e., phototropism. The com- formation.
pound (auxin) found by Went is relatively abun-
dant in coleoptile tips

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 PLANT GROWTH AND DEVELOPMENT
EXERCISE

24. (D) Phytochrome is a chromoprotein which exist in
P-2 (AIIMS)
two forms, P r and P fr . These are inter-
convertible.When plants get red right this protein 1. (B) Growth regulators are organic substances, other
gets converted into Pfr form Pr and vice versa. It than nutrients, which in low concentration regulate
controls the photoperiodism in the plants. growth differentiation and development by
promoting or inhibiting the same. Phytohormones
25. (B) Bioassay is a quantitative and qualitative test are growth regulators produced naturally in plants
used to determine the nature and function of a bio- and translocated to another region for rregulation
one or more physiological reactions when present
chemical by using living material, e.g. Avena curva-
in low concentration. Phytohormone can have a
ture test is used as bioassay usually for auxins (In- promoting or inhibiting effect on a process.
dole Acetic Acid).
2. (C)
26. (C) Auxin delay abscission of leaves and fruits at 3. (D)
early stages. Whenever leaf or fruit fall occurs, the 4. (B) Auxins promote root initiation at a concentration
organ concerned stops producing auxin. However, whihc otherwise is inhibitory for growth of intact
it promotes abscission of older, mature leaves and root. Auxins are often employed for inducing
fruits. flowering in litchi and pineapple. Application of
auxins to upollinated pistils make them develop into
seedles fruits or parthenocarps.
5. (C) Vernalisation refers specially to the promotion
of flowring by exposure to a period of low
temperature. Many temperate plants have
vernalisation requirement and must experience a
period of low temperature in winter, to initiate or
accelerate flowering process, or in many fruit tree
species, to induce dormany and then break dormany
prior to flowering.
6. (B) Gibberellins induce the production of
hydrolysing enzymes in the endosperm of
germinating seeds. It stimulates the production of
digestive enzymes like proteases, amylase and lipase
which help to mobilise stored nutrients.
7. (C) Spraying juvenile conifers with gibberellins
hastens their maturity period, thus leading to early
seed production. Auxin controls xylem
differentiation. Abscisic acid (ABA) increases the
tolerance of plants to various kinds of stresses
therefore, is also known as stress hormone.
8. (A)
9. (A)
10. (A)
ASSERTION AND REASON
11. (A) The relative ratio of cytokinin (Kinetic) to auxin
(IAA) was considered important in determining the
nature of organogensis in tobacco pith tissue. It
was shown that high level of kinetic caused bud
initiation, while high concentration of auxin
favoured rooting.

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BIOLOGY FOR NEET & AIIMS
12. (C) Anthocyanin is a colouring pigment of certain and self perpetuate. They produce cells which lose
higher plants that imparts a bluish or reddish colour. the capacity to divide and enter G0 phase for
Rhoeo leaves contain anthocyanin pigments in undergoing differentiation to form particular tissues
epidermal cells. and organs. The meristem which is consumed in
13. (B) Term vernalization was first given by T.D. the formation of an organ is called determinate
Lysenko (1928). In colder countries, there are cereals meristem. The meristem which continues its activity
of physiological types, i.e., winter cereals and throughout life of the plant is called indeterminate
spring cereals. Winter cereals are sown in winter meristem. It is the reason behind indefinite growth
and flower in following summer whereas spring of plants.
cereals are sown in spring and flower in summer. If 16. (B) Plant growth regulators (PGRs) are small, simple
winter cereal is sown in spring, it shown vegetative molecules of diverse chemical composition, which
growth but does not flower unless it receives low in low concentration regulate growth, differentiation
temperature of winter. But winter cereal can be and development by promoting or inhibiting the
converted into spring cereal by providing artificial same. One type of plant growth regulators are plant
low temperature treatment, (i.e., springification.) hormones or phytohormones. Auxins are the
Some plants requiring low temperature requirement phytohormones. They do not induce flowering in
(vernalization) for flowering are Secale cereal gymnosperms.
(European rye), Triticum vulgare, Brassica 17. (C) Some seeds are capable of withstanding
oleracea, Beta vulgaris, Apium and Lolium exposure to low temperature (–10°C to –20°C). Some
perenne, etc. Site of vernalization is apical meristem of properly dried seeds can withstand low
or all the meristematic cells. As a result of temperature of even liquid nitrogen (–196°C). This
vernalization, a flowering hormone called “vernalin” reduces respiration and enzymatic activity to bare
is formed (reported by Melchers), but venalin has minimum which is required for sustaining the living
never been isolated. Once a plant is vernalized, it of the seeds. Samples of the seeds are periodically
can be devernalized by exposing the plant to tested for germination ability.
temperature of 30°C or above. For establishing
vernalization, plant should be kept at 20°C for 4 - 5
days.

14. (B) Application of cytokinins to marketed

vegetables can keep them fresh for several days.
Shelf life of cut shoots and flowers is prolonged by
employing the hormone cytokinin. The reason is
that the cytokinin increases retention of chlorophyll
and delayed senescence in leaves. Cytokinin as the
name suggests, is essential for cell division or
cytokinesis. It promotes cell division along with
auxin by controlling the activity of cyclin dependent
kinases.
15. (A) Unlike animals, plants do not stop growing after
reaching maturity. They continue to grow and bear
new roots, leaves, branches, flowers, etc. While
roots, stems and their branches have indefinite
growth, other organs like leaves, flowers and fruits
show limited or definite growth. They appear and
fall off periodically and sometimes repeatedly. In
lower plants, growth is diffused as every cell can
divide and enlarge. Higher plants possess specific
areas which take part in the formation of new cells.
These areas are called meristems. Meristems are of
three types– apical, intercalary and lateral. Cells of
the meristematic region have the capacity to divide

105
DIGESTION AND ABSORPTION
CHAPTER
15
“Happiness: a good bank account, a good cook, and a good digestion”

“ JEAN-JACQUES ROUSSEAU (1712-1778)”

INTRODUCTION

F
ood is one of the basic requirements of all living organisms. The major and important
component of our food are carbohydrates, proteins and fats. Vitamins and minerals
are also required in small quantities. Bio-macromolecules in food cannot be utilized
by our body in thir original form. They have to be broken down and converted into
simple substance in the digestive system.This process of conversion of complex
food substances to simple absorbable forms is called digestion and is carried out by
our digestive system by mechanical and biochemical methods.
The water we take in, plays an important role in the metabolic processes and also
prevents dehydration of the body.

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BIOLOGY FOR NEET & AIIMS

INTRODUCTION
Food is one of the basic requirement of the living organisms. To perform various functions of the body energy is required,
which is obtained from food. The process of conversion of complex food material in to simple and diffusible forms by
hydrolysis is termed as Digestion.
Major component of food are carbohydrates, proteins and fats, vitamins minerals are also required in small quantities.

The alimentary canal is tubular structure which extends from mouth to anus. It develops from ectoderm &
endoderm.
Ectoderm – up to hard palate
Endoderm – from soft palate to rectum
Ectoderm – from anal canal to Anus
The alimentary canal is divided into following parts–
(1) Mouth and Buccopharyngeal cavity, Pharynx
(2) Oesophagus
(3) Stomach
(4) Intestine

107
 DIGESTION & ABSORPTION

INTESTINE

Small

Duodenum Jejunum IIeum

Large

Caecum Colon Rectum

Anal Canal

Anus

(1) Mouth and Buccopharyngeal Cavity or Oral Cavity

Mouth is a horizontal transverse slit like aperture which is surrounded by upper and lower lip and left and right outer
cheeks. Orbicualaris oris voluntary muscles are found in lips.
1. Sebaceous glands are found on the outer part of lip.
2. Serous glands are found on the inner part of lip. Serous glands are the modification of mucus glands. Its
secretorysubstance is watery.

Mouth opens into a space or cavity called oral cavity. cavity is like a room.
(1) Oral cavity – It is inner & central part which is surrounded by upper and lower Jaw, lined by stratified squamous
epithelium. Upper Jaw is fixed and Lower jaw is movable.
(i) Buccal vestibule (Boundary) – It is a peripheral part which is present between the gums and cheeks where the food
is stored temporarily for some time.
(ii) Palate: The roof of oral cavity is called as Palate. It seperates mouth and nose. This palate is horizontal partition
which situated between oral cavity and nasal chamber. Upper jaw is called Maxilla and lower jaw is called Mandible.

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BIOLOGY FOR NEET & AIIMS

Palate is differentiated into two parts:

(i) Hard Palate –
It is the anterior part of the palate. It is made up of Maxilla and palatine bone in human.
On the ventral surface of hard palate, some projection or transverse ridges are present which are called as
palatine rugae.
These rugae are well developed in carnivorous animals.
These rugae prevent slip out of the food from buccal cavity during mastication.

(ii) Soft Palate –

It is the posterior part of palate. It is made up of involuntary muscle, fibrous connective tissues and mucous
epithelium. (Stratified squamous epithelium)
One pair of large lymph node is present on the posteriolateral surface of soft palate, called as Palatine tonsil or
Tonsils

109
 DIGESTION & ABSORPTION
The posterior part of soft palate becomes out grow and hangs down in the form of finger like process called
as Uvula or Velum palati
Soft palate is situated in the pharynx and is divided into two parts. Upper and dorsal part of pharynx is called as
Nasopharynx which is related to the nasal chamber. The lower and ventral part of pharynx is called oropharynx
which is related to the oral cavity. One pair of opening of Eustachian tube (control air pressure) is present in the
nasopharynx. This Eustachian tube is related to the middle ear.
TONGUE:

On the floor of oral cavity a muscular, flat, fleshy plate like structure is present which is called tongue. The surface
of tongue is connected to the floor of buccal cavity through a very flexible membrane/ligamentous fold called as
frenulum linguae The anterior part of tongue is free while posterior part of Tongue is connected to the Hyoid
bone.

On the dorsal surface of tongue, it is divided into two unequal parts by a V shaped sulcus, called as sulcus
terminalis. The two limbs of the ‘V’ meet at a median pit named Foramen Caecum.

It is divided into two parts –

(I) Pharyngeal or Lymphoid Part – It is the posterior 1/3 part of the tongue. Many small lymph nodes
are present in this part which are called Lingual tonsil.

(II) Oral or papillary Part – It is anterior 2/3 part of tongue. Four types of papillae are found in this part
in which gustatory or taste receptors are present.

(ii) Filiform Papillae (Conical papillae) –

They are thread like, white coloured & conical in shape. They are also found on the entire surface of tongue. They
are most numerous.They are devoid of taste buds.
(ii) Fungiform Papillae –
It is pink coloured, small & spherical in shape. It is found on the entire surface of tongue but their maximum
concentration at the anterior tip part of tongue. It is attached to tongue with the help of small pedicle. It provides
pink colour to the tongue. Taste buds are present.

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BIOLOGY FOR NEET & AIIMS
(iii) Foliate Papillae –
They are found on the mid lateral surface of tongue. They are vestigeal in the human. Their structure is leaf like
present in rabbit and other mammals.They are devoid of taste buds.

(iv) Circumvallate papillae –

They are large spherical shape papillae which are found near to sulcus terminalis. They are least in number. Taste
buds are present.
Two types of muscles are present in tongue
1. Extrinsic muscle
It is found on outer and superficial part of tongue.Also, It helps in outward and inward movement of tongue.
2. Intrinsic muscle
It is situated in the deep part of tongue.Also,It helps in the change of shape of tongue
Teeth
Teeth are ectomesodermal in origin. Part of tooth present outside the gums only is derived from ectoderm or
Epidermis (Enamel part). Major portion of teeth arises from Dermis.

In human teeth, upper jaws are attached to the maxilla bone, while teeth of lower jaw are attached to Mandible bone.

STRUCTURE OF TEETH
There are a three parts of the tooth
1. Crown : It is the outer part of the tooth, exposed outside gums

2. Neck : It is the middle part of the tooth which is embedded inside the gums.

3. Root : It is the part of tooth that is inserted inside the socket of jaw bone. (Alveoli) The crown part of the tooth
is made up of a very hard substance called the Enamel. It is the hardest material of animal kingdom.

Enamel is ectodermal. It surrounds only crown of tooth.It is secreted by Ameloblast cells of the ectoderm.
a. It has maximum amount of inorganic salt (96%) in it, Inorganic salt are mainly found in the form of phosphate and
carbonate of Ca, Mg, Na and K. 3% of water is found in the enamel.
b. Along with the keratin & ossein protein (1%) are also found in teeth. Ossein is a protein of bones. Remaining part
of tooth develops from mesoderm of embryo.
Dentine is the main part of tooth present in both crown and roots.. Approximately 69% inorganic salts are present
in dentine derives from mesoderm.

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 DIGESTION & ABSORPTION
z Dentine surrounds a cavity called pulp-cavity. This cavity contains soft connective tissue, blood capillaries,
and nerve fibres.
1. Pulp cavity is neccessary for the nutrition and survival of the teeth. At the base of pulp-cavity an aperture is
present.
2. Through this aperture, blood capillaries and nerve fibres enter inside the teeth. This aperture is called apical-
foramen.
3. A special type of cells form the lining of the pulp-cavity called the Odontoblast cells. These cells are the
dentine secreting cells.
4. Cytoplasmic process of Odontoblast is to embedded into dentine in the form of fine tubule. These processes
are called canaliculi. These canaliculi secrete dentine. The teeth continue to grow till the Odontoblast cells
remain active.
5. In adults, the pulp-cavity shrinks and the Odontoblast become inactive so the tooth stops to grow. The
cement layer is made up of the cementocytes cells. Between the root and the bones of the teeth a periodontal
membrane is present.

Four type of teeth found in mammals’ are–

1. Incisor – These are long, chisel like teeth for gnawing the food. They are more developed in gnawing animals e.g.
lagomorphs, rodents, tusk of elephant are modification of upper Incisor. Tusk is used to protection from enemies,
attack on enemies (not for feeding purpose)

2. Canines – These are sharp pointed teeth meant for tearing the food. Canines are most developed in carnivorous
animals. Canines are absent in herbivorous animals. In herbivorous, the space of canine in gums is empty and this
empty space is called diastema.

3. Pre molar – They are triangular in shape, these teeth are meant for chewing and crushing of food.

4. Molars (Cheek teeth) – These also meant for chewing & crushing of food. They are rectangular in shape. Premolar
and molar help in the mastication of food. In human teeth of upper jaw are attached to the maxilla bone, while teeth
of lower jaw are attached to the mandible bone.

z In animals, except Premolar and Last molar, all type of teeth appears twice in life. Teeth which appear during
childhood are called milk teeth or temporary teeth. Due to the activity of osteoclast cells, these milk teeth are
shed, off then permanent teeth appear.

z When temporary molars are shed, their socket are filled by premolar and new socket are formed for permanent
molar. This occurs once in life time.

z In frog, only upper jaw has teeth.

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TYPE OF TEETH

1. Monophyodont – The teeth which appear only once in life e.g. Pre Molar & Last molar of man.

2. Diphyodont – The teeth which appear twice in life e.g. Incisors, Canines, Molars of human.

3. Polyphyodont – The teeth which appear more than twice in life. e.g. Fish, Amphibians.

4. Thecodont – The teeth which are present in bony socket of jaw. e.g. Man & crocodile
5. Heterodont – When the teeth are of different type in mammals on the basis of structure and function.
e.g. Mammal.
6. Homodont – Whether all teeth are of similar type in animal on the basis of structures and function e.g.
Fish, Amphibians.

7. Pleurodont – The teeth which are present on the lateral side of jaw bone. e.g. Reptiles

8. Acrodont – The teeth which are present on the terminal part of Jaw bone. eg. Fish, amphibian

Wisdom teeth – These are the last molar teeth of humans which appear in the age of 18 to 25 year.

Brachyodont (Cheek teeth) :

In this type of teeth crown part is small root is long such as premolar and molar

Hypsodont (Smiling teeth):

In this type of teeth the crown part is large root is either absent or small such as incisor and canine.
These teeth are also called as smiling teeth.
Secodont:
These are canine teeth of carnivorous animals.
In this type of structure canine teeth become long and pointed which, is bended towards the backward
direction.
Lophs or Cusps–

The upper surface of premolar & molar is broad and some small projections are present in the upper surface of
premolar and molar.

These projections are called Lophs or cusps. On the basis of structure of Lophs, these teeth are of four types–
(i) Carnesial – in this type of teeth the lophs are long & pointed e.g. Carnivorous Animal.

(ii) Bunodont – In this type of teeth. Lophs are small and spherical in shape , such as human
(iii) Lophodont – In this type of teeth the lophs are large, wide and flat such as rabbit & elephant.
(iv) Solenodont – In this type of teeth the lophs are large and semilunar shape e.g. Ruminant animals (Cow,
Buffalo).

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Dental Formula :
2 1 0 2 5 10
Child = 1 C PM M u2 20 2102/2102
2 1 0 2 5 10
2 1 2 2 7 14
17 yr. old = 1 C PM M u2 28 2122/2122
2 1 2 2 7 14
2 1 2 3 8 16
Adult = 1 C PM M u2 32 2123/2123
2 1 2 3 8 16
CHECKPOINT: In humans, premolar teeth appear in the alveoli of molar teeth while permanent molar teeth are
developed in new alveoli. Alveoli is socket in gums inside which teeth get embedded.
SALIVARY GLANDS:
In mammals, 3 pair of salivary glands are present: exocrine type of glands, Duct plus glands and enzymatic secretion.
1. Parotid-glands (largest salivary glands)
These glands are located just below the external auditory canal (in front of ear). Their duct is called Parotid duct/
Stenson’s duct which open in the upper jaw i.e. the Buccal-vestibule.
Whenever in human, these glands are infected by viruses this disease is called as Mumps. Due to this, the gland
swells up.

2. Sub maxillary or submandibular glands – These are located at the junction of the upper and the lower jaw. Their
duct is called Wharton’s duct (largest salivary duct). These ducts open in the lower jaw just behind the Incisor
teeth.

3. Sublingual glands – These are the smallest salivary glands. These glands are found in the lower jaw. Many ducts
arise from these glands called as the Duct of Rivinus or also the Bartholin’s ducts. These ducts open in
the Buccopharyngeal cavity on the ventral side of the tongue
Glands Histology % of total saliva Nerve
Parotid Purely serous 25% IX
Mixed
Submandibular 70% VII
Serous & mucous
Mixed
Sublingual 5% VII
Serous & Mucous

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Serous
Acinar Isotonic
Secretory

Inter Hypotonic
lobular As compare to plasma
Intra
lobular

Mucus
acinar

Sialorrhoea – Hyper secretion of saliva – e.g. Parkinson’s disease, Mental retardation, Chordo tympani nerve damage.
z Aptyalism/Xerostomia - deficiency in secretion of saliva, fear, anxiety etc.
z Maximum saliva is secreted by the Sub-maxillary glands or Submandibular gland.
Salivary glands are Exocrine glands. The secretion of salivary gland is termed as the saliva.
z Aldosterone – increases the K+ and decreases the Na+ concentration in saliva.
z Oryfood – increases the secretion of saliva.

In saliva, water, mucous, starch-digesting Ptyalin enzyme (Saliva amylase), Lysozyme and Thiocyanates are present.
Ptyalin is secreted only by parotid gland. Lysozyme and Thiocyanates mainly kill bacteria. They also check the growth
of bacteria in Buccopharyngeal cavity.
Waldeyer’s Ring: – The lymphatic tissues of the pharynx and oral cavity are arranged in a ring like manner, which are
collectively called Waldeyer’s ring (= Waldeyer’s lymphatic ring). The ring mainly consists of the following:

(i) Nasopharyngeal Tonsil (= Pharyngeal Tonsil): - Refer to the nasopharynx. In children nasopharyngeal tonsil may
become enlarged and referred as adenoids. The resulting swelling may be a cause of obstruction to normal breathing.
(iv) Lingual Tonsil: – They are situated on posterior part of tongue.

(iii) Palatine Tonsils (= Facial Tonsils): – Refer to the oropharynx. The Palatine tonsils are often infected (tonsillitis)
leading to sort throat.
Such enlarged tonsils may become a focus of infection and their surgical removal (Tonsillectomy) becomes necessary.
(ii) Tubal Tonsil: – Refer to the nasopharynx.

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Alimentary Canal

OESOPHAGUS:
Two apertures are found in central part of Buccopharyngeal cavity
z The Dorsal and upper aperture is called Gullet which opens into oesophagus.
z Ventral or lower aperture is called Glottis which is related to the Larynx and guarded by epiglottis
z Oesophagus is simple uniform tube which runs downward and pierces the diaphragm and finally opens
into stomach.
z In Oesophagus, longitudinal folds are found on inner surface.
z Only mucous glands are present in its lumen, digestive glands are absent.
z Voluntary muscles are found on the upper 2/3 part of oesophagus while, involuntary muscles are found
in lower 1/3 part of oesophagus.
CHECKPOINT: The length of oesophagus depends on length of neck so the longest Oesophagus is present in Giraffe.
Stomach = Greek word Gaster
It is situated on left side of abdominal cavity. It is the widest part of alimentary canal. It is a bag like muscular structure,
J shaped in empty condition. The stomach is divided into three part (Fundus, Body, pylorus or antrum).It has two
orifices (opening)

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(i) Cardiac orifice: It is proximal aperture of stomach which is joined by the lower end of the oesophagus.
(ii) Pyloric orifice: It distal aperture of stomach which opens into the duodenum.
Mucous membrane of the stomach is thick. In empty stomach numerous longitudinal folds are found called gastric
rugae. They disappear when stomach is distended. Stomach is covered by layer of peritoneum, lymph tissue
deposits on the peritoneum and fat tissue. Such type of peritoneum is called Omentum. Left curved surface of
stomach is called greater omentum. Right curved surface of stomach is called lesser omentum.
Gastric Glands:
These are numerous microscopic, tubular glands formed by the epithelium of the stomach. The following types of cells are
present in the epithelium of the gastric glands.

(i) Chief cells or Peptic cells (=Zymogen cells) are usually basal in location and secrete gastric digestive enzymes as
pro-enzymes or zymogens, pepsinogen and pro-rennin. The chief cells are also produce small amount of gastric
amylase and gastric lipase. Gastric amylase action is inhibited by the highly acid condition. Gastric lipase contributes
little to digestion of fat. Pro-rennin is secreted in young mammals. It is not secreted in adult mammals.
(ii) Oxyntic cells: (=Parietal cells) are large and are most numerous on the side walls of the gastric glands. They are
called oxyntic cells because they stain strongly with eosin dye. They are called parietal cells as they lie against the
basement membrane. They secrete hydrochloric acid and Castle intrinsic factor.
(iii) Mucous cells: (= Goblet cells) are present through out the surface epithelium and secrete mucus. The epithelium
of gastric glands also has the following two parts of cells.
CHECKPOINT: Argentaffin cells produce serotonin (its precursor is 5-hydroxy-tryptamine, 5-HT), Somatostatin and
Histamine. Gastrin cells (G-cells) are present in the pyloric region and secrete and store the hormone Gastrin.
z Serotonin is vasoconstrictor and stimulates the smooth muscles.
z Somatostatin suppresses the release of hormones from the digestive tract.
z Histamine dilates the walls of blood vessels (vasodilator).
z Gastrin stimulates the gastric glands to release the gastric juice.
Intestine (6 to 9 meters): It is divided into two part
(i) Small intestine (ii) Large intestine
(i) Small Intestine – Small intestine is differentiated in to three part
(i) Duodenum (ii) Jejunum (iii) Ileum

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First part is duodenum, it is 25 cm long, c-shaped in humans and has opening of hepatopancreatic duct (bile duct
+ pancreatic duct)
CHECKPOINT: A small swelling is present at the opening of hepatopancreatic duct and is called ‘Ampulla of
Vater’ or hepatopancreatic ampulla and the opening is regulated by sphincter of oddi.
Next parts of small intestine are jejunum and ileum. The wall of intestine has thin layers of longitudinal and circular
muscles. Mucosa has folds plicae circulares (folds of Kerckring) and villi towards lumen of the intestine.
Epithelial cells lining the villi have microvilli which further increase the absorptive area. Intestinal glands or Crypts
of Lieberkuhn have epithelial cells (secrete mucus), Paneth cells (secrete digestive enzymes) and Argentaffin
cells (probably secrete hormones). In duodenum Brunner’s glands are also present (located in submucosa) which
secrete mucus. Diffused patches of lymphoid tissue are present through out the small intestine and are aggregated
in ileum to form Peyer’s patches.
(ii) Large intestine:
It is 1.5 m long and consists of three part caecum, colon and rectum. A blind pouch of caecum is vermiform
appendix. These parts help in digestion of cellulose in herbivores. Wall of colon has sac like Haustra. Histologically
wall of colon has three bands of longitudinal muscles called taenia coli. Another characteristic of colon surface is
the presence of small fat filled projections called epiploic appendages. The colon part is divisible into ascending,
transverse, descending and sigmoid colon. Sigmoid colon is also called as pelvic colon .Ascending colon is the
smallest and is without mesentery. Last part of rectum is anal canal having a strong sphincter. It opens outside by
anus. In certain conditions (like persistent constipations) rectal veins can get distended or enlarged due to
weakening of valves of it (varicosity). It leads to swollen areas called Hemorrhoids.

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Histology of alimentary canal

Wall of alimentary canal is made up of four layer (outer to inner)
(1) Serosa: It is outer most layer of alimentary canal , it is called tunica adventia in oesophagus, which is made up of
fibrous connective tissue. Except oesophagus, remaining part of alimentary canal in covered by serosa layer which
is made up of visceral peritoneum while, tunica adventia is made up of white fibrous connective tissue.
(2) Muscularis Externa or Mucularis coat: It is made up of two types of muscle outer muscle layer is made up of
longitudinal muscle while inner layer is made up of circular muscle. Thickest muscular coat is found in stomach so
maximum peristalsis are found in stomach least muscles are found in rectum so least peristalsis are found in rectum.
(3) Sub mucosa: It is made up of loose connective tissue layer with blood lymph vessels and nerves.
(4) Mucosa: It is the inner most layer of gut which contains the secretary and absorptive cells. It is differentiated into
3 parts.
(i) Outer part: Called mucosa Muscularis or Muscularis interna.
z It is made up to longitudinal and circular muscles.
z But these muscles are vestigeal.
z They provide support to the folds of alimentary canal.
(ii) Middle part: Called lamina propria.
z It is made up of reticulate and fibrous connective tissue, dense network of blood capillaries are found in
this part.

(iii) Innermost part: Called mucosal layer.

z In oesophagus this layer is made up of non keratinized stratified squamous epithelium.
z Except oesophagus this layer is single layer thick.
z This layer makes the lining of lumen of Alimentary canal.
z This layer is made up of columnar mucous epithelium.
z Folds of oesophagus are less developed
z This layer makes the folds of alimentary canal
z Folds of stomach are finger shaped.
z Folds of small intestine are conical shaped called Villi.
z Small slit like space is found at the base of villi.

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z These spaces are called crypts of Lieberkuhn

z Villi of Duodenum are small blunt.
z Villi of jejunum and Ileum are long and pointed.
z Maximum villi are found Jejunum.
Peyer’s patches
z They are small lymph nodes which are found in the mucosa of small intestine (Jejunum and Ileum more in
number). They are also called intestinal tonsils and provide immunity.
Brunner’s Gland :
z They are small spherical multicellular glands.
z They open into crypts of Lieberkuhn with the help of fine tubules.
z These glands are found in the submucosa and mucosa of duodenum.
z They synthesize and secrete the non enzymatic secretion of intestinal juice.
Paneth Cells :
z These cells are found in mucosal layer of crypts of Lieberkuhn of jejunum.
z They are unicellular gland.
z They synthesize and secrets enzymes of intestinal juices.
z The secretory substances of Brunner’s glands and Paneth cells are combinedly called intestinal juice or
Succus entericus.
Nerve supply:
Two types of Nerve plexus are found in muscle of alimentary canal. (These control muscle contraction).
(1) Auerbach’s Nerve Plexus: This nerve plexus is found between longitudinal muscles and circular muscles.
(2) Meissner’s Nerve Plexus: Found between circular muscles and sub mucosa but in stomach it is found between
oblique muscle & submucosa.
LIVER = Greek word Haper

In human liver is made up of four lobe. Left lobe is small right proper lobe is large, two addition lobe quadrate and
caudate lobe are also found on posterior side of right proper lobe.
It develops from endoderm. It almost weighs for 1.5 kg, both exocrine and endocrine.
z In human it is found in right side of abdominal cavity, below the diaphragm.

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z The liver is the largest gland of body.

z Gall bladder is situated below right lobe of liver.
z Cystic duct of gall bladder is connected to common hepatic duct and form a common bile duct which also
called Ductus choledochus or common bite duct.
z Right and left hepatic duct develops from right and left liver lobe both these ducts combine to form a Common
Hepatic duct.
z Right and left liver lobe are separate from each other by the falciform ligament, (Fibrous connective tissue)
which is made up of fold of peritoneum.

z Internally liver is made up of numerous polygonal lobules. These lobules are covered by fibrous connective
tissue, covering layer is called Glisson’s Capsule.
z Each lobule consists of radial rows of hepatic cells; two rows of hepatic cells are combinedly called as hepatic
cord. Each hepatic cord is lined by endothelial layer.
The bile canaliculi run in between the two layers of hepatic cells in each hepatic cord. Hepatocytes (hepatic cells)
pour bile into the canaliculi. Canaliculi open into branch of hepatic duct which is situated at the angular part of
lobule in the Glisson’s capsule. All branches of hepatic duct of right and left lobe are combined to form right and left
Hepatic duct which come out from the liver and forms a common hepatic duct.
In between the hepatic cord, a space is present called as hepatic sinusoid. These sinusoids are filled with blood.
Sinusoids are lined by the endothelial cells mostly but, a few macrophages cells are also present.
These are called as kupffer’s cells. (Phagocyte cells)

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Hepatic artery and hepatic portal vein enter into liver and divide to form many branches. These branches are also
found at the angular part of Glisson’s capsule. Its fine branches open in to hepatic sinusoids. Branch of hepatic
portal vein, branch of hepatic artery and branch of hepatic duct are collectively called as Portal triad. All hepatic
sinusoids of one Glisson’s capsule are open into central vein or intra lobular vein, all Central veins are combined
and form one pair hepatic vein which, comes out from liver and opens into inferior vena cava.
FUNCTION OF LIVER:
(Liver is known as chemical factory of the body) Most of the biochemical functions of the body are done by the liver.
1. Secretion & synthesis of bile – This is the main function of liver. Bile is yellowish-green, alkaline fluid. In bile juice,
bile salts, sodium bicarbonate, glycocholate, taurocholate, bile pigments, cholesterol, Lecithin etc. are present.
Bile salts help in emulsification of fats. Bile prevents the food from purification. It kills the harmful bacteria.
2. Carbohydrate Metabolism – The main centre of carbohydrate metabolism is liver. Following steps are related with
carbohydrate metabolism.
(I) Glycogenesis – The conversion and storage of extra amount of glucose into glycogen from the digested food
is called glycogenesis. The main stored food in the liver is glycogen
(II) Glycogenolysis – The conversion of glycogen into glucose back when glucose level in blood falls down is
called glycogenolysis.
(III) Glyconeogenesis – Synthesis of glycogen from lactic acid (which comes from muscles) is called
Glyconeogenesis.
(IV) Gluconeogenesis – At the time of need, liver converts non-carbohydrate compounds (e.g. Amino acids. Fatty
acids) into glucose. This conversion is called gluconeogenesis. This is the neo-formative process of glucose.
3. Liver stores vitamin A, D, E, K and B12
4. Detoxification – In this process liver converts the toxic substances into non-toxic substances.
The toxic substances are formed by metabolic activities of the body. E.g. Prussic acid is converted into neutral
Potassium sulfocynide (It is a non-toxic salt) by the liver.
5. Storage of fats – Liver stores fats in a small amount. Hepatic cell play an important role in fat metabolism. The
storage of fats is increases in the liver of alcohol addict persons (Fatty liver). this storage of fats decreases the
activity of liver. The damage of liver due to alcohol intake is called Alcoholic Liver cirrhosis.
6. Synthesis of Vitamin A– The liver converts the E-carotene into vitamin A: E- carotene is a photosynthetic pigment
which is obtained from plants. It is abundantly found in carrot.
7. Most of the blood clotting factor is synthesized in the liver.
8. Purification of blood – The spleen and liver separate dead blood cells and bacteria from the blood. Kupffer’s cells
in liver and phagocytes in spleen perform this function.
9. Storage of minerals– Liver stores iron in the form of ferritin. Liver also stores the, copper, zinc, cobalt, molybdenum
etc Liver is a good source of iron.
10. Deamination and Urea formation – Deamination of amino acids is mainly done by liver (Amino acid oNH3 separation
of ammonia from the amino acids is done by the liver) Liver converts ammonia (obtained form deamination) into
urea through Orinithine cycle. So after the spoilage of liver, the ammonia level in the animal body is increased and
the animal dies.
11. Synthesis of plasma proteins– Many types of proteins are present in blood plasma. Except gamma globulins all
type of plasma proteins are synthesized in the liver.
12. Synthesis of heparin– Heparin is an anticoagulant (Mucopolysaccharide).
z Some heparin is also formed by basophiles, which are special type of white blood cells
13. Yolk synthesis – Most of the yolk is synthesized in liver.
14. Secretion of enzymes – Some enzymes are secreted by liver, participate in metabolism of proteins, fats and
carbohydrates e.g. Dehydrogenase, cytochrome oxidase etc.
15. Heamopoiesis – The formation of blood cells is called Heamopoiesis. In embryonic stage R.B.C. and WBC are
formed by liver.

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16. Prothrombin and fibrinogen proteins are also formed in hepatic cells. These help in blood clotting
17. Factors I, II, V, VII, IX and X are formed in liver, which are responsible for blood clotting.
PAncreas (Sweet bread)

Develop from endoderm. It is soft, lobulated and elongated organ..It is made up or numerous acinus. Acinus is
a group of secretory cells surrounding a cavity.Each acinus is lined by pyramidal shaped cells. These acinus cells
secrete the enzyme of pancreatic juice.
z Each acinus opens into pancreatic ductule. Many pancreatic ductules combine to from main pancreatic duct (duct
of wirsung). The main pancreatic duct is join with the bile duct to form the hepatopancreatic ampulla which opens
into duodenum. The accessory pancreatic duct (duct of santorini) opens into duodenum with separate openings
located above the opening of main pancreatic duct.
z Some group of endocrine cells also found in between group of acinus called islets of Langerhan’s. These islets
secrete insulin & glucagons hormone. So this gland is exocrine as well as endocrine. Its 99% part is exocrine
while 1% part is endocrine (Heterocrine)

z Bile duct opens into proximal limb of duodenum and is controlled by sphincter choledochus.
z Pancreatic duct opens into distal limb of duodenum and is controlled by sphincter pancreaticus.
z In humans both bile duct and main pancreatic duct combine to form common duct called as Hepto-Pancreatic duct.
The terminal end of common duct is swollen and is called as Ampulla of Vater or Hepato-Pancreatic ampulla.
Ampulla of Vater opens into middle part of Duodenum and is controlled by sphincter of Oddi while, bile duct is
controlled by sphincter of Boyden

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PHYsiology of digestion
(I) DIGESTION IN ORAL CAVITY
Food enters through mouth food is tasted in oral cavity and mixed with saliva; tongue mixes the food with saliva.
This food with saliva is called bolus. This saliva (pH 6.8 – 7.0) contains water (99.5 %) and electrolytes (Na+, K+, Cl–
, HCO3– and Thiocyanates)

Chemical digestion: -
In this type of digestion, saliva act with food particles.Saliva contains 99.5 % water & 0.5 % salts.These salts are
organic and inorganic type. The main contents are Mucin, Lysozyme, Thiocyanates and Ptyalin
(A) Mucin
It is a glycoprotein. It lubricates the food particles. It helps in the swallowing of food.
(B) Lysozyme
It is an enzyme which kills the harmful bacteria. Due to this reason saliva is a antiseptic lotion.
(C) Thiocyanates
It is a special salt which kills the harmful bacteria. So it is called bactericidal salt.
(D) Ptyalin

Starch ptyalin
 o Maltose  Limit Dextrin
Ptyalin is found in human saliva, because human food is mainly made up of starch. It does not digest the raw
starch. Ptyalin digests only ripe and cooked starch.
CHECKPOINT: Ptyalin is absent in saliva of carnivorous animal, because food of animal is mainly made up of cellulose.
Bolus is pushed inward through the pharynx into the oesophagus. The tongue blocks the mouth. Soft palate close
off the nasopharynx and larynx rises so that epiglottis bend and closes off the glottis food move downward into
the oesophagus A traveling wave of contractions are called peristalsis pushes the Bolus (food) downward.
When a peristaltic wave reaches the end of the oesophagus (Digestion or digestive enzymes are absent in
Oesophagus) the sphincter opens allowing the passage of bolus food to the stomach. Gastro esophageal sphincter
of the oesophagus and stomach normally remains closed and does not allow contents of the stomach to move
back.
CHECKPOINT: Peristalsis is produced by involuntary contractions of circular muscles, which is preceded by a
simultaneous contraction of the longitudinal muscle and relaxation of the circular muscle lining the gut.

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z Secretion of saliva is mainly controlled by nervous type. Sympathetic nerve decreases the secretion of saliva while
secretion of saliva increases by parasympathetic nerve.
z Secretion of saliva also controlled by reflex action e.g. smells of food, sight reflex etc.
(II) DIGESTION OF FOOD IN STOMACH
When the food enters into stomach G-cells secrete gastrin hormones which stimulate the secretion of gastric juice
by gastric glands.
Secretion of gastric juice is controlled by nerve, hormones and chemical substances.Secretion of gastric juice is
divided into 3 phases–
1. Cephalic Phase – This phase is mediated by parasympathetic. It is the first of step of secretion. When person see
the food then due to sight or optic reflex small amount of gastric juice secretes in the stomach.
2. Gastric phase – When food enters into stomach then gastric phase is started. When food particles strike to the
fundic part of stomach then small amount of gastric juice is secreted due to strike reflex action and distension.
Gastric juice develops the peristalsis movement in the stomach. Due to peristalsis food particles are rubbed on
mucosal layer of stomach. Due to rubbing process cells stimulates and secretes gastrin hormone. This hormone
powerfully stimulates the gastric glands for secretion of gastric juice.
3. Intestinal phase – When food reaches at the Ileum then mucosal layer of ileum secretes a chemical substance. Its
nature is similar to the histamine or gastrin. This chemical substance goes into stomach through blood circulation
where it stimulates the secretion of gastric juice.
Composition of Gastric juice
Water = 99.5 %
HCl = 0.2 – 0.3 %
pH = 1.5 to 2.5 (very acidic)
rest part = mucous water, HCl and gastric enzymes (Pepsinogen, Prorennin, Gastric Lipase Gastric amylase etc.)
Functions of HCl
1. The main function of HCl is to convert inactive enzymes (zymogens) into active enzymes.
HCl
Pepsinogen o Pepsin

HCl
Prorennin o Rennin.
Pepsinogen and Prorennin are inactive enzymes.
2. It destroys harmful the bacteria present in the food.
3. It releases the fat globules from tissue or cells which found in food

4. Nucleoproteins HCl
o Nucleic acid  protein.
5. HCl stops the action of saliva on food. In stomach, the medium is highly acidic.
6. HCl of gastric juice converts Fe+3 into Fe+2 which make the absorption of iron possible.
7. It dissolves the hard portions of the food and makes it soft.
Digestion by Rennin (Chymosin)
Rennin is active in the childhood stage of mammals only. It converts milk into curd like substance (clot the milk) .
Rennin, acts on milk protein casein. Casein is a soluble protein.
In the presence of Rennin, Casein gets converted into insoluble Calcium-paracaseinate, this process is termed as
Curdling of milk. After becoming insoluble, milk can remain in the stomach for a longer time. Rennin is absent in human
(clotting of milk is done by HCl in human).

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Digestion by Pepsin–
Inactive pepsinogen on getting proper pH converts into active pepsin.
Peptidase – An enzyme which breaks the peptide bond. This peptidase is of two types.
(a) Exopeptidase: The peptidase enzyme which breaks the outer and marginal bond of polypeptide called Exopeptidase.
In this process amino acid and polypeptides are formed.
(b) Endopeptidase: The peptidase enzyme which breaks the inner peptide bond of large polypeptide and forms the
small polypeptides such as peptone, proteases and peptides.
Pepsin is a strongest Endopeptidase. It breaks proteins into smaller molecules.
Pepsin
Proteins  o Peptones  Proteoses  Peptides

In stomach, Endopeptidase is found so only digestion of proteins can take properly in the stomach.
Digestion by Gastric Lipase – It converts fats into fatty-acids and glycerol. It is secreted in a less amount so less
digestion of fats takes place here.
This lipase acts on emulsified fat and convert it into fatty acid & glycerol. 1% emulsified fat is already present in
the food. Peristalsis. Continues during the process of digestion so the gastric-juice mixes properly with the food.
Due to peristalsis the food is converted into a paste. This form which is thick, acidic & semi digested in the
stomach is called chyme.

(III) DIGESTION OF FOOD IN DUODENUM

When food leaves the stomach through its pyloric end enters the duodenum it is called chyme (Acidic). The
HCl of chyme stimulates the wall of duodenum to secrete hormones. It secretes various hormones–

1. Gastric inhibitory polypeptide (GIP) – It inhibits the secretion of gastrin hormone.

2. Enterogasterone – It inhibits the secretion of HCl in stomach.
3. Duocrinin - It stimulates the Brunner’s gland for synthesis and secretion of non-enzymatic part of intestinal juice.
4. Vasoactive intestinal peptide and Somatostatin – They inhibits the motility of stomach
5. Cholecystokinin – It stimulates the liver and the gall bladder (mainly gall bladder) to secrete bile juice.
6. Secretin: It is the most important hormone of digestive tract and also first discovered hormone. This hormone
stimulates pancreas for synthesis and secretion of non enzymatic part of pancreatic juice. It also stimulates liver
for secretion of bile juice and inhibit the gastric juice secretion in stomach and reduce rate of contraction of
stomach.
7. Hepatocrinin – It promotes the synthesis and secretion of Bile juice from liver.
8. Pancreozymin – It stimulates the synthesis as well as secretion of enzymatic part of pancreatic juices.
z Secretin promotes the secretion of the non enzymatic part of the pancreatic-juice. While pancreozymin promotes
the secretion of enzymatic part of the pancreatic juice.
9. Enterocrinin - This hormone stimulated Paneth cells for synthesis and secretion of enzymatic part of intestinal
juice.
10. Villikinin – It stimulates the activity of villi.

BILE-JUICE:
In the proximal part of the duodenum bile-juice is secreted. The parenchyma cells of the liver produce bile-juice
and it is stored in the Gall-bladder. Bile-juice does not contain any digestive enzyme. Therefore it is not a true digestive
juice (Pseudo digestive-juice).

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Composition of Bile-juice – Bile juice is a greenish (Biliviridin) with yellow (Bilirubin) coloured alkaline fluid.
Bile juice
pH 8.0
H2O 98 %
Organic constituent are bile acid, bile pigment, cholesterol, Lecithin, inorganic constituents
Na+, K+, HCO3– etc
Bile-pigments are the excretory-substances of the liver.
Bile-salts are of two types–
(a) Organic salts – Organic salt like Na-glycocholate and Na-taurocholate are found in Bile juice. The main function
of these salts is the emulsification of fats because pancreatic Lipase can act only on emulsified fats.
(b) Inorganic salts – Bile-juice contains NaCl, Na2CO3, and NaHCO3 etc in it. Inorganic salts neutralize the acidity of
the food and make the medium basic. It is necessary for the medium to become basic because the pancreatic-juice
enzymes can act only in basic medium.
Bile salts also help in the absorption of fat and fat-soluble vitamin (A, D, E, K) Bile salts combine with fats and
these vitamins to form compounds called Micelles which are absorbed rapidly.
Bile salts promote peristalsis in the small-intestine.Bile-pigments, cholesterol and Lecithin are the excretory
substances found in Bile-juice.
Obstructive Jaundice - If the passage of bile is blocked then the amount of bilirubin increases in the blood. So the
yellowish colouration of body like skin, cornea and nails appear yellow. Urine also becomes yellow.
Gall Stone–Sometimes the passage inside the bile-duct gets blocked or becomes narrow, so the cholesterol gets
deposited or precipitated in the gall-bladder. This is termed as the Gall-stone (Cholelithiasis)
PANCREATIC JUICE :
The pancreatic-juice is secreted by the exocrine cells of the pancreas.Pancreatic juice is highly odoriferous,
colourless basic fluid which contains enzymes and salts.
Composition of Pancreatic juice-
Total amount in man = 500 – 800 ml/day
Water = 98%, pH = 7.5– 8.3, Salts =2 %
z Pancreatic juice contains only inorganic-salts. The action of enzymes present in the pancreatic juice is as
follows–
(1) Pancreatic D-Amylase : Amylase or Amylopsin dissociates starch into Maltose. Majority of starch breaks up into
the duodenum.
(2) Trypsinogen and Chymotrypsinogen – The step of these enzymes is as follows–
Ca  
Trypsinogen        o Trypsin
Enterokina seorEntero peptidase

Trypsin
Chymotrypsinogen  o Chymotrypsin

Enterokinase is secreted by the duodenal mucosa.

Trypsin and chymotrypsin are Endopeptidase type of enzymes. They dissociate protein into peptones and proteases.
Majority of proteins are broken into the stomach and the remaining are broken into the duodenum.
Trypsin and
Proteins Chymotryps
   o Large peptide
in

(3) Fat Digesting enzyme – In pancreatic-juices various Fat-digesting enzymes are found which are collectively called
steapsin.

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Amino peptidase
(4) Large Peptides     o Oligopeptide

Elastase
(5) Elastin  o Oligopeptides

(6) Procarboxy Peptidase – These are also called zymogens. Trypsin convert it into active Carboxy-peptidase.

Carboxy
Large peptides peptidase
  o Amino-acid

(7) DNase and RNase – For digestion of DNA and RNA.

(I) Pancreatic Lipase – It converts triglyceride into monoglyceride, fatty acid, glycerol
(II) Phospholipase – These digest phospholipids.
(III) Cholesterol esterase – It digest cholesterol esters. These esters are made up of cholesterol and fatty acid
Like- Lanolin, (cholesterol and Palmitic acid).

(IV) DIGESTION IN JEJUNUM AND ILEUM

These hormones stimulate the crypts of Lieberkuhn to secrete Succus-entericus or intestinal juice. This succus
entericus mainly contain water (99%) and digestive enzymes (< 1%). Intestinal juice act on food (chyme).
Succus- entericus mainly contains the following enzymes-
1. Peptidase or Erepsin - This is a type of Exopeptidase. It converts oligopeptides into amino-acids
2. Disaccharidases

Sucrase
sucrose  o Glucose  Fructose

Maltase – It convers maltose sugar into Glucose molecules.

maltase
Maltose  o Glucose + Glucose

Sucrose – It is also known as invertase. It converts sucrose into glucose and fructose.
Lactase –This enzyme is found only in mammals. It converts milk sugar lactose into Glucose and Galactose.

Lactase
Lactose  o Glucose + Galactose

4. Nucleotidase and Nucleosidase –These act in the following way–

Nucleotidase
(i) Nucleotides   o Nucleosides  Phosphate

Nucleosidase
(ii) Nucleosides     o Pentose  Nitrogen base

z maximum digestion of carbohydrates is done in duodenum, but its digestion is completed in Jejunum.
3. Intestinal Lipase– This fat-digesting enzyme converts fats into Fatty-acids and Glycerol.

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(V) DIGESTION IN CAECUM

In herbivores, the symbiotic bacteria and protozoans present in the caecum help in digestion of cellulose into glucose.
So the digestion of cellulose takes place in caecum by the process of decompostion. This decomposition process is
very slow.Therefore, very less amount of cellulose is digested at a time in caecum.
In the last part of the large intestine faeces is temporarily stored.

Maximum digestion of food  Duodenum

While digetion of food complete in  Jejunum
Maximum absorption of food in  Jejunum

Millions of microscopic folds or fingers like projection are present in the lumen of gut which are called villi. These villi
are supplied with a network of blood capillaries and Lymphatic vessels. Largest of which is central Lacteal. The cells
that line the surface of villi numerous microscopic bristle like projections are called microvilli These further increase
the surface area for the absorption of the nutrients/digested food. On the surface of the mucous epithelium are billions
of single cell mucous glands called mucous or goblet cells. These cells mainly secrete mucus that acts as a lubricant
and protects the epithelial surface from damage and digestion.

Epithelial cells of small intestine showing absorption of nutrients. (A) Absorption of a aminoacid. (B) Absorption of
monosaccharides. (C) Absorption of fatty acids.

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Hormone Source Secretion Stimulus to Target/Action

Gastrin Pyloric stomach and Vagus nerve activity, Secretory cells and muscles of
duodenum/G-cells peptides and proteins in stomach, secretion of HCl and
stomach stimulation of gastric mobility.
Cholecystokinin Upper small intestine Food (Fatty chyme and Gall bladder, contraction of
(CCK) (Duodenum) amino acids) in duodenum gall bladder (Bile release)
Secretin Intestinal wall Food and strong acid in Pancreas, secretory cells and
(Duodenum) stomach and intestine muscles of stomach, secretion
of water and bicarbonate
(NaHCO3), inhibition of
gastric motility
Gastric Inhibitory Upper small intestine Monosaccharides and fats Gastric mucosa and muscles,
Peptide (GIP) (Duodenum) (fatty chyme) in inhibition of gastric secretion
duodenum and mobility/motility (slowing
food passage)

An Overview of the Action of Major Enzymes in Human

Enzyme Site of Action Substrate Products of Action
Gastric Juice (Stomach)
Pepsinogen : pepsin Stomach Proteins Large peptides
Salivary Juice (Salivary Gland)
Salivary amylase of Mouth and stomach Starch Disaccharides (few)
Ptyalin Buccal cavity

Intestinal Juice (Small Intestine)

(a) Enteropeptidase Duodenum Trypsinogen Trypsin
or enterokinase
(b) Peptidase Duodenum Oligopeptides Amino acids
(c) Disaccharidases Duodenum Disaccharides Monosaccharides
(d) Nucleotidase Duodenum Nucleotides phosphoric Nucleosidases
acid
(e) Nucleosidases Duodenum Nucleosides pyrimidines Sugars, purines
Pancreatic Juice (Pancreas)
(a) Pancreatic Small intestine Starch Disaccharides
D-amylase
(Duodenum)
(b) Trypsinogen: Small intestine Proteins Large peptides
Trypsin
(c) Chmotrypsin Small intestine Proteins Large peptides
(d) Elastase Small intestine Elastin Oligopeptides
(e) Carboxypeptidases Small intestine Large peptides Amino-acid
(f) Aminopeptidase Small intestine Large peptides Oligopeptides
(g) Lipase Small intestine Triglycerides fatty acids, Monoglycerides
glycerol
(h) Nuclease Small intestine Nucleic acids Nucleotides

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The lining cells of the villi are columnar epithelial cells called enterocytes. On the surface of enterocytes, numerous
microvilli are found; they increase the surface area of mucous membrane.

ABsorption of Digested food

The process through which the food stuff diffuses through the intestinal mucous membrane and reaches the blood, is
termed as absorption. The process of absorption in different parts of the alimentary takes place in the following
manner:

(1) Absorption in Buccal-Cavity

No absorption of food takes place in the oropharynx and the oesophagus. Only some chemicals/medicines and
alcohol are absorbed in oro-pharyngeal cavity.

(2) Absorption in stomach

In the stomach, absorption of water, some salts, alcohol and glucose takes place, complete absorption of alcohol
takes place in the stomach.

(3) Absorption in duodenum–

Iron & calcium ion are absorbed in the duodenum.

(4) Absorption in Jejunum–

Maximum absorption takes place in jejunum.

Carbohydrate
The principal carbohydrate of our food is usually starch (from rice or wheat) which is broken down by the pancreatic
amylase. Disaccharides are broken down to their monosaccharide by enzymes of the succus-entericus. Monosaccharides
are absorbed via the capillary blood with in the villus to finally reach into portal vein. Absorption of glucose molecules
occurs along with Na+ by active symport. Fructose is absorbed passively.
Digestion and absorption of amino acid–
All these proteins are exposed to pepsin, trypsin, chymotrypsin, carboxypeptidases etc and as a result they are
converted into tri and dipetides or free amino acids. Amino acids are of two types L-amino acid &
D-amino acid. The L-amino acids are absorbed by active process against the concentration gradient while D-amino
acid are absorbed passively by diffusion.
Di–and tripeptide enter the enterocytes where they are hydrolyzed to amino acids by dipeptidases and then absorbed
via portal blood.
Digestion and absorption of Fat–
One molecule of triglyceride is hydrolyzed into one molecule of monoglyceride and two molecules of fatty acids by
pancreatic lipase.
After hydrolysis, the bile salt, monoglyceride and the fatty acid together produce a complex called a mixed micelle. These are
water soluble & enter in the enterocytes. Monoglyceride and fatty acid are resynthesized with in enterocyte to form a
molecule of triglyceride (TG).TG combines with a small amount of protein Phosphate and cholesterol and resultant complex is
called chylomicron (150Pm, white) Chylomicron enters the lacteal
Fat soluble vitamins are absorbed along with dietary fat whereas water soluble vitamins are absorbed by passive
diffusion. Vit. B12 is absorbed with intrinsic factor by forming a complex.
In illeum Vit.B12 & Bile salt are absorbed. In colon only metabolic water is absorbed.

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All lymph capillaries coming out of the alimentary canal and unite to form Lymph vessels. All lymph-vessels coming
from the alimentary canal open into the Left Thoracic Lymph Duct. This duct now opens into the Left Subclavian vein.
Through the blood, fats reach the heart and from here it is distributed throughout the body.
z Besides fats, other substances of the digested food like-sugars, amino-acids, vitamins, minerals-salts after being
absorbed, enter the blood capillaries. All blood-capillaries coming out of the alimentary canal, join together to form
the Hepatic portal vein. This vein takes the digested food material into the liver. From the liver, the Hepatic vein and
the inferior or post – vena cava vein takes them to the heart. Heart distributes them throughout the body. Liver
performs some necessary and important actions on the digestive food.

Maximum water absorption occurs from upper part of small intestine passively.
(4) Absorption in colon – Colon absorbs metabolic water form the undigested food. Due to Haustra the water-
absorbing surface of colon increases and it efficiently increases absorption of water.
Symbiotic bacteria found in colon. Bacteria synthesis vitamin-K, B1, B2.
Undigested food goes into rectum where it gets converted into faeces contains – water and solid matter. Solid
matter contains dead bacteria 30%, fat 10-12%, proteins 2-4% and others.
These faeces ejected outside through anus.

Brown colour of the excreta is due to 2 pigments-Sterobilin and Urobilin. Both of them are formed due to the
degradation of Bilirubin. Foul smell of the excreta is due to Indole, Scatole and Typtophan. CH4 , NH3 , H2S. These
are found in the colon due to the decomposition of undigested protein by bacteria. Pellets of rabbit don’t have a
foul smell because it has minimum amount of proteins in its diet. Carnivores have excess protein-rich diet so there
is highly foul-smelling.

Compound stomach -
Stomach of Ruminant made of 4 chambers:
Rumen o largest
Reticulum o Smallest Omasum
Abomasum o true stomach

Gastric juice secreted by Abomasum. So it is called true stomach. Inner surface of Rumen and Reticulum lined by
keratinized epithelium. Symbiotic bacteria found in Rumen and Reticulum. Voluntary muscles are found in Rumen
and Oesophagus. Hence reverse peristalsis are found in Rumen and oesophagus which is controlled by will power
of animal. Omasum is absent in Camel and Deer.

Calorific Value:
The amount of heat liberated from complete combustion of 1 gm food in a bomb calorimeter (a closed metal
chamber filled with O2) is its gross calorific value or gross energy value (G.C.V.).
The actual amount of energy liberated in the human body due to combustion of 1 gm of food is the physiologic
calorific value (P.C.V.) of food.

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Food substance G.C.V. P.C.V.

(in K.cal/gm) In K. cal/gm
Carbohydrate 4.1 4.0
Protein 5.65 4.0
Fats 9.45 9.0
Assimilation:
The use of absorbed digested food by the body is termed as assimilation. Amino-acids synthesize proteins, which
in turn synthesis enzymes and new protoplasm. Glucose fatty-acids and glycerol on oxidation provide energy.

DISORDERS OF DIGESTIVE SYSTEM

PROTEIN ENERGY MALNUTRITION
(1) Kwashiorkor –
z It is a protein deficiency disease.
z It commonly affects infants and children between 1 to 3 year of age.
Symptoms – Underweight, stunted growth, poor brain development, loss of appetite, anaemia, oedema on lower
leg and face.
Cure – Proteins are necessary for growth, repair of tissue and for body defense therefore adequate amount of
proteins must be present in the diet.
Daily requirement –1 gm protein per kg. Body weight in adult.
2 gm protein per kg body weight in growing children.
Sources in food – Cereals pulses, meat, fish, milk, groundnut, peas, leafy vegetables etc.

(2) Marasmus – It is caused by Protein-Energy-Malnutrition (PEM) or deficiency of protein and total food caloric
value.
Symptoms – Impairs physical growth, subcutaneous fat disappears, ribs become very prominent, limbs become
thin and skin becomes dry, thin & wrinkled. There is no oedema on leg and face but loss of weight occurs.
Cure – Diet with adequate proteins and proper caloric value should be given to the infants.
Source in food – Same as kwashiorkor.
(3) Hypercholesterolemia – It is caused due to intake of excess of saturated fat such as butter, ghee, red meat, egg.
Cholesterol level in blood rises abnormally (hypercholesterolemia) this may cause thrombosis and heart attack.
(4) Obesity – It is caused by excessive intake of high caloric nutrients such as sugar, honey and saturated fat. Fat
accumulates in the tissue. This may cause high blood pressure, diabetes and heart diseases. Regular exercise and
taking of green leafy vegetable are recommended to such persons.
(5) Hypervitaminosis – It is caused by excessive intake of vitamin. Such as excess of vitamin D causes deposition of calcium
in soft tissue. Excess of vitamin A causes lack of appetite, itching rash etc. Hypervitaminosis of vitamin ‘D’-Nausea,
anorexia, hypocalcaemia, hyperphosphetemia, calcification of soft tissue.
(6) Fluorosis – It is caused by excessive intake of fluorine. It is characterized by mottled (brownish discolouration)
teeth.

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(7) Constipation – Because of slow reaching of excreta into the large-intestine hard and dry excreta deposits in the
colon.
(8) Diarrhoea – Fast and rapid removal of excreta from the large-intestine is called Diarrhoea. It may be due to viral or
bacterial infection in the intestine.

Types of food relative to their nature of Nutrients and Basic Functions

Major Food Nutrient Function
Sugar, glucose , sugarcane, honey Carbohydrates
and milk Sugars
Wheat, bread, maize, corn, rice and Starch
potatoes
Butter, sunflower oil, seeds and Lipids Energetic
vegetable oils, nuts, almonds, Fats and oil
cheese, liver oils and egg yolk
Flesh (meat, chicken, fish), milk, Proteins
pulses, cereals, egg (albumen and Amino acids
yolk) and cheese
Table salts, pickles and butter Minerals
Sodium
Constructive
Table salts, pickles and butter Chlorine
Jaggary, banana, date palm and Potassium
potato
Milk, cheese, curd, fish, eggs, Calcium
pulses, carrot, cabbage and dark
green leaves
Meat, fish, milk, cheese, egg, Phosphorus
pulses and cereals
Meat, liver, egg-yolk, fish, green Iron
leaves, nuts, fig, and pulses
Sea-fish, sea-weed, onion and Iodine
iodised table salt
Cod and shark liver oil, kidneys, Vitamins
egg-yolk, green and yellow A (Retinol)
vegetables, (carrot, mango, lettuce,
cabbage), tomato, yeast, milk and
butter
Whole cereals, dried beans, pork B1 (Thiamine)
meat, egg-yolk, yeast
Meat, liver, fish, milk, egg, cheese, B2 (Riboflavin )
legumes and green leafy vegetables
Pulses, cereals, meat, liver, fish, PP (Pellagra preventing) or Protective
intestinal bacteria and yeast (Also nicotinamide
synthesized in the human body
from the amino acid, tryptaphan)
Citrus fruits, vegetables, tomato, C (Ascorbic acid)
and peppers
Cod and shark liver oil, chicken, D (Calciferol)
egg-yolk, milk, butter, etc. (Also
synthesized in human skin in
presence of sunlight.)

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SOME IMPORTANT MINERALAND THEIR FUNCTIONS
Mineral Functions
Calcium Component of bone and teeth ; essential for normal
blood clotting , needed for normal muscle and nerve
function.
Chlorine Principal anion of interstitial fluid ; important in fluid
and acid-base balance.
Copper Component of enzyme for melanin synthesis; essential
for haemoglobin synthesis.
Iodine Component of thyroid hormone. Its deficiency causes
goiter.
Iron Components of respiratory pigments (like
haemoglobin and myoglobin), respiratory enzymes
(like cytochromes) and oxygen transport enzymes. It's
deficiency causes anaemia.
Phosphorus Important structural component of bones, DNA and
RNA; essential in energy transfer, storage of energy
(ATP) and other metabolic activites; maintains normal
blood pH (buffer action.)
Potassium Principal cation in the cytoplasm; controls nerve
excitability and muscle contraction. Dietary deficiency
causes rickets among children.
Sodium Principal cation of interstitial fluid; maintains fluid
balance ; essential for conduction of nerve impulse.
Sulphur Components of hormones (e.g. insulin) ; necessary for
normal metabolism.
Zinc Component of at least 70 enzymes, like carbonic
anhydrase, and some

NUTRITIONAL DISORDERS DUE TO DEFICIENCY OF DIETARY COMPONENT

PROTEIN
Nutrient Name of Disease Deficiency symptoms
Protein Kwashiorkor Wasted muscles, thin limbs,
retarded growth of body and brain,
oedema, pot belly and diarrhoea.
Protein and calorie Marasmus Impaired growth and replacement
of tissue proteins, thin limbs and
prominent ribs (emaciated body),
dry, wrinkled and thin skin,
diarrhoea.

minerals
Nutrient Name of Disease Name of Disease
Iodine Goitre Swelling of the thyroid gland,
reduced mental function, increased
risk of stillbirths, abortions and
infant deaths.
.
Iron Anaemia, failure to mature RBC Low haemoglobin condition,
weakness, tiredness, reduced
learning ability, increased risk of
infection and even death during
childbirth.

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Vitamins
Nutrient Name of Disease Name of Disease
Retinol (A) Night blindness Dry, keratinized epithelia of skin,
respiratory and urinogenital tracts,
especially among children.
Calciferol (D) Rickets (Osteomalacia) Weak and soft bones, distorted
skeletal, poor muscular
development.
Tocopherol (E) Anaemia RBC devoid of haemoglobin or
maintains erythrocytes.
Menadione (K) Severe bleeding Slow or delayed blood clotting and
haemorrhage (blood loss)
Ascorbic acid (C) Scurvy (failure to form Bleeding gums, loose teeth,
connective tissue) anaemia, painful and swollen
joints, delayed healing of wounds,
and emaciation,
Thiamine (B1) Beriberi Loss of appetite, fatigue, muscle
atrophy, paralysis, mental
confusion, cardiac oedema.
Ribofavin (B2) No specific disease Digestive disorder, burning
sensation of the skin and eyes,
lesions at the corners of the mouth,
headaches, mental depression.
Pyridoxine (B6) No specific disease Dermatitis, impairment of antibody
synthesis.
Cyanocobalamine (B12) Pernicious anaemia Large, immature and nucleated
RBC devoid of haemoglobin.
Folic acid Macrocytic anaemia, malformed Impairment of antibody synthesis,
(Pteroglutamic acid) RBC stunted growth.
niacin Pellagra and canine (dog) disease Scaly, pigmented skin, irriation of
(nicotinic acid, nicotinamide) (black tongue) the GI tract (diarrhoea)
.Biotin (Vit-H) Dermatitis Scaly skin, muscle and pains and
or (B4 or B7) weakness.

SOME IMPORTANT VITAMINS AND THEIR FUNCTIONS

FAT SOLUBLE VITAMINS
Vitamin Functions
Retinol (A) Principal component of retinal pigments; promotes
normal vision, growth of bones and teeth maintenance
of epithelial tissue.
Calciferol (D) Absorption of Ca2+ from small intestine, needed for
growth maintenance of bone (synthesised in human
skin in presence of sunlight)
Tocopherol (E) Inhabit oxidation of unsaturated fatty acids and
vitamin A.
Naphthoquinone (K) Essential for coagulation of blood (proudcued by
intestinial bacteria).

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WATER SOLUBlE VITAMINS
Vitamin Functions
Ascorbic Acid (C) Synthesis of collagen, bone matrix, tooth dentine and
other extracellular materials, metabolism of may
amino acids ; helps body to with stand injury from
burns and acts as antioxidant.
Cyanocobalamine (B12) Important for nucleoprotein synthesis and formation
of RBC (produced by intestinal bacteria).
Biotin (B7) Coenzyme needed for protein and fatty acid synthesis,
CO2 fixation and transamination .
Folic Acid Coenzyme needed for nucleoprotein synthesis and
(folacin, pteroglutamic acid) formation of RBC.
Niacin Coenzyme in hydrogen transport (NAD, NADP).
Pantothenic Acid Component of coenzyme A (CoA).
Pyridoxine (B6) Coenzyme for amino and fatty acid metabolism.
Riboflavin (B2) Flavoproteins in oxidative phosphorylation.
Thiamine (B1) Formation of carboxylase enzyme involved in
decarboxylation (citric acid cycle).

VITAMINS

z The study of vitamins is called as vitaminology.

z Vitamins were discovered by ‘’Lunin’’ .
z The term ‘’Vitamin’’ was given by ‘’Funk’’ and ‘’Hopkins’’ (B1 from unpolished rice – 1912)
z Vitamins are micronutrients, biological regulators and metabolic regulators (Vitamin theory)
z Vitamins are important to maintain health, but cannot synthesize in the body.
z Earliest known vitamin - vitamin ‘C’ (James Lind – Scottish naval surgeon – 1747.)
z Earliest extracted vitamin = Vitamin - B1

Vitamins are following types –

(1) Fat soluble
(2) Water soluble vitamin

FAT – SOLUBLE VITAMIN

Vitamin- ‘A’ (Retinol) –
z Can be synthesized in liver from yellow and red carotenoid pigment.
z It is also known as anti-infectious and anticancer vitamin.
z It is also known as anti-xeropthalmic vitamin.
z Isomer of vitamin ‘A’ are –
z (i) A1 – Retinol for vision.
(ii) A2 – Dehydro retinol which is essential for epithelial lining of glands and tear production . It is
essential for growth and epithelical cell division.
Deficiency diseases –
(1) Night blindness – Due to deficiency of A1
It is also known as Nyctolopia (Inability to see in dark)

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(2) Xeropthalmia – due to deficiency of A2
Tear formation is absent.
In this disease conjunctiva & cornea become dry due to keratinization of conjunctiva & cornea .
It is the main problem of blindness in children throughout the world.
Source – Good source is carrot, other sources are Guava, papaya, mango, spinach etc.

(3) Vitamin – ‘’D’’ (Calciferol)

It is also known as ‘’Sunshine vitamin’’ or ‘’Anti Ricket’’ vitamin.
Synthesized in skin from cholesterol by UV light.
It is necessary for bone & teeth.
It regulates the absorption of calcium & phosphorous.
It organize the calcium in bone and teeth.

Deficiency diseases –
Rickets in children and osteomalacia in adult.
Source – Good source cod liver oil and shark liver oil for both ‘A & ‘D’, Other sources are meat, liver, egg,
milk etc.
Vitamin ‘E’ (Tocopherol) –

z It is also known as ‘’antisterility’’ vitamin or ‘’beauty’’’ vitamin.

z This vitamin removes scar & wrinkles from skin.
z It is essential for gametogenesis, pregnancy and muscular work.
z It maintains the cell membrane of RBCs.
Deficiency diseases – Sterility, Fragile anaemia.
Source – Egg, meat, cotton, seed oil.
Vitamin ‘K’ (Naphthoquinone) –
z It is alos known as ‘’antihaemorrhagic’’ vitamin.
z Essential for synthesis of prothrombin.
Menadione is the important source of the synthetic vitamin K.
Deifciency disease – Bleeding or delayed blood clotting. (Hypoprothrombinemia).
Source – Carrot, tomato, liver, cabbage etc.
WATER – SOLUBLE VITAMIN
Vitamin B1 (Thiamine) –
z It is also known as ‘’anti beri-beri’’ factor or antineuritic factor.
z Beri-Beri affects peripheral nervous system, alimentary canal & cardiovascular system.
z It is essential for formation of coenzyme carboxylase in carbohydrate and amino acid metabolism.
z Defi disease – Beri-Beri, Wernicke’s encephalopathy. Anorexia, constipation, weak-Heart and muscle
atrophy.
Source – Rice, wheat, egg and fish etc.
Vitamin B2 (Riboflavin)
z it is also known as vitamin ‘’G’’ or lactoflavin or yellow enzyme.
z it is essential for formation of FMN & FAD.
z It maintain the oral epithelial lining.
Defi. Disease – Cheliosis (Cracked lips at the corner of mouth) sore mouth and ulceration, digestive
disorder, Pellagra like, beri-beri like.
Source – Cow’s milk, egg, liver, yeast etc.

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Vitamin B3 (Niacin or Nicotinic acid) –
It is also known as ‘’antipellagra’’ factor or vitamin PP (Pellagra preventing factor)
It forms essential component of NAD & NADP.
It maintains the epithelial lining of lumen of alimentary canal.
Defi. Disease – Pellagra in human beings (diarrhoea, dermatitis, dementia) and black tongue (hyper pigmentation)
disease in dogs.
Source – Kidney, liver, milk, yeast, egg etc.
Vitamin B5 (Pantothenic acid) – greek word pantothen = everywhere
z It is also known as yeast factor or chick antidermatitis factor.
z it is help in formation of acetylcholine and co enzyme A. It regulated the secretion of steroid hormones.
Defi. Disease – Burning feet syndrome, fatigue & paralysis of muscles.
Source – Liver, meat, yeast, milk, egg, meat etc.

Vitamin B6 (Pyridoxine)
Function as co-enzyme. It is also known as antidermatitis factor.
Defi disease – Dermatitis, Anaemia, nervousness.
Source – Liver, meat, yeast, egg etc.

Vitamin B7 (Biotin)
It is also known as vitamin ‘H’ or antiegg white injury factor (egg white contain avidin protein which is antagonist to
vit. B7) – Dermatitis, hair loss, nervous symptom). It is essential for fat synthesis and energy productio
Defi. Disease – Dermatitis
Source – Vegetables, yeast, wheat egg etc.
Vitamin B12 (Cyanocobalamine) –
Extrinsic factor of castle It is also known as ‘’ antipernicious anaemic’’ factor or ‘’ RBC maturing’’ factor It promotes
DNA synthesis & Maturation of RBCs.
Defi. Disease – Pernicious anaemia.
Source – meat, liver etc.
Folic Acid –
It is also known as folacin or Vitamin M.
It is needed for formation of RBC & synthesis of DNA
Deficiency disease – Anaemia.
Source – green foliage of plant – cabbage, cauliflower.
Vitamin ‘ C’ (Ascorbic Acid)
It is also known as ‘’ anti-scurvy’’ or anti-viral, anti-cancer vitamin.It is necessary for healing of the wound and
formation of collagen fibre
Deficiency disease – Scurvy (deficient formation of collagen fibres).
Source-Amla, Tomato, orange, Guava, Lemon (citrus fruit).

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KEY PO INTS

1. Spoil hay of Sweet clover (melilotus indica) (Fodder and green manure) contains a substance called dicumarol.
Dicumarol prevents the action of vitramin ‘K’
2. Non-secretion of HCl is called as achlorhydria condition.
3. Chalogogues are substances which cause. The contraction of gall bladder
4. Choloretic are substances which increase bile juice from liver.
5. ‘’Achalasia Cardia’’ condition is characterized by failure of cardiac sphincter to relax completely on swallowing
causing accumulation of food in oesophagus and proximal oesophagus dialates.
6. One pair of vomerine teeth is found in the palate of frog.
7. Fangs are the poison teeth of snakes, these are the maxillary teeth.
8. Upper incisor teeth are modified in tusk in elephant.
9. Upper canine teeth are modified in tusk in walrus.
10. Homodont type dentition are found in toothed whale.
11. Enamel is absent in sloth and Armadillo.
12. Salivary glands are absent in whale.
13. The tongue is non-motile in whale.
14. Gall bladder is absent in lemprey, whale, rat and horse.
15. The main pancreatic duct is also known as duct of wirsung while accessory pancreatic duct is known as duct of
santorini.
16. Citrin is also known as vitamin ‘P’ and controls vascular permeability.
17. Vitamin B17 – It is recently discovered anticancer vitamin.
18. Vitamin Q – helps in blood clotting.
19. Vita B15 – It is also known as pogonic acid, deficiency causes disorder in liver.
20. Vitamin B6 also used in the treatment of tuberculosis.
21. Thecodont teeth are also found in crocodile.

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o Biomacromalecules in food cannot be utilised by our body in their original form. They have been broken down and
conveted into simple substances in the digestive system. This proces of conversion of complex food subtances to
simple absorbable forms is called digestion.

o No significant digestive activity occurs in the large intestine.“The functions of large intesitine are
(a) absorption of some water, minerals and certain drugs.
(b) secretion of mucous, which helps on adhering the waste particles together and lubricating it for an easy
passage.
o The undigested, unabsorbed substances called faeces enters into the caecum of large intestine through ileocaecal
value, which prevents the backflow of the faecal matter. It is temporarily store in the rectum till defaecation.
o Absorption of digested product :
o Absorption is the process by which the end products of digestion pass through the intestinal mucosa into the
blood or lymph.

1. Disorders of digestive system :

o Jaundice : The liver is affected, skin and eyes tum yellow due to the deposite of bile pigments.
o Vomitting : It is the ejection of stomach contents through the mouth. This reflex action is controlled by the
vomit centre in the medulla. A feeling of nausea precedes vomitting.
o Diarrhoea : The abnormal frequency of bowel movement and increased liquidity of the faecal discharge is
known as diarrhoea. It reduces the absorption of food.
o Constipation : In constipation, the faeces are retained within the rectum as the bowel movements occur
irregularly .
o Indigestion : In this condition, the food is not properly digested leading to a feeling of fullness. The causes
of indigestion are inadequate enzyme secretion, anxiety, food poisoning, over eating and spicy food.

o When chyme enter into doudenum HCL of chyme stimulate different enteroendocrine cells of intestine to secrete
following hormones.

1. Secretin - 1st discovered hormone, stimulate pancreas to synthesise and secrete nonenzymatic part of
pancreatic juice.
2. Pancreozymin stimulate pancreas to synthesise and secrete enzymatic part of pancreatic juice.
3. Hepatocrinin stimulate liver cells for synthesis and secretion of bile juice.
4. Cholecystokinin stimulate liver and Gall Bladder for secretion of bile juice.

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5. Duocrinin stimulate Brunner's glands for synthesis and secretion of Intestinal juice's nonenzymatic part.
6. Enterocrinin stimulate paneth cells to synthesise and secrete enzymatic part of intestinal juice.
7. Villilkinin stimulate the activity of villi.
8. Entrogasterone inhibit secretion of HCl in stomach.
9. Gastric Inhibitory polypeptide inhibit secretion of Gastrin hormone.
10. Vasa Active Intestinal Polypeptide decreases peristalsis in stomach and increases peristalsis in intestine.
11. Glucose dependent Insulinotropic Peptide is secreted by K cells of intestine and stimulate secretion of
insulin from b cells of pancreas.
2. BILE-JUICE
o pH = 8.0, daily formed 500 to 800 ml,
o Pseudo digestive juice because donot contain any enzyme.
H2O (98 %)
Other (2 %)
o Bile pigments - Bilirubin (yellow) and Biliverdin (Green)
o Inorganic - NaCL, Na2CO3, NaHCO3 - provide alkaline medium in duodenum Organic Bile Salts o Na glycolate, Na
taurocholate o helps in emulsification of fats.

Other function of bile juice :

o Active pancreatic lipase
o Increase peristalsis in intestine
o Neutralise the acidity of HCl
o Prevent food from decomposition.
o Helps in absorption of fats and fat soluble vitamins.

3. PANCREATIC JUICE
o pH= 7.5 to 8.3, daily formed 1l to 1.5 l
o Contain many enzymes which helps in digestion in duodenum.
o ABSORPTION IN ILEUM : Vitamin B12 and bile salts are absorbed
o DIGESTION IN CAECUM : In human beings caecum and appendix both are vestigeal. In Rabbit both are functional.
o In caecum of Rabbit, cellulose is digested with the help of an enzyme cellulase by decomposition process. Digestion
of cellulose is very slow process.

ABSORPTION IN COLON: Water is absorbed. Haustra increases surface area of colon for H2O absorption.

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4. ASSIMILATION OF FOOD :
(1) Proteins and amino acids - Amino acids are not stored in body as they are highly reactive so converted into proteins
which are building blocks of body. Excess of amino acids are converted into Glucose by Gluconeogenesis in liver.
NH3 is removed in this process and step is deamination. Deamination takes place in each and every cell of body but
liver and kidney are chief sites of deamination.
(2) Carbohydrates : Glucose is instant source of energy.
Glucose o Glycogen in liver (Glycogenesis) (Glycogen in stored food material)
Whenever required, Glycogen o Glucose (Glycogenolysis)
Amino acids and fats o Glucose in liver (Gluco neogenesis)
Lactic acid formed in muscles o Glycogen in liver by Glyconeogenesis
(3) Fats : Stored in body, help in insulation and thermoregulation.
Rich source of energy
(4) Minerals, water and vitamins plays vital role in many vital processes of body.

5. EGESTION : Undigested food material is stored in the form of faecal matter in rectum. Removal of faecal matter from
body is called egestion. Faecal matter is yellowish brown in color due to the presence of two pigments (Stercobilin and
Urobilin). These two are formed due to degradation of bile salts. Foul smell in excreta is due to the presence of CH4, NH3,
indole, scatole, tryphtophan and H2S.

Rabbits faecal matter is in the form of pellets which contain more amount of cellulose in it Rabbit feed on its own faced
matter in order to digest the extra amount of cellulose present in it this process is called coprophagy (pseudorumination).
Rabbit's excreta donot have much smell as main component of excreta is cellulose .
Carnivore's excreta have much smell as main component of excreta is protein .

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SOLVED EXAMPLE
Ex.1 In mammals the lower jaw is made up of Ex.6 The site of protein digestion is
(A) Dentary (B) Maxilla Or
(C) Premaxilla (D) Palatine
A rabbit eats a lot of gram, Then its digestion starts
Sol. (A) : The lower jaw of man is formed by the fusion of
in
dentary bone only.
(A) Gullet (B) Stomach-Fat
Ex.2 The hardest substance of vertebrate body is (C) Small intestine-Protein (D) Mouth-Starch
Or
Sol. (B) : The site of protein digestion is stomach where
Crown of teeth is covered by
pepsin enzyme occur which changes protein to
(A) Keratin (B) Enamel
peptones + proteases.
(C) Dentine (D) Chondrin
Sol. (B) : Crown of the teeth is covered by the hardest Ex.7 Which of the following statement is not correct
substance of the body called enamel (A) Goblet cells are present in the mucosa of intestine
Ex.3 In mammals the teeth are and secrete mucus
(i) Of different types (B) Oxyntic cells are present in the mucosa of
(ii) Embedded in the cup-like socket of the jaw bones stomach and secrete HCl
(iii) Only two sets, present throughout life (C) Acini are present in the pancreas and secrete
These conditions are reffered as carboxypeptodase
Or (D) Brunner's glands are present in the submucosa
Teeth of rabbits are of stomach and secrete pepsinogen
(A) Heterodont, thecodont and diphyodont Sol. (D) : Brunner's glands are present in the submucosa
(B) Thecodont, heterodont and diphyodont of duodenum and secrete HCO–3
(C) Diphyodont, thecodont, and heterodont
(D) Heterodont, diphyodont and thecodont Ex.8 The predominant antibody in saliva is
(E) Thecodont, diphyodont and heterodont (A) IgG (B) IgA
Sol. (A) (C) IgM (D) IgD

Ex.4 The mucosal layer in the stomach form irregular folds Sol. (B)
known as
Ex.9 In man, Glisson's capsule is associated with the
(A) Villi
(A) Digestive system
(B) Lumen
(B) Excretory system
(C) Rugae
(D) Crypts of Lieberkuhn (C) Nervous system
(E) Lacteals (D) Reproductive system
Sol. (C) (E) Endocrine system
Sol. (A)
Ex.5 Dental formula of human beings is
(A) I2, C2, P1, M3 (B) I2, C1, P2, M3 Ex.10 Which of the following is the symptom of Ulcerative
(C) I3, C1, P2, M2 (D) I2, C2, P3, M1 colitis
Sol. (B) : Dental formula of human is (A) Watery stools containing blood and mucus
2,1, 2,3 8 (B) Difficulty in swallowing
u2 32 . It shows the number of incisor
2,1, 2,3 8 (C) Loss of appetite
2, canine 1, premolar 2 molar 3 in each half upper and (D) Eyes turn yellow
half lower jaw with 32 teeth in buccal cavity. Sol. (A)

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BIOLOGY FOR NEET & AIIMS
Ex.11 Which of the following is not the reason for very Sol. (B)
high load of bilirubin in a new born
Ex.17 Choose the wrong statement
(A) Excessive red blood corpuscles in the newborn
(A) Lipases and nucleases are not present in
burst, releasing the bilirubin
pancreatic juice
(B) The liver of the newborn is too young to cope
(B) Goblet cells secrete mucus
up with the heavy load of bilirubin
(C) Brunner's glands are sub-mucosal glands
(C) Mother's milk contain a high amount of bilirubin
(D) Carboxypeptidase catalyses conversion of
(D) Insoluble bilirubin in the intestine is reabsorbed proteins, peptones and proteoses to dipeptides
by the blood
(E) Bile contains no enzymes
Sol. (C) Sol. (A)
Ex.12 One of the following is specific function of the liver. Ex.18 Pancretic secretion and gall bladder contraction are
Mark it stimulated by
(A) Excretion (B) Glycogenolysis (A) Gastrin
(C) Digestion (D) Histolysis (B) Enterocrinin
Sol. (B) : Glycogenesis and glycogenolysis both process (C) Enterogastrone
found in liver (D) Cholecystokinin pancreozymine
Ex.13 The largest gland in the human body is Sol. (D) : Cholecystokinin-pancreozymine hormone is
secreted by the epithelium of entire small intestine.
(A) Liver (B) Brain
It stimulates the gall bladder to realese bile and
(C) Pancreas (D) Thyroid pancreas to screte and release digestive enzymes
Sol. (A) : The largest gland in human body is liver. in the pancreatic juice.
Ex.14 Fructose is absorbed into the blood through mucosa Ex.19 Which one of the following enzymes initiates protein
cells of intestine by the process called digestion
(A) Simple diffusion (A) Aminopeptidase
(B) Co-transport mechanism (B) Carboxypeptidase
(C) Active transport (C) Trypsin
(D) Facilitated transport (D) Pepsin
Sol. (D) : Fructose is absorbed with the help of the carrier Sol. (D) : Pepsin intiates the digestion of protein in
ions like Na+. This mechanism is called facilitated stomach producing proteoses and peptones.
transport. Ex.20 Cholecystokinin is a secretion of
Ex.15 Which enzymes are likely to act on the baked (A) Stomach which stimulates pancreas to release
the pancreatic juice
potatoes eaten by a man, starting from the mouth
and as it moves down the alimentary canal (B) Liver synthesised from cholesterol and controls
secondary sexual characters
(A) Pancreatic amylase o salivary amylase o
(C) Duodenum and makes the gall bladder to
lipases
contract and release bile
(B) Disaccharidase like maltase o lipases o
(D) Goblet cells of ileum and stimulates the secretion
nucleases
of succus entericus
(C) Salivary amylase o pancreatic amylase o
Sol. (C) : Cholecystokinin is a polypeptide hormone
disaccharidases
produced by the mucosa of the upper intestine
(D) Salivary maltase o carboxy peptidase o which stimulates contraction of gall bladder.
trypsinogen
Sol. (C) Ex.21 The gastrointestinal hormone which stimulates
insulin secretion is
Ex.16 Which of the following is secreted by pancreas (A) Gastrin (B) CCK
(A) Dipeptidases (B) Amylase (C) Secretin (D) GIP
(C) D-Dextrins (D) Pepsin Sol. (D)

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 DIGESTION & ABSORPTION
Ex.22 When breast feeding is replaced by less nutritive Ex.28 During absorption of carbohydrates in the blood
food low in proteins and calories; the infants below the most rapidly transported monosaccharide is
the age of one year are likely to suffer from (A) Glucose (B) Galactose
(A) Marasmus (B) Rickets (C) Fructose (D) Sucrose
(C) Kwashiorkor (D) Pellagra Sol. (B)
Sol. (A) : Marasmus occurs due to prolonged
malnutrition and deficiency of proteins and calories. Ex.29 Where do certain symbiotic microorganisms
normally occur in human body
Ex.23 Hypochromic microcytic anaemia and leucopenia
(A) Caecum
are caused by the deficiency of ........ respectively
(B) Oral lining and tongue surface
(A) Pyridoxine and riboflavin
(C) Vermiform appendix and rectum
(B) Pyridoxine and folacin
(D) Duodenum
(C) Biotin and folacin
Sol. (A) : Caecum is small blind sac which host some
(D) Biotin and cyanocobalamin
symbiotic micro-organism.
Sol. (B)
Ex.30 Anxiety and eating spicy food together in an
Ex.24 Which of the following elements is a constituent of
otherwise normal human, may lead to
biotin
(A) magnesium (B) Calcium (A) Indigestion (B) Jaundice
(C) Phosphorus (D) Sulphur (C) Diarrhoea (D) Vomitting
Sol. (D) : Biotin or nicotinic acid consists of sulphur. It Sol. (A)
acts as coenzyme needed for protein and fatty acid
Ex.31 A triglyceride molecule has or A typical fat molecule
synthesis, CO2 fixation and transmination
is made up of
Ex.25 Rickets in children and osteomalacia is adults is (A) Three fattyacids with one glycerol molecule
caused by the deficiency of (B) Three fattyacids with two glycerol molecule
Or (C) Two fattyacids with two glycerol molecule
Weakening of limb bones may be due to deficiency (D) One fattyacids with one glycerol molecule
of Sol. (A) : Triglyceride molecule is completely hydrolyzed
(A) Vitamin A into three molecules of fatty acid + one molecule of
(B) Vitamin B glycerol.
(C) Vitamin C
(D) Vitamins D (calciferol) Ex.32 Choose the correct answer among the following:
Sol. (D) : Vitamin D also known as calciferol. The (A) Gastric juice contains
deficiency of calciferol causes, thechildren suffer (i) pepsin, lipase and rennin
from rickets and adults from osteomalacia. (ii) trypsin lipase and rennin
(iii) trypsin, pepsin and lipase
Ex.26 Average kilocalorie of energy needed by women is
(iv) trypsin, pepsin and renin
(A) Less than man (B) More than man
(C) Equal to man (D) Cannot be predicted (B) Succus entericus is the name given to
Sol. (A) (i) a junction between ileum and large intestine
(ii) intestinal juice
Ex.27 Milk sugar is (iii) swelling in the gut
(A) Sucrose (B) Galactose (iv) appendix
(C) Lactose (D) Glucose
(E) Fructose Sol. (A): (i) Pepsin, lipase, and rennin
Sol. (C) : Lactose or milk sugar is a disaccharide formed Gastric juice contains pepsin, lipase, and rennin.
by the union of one molecule of galactose and one Pepsin is secreted in an inactive form as pepsinogen,
molecule of glucose. Beside milk it is found in flowers which is activated by HCl. Pepsin digests proteins
some plants. into peptones. Lipase breaks down fats into fatty

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BIOLOGY FOR NEET & AIIMS
acids. Rennin is a photolytic enzyme present in the Sol. There are four different types of teeth in an adult
gastric juice. It helps in the coagulation of milk. human. They are as follows:
(B): (ii) Intestinal juice (i) Incisors : The eight teeth in the front are incisors.
Succus entericus is another name for intestinal juice. There are four incisors each in the upper jaw and
It is secreted by the intestinal gland. Intestinal juice the lower jaw. They are meant for cutting.
contains a variety of enzymes such as maltase, (ii) Canines : The pointy teeth on either side of the
lipases, nucleosidases, dipeptidases, etc. incisors are canines. They are four in number, two
each placed in the upper jaw and the lower jaw. They
Ex.33 Match column I with column II Column I
are meant for tearing.
Column I Column II
(iii) Premolars : They are present next to the canines.
(A) Bilirubin and bilivirdin (i) Parotid They are eight in number, four each placed in the
(B) Hydrolysis of starch (ii) Bile upper jaw and the lower jaw. They are meant for
(C) Digestion of fat (iii) Lipases grinding.
(D) Salivary gland (iv) Amylases

Sol. Column I Column II

(A) Bilirubin and bilivirdin (ii) Bile
(B) Hydrolysis of starch (iv) Amylases
(C) Digestion of fat (iii) Lipases
(D) Salivary gland (i) Parotid

Ex.34 State the role of pancreatic juice in digestion of

proteins.

Sol. Pancreatic juice contains a variety of inactive

enzymes such as trypsinogen, chymotrypsinogen,
and carboxypeptidases. These enzymes play an
important role in the digestion of proteins.
“Physiology of protein-digestion “The enzyme
enterokinase is secreted by the intestinal mucosa. It
activates trypsinogen into trypsin.

Ex.35 What would happen if HCl were not secreted in the

stomach?

Sol. Hydrochloric acid is secreted by the glands present

on the stomach walls. It dissolves bits of food and
creates an acidic medium. The acidic medium allows
pepsinogen to be converted into pepsin. Pepsin
plays an important role in the digestion of proteins.
Therefore, if HCl were not secreted in the stomach,
then pepsin would not be activated. This would
affect protein digestion. A pH of about 1.8 is
necessary for proteins to be digested. This pH is
achieved by HCl.

Ex.36 Name different types of teeth and their number in an

adult human.

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BIOLOGY FOR NEET & AIIMS

Exercise PART - 1 PREVIOUS YEAR (NEET/AIPMT)

6. Which group of three of the following five state-

1. During prolonged fasting, in what sequence are the ments (a-e) contain is all the three correct state-
following organic compounds used up by the body ments regarding beri-beri -
: [CBSE AIPMT 2003] [CBSE AIPMT 2005]
(A) First carbohydrates, next proteins and lastly A. A crippling disease prevalent among the native
lipids population of sub-Saharan Africa.
(B) First proteins, next lipids and lastly B. A deficiency disease caused by lack of thia-
mine (vitamin - B1).
Icarbohydrates
C. A nutritional disorder in infants and young chil-
(C) First carbohydrates, next fats and lastly dren when the diet is persistently deficient in
proteins essential protein.
(D) First fats, next carbohydrates and lastly D. Occurs in those countries where the staple diet
proteins is polished rice.
2. The richest sources of vitamin B12 are :- E. The symptoms are pain from neuritis, paraly-
[CBSE AIPMT 2004] sis, muscle wasting, progressive oedema, men-
tal deterioration and finally heart failure.
(A) Goat’s liver and Spirulina
(A) A, B and D (B) B, C and E
(B) Chocolate and green gram (C) A, C and E (D) B, D and E
(C) Rice and hen’s egg 7. Secretin and cholecystokinin are digestive hor-
(D) Carrot and chicken’s breast mones. They are secreted in -
[CBSE AIPMT 2005]
3. Which one of the following is the correct matching (A) Oesophagus (B) Ileum
of a vitamin, its nature and its deficiency disease : (C) Duodenum (D) Pyloric stomach
[CBSE AIPMT 2004]
8. A patient is generally advised to specially consume
(A) Vitamin A–Fat soluble – Night blindness more meat, lentils, milk and eggs in diet only when
(B) Vitamin K–Fat soluble –Beri Beri he suffers from - [CBSE AIPMT 2005]
(C) Vitamin A – Fat soluble – Beri Beri (A) Kwashiorkor (B) Rickets
(D) Vitamin K – Water soluble – Pellagra (C) Anaemia (D) Scurvy

4. Duodenum has characteristic Brunner’s glands 9. Epithelial cells of the intestine involved in food ab-
sorption have on their surface -
which secrete two hormones called -
[CBSE AIPMT 2005]
[CBSE AIPMT 2004]
(A) Phagocytic vesicles
(A) Kinase, estrogen (B) Microvilli
(B) Secretin, Cholecystokinin (C) Zymogen granules
(C) Prolactin, parathormone (D) Pinocytic vesicles
(D) Extradiol, progesterone
10. Which one of the following is a fat -soluble vitamin
5. Which one of the following pairs is not correctly and its related deficiency disease?
matched : - [CBSE AIPMT 2005] [CBSE AIPMT 2007]
(A) Ascorbic acid – Scurvy
(A) Vitamin B12 – Pernicious anaemia
(B) Retinol – Xerophthalmia
(B) Vitamin B1 – Beri-beri
(C) Cobalamine – Beri-beri
(C) Vitamin C – Scurvy (D) Calciferol – Pellagra
(D) Vitamin B2 – Pellagra

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 DIGESTION & ABSORPTION
11. What will happen if the secretion of parietal cells of 16. A young infant may be feeding entirely on mother’s
gastric glands is blocked with an inhibitor? milk which is white in colour but the stools which
[CBSE AIPMT 2008] the infant passes out is quite yellowish. What is
(A) Gastric juice will be deficient in chymosin this yellow colour due to ? [CBSE AIPMT 2009]
(B) Gastric juice will be deficient in pepsinogen (A) Intestinal juice
(C) In the absence of HCI secretion, inactive (B) Bile pigments passed through bile juice
pepsinogen is not converted into the active (C) Undigested milk protein casein
enzyme pepsin (D) Pancreatic juice poured into duodenum
(D) Enterokinase will not be released from the
17. If for some reason our goblet cells are nonfunc-
duodenal mucosa and so trypsinogen is not
tional, this will adversely affect ?
converted to trypsin
[CBSE AIPMT 2010]
12. Which one of the following is the correct matching (A) Production of somatostatin
of the site of action on the given substrate, the en- (B) secretion of sebum from the sebaceous glands
zyme acting upon it and the end product? (C) maturation of sperms
[CBSE AIPMT 2008]
(D) smooth movement of food down the intestine
(A) Duodenum : Triglycerides Trypsin
Monoglycerides 18. Carrier ions like Na+ facilitate the absorption of
(B) Small intestine : Starch D- amylase disaccha- substances like ? [CBSE AIPMT 2010]
ride (Maltose) (A) Amino acids and glucose
(C) Small intestine : Proteins pepsin amino acids (B) Glucose and fatty acids
(D) Stomach : Fats , Lipase Micelles (C) Fatty acids and glycerol
(D) Fructose and some amino acids
13. Which one of the following statement is true re- 19. Anxiety and eating spicy food together in a other-
garding digestion and absorption of food in hu- wise normal human, may lead to
mans : [CBSE AIPMT 2009] [CBSE AIPMT 2012]
(A) Oxyntic cells in our stomach secrete the (A) Indigestion (B) Jaundice
proenzyme pepsinogen (C) Diarrhoea (D) Vomiting
(B) Fructose and amino acids are absorbed 20. Select the correct match of the digested products
through intestinal mucosa with the help of in humans given in column I with their absorption
carrier ions like Na+ site and mechanism in column II. [NEET 2013]
(C) Chylomicrons are small lipoprotein particles Column I Column II
that are transported from intestine into blood (A) Glycine and glucose Small intestine, active
capillaries absorption
(D) About 60% of starch is hydrolysed by salivary (B) Fructose and Na+ Small intestine and
amylase in our mouth passive absorption
(C) Glycerol, fatty acids Duodenum and move
14. When breast feeding is replaced by less nutritive as chilomicrons
food low in proteins and calories, the infants below
(D) Cholesterol and Large intestine and
the age of one year are likely to suffer from :
maltose active absorption
[CBSE AIPMT 2009]
(A) Marasmus (B) Rickets 21. Fructose is absorbed into the blood through
(C) Kwashiorkor (D) Pellagra mucosa cells of intestine by the process called
[CBSE AIPMT 2014]
15. Which one of the following pairs of food com- (A) Active transport
pounds in humans reaches the stomach totally un-
(B) Facilitated transport
digested - [CBSE AIPMT 2009]
(C) Simple diffusion
(A) Protein and starch (B) Starch and fat
(D) Co-transport mechanism
(C) Fat and cellulose (D) Starch and cellulose

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BIOLOGY FOR NEET & AIIMS
22. The initial step in the digestion of milk in humans 29. Which cells of ‘Crypts of Lieberkuhn’ secrete anti-
is carried out by? [CBSE AIPMT 2014] bacterial lysozyme? [NEET 2017]
(A) Lipase (B) Trypsin (A) Argentaffin cells (B) Paneth cells
(C) Rennin (D) Pepsin (C) Zymogen cells (D) Kupffer cells
23. The primary dentition in human differs from perma- 30. Good vision depends on adequate intake of
nent dentition in not having one of the following carotene rich food Select the best option from the
type of teeth : [CBSE AIPMT 2015] followingstatements [NEET 2017]
(A) Canine (B) Premolars I. Vitamin A derivatives are formed from
(C) Molars (D) Incisors carotene
24. The enzymes that is not present in succus entericus II. The photopigments are embedded in the
is : [CBSE AIPMT 2015] membrane discs of the inner segment
(A) maltase (B) nucleases III. Retinal is a derivative of vitamin A
(C) nucleosidase (D) lipase IV. Retinal is a light absorbing part of all the
visual photopigments
25. Which hormones do stimulate the production of
(A) (I) and (II) (B) (I), (III) and (IV)
pancreatic juice and bicarbonate? [NEET 2016]
(C) (I) and (III) (D) (II), (III) and (IV)
(A) Angiotensin and epinephrine
(B) Gastrin and insulin 31. Which of the following options best represents the
(C) Cholecystokinin and secretin enzyme composition of pancreatic juice?
(D) Insulin and glucagon [NEET 2017]
(A) Amylase, peptidase, trypsinogen, rennin
26. Which of the following guards the opening of (B) Amylase, pepsin, trypsinogen, maltase
hepatopancreatic duct into the duodenum? (C) Peptidase, amylase, pepsin, rennin
[NEET 2016] (D) Lipase, amylase, trypsinogen,
(A) Ileocaecal valve (B) Pyloric sphincter procarboxypeptidase
(C) Sphincter of Oddi (D) Semilunar valve
32. A baby boy aged two years is admitted to play
27. In the stomach, gastric acid is secreted by the school and passes through a dental check-up. The
[NEET 2016] dentist observed that the boy had twenty teeth.
(A) Parietal cells Which teeth were absent? [NEET 2017]
(B) Peptic cells (A) Incisors (B) Canines
(C) Acidic cells (C) Pre-molars (D) Molars
(D) Gastrin secreting cells 33. Which of the following terms describe human
dentition ? [NEET 2018]
28. The hepatic portal vein drains blood to liver from
[NEET 2017] (A) Pleurodont, Monophyodont, Homodont
(B) Thecodont, Diphyodont, Heterodont
(A) Heart (B) Stomach
(C) Thecodont, Diphyodont, Homodont
(C) Kidneys (D) Intestine
(D) Pleurodont, Diphyodont, Heterodont

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 DIGESTION & ABSORPTION

Exercise PART - 2 PREVIOUS YEAR (AIIMS)

6. Which match is true ?

1. Continued consumption of a diet rich in butter, red
meat and eggs for a long period may lead to [2003] Vitamin
deficiency Vitamin Source
(A) vitamin toxicity deisezse
(B) kidney stones (a) Severe bleeding Tocopherol Milk, egg
(b) Anaemia Ascorbic acid Lemon, orange
(C) hypercholesterolemia (c) Night blindness Retinol Carrot, milk
(D) urine laden with ketone bodies. (d) Sterility Calciferol Milk, butter

2. People recovering from long illness are often ad- 7. Duodenum has characteristic Brunner’s gland which
vised to include the alga Spirulina in their diet be- secretes two hormones called [2009]
cause it [2003] (A) prolactin, parahormone
(A) makes the food easy to digest (B) secretin, cholecystokinin
(D) is rich in proteins (C) enterocrinin, duocrinin
(C) has antibiotic properties (D) gastrin, enterogastrone.
(D) restores the intestinal microflora.
3. Cattle fed with spoilt hay of sweet clover which 8. Vitamin B6 is also called [2010]
contains dicumarol [2004] (A) thiamine (B) pantothenic acid
(A) are healthier due to a good diet (C) pyridoxine (D) retinol
(B) catch infections easily
9. Which of the following is correct ? [2010]
(C) may suffer vitamin K deficiency and prolonged
bleeding (A) Paneth cells secrete pepsinogen
(B) Parietal cells secrete hydrochloric acid
(D) may suffer from beri-beri due to deficiency of B
vitamins. (C) Argentaffin cells secrete mucus
(D) Chief cells secrete gastrin
4. Which one of the following pairs of the kind of cells
and their secretion is correctly matched ? [2006] 10. Animals take phosphorus from [2010]
(A) Oxyntic cells – a secretion with pH between 2.0 (A) water (B) plants
and 3.0 (C) rock (D) soil
(B) Alpha cells of islets of Langerhans – secretion 11. Which of the following elements is present in very
that decreases blood sugar level
less quantity in the body ? [2011]
(C) Kupffer cells – a digestive enzyme that hydroly- (A) K (B) Ca
ses nucleic acids
(C) Mg (D) Cu
(D) Sebaceous glands – a secretion that evaporates
for cooling 12. In a normal adult, ascending order of concentration
of following molecules is [2012]
5. A child took sugar cane and sucked its juice. Re-
(A) K > Na > Fe > Cu (B) Na > K > Cu > Fe
garding this which of the following match is correct
(C) Fe > Na > K > Cu (D) Na > Fe > K > Cu
Site of Products
Substrate Enzyme secretion formed 13. Which of the following gastric secretions is cor-
of enzyme rectly matched with its source ? [2013]
(a) Proteins Pepsin Duodenum Polypeptides
(A) Pepsinogen – Chief cells
(b) Starch Amylase Salivary Glucose (B) Chymotrypsin – Parietal cells
glands (C) HCl – Goblet cells
(c) Lipids Lipase Pancreas Fat globules (D) Mucus – Oxyntic cells
(d) Sucrose Invertase Duodenum Glucose +
Fruclose

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BIOLOGY FOR NEET & AIIMS
14. Which one of the following vitamins is 24. Assertion : Small intestine is the principal ortgan
antihaemorrhagic ? [2014] for absorption of nutrients. [2013]
(A) Vitamin B12 (B) Vitamin B5 Reason : Absorption of water, simple sugars and
(C) Vitamin C (D) Vitamin K alcohol etc. takes place in small intestine.

25. Assertion : HCl converts pepsinogen into active

15. Which of the following statement is true ? [2017] enzyme pepsin. [2014]
(A) Pepsin cannot digest casein. Reason : Pepsin converts protein into proteoses
(B) Trypsin can digest collagen. and peptones.
(C) Pepsin cannot digest collagen. 26. Assertion : Carbohydrates are more suitable for the
(D) Chymotrypsin can digest casein. production of energy in the body than proteins and
fats. [2016]
16. Which of the following has highest pH? [2018] Reason : Carbohydrates can be stored in the tis-
(A) Human saliva (B) Human blood sues as glycogen and can be used for the produc-
(C) Gastric juice (D) Urine tion of energy, whenever necessary.

ASSERTION AND REASON 27. Assertion : Water and electrolytes are almost
fully absorbed in the large intestine. [2017]
17. Assertion : Bile is essential for the digestion of lip-
ids. [2010] Reason : In large intestine, haustral contractions
Reason : Bile juice contains enzymes bilirubin and (slow segmenting movements) roll the forming
biliverdin. faeces over and over, causing absorption of
water and electrolytes.
18. Assertion : Pantothenic acid deficiency is probably
28. Assertion : Chymotrypsinogen and trypsinogen are
the most common vitamin deficiency. [2010] released from gastric glands. [2018]
Reason : Macrocytic anaemia is a characteristic fea- Reason : They help in the digestion of fats.
ture of pantothenic acid deficiency.
19. Assertion : Glycerides are important nutrients for
body. [2011]
Reason : Glycerides are hydrolysed into glycerol
and fatty acids which are further absorbed in intes-
tine by the formation of chylomicron.

20. Assertion : Emulsification is neccessary for the di-

gestion of fats. [2012]
Reason : After fats are emulsifed, the action of en-
zyme amylase gets significantly increased.

21. Assertion : In jaundice, the skin and mucous mem-

branes assume a yellowish hue. [2012]
Reason : yellow pigment bilirubin imparts pale yel-
low colour to blood plasma.

22. Assertion : Cattles feed on leaves of maize to get

nutrition for growth and development. [2013]
Reason : A number of symbiotic bacteria are present
in rumen of cattle.

23. Assertion : Duodenum is the main organ of small

intestine. [2013]
Reason : In duodenum, digestion and absorption
mainly occurs.

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 DIGESTION & ABSORPTION

ANSWER KEY

EXERCISE : PART - 1
1. C 2. A 3. A 4. B 5. D 6. D 7. C 8. A 9. D 10. B 11. C 12. B 13. C
14. C 15. C 16. B 17. D 18. D 19. A 20. A 21. B 22. D 23. B 24. B 25. C 26. C
27. A 28. D 29. B 30. B 31. D 32. C 33. B

PART - 2
1. C 2. B 3. C 4. A 5. D 6. C 7. B 8. C 9. B 10. B 11. D 12. A 13. A
14. D 15. D 16. B 17. D 18. D 19. C 20. C 21. B 22. A 23. D 24. C 25. B 26. B
27. A 28. D

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BIOLOGY FOR NEET & AIIMS

HINTS & SOLUTIONS

EXERCISE
P-1 (NEET/AIPMT)

1. (C) During prolonged fasting, first of all carbohy- 5. (D) Pellagra (Italian Pelle = skin, agra = rough) is a
drates are utilised which include glycogen stored skin disease which is caused by the deficiency of
in liver. This is followed by the breakdown of adi- vitamin-B3 or niacin. Pellagra is especially frequent
pose tissue, thus providing lipids and lastly the among the people eating food with low tryptophan
body utilises proteins. (an essential amino acid).

2. (A) Vitamin-Br12 (cyanocobalamin) is the only vita- 6. (D) The deficiency of vitamin-B1 or thiamine causes
min which is not found in vegetables. It is present the disease beri-beri. This disease occurs in those
in animal protein such as meat, liver, fish and countries where the staple diet is polished rice.
Spirulina (single cell protein). It promotes DNA syn- The symptoms of this disease are pain from neuri-
thesis, maturation of RBCs and myelin formation. tis, paralysis, muscle wasting, progressive oedema,
mental deterioration and finally heart failure.
3. (A) Fat soluble vitamins are A, D, E and K. Defi-
ciency of vitamin-A leads to night blindness or nyc-
talopia because vitamin-A is essential for synthe-
sis of visual pigments (rhodopsin)
4. (B) Brunner’s gland secrete large amount of mucus
and bicarbonates to protect duodenal mucosa and
to neutralise the acidic chyme. It also secretes two
hormones:
(A) Secretin
(B) Cholecystokinin (CCK)
These stimulate:
(i) Secretion of pancreatic juice by pancreas.
(ii) Release of bile from gall bladder.
(iii) Formation of bile by liver and pancreatic juice.

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BIOLOGY FOR NEET & AIIMS
7. (C) Secretin and cholecystokinin (CCK) are two The pancreatic juice also contains proenzyrnes
main gastrointestinal (GI) hormones secreted in trypsinogen, chyrnotrypsinogen and
duodenum of alimentary canal. CCK stimulates gall procarboxypeptidase. The trypsinogen is converted
bladder contraction and thus increases the flow of to active trypsin in intestine by enterokinase of in-
bile salts into the intestine. testinal juice. The trypsin converts proteins into
Secretin stimulates the release of an alkaline pan- large peptides and the large peptides are converted
creatic fluid that neutralises stomach acid as it en- to dipeptide and amino acids by carboxypeptidase.
ters the intestine.
13. (C) Chylomicrons are lipoprotein particles
8. (A) The deficiency of proteins within the body is synthesised by intestinal epithelial cells and con-
responsible for a disease, known as kwashiorkor. sisting mainly of triglycerides. Chylomicrons are
So, a kwashiorkor diseased patient is generally ad- the form, in which dietary fat is transported in the
vised to specially, consume more meat, lentils, milk circulatory system.
and eggs because these are rich sources of protein.
14. (C) Prolonged starvation causes marasmus disease
9. (D) The mucosa and sub-mucosa of small intestine due to a generalised wasting of body because of
are thrown into folds. Surfaces of these folds are both energy and protein deficiency. The body be-
covered by fine, finger-like projections of the epi- comes lean and weak, eyes depressed and skin
thelium. wrinkled.
These projections are called villi. In addition, the Kwashiorkor is a disease caused by continued de-
epithelial cells of the villi are covered on their ex- ficiency of proteins in diet although energy intake
posed surface by cytoplasmic projections called may be adequate.
microvilli. Rickets (in children) occurs due to the deficiency of
vitamin-D.
10. (B) Xerophthalmia is caused due to the deficiency
Pellagra occurs due to the deficiency of nicotina-
of vitamin-A (retinol). Retinol and calciferol are fat
mide (vitamin-Bs )
soluble vitamins but pellagra is not the deficiency
disease of calciferol. 15. (C) In humans, starch is digested in
buccopharyngeal cavity. Cellulose is not digested
11. (C) The parietal cells (oxyntic cells) are large and
in the humans because cellulose contains E-1, 4-
most numerous on the side walls of gastric glands.
linkage and vertebrates themselves do not possess
These secrete hydrochloric acid and castle intrin-
any enzyme capable of hydrolysing E-1, 4-linkages.
sic factor. The peptic cells (zymogen) of gastric
Protein is digested in stomach and fat in small in-
glands secrete gastric digestive enzymes as proen-
testine. Thus, in the given options, fat and cellu-
zymes-pepsinogen and prorennin ald small amount
lose reach totally undigested in the stomach of hu-
of gastric amylase and gastric lipase. The hydro-
mans
chloric acid maintains a strongly acidic pH of about
1. 5-2.5 in the stomach . HCI converts pepsinogen 16. (B) The stools, which the infant passes out is quite
and prorennin to pepsin and rennin respectively. yellowish due to the bile pigments. These bile pig-
ments are released in the bile juice.
12. (B) In small intestine food meats with the pancre-
atic juice containing D-amylase, which converts 17. (D) Goblet cells are something like a wineglass that
starch into maltose, isomaltose and D-dextrins in present in the columnar epithelium of the mamma-
small intestine. lian intestine and secrete mucin, a mucoprotein that
Starch o
Pancreatic α -amylase
Maltose(disaccharide) forms mucus when in solution. If Goblet cells be-
come non-functional, this will adversely affect

155
 DIGESTION & ABSORPTION
smooth movement of food down the intestine due There are no premolars in primary dentition (de-
to the absence of mucin. ciduous or boby teeth). These are found only in
permanent dentition (adult teeth).
18. (D) Active transport occurs with the help of energy,
usually against concentration gradient. For this, cell 24. (B) Succus entericus or intestinal digestive juice
membrane possesses carriers and gated channels. contains a variety of enzymes like disaccharidases
Active transport of one substance is often accom- (e.g. maltase), dipeptidases, lipases, nucleosidases.
panied by permeation of other substances. Nucleases are enzymes present in pancreatic juice
The phenomenon is called secondary active trans- that break nucleic acids into nucleotides
port. It is of two main types, i.e. Co-transport, (e.g.
glucose and some amino acids along with inward 25. (C) Cholecystokinin (CCK) and secretin are the pep-
pushing of excess Na+) and counter transport (Ca2+ tide hormones that stimulate the production of pan-
and H+ movement outwardly as excess Na- passes creatic juice and bicarbonates within the alimentary
inwardly) canal.
Secretin acts on the exocrine pancreas and stimu-
19. (A) Unhealthy eating habits together with anxiety, lates the secretion of water and bicarbonate IONS.
stress or panic attacks may cause indigestion, stom-
CCK acts on both pancreas and gall bladder and
ach ache, stomach palpitations, nausea, etc.
stimulates the secretion of pancreatic enzymes and
bile juice respectively. Hence, option (C) is correct.
20. (A) Amino acids, monosaccharides like glucose,
electrolytes like Na+ are absorbed into the blood by
active transport. Fructose and some amino acids 26. (C) Sphincter of Oddi gmqrds the opening of
are absorbed with the help of the carrier ions like hepatopancreatic duct into the duodenum.
Na+ by facilitated transport. Hepatopancreatic duct brings secretion of liver as
Fatty acid and glycerol cannot be absorbed into well as pancreas to the duodenum.
the blood. They are first incorporated into small
27. (A) In stomach, gastric acid (HCl) is secreted by
droplets called micelles, which move into the intes-
parietal cells of gastric gland. It makes the medium
tinal mucosa.
of food in stomach acidic for stimulation of pro-
21. (B) Fructose is absorbed into the blood through teolytic enzyrnes of stomach.
mucosa cells of intestine by the process called fa-
28. (D) In the hepatic portal system, the hepatic veins
cilitated transport thus, facilitated transport is the
takes blood from intestine to the liver. This way, it
process of spontaneous passive transport of the
takes all the nutrients absorbed from intestine to
molecules or ions across a biological membrane via
the liver first, where screening and storing of nutri-
specific transmembrane integral protein.
tion takes place.
22. (D) In humans, the milk protein digesting enzyrne Concept Enhancer
in stomach is pepsin. In calves it is rennin. It is also The portal system is a system of veins in which
present in small amounts in human infants but not vein takes blood to some organs/tissue of the body
adults. Pepsin acts on water soluble ‘caseinogen other than heart. In this, the vein has capillary net-
(milk protein) to form soluble ‘casein’. This com- work at it’s both ends.
bines with calcium salts to form insoluble calcium
There is one more portal system in human body
paracaseinate, which gets readily digested enzy-
named hypophyseal portal system present in the
matically
hypothalamus, which brings neuro secretions of
23. (B) There are four classes of teeth, i.e. incisors, ca- hipothalamus to pituitary gland.
nines, premolars and molars.
The renal portal system is found in fishes and am-

156
BIOLOGY FOR NEET & AIIMS
phibians. It supplies blood from posterior region of 31. (D) Pancreas consist of exocrine and endocrine part.
the body to the kidneys by renal portal veins to Exocrine part secrets alkaline pancreatic juice. This
remove waste products before sending it to heart juice contains trypsinogen, chyrnotrypsinogen,
via renal veins and post canal veins. procarboxypeptidase, lipase, amylase, elastase.
Concept Enhancer Renin and pepsin enzymes are
29. (B)The mucosa present in between the bases of
present in gastric juice. Maltase is present in the
villi of small intestine (Crypts of Lieberkuhn) con-
intestinal juice.
tain paneth, which secrete antibacterial lysozyrne
32. (C) In human beings, after birth the first set of teeth
that develops are deciduous teeth or ternporary
teeth. These are 20 in number. The dental formula of
child is 2102/2102.
Thus, they have 2 incisors, 1 ,canine, 0 premolars
and 2 molars. Therefore, the baby boy would not
have premolars

33. (B) Human teeth are of different types (Heterodont),

most of them appears twice in life time (diphyo-
dont) and are embedded in jaw bone (Thecodont).

A section of srnall intestinal rnucosa showing villi

and the Crypts of Lieberkuhn
Concept Enhancer Kupffer cells are phagocytic cells
of liver.
Zymogen cells produce enzyme. Argentaffin cells
produce hormones.

30. (B) Vitamin-A is a group of unsaturated nutritional

organic compounds that includes retinol, retinal,
retinoic acid and E-carotene.
Vitamin-A is needed by the retina of eye in the form
of retinal, which combines with protein opsin to
form rhodopsin, the light absorbing molecule.

157
 DIGESTION & ABSORPTION
EXERCISE
dessication.
P-2 (AIIMS) 5. (D) Sucrose (cane sugar, beet sugar, saccharose) is
a sugar comprising one molecule of glucose linked
1. (C) Cholesterol is a soft waxy substance that is a to a fructose molecule. It occurs widely in plants
natural component of the fats in the blood-stream and is particularly abundant in sugar cane and sugar
and in all the cells of the body. In our body 8% to beet (15-20%), from which is extracted and refined
10% of the saturated fatty acids are coming from for table sugar. If heated to 200°C, sucrose becomes
animal product, such as butter, egg, red meat. Con- caramel. Sucrose is broken down into the monosac-
tinuous consumption of this type of diet leads to charides glucose and fructose with the help of car-
hypercholesterolemia due to the presence of excess bohydrate digesting enzyme, invertase, produced
amount of saturated fatty acid. in the small intestine (duodenum).
2. (B) Spirulina is a blue-green algae. Spirulina 6. (C) Night blindness is the inability to see in dim
platensis is one of the richest sources of protein, light or at night. It is due to disorder of the cells in
containing 40-50 percent crude protein on dry weight the retina that are responsible for vision in dim light
basis which under favourable condition may reach and can result from dietary deficiency of vitamin A
upto 70 percent. Its protein has balanced composi- (retinol).
tion containing all essential amino-acids lysine and Name Sources Effect of deficiency
tryptophan being present in sufficient quantities.
Vit. C Lemon, organce and Scurvy (also called
Spirulina is also rich in vitamins, particularly Vit. (Ascorbic other citrus fruits. sailor’s disease) is
B12, which is not common in plant products and acid) tomatoes, green characterised by wound
vegetables, potatoes, - healing and growth
contains considerable amounts of fats, carbohy- carrots, pepper etc. retardation etc.
drates and minerals. It’s lipids are made up of un-
Vit. D Synthesized in skin Rickets, a disorder of
saturated fatty acids that do not form cholesterol. (Ergocal- cells in sunlight from children of 6 months to
ciferol 7-dehydrocholesterol 2 years, and
3. (C) A better understanding of the mode of action of and (i.e., provitamin D3), osteomalacia, a disorder
vitamin K is made possible by the use of an anti- Cholecal- also found in butter, of adults.
ciferol) liver, kidney, egg
coagulant. One such naturally occurring antago- yolk, fish, oil, etc.
nist of vitamin K is known as Dicumarol. The dis-
Vit. E Green vegetables, Reversible sterility in
covery of the anti-coagulating property of Dicuma- (Tocoph- oils, egg yolk, female. In male causes
rol took place when it was established that con- erol) wheat, animal atrophy of spermatogenic
tissues tubules of testes.
sumption of improperly cured sweet clover hay
caused cattle to develop the so-called “sweet clo-
ver disease” which is attributable to a serious alter- 7. (B) Secretin and cholecystokinin are secreted by
nation in the coagulability of the blood that, in turn, Brunner’s gland located in duodenum. Secretin
often result in fatal haemorrhage. causes the pancreas to secrete alkaline pancreatic
juice and stimulates bile production in the liver.
4. (A) Oxyntic (or parietal) cell is present in the wall of Cholecystokinin induces the gall bladder to con-
the stomach that produce HCl with forms the part tract and eject bile into the intestine and stimulates
of gastric juice. Oxyntic cell also produce intrinsic the pancreas to secrete its digestive enzymes.
factor which is involved in the absorption of vita-
min B12 in the small intestine. The pH of gastric acid 8. (C) Vitamin B6 , also called pyridoxine is widely dis-
is 2-3 in the stomach of the lumen. Alpha cell of tributed in cereal grains, yeast, liver, milk, etc. It is a
islets of Langerhans secrete glucagon hormone constituent of a coenzyme (pyridoxal phosphate)
which raises blood glucose level by stimulating liver involved in amino acid metabolism. Deficiency
to convert glycogen to glucose and by stimulating causes retarded growth, dermatitis, convulsions,
the conservation of fatty acids and amino acids to and other symptoms.
glucose. 9. (B) Parietal cells are present in the epithelium of the
Kupffer cells, named after Karl Wilhem Von Kupffer, gastric glands. They are large and are mostly on the
are found in the bloodstreams and in the liver, at- side walls of the glands.
tached to the walls of the sinusoids. Sebaceous They are also called oxyntic cells as they stain
gland is a simple or branched glands in the skin that strongly with eosin. They secrete hydrochloric acid
secrete an oily substance, sebum which is fatty and Castle’s intrinsic factor.
mildly antiseptic material that protects, lubricates,
and waterproofs the skin and hair and help prevent

158
BIOLOGY FOR NEET & AIIMS
10. (B) Phosphorus is a major constituent of biological despite the involvement of pantothenic acid (as
membranes, nucleic acids and cellular energy transfer coenzyme A) in a great number of metabolic reac-
systems. Many animals also need large quantities tions, its deficiency manifestations have not been
of this element to make shells, bones and teeth. The reported in humans, presumably because of the wide
natural reservoir of phosphorus is rock, which con- occurrence of this vitamin in almost all foods and
tains phosphorus in the form of phosphates. When because small amount can be synthesized in the
rocks are weathered, minute amounts of these phos- body. Folic acid deficiency is probably the most
phates dissolve in soil solution and are absorbed common vitamin deficiency. The macrocytic anaemia
by the roots of the plants. Herbivores and other (abnormally large RBC) associated with megaloblas-
animals obtain this element from plants. tic changes in bone marrow is a characteristic fea-
11. (D) Trace elements or microelements (e.g. iron, io- ture of folate deficiency.
dine, zinc, manganese, cobalt, copper, molybdenum, 19. (C) Glycerides, mainly triglycerides are a principle
etc.) are required in very small amounts in our body. form of fats present in our food. During digestion,
fats are digested to form monoglycerides and free
12. (A) Daily requirement of these minerals are :
fatty acids. They first become dissolved in the cen-
K – 4500 mg tral lipid portions of bile micelles which are soluble
Na – 3500 mg in chyme. In this form, the monoglycerides and free
Fe – 13.7 mg fatty acids are carried to the surfaces of the mi-
Cu – 1.2 mg crovilli of the intestinal cell brush border and then
13. (A) Parietal cells (or oxyntic cells) secrete hydro- penetrate into the interior of the epithelial cells,
chloric acid (HCl) and Castle’s intrinsic factor. Chief which is possible because the lipids are also soluble
cells (or peptic cells) secrete gastric digestive en- in the epithelial cell membrane. This leaves the bile
zymes as proenzymes – pepsinogen and prorennin. micellels still in the chyme, where they function
HCl helps in converting pepsionogen to pepsin. again and to help absorb still more monoglycerides
Goblet cells secrete mucus which helps to neutralise and fatty acids.
acid in stomach and protects stomach wall against After entering the epithelial cell, the fatty acids and
HCl action. monoglycerides are taken up by the cell’s smooth
endoplasmic reticulum; here they are mainly used
14. (D) Anti-haemorrhagic vitamins are those sub-
to form new triglycerides that are subsequently re-
stances which promote haemostasis or stop bleed-
leased in the form of chylomicrons through the base
ing. Vitamin K is one of them. of the epithelial cell, to flow upward through the
15. (D) Milk protein can be digested by pepsin and thoracic lymph duct and empty into the circulating
chymotrypsin. blood. Thus, chylomicrons help in transport of glyc-
16. (B)Human saliva - 6.8 erides through blood circulation to various body
Human blood - 7.4 parts.
Gastric Juice - 1.8 20. (C) Being insoluble in water, fats and oils form large
Urine -6 immiscible droplets in aqueous media but the en-
zymes which hydrolyse fats and oils (called lipases)
are insoluble in fats and soluble in water. Therefore,
17. (D) Bile (gall) is a bitter-tasting greenish-yellow al- lipases can act only on the water adjoining sur-
kaline fluid produced by the liver, stored in the gall faces of fat droplets. Evidently, the larger the sur-
bladder, and secreted into the duodenum of verte- face area of fat droplets, the greater is the action of
brates. It assists the digestion and absorption of the lipase on them. We know that the smaller the
fats by the action of bile salts, which chemically size of a droplet, the larger is its surface area rela-
reduce fatty substances and decrease the surface tive to its mass. thus lipases can digest fat in sig-
tension of fat droplets so that they are broken down nificant amounts only when large fat droplets are
and emulsified. Bile may also stimulate gut muscle broken into tiny droplets to form a fine emulsion.
contraction (peristalsis). Bile also contains the bile This is the reason why emulsification is so neces-
pigments, bilirubin and biliverdin, which are pro- sary for the digestion of fats. Enzyme amylase, on
duced by the breakdown of the blood pigment hae- the other hand, is a starch - hydrolysing enzyme
moglobin. which has no role in fat digestion.
18. (D) Pantothenic acid, formerly known as chick anti- 21. (B) Bilirubin is a yellow pigment which arises from
dermatitis factor or filtrate factor is widely distrib- the catabolism of red pigment haemoglobin of old
uted in nature. It is a surprise to biochemists that and worn out RBCs. The pale yellow colour of blood

159
 DIGESTION & ABSORPTION
plasma is largely due to the presence of bilirubin. It acids are absorbed through the mucosa into the
has to be excreted into the bile and from there it is blood stream and lymph. Absorption of water, single
excreted out of the body along with the faecal mat- sugars and alcohol, etc. takes place in stomach. In
ter. If, all of the bilirubin can not be excreted from larger intestine, absorption of water, some minerals
the body then the skin and mucous membranes as- and drugs takes place.
sume a yellowish hue, giving rise to the condition 25. (B) Pepsin is a digestive enzyme that is released in
called jaundice. stomach as proenzyme-pepsinogen. HCl which is
22. (A) The cattles, buffaloes, goats, sheep, deer and secreted by gastric glands of stomach converts
camels are herbivorous animals that feed on plant proenzyme pepsinogen into the active enzyme pep-
leaves, twigs, etc. Their stomach consists of 4 cham- sin. Pepsin converts proteins into proteoses and
bers : rumen (paunch), reticulum (honeycomb), peptones.
omasum (psalterium) and abomasum (rennet). In the 26. (B) Carbohydrates are more suitable for the pro-
rumen, food undergoes mechanical and chemical duction of energy in the body than proteins and
breakdown. Mechanical breakdown results from fats because carbohydrate molecules contain rela-
thorough churning brough about by muscular con- tively more oxygen than the others and conse-
tractions and aided by cornified surface of villi. quently, require less molecular oxygen for their oxi-
Chemical breakdown is caused by symbiotic micro- dation. In other words, for each litre of oxygen con-
organisms, bacteria such as Ruminococcus and cili- sumed, carbohydrates yield far more energy than
ate such as Entodinium caudatum. These proteins or fats. Carbohydrates are also stored in
micoorganisms live as symbionts in the rumen and the tissues as glycogen for use in the production of
reticulum of the stomach of the ru minants (e.g., energy, when necessary.
cows and buffaloes) and in the large intestine of 27. (A) In the following questions, a statement of As-
other herbivorous mammals (e.g., horses and don- sertion is followed by a statement of Reason.
keys) and release enzymes, cellulases, which act on (a) If both Assertion and Reason are true and the
cellulose and simplify it to short-chain fatty acids. Reason is the correct explanation of the Assertion.
Cellulose is not digested in human being. (b) If both Assertion and Reason are true but the
23. (D) Principal organ for digestion and absorption for Reason is not the correct explanation of the Asser-
nutrients is small intestine. Small intestine is distin- tion.
guishable into three regions, a 'U' shaped duode- (c) If Assertion is true but Reason is false.
num, a long coiled middle portion jejunum and a (d) If both Assertion and Reason are false.
highly coiled ileum. Mainly iron, calcium and amino 28. (D)
acids are absorbed in duodenum; fatty acids, glyc-
erol, monosaccharides and vitamins are absorbed
in jejunum and absorpton of vitamin B12 , bile salts
and water occur in ileum.
24. (C) Absorption of substances takes place in differ-
ent parts of the alimentary canal, like mouth, stom-
ach, small intestine and large intestine. However,
maximum absorption occurs in the small intestine.
Hence, small intestine is the principal organ for ab-
sorption of nutrients. The digestion is completed
here and the final products of digestion such as
glucose, fructose, fatty acids, glycerol and amino

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CHAPTER
16
EXCHANGE OF GASES
“To be a Christian without prayer is no more possible than to be alive
without breathing.”

“ MARTIN LUTHER (1712-1778)”

INTRODUCTION

A
ll animals to perform function like breathing require energy which is derived from the
breakdown of nutrients molecules like glucose. Carbon dioxide which is harmful is
also released during the catabolic reactions, also energy is released in the form of
ATP. Now, this ATP is utilised by various animals to carry out their body functions
readily.
Therefore it is an evident that O2 Has to be continuosly provided to the cells, CO2
released by the cells.This process of exchange of O2 from the atmosphere with CO2
produced by the cells is known as Breathing, which is commonly called as Respiration.
Breathing includes expiration and inhalation. Inspiration means to inhale prior to
breathe in and Expiration means to exhale or to breathe out.

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INTRODUCTION
Definition
Respiration is the physiological catabolic process in which gaseous exchange occurs to oxidise food. The energy
generated is utilized and by products, CO2 and H2O are given out.
So, respiration is a physio-chemical process. The surface at which exchange of gases occurs is called
respiratory surface, and the compounds oxidised in respiration are called respiratory substrate.
TYPES OF RESPIRATION
Following are the types of respiration.
Direct and Indirect respiration
Aerobic and Anaerobic respiration

Direct and Indirect respiration

Direct respiration
(i) In this type of respiration, there is direct exchange of gases in between body cells and respiratory
medium.
(ii) Exchange of gases occurs on the principle of diffusion, through moist body surface.
(iii) Direct respiration is found in unicellular organisms like, aerobic bacteria, amoeba, ssponges, hydra,
flatworm, roundworm etc.
Indirect respiration
(i) In this type of respiration, their is no direct contact in between the body cells and respiratory medium.
(ii) Indirect respiration is found in complex and higher form of organism.
(iii) Higher organism have some specialized, structure for gaseous exchange which are called respiratory
organs.
e.g.
(a) Skin - Skin is respiratory organ in annelida and amphibians.
(b) Gills - Most of crustaceans, mollusca, all fishes and some amphibians the exchange of gases in gills
is called branchial respiration.
(c) Lungs - Lungs is respiratory organ in snails, some amphibians, all reptiles, birds and mammals.
(d) Trachea - Trachea is respiratory organ in insects.

AEROBIC AND ANAEROBIC RESPIRATION

Aerobic respiration
(i) Respiration which occurs in presence of oxygen is called aerobic respiration.
(ii) The oxygen completely oxidises the food to CO2 and H2O releasing large amount of energy. This process
can be shown by following way.
C6H12O6 + 6O2 o 6CO2 + 6H2O + 2880 KJ Energy
(iii) Such type of respiration (aerobic respiration) found in most animals and plants.
Phases of aerobic respiration
There are two phases of aerobic respiration.
A- External respiration
B- Internal respiration

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 BREATHING & EXCHANGE OF GASES
A- External respiration
(i) External respiration is also called breathing or ventillation.
(ii) It is gaseous exchange in between respiratory organ and outer environment.
e.g. Exchange of gases in between lungs and air.
B-Internal respiration
(i) Internal respiration is also called tissue respiration.
(ii) It is the exchange of oxygen of blood and carbon dioxide of body cells through tissue fluid at the
cellular level
(iii) It involves cellular respiration in which glucose is oxidised inside the mitochondria of cell to produce
H2O, CO2 and energy.
Anaerobic respiration
(i) Respiration which occurs in absence of oxygen is called anerobic respiration, anaerobic respiration is
also called fermentation.
(ii) It is found in bacteria, yeast, parasitic worms
(iii) In this type of respiration food is partially oxidised. It can be shown by following way.
In int estinal worms
C6H12O6       o 2CH3CHOHCOOH + Energy
(Lactic acid)
Note :
Anaerobic respiration even takes place in certain particular body tissues of aerobes.
e.g. In skeletal muscles fibres, In mammalian RBC.
(iv) In skeletal muscle fibres during vigrous exercise glucose is metabolised into lactic acid. The rapid
formation and accumulation of lactic acid are responsible for muscle fatigue.
(v) In mammalian RBC anaerobic respiration is found, because no mitochondria is found in mammalian
RBC.
Mammalian (Human) Respiratory system
Mammalian respiratory system is formed of following parts-
(1) Nostril (2) Nasal chamber (3) Internal nare (4) Pharynx
(5) Laryngopharynx (6) Larynx (7) Vocal cord (8) Trachea
(9) Primary bronchi (10) Lungs

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Nostril
(i) It is also called external nare.
(ii) It is oval aperture of nose present at the lower end.
Note : Presence of two nares is called dirhynous stage.
Nasal chamber
Nasal septum (made of Hyaline cartilage) divides nasal cavity into two nasal chamber by the nasal septum.
Each nasal chamber can be divided into three regions. These three parts are as follows -
(i) Vestibular part
It is smaller and anterior part, and is lined by hairy skin which acts as filter and prevents entry of dust
particles.
(ii) Respiratory part
It is middle part and is lined by pseudo-stratified epithelium which acts as air conditioner and brings the
inspired air at the body temperature.
(iii)Olfactory part
It is upper part of nasal chamber and is lined by olfactory epithelium called schneiderian membrane. It
looks yellowish brown, This region acts as an organ of smell. Three bony ridges the superior, middle and inferior
nasal conchae arises from the wall of each nasal chamber. The nasal conchae increases the surface area of nasal
chamber for better air conditioning
Internal nares
There are posterior opening of nasal chambers that leads into nasopharynx.
Pharynx
Pharynx comprises nasopharynx, oropharynx and laryngopharynx. The pharynx provides passage to both
air and food.
Laryngopharynx
It is the lower part of pharynx and has a slit like aperature called glottis, which can be closed by a leaf
like bilobed cartilage epiglottis, during swallowing of food bolus.
LARYNX
(i) It is also called voice box or adam's apple or pomas adami.
(ii) After puberty it get more developed in males in comparison to female, because of this very reason,
males have deeper voice.

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(iii) It is supported by four cartilage which prevent its collapsing these cartilage are as follows.
– Cricoid-1 – Thyroid-1 – Arytenoid-2 – Cartilage of santorini-2

(i) Thyroid cartilage

z It is single in number (Hyaline Cartilage).
z It is largest size and c shaped cartilage which supports anterior and lateral sides of upper part of the
larynx.
(ii) Cricoid cartilage
z It is single in number. (Hyaline Cartilage)
z It is some what smaller, thicker and a complete ring or collar like cartilage around the larynx behind
the thyroid cartilage.
z It is broad dorsally and narrow ventrally.
(iii) Arytenoid cartilage
z These are two pyramid shaped cartilage.(Hyaline cartilage)
z It is smallest cartilage which support posterior wall of upper part of larynx.
(iv) Cartilage of Santorini
Each arytenoid terminates in front in a Swollen knob called the cartilage of santorini.
(Elastin Cartilage)
VOCAL CORDS
z In larynx, 2 pairs of vocal cord is found outer pair is false vocal cord whereas, inner pair is true vocal
cord when air is forced through the larynx it cause vibration of true vocal cards and sound is produced.
z The pitch of the sound is determined by the tension of vocal cards, the greater the tension the
higher the pitch.
z Vocal cards are modified mucous folds of larynx.
Note :
(i) Sound get converted into speech by Tongue. Movement of Tounge is controlled by Speech centre of the
brain.
(ii) Speech centre is not well developed in dumb persons.
(iii) Voice of rabbit is called Quacking.
(iv) False vocal cord remain absent in Elephant.
(v) True vocal cord remain absent in Hippopotamus.
(iv) Voice apparatus of birds is called syrinx.

Trachea (Wind pipe)

z It is long, tubular structure which runs downward through the neck in front of oesophagus.
z It is supported by 16-20 dorsally incomplete C-shaped cartilagenous tracheal ring, which prevents its
collapsing.
z It is lined by pseudostartified ciliated epithelium with mucous secreting goblet cells.
Primary bronchi
z These are one pair of small thin walled tubular structure formed by the division of trachea at the level
of 5th thoracic vertebrae near the heart.

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z The right bronchus (2.5 cm) is wider shorter and more vertically placed then the left bronchus.
z Like trachea primary bronchi is supported by cartilaginous rings.
z Each primary bronchus enters the lungs of its own side.
Bronchial tree (B.T.) & Respiratory Tree (R.T.)
z When trachea enter into thoracic cavity, it divides in two branches called as primary bronchus. Branches
of Primary Bronchus upto terminal bronchioles makes bronchial tree
z Terminal bronchioles divide to form respiratory bronchioles & branches of respiratory bronchioles makes
respiratory tree
z In bronchial tree, cartilage rings are present, while these are absent in respiratory tree.
z Gaseous exchange occurs in respiratory tree while it is absent in bronchial tree.
z Volume of air which is filled in B.T. is a part of dead space volume. which doesn’t take a part in
gaseous exhange. (150 ml)
There are two zones.

External nostrils

Vestibule

Nasal Chamber

Internal nares

Naso pharynx

Pharynx
Glottis
Larynx

Trachea
Conducting Zone
Bronchial Tree

Trachea

Primary Bronchus

Bronchial Secondary Bronchus

Tree
Tertiary/Segmental Bronchus

Total Pulmonary Bronchioles

Terminal Bronchiole

Respiratory Bronchiole

Alveolar Duct

ATRIA
Exchange Zone

Alveolar Sac
Respiratory tree

l
Alveoli
LUNGS

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Position
Lungs are present in thoracic cavity on either side of heart.
Pleural membranes
z Each lung is enclosed with double membrane pleural membrane.
z The outer membrane is called parietal pleura. Whereas inner membrane is known as visceral pleura.
z In between two pleural membranes, hollow space is found which is called pleural cavity.
z Pleural cavity is filled with watery fluid called pleural fluid. Pleural fuild is secreted by pleural
membrane.
Pleural fluid perform three function which are as follows-
(a) It allows free frictionless movement of lungs.
(b) It protects the lungs from mechanical shock.
(c) It prevents pleural membrane from sticking together.
Note :
Accumulation of fluid between the pleura is called pleural effusion or pleuricy. It happens because of
bacterial infection and the person feel difficulty in breathing. due to the increased intrapleural pressure
External structure of lungs
z The lungs are spongy, soft, pinkish elastic organs.
z The most upper portion of each lungs is called the apex and the most lower portion is called the base.
z Right lung is slightly larger and broader in size.
z Each lung is a lobulated structure and is divided externally into the lobes by transverse and oblique grooves
called fissures.

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Lobes of lungs
Lobes of lungs in man
(i) Left lung is 2 lobed, upper superior lobe, and lower inferior lobe. (575 gm)
(ii) Right lung is 3 lobed; upper superior lobe, middle lobe and lower inferior lobe. It is demarcated by
transverse and oblique fissures. (625 gm)
Alveoli : Each lobe is further divided into several lobules by septas of connective tissue. Each lobule is
further divided into several airsacs ; and in the end, each air-sac is lastly divided into 3 or 4 alveolis ; which
are also termed as the units of lungs.
Sturctural & functional unit of lungs is called alveoli
Approximately 300 million alveoli are present in Both lungs. Inner (Alveolar) surface area of both lungs is
approximately 100 m2. Wall of alveoli consists of two layers, outer layer is composed of yellow fibrous C.T.
Inner layer is composed of Simple Squamous Epithelium
z squamous cells are called as pneumocytes.
z most of these Pneumocytes help in gasesous exhanges while few pneumocytes which are larger in
size (type II pneumocyte) secrete LECITHIN (Phospholipid) this acts as surfactant which prevents
alveoli from remaining collapse by reducing its surface tension.
Alveoli internal surface is termed as the Respiratory
surface. It is derived from the endoderm of the embryo.
Rest whole lung is mesodermal. The middle part of
alveoli wall is made up of connective tissue.It is richly
supplied with blood capillaries, a dense network of
blood capillaries is found in alveoli.
These blood capillaries come from pulmonary artery.
Pulmonary artery divides into blood capillaries after
reaching in lungs. These capillaries from a dense
network in the walls of alveoli. All these capillaries
combine to form pulmonary vein at the another end.
These veins carries pure blood to the left auricle of
the heart. There are small pores present in the walls of
alveoli. These pores make difusion of gases easy.
These pores are called pores of Kuhn. It is the
characterstic feature of mammalian lungs, that there
is no central cavity, Mammalian lungs are solid and
spongy.
Muscles are absent in the lungs of mammals. So the
power of self-contraction and self-expansion is absent
in these lungs. (Sucken lungs).

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Internal structure of lungs

Thoracic cavity
z Thoracic cavity is like a cage, so also called thoracic cage.
z Thoracic cavity is combination of following structure.
(a) Vertebral column - Found on dorsal part of thoracic cavity.
(b) Sternum - Found on ventral part of thoracic cavity.
(c) Ribs - Found on lateral part of thoracic cavity.
(d) Diaphragm - Found on posterior part of the throacic cavity.
Diaphragm
A muscular septum which is found only in mammals (and crocodile). Normal shappe of it
is dome like which divides body cavity in two parts upper thoracic cavity & lower adbominal cavity.
In it radial muscles are present. They originate from periphery and inserted in central region of diaphragm.
By the contraction in these mucles, diaphragm become flattened in shape. So, volume of thoracic cavity
increases. Therefore, diaphragm helps in inspiration.
Intercostal muscles (ICM)
Space between two ribs is called intercostal space in which 2 types of muscles are present
z External Intercostal Muscle (EICM)
z Internal Intercostal Muscle (IICM)
EICM
They originate from dorsal part of upper rib & insert on ventral part of lower rib. By the contraction in this
muscles, rib. and sternum shifts upward and outward. So they helps in inspiration.
IICM
They originate from dorsal part of lower rib and insert in ventral part of upper rib. By the contraction in
these muscles, ribs and sternum shifts downward and inward respectively, so it helps ih forceful expiration
which is a voluntary acitivity. So contraction of IICM is under the control of cerebrum.
Mechanism of RESPIRATION or BREATHING
Mechanism of Breathing involves two phases
Inspiration
Expiration
Inspiration
Sternum Vertebral
column

Ribs

Expiration
Position of ribs
(Thoracic respiration)

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INSPIRATION
(i) It is a process by which fresh air enters the lungs, the intercostal muscles, diaphragm, and abdominal
muscles play an important role.
(ii) During inspiration, diaphragm becomes flat and gets lowered by the contraction of its radial muscle
fibres, This increases vertical diameter of Thoracic cavity.
(iii) Due to contraction of external intercostal muscles, ribs and sterum are pulled upward and outward and
it also result in increase of transverse diameter of thoracic cavity.
(iv) Due to increase in both diameters of thoracic cavity, intrapleural pressure falls causing decompression
of lungs so lungs expand due to elastic recoil and air pressure within lungs decrease. The greater
pressure outside the body now causes air to flow rapidly into lungs.

EXPIRATION
(i) It is a process by which the foul air (carbon dioxide) is expelled out from the lungs.
(ii) It is passive process
(iii) During expiration muscles fibres of the diaphragm relax, so diaphragm becomes convex towards thoracic
cavity, it results in decrease vertical diameter of thoracic cavity.
(iv) Due to relaxation of external intercostal muscles, ribs and sternum return back to their original position and
this also results in decrease in transverse diameter of thoracic cavity.
(v) Due to decrease in both diameter of thoracic cage, intrapleural pressure increases, lungs are now compressed
so pressure within lungs increase, the greater pressure within lungs force foul air from lungs to outside of
body.

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 BREATHING & EXCHANGE OF GASES
Forceful expiration
During forceful expiration as during exercise coughing and sneezing, abdominal muscles and internal
intercostal muscles come into action which rapidly reduces volume of thoracic cavity. So, abdominal
muscles and internal intercostal muscles are called expiratory muscles.
REGULATION OF BREATHING
Breathing is an involuntary process and is controlled by medulla oblongata, but it can be made
voluntary for a short while, during this period it is controlled by cerebrum, those involuntary process
which can be made voluntary are called Reflex action.
Breathing is regulated by two controls
Nervous control
Chemical control
NERVOUS CONTROL
The respiratory rhythm is controlled by the nervous system. The rate of respiration can be enhanced as per
demand of the body during strainous physical exercises. A number of groups of neurons
are located bilaterally in the medulla oblongata control the respiration, these are called respiratory
centres.
Three groups of respiratory centres have been indentified, namely : dorsal respiratory groups, ventral respiratory
group and pneumotaxic centre
The dorsal respiratory group is present in the dorsal portion of medulla oblongata. The signals from these neurons
generate the basic respiratory rhythm. The nervous signal released from this group is transmited to the diaphragm,
which is the primary inspiratory muscles & EICM.
The ventral respiratory group of neurons are located anterolateral to the dorsal respiratory group During normal
respiration, this remains inactive and even does not play any role.

Pneumotaxic center

Pons varoli

Ventral group
Dorsal group (Expiration and
(Inspiration) inspiration)
Medulla
Vagus nerve

Spinal cord Sensory nerves from

stretch receptors in lungs

Motor nerves to
muscles of diaphragm Motor nerves to
and to intercostal intercostal muscles
muscles that raise ribs that lower ribs

Diagram showing nervous control of breathing

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BIOLOGY FOR NEET & AIIMS
In this enhanced respiratory drive, the respiratory signal of this group contributes to fulfil the demand by
regulating both inspiration and expiration. Few of the neurons of this group control inspiration, while few other
control expiration, thus regulating both. The pneumotaxic centre is located dorsally in the upper pons. It transmits
signals to the inspiratory area. Primarily, it controls the switch off point of inspiration. When this signal is strong
(high frequency), the inspiration lasts for a shorter duration and lungs are filled partially. During weak pneumotaxic
signal, inspiration lasts for a longer duration resulting into complete filling of lungs. The strong signal (high
frequency) causes increased rate of breathing, because duration inspiration as well as expiration, is shortened.
The concentration of CO2 and H+ cause increased strength of inspiratory, as well as expiratory signal. However,
oxygen has no such direct effect.
Heiring breuer reflex arch :
In the walls of terminal bronchioles and atria stretch receptors are present, Which are normally inactive but
they become active when the lungs are excessively inflated due to failure of switch off of inspiration. The
heiring breuer reflex arch now becomes activated and sends inhibitory signals to the inspiratory centre to
switch off inspiration. This prevents the alveoli from over stretching and bursting. Thus Heiring Breuer reflex
arch is a protective reflex which works only when normal mechanism of switch off of inspiration does not
work timely due to any reason.
CHEMICAL CONTROL
Effect of CO2
z Chemoreceptors are found in the carotid bodies (located in the wall of carotid arteries) and in the
aortic bodies (located in the wall of aorta).
z These chemoreceptors are stimulated by an increase in carbon dioxide concentration and by an
increase in hydrogen ion concentration (pH) in the arterial blood.
z Increased CO2 concentration lowers the pH resulting in acidosis. These chemoreceptors sends signals
to inspiratory and expiratory centres, thus rate of breathing is increased.
Note :
Activity and function of respiratory centre also get affected by body temperature and blood pressure.
In case of increased blood pressure or increased body temperature the breathing rate also increases.
Exchange of gases
(i) Ledwig at first described exchange of gases in blood.
(ii) Exchange of gases occurs in lungs and body tissue.
Exchange of gases in lungs
z Exchange of gases in lungs is also called pulmonary gas exchange.
z In the lungs exchange of gases takes place between the air in the alveoli and the blood in the
capillaries around the alveoli.
z In this exchange of gases blood takes up oxygen from the alveolar air and release CO2 to the alveolar
air.
Uptake of oxygen (O2) by pulmonary blood
The pO2 (partial pressure of oxygen) of the alveolar air is 104 mm Hg and PO 2 of blood in alveolar
capillaries is 40 mm Hg. Due to pO2 differences of 64 mm Hg between air and blood. Oxygen diffuses
rapidly from the alveolar air into the blood of alveolar capillaries raising PO 2 of blood to about
95 to 104 mm Hg.
Uptake of CO2 by the air
The pCO2 of the venous blood entering the pulmonary capillaries is 46 mm Hg while that of the alveolar
air is 40 mm Hg. Therefore CO2 diffuses from the blood of alveolar capillaries into the alveolar air till the
pCO2 of blood falls to 40 mm Hg.

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 BREATHING & EXCHANGE OF GASES
Exchange of gases in tissue
(i) The oxygenated blood is send from the pulmonary blood capillaries to the heart. The heart distributes
this oxygenated blood to various body parts and tissues through arteries. The arteries divide to form
arterioles which further divide to form capillaries.
(ii) In tissues exchange of gases occurs between the blood and the tissue cells. The exchange occurs
through tissue fluid that surrounds the tissue cells.
(iii) The blood reaching the tissue capillaries has PO2 of 95 to 104 mmHg and PCO2 of 40 mmHg. The
tissue cell have lower pO 2 and higher pCO 2 . Due to pO 2 and pCO 2 difference between
blood and tissue cell, oxygen separates from oxyhaemoglobin and diffuses from the blood into the
tissue fluid and finally into the tissue cells. CO2 diffuses from tissue cell into the tissue fluid and
finally into the blood present in the tissue capillaries, as a result of this, the blood becomes
deoxygenated. The deoxygenated blood returns to right side of the heart that sends it to lungs for
reoxygenation.
(iv) In inspired air oxygen is 19.6% whereas in expired air oxygen is 15.7%, hence, nearly 4% oxygen
comes in from air to blood, similarly in inspired air CO2 is 0.04%. Whereas in expired air CO2
is 3.6% hence nearly 3.56% CO2 comes out from blood into air.
Table of partial pressures and percentage concentrations (in brackets) of gases in various airs

Gas Atmospheric air Inspired Functional residual Expired air

(= humidified air) alveolar air

N2 597.0(78.62%) 563.4(74.09%) 569.0(74.9) 566.0(74.5%)

O2 159.0(20.84%) 149.3(19.67%) 104.0(13.6%) 120.0(15.7%)
CO2 0.3(0.04%) 0.3(0.04%) 40.0(5.3%) 27.0(3.6%)
H2O 3.7(0.5%) 47.0(6.2%) 47.0(6.2%) 47.0(6.2%)

760.0(100%) 760.0(100%) 760.0(100%) 760.0(100%)

Partial Pressure Alveolar air Pulmonary Arterial Blood Pulmonary Venous Blood

PO2 104 mm Hg 40 mm Hg 95 - 104 mm Hg

PCO2 40 mm Hg 45 - 46 mm Hg 40 mm Hg

TRANSPORT OF GASES IN BLOOD

Blood carries oxygen from lungs to the heart and from the heart to various cells and tissue.
The blood also brings CO2 from cells and tissue to the heart, from heart to lungs, for expiration.
TRANSPORT OF OXYGEN
As much oxygen comes in the blood from air, approximately 3% of it dissolves in the blood plasma.
Remaining 97% oxygen combines with haemoglobin to form oxygaemoglobin. One molecule of haemoglobin
combines with 4 molecules of oxygen Haemoglobin is made up of 4 units. Every unit of it, reacts with one
molecule of oxygen. 1 gm haemoglobin can combine with a maximum of 1.34 ml of oxygen and 100 ml
blood carries about 15 gm haemoglobin so 100 ml blood transports approximately 20 ml of oxygen. Oxygen
does not oxidise haemoglobin. Formation of oxyhaemoglobin is a process of oxygenation. The valency of
iron is 2 in oxyhaemoglobin. Some gases (eg. Ozone SO 3, NO, NO 2 etc.) oxidise haemoglobin. This
oxidised haemoglobin is alled Methamoglobin. This is a colourless compound. This type of gases are

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enviromental pollutant. At the time, oxyhaemoglobin reaches upto the tissues it dissociates. O2 freed it
goes into the tissue fluid from blood. In place of it, CO2 from tissue fluid comes into blood. Gaseous
exhange between blood and tissue is called internal respiration. It is also done by
simple diffusion. In a conduction cycle blood gives its 25%O 2 to tissues . The rate of saturation of
haemoglobin with O2 is directly proportional to concentration of oxygen as with a rise in pO2 the affinity
between O2 and Hb also increases.

Oxygen dissociation curve

(i) The relationship between the saturation of haemoglobin and oxygen tension is studied by examination
of dissociation curve of oxyhaemoglobin.
(ii) Oxygen dissociation curve is sigmoid. It is also called oxygen equilibrium curve.
(iii) At normal condition it is sigmoid & normal.
(iv) With increase in concentration of CO2 in tissues curve shifts towards right side and % of O2 in Hb
decreases due to more dissociation of oxyhaemoglobin.
(v) By decrease in conc. of CO2 in tissues curve shifts towards left side and % of O2 in Hb becomes more
due to low dissociation of oxyhaemoglobin.
(iv) p50 is the partial pressure of O2 at which Hb is 50% saturated with O2. Its normal value is 30 mmHg.

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Factors affecting oxygen dissociation curve

(a) Temperature - Oxygen dissociation curve turns to right side with increase in temperature.
(b) pCO2 - Oxygen dissociation curve turns to right side and oxygen binding capacity of haemoglobin is
lowered with increase in pCO2.
(c) pH - Oxygen dissociation curve turns to right side with decrease in pH. Moreover dissociation of
oxyhaemoglobin will increase when pH of blood falls or H+ concentration of blood rises.
(d) Fetal Haemoglobin - Pressure of Fetal Hb shifts the curve towards left. Because fetal Hb has a higher
degree of affinity with oxygen than normal haemoglobin.
Bohr effect
(i) Bohr effect is the effect of CO2 on oxyhaemoglobin.
(ii) Dissociation of oxyhaemoglobin is directly proportional to blood pCO2. Because with a rise in pCO2
the affinity between oxygen & haemoglobin decreases.
Haldane effect
According to haldane effect the oxyhaemoglobin behave like strong acid and cause dissociation of CO2
from its carrier compounds.
TRANSPORT OF CARBON DIOXIDE
During oxidation of food CO2, water and energy are produced. From the cells carbon dioxide in gaseous
state diffuses out of the cells into the capillaries. From capillaries it is transported by 3-ways.
1. As a dissolved gas
A very small amount of CO2 about 5% to 7% dissolves in the plasma and is carried as a physical solutions
to the lungs.
2. As bicarbonates
(i) About 70% of CO2 enters the erythrocytes where it react with water to form carbonic acid in the
presence of an enzyme called the carbonic anhydrase.
(ii) In erythrocytes most of the carbonic acid rapidly dissociates to form bicarbonate and hydrogen ion.
(iii) Bicarbonate ion passes out from the erythrocytes into the plasma. This causes significant difference
in ionic balance between ions in the, plasma and those inside the erythrocytes. To restore the ionic
balance the chloride ion diffuse from the plasma into the erythrocytes. This movement of chloride ions
is called chloride shift or Hamburger's phenomenon reported by Hamburger in 1918. The chloride
shift maintains an acid base equilibrium of pH 7.4 for the blood and electrical balance between
erythrocytes and plasma.
(iv) Some of the bicarbonate is carried in erythrocytes while most of bicarbonate is released into plasma
and carried or transported by it

7% CO2 is carried
77% CO2 dissolved in Plasma
CO2
70% diffuses inside RBC
C.A.
Tissue CO2 + H2O H2CO3
Level
H + HCO 3
+
H2CO3
KHbO2 KHb + O2
HCO3 KHb K+ + Hb
+
23% CO2 K + Hb H.Hb
CO2 + HHb H.Hb.CO2
+
K + Cl¯ KCl
+
NaCl Na + Cl¯
Cl¯
HCO 3 + Na
+
NaHCO3

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BIOLOGY FOR NEET & AIIMS

3. As carbaminohaemoglobin
About 23% of CO2 it transported as carbamino haemoglobin which is formed by the reversible combination
of CO2 with amino group of globin part of the haemoglobin.
Pulmonary capacity (SPIROMETRY)

1. Tidal volume
z Volume of air inspired or expired with each normal breath (in voluntarily) is called tidal volume.
z In normal person tidal volume is 500 ml.

2. Inspiratory reserve volume (IRV) or complimental air volume

z It is the extra volume of air which can be inspired by deepest forced inhalation beyond tidal volume.
z It is about 3000 ml
3. Inspiratory capacity
z It is total volume of air that can be inhaled forcefully after a normal exhalation.
IC = TV + IRV
= 500 + 3000
= 3500 mL.
4. Expiratory reserve volume (ERV)
z It is extra amount of air that can be expired forcibly after a normal expiration. It is about 1100 ml.
5. Residual volume (RV)
z It is volume of air which remains still in the lungs even after the most forceful expiration.It is about
1200 ml.
6. Functional residual volume (FRV)
z It is the amount of air that normally remains inside lungs after a normal expiration.
z It is equal to the sum of expiratory reserve volume and the residual volume.
E.R.V. + R.V. = FRC
z It is about 2300 ml

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 BREATHING & EXCHANGE OF GASES
7. Vital capacity of lung (V.C)
z It is the maximum amount of air that can be expelled from the lungs by forced exhalation after a
deepest forced inhalation. It is equal to sum of tidal volume, inspiratory reserve volume and expiratory
reserve volume.
V. C. = TV + IRV + ERV
= 500 + 3000 + 1100
= 4600 ml
Vital capacity is higher in mountain dwellers, atheletes, young person and men.

8. Total lung capacity (TLC)

z It is the total amount of air that can be present in the lungs after a maximum inhalation effort.
TLC = VC + RV OR TV + IRV + ERV + RV
= 5-6 litre (Average 5800 ml)
Some DISORDERS of respiratory system
1. Laryngitis
It is an inflammation of larynx.
2. Pharyngitis
It is an inflammation of pharynx.
3. Bronchitis
It is inflammation of bronchi.
4. Pneumonia
In pneumonia fluid and white blood corpuscles accumulates in the lung tissue due to infection.
5. Hypoxia
It is an insufficiency of oxygen reaching the tissue of the body or in other world it is a condition of oxygen shortage
in the tissue. Hypoxia is of two types
Artificial hypoxia -
It results from shortage of oxygen in the air as at height over 2400 m altitude.
Anaemic hypoxia -
It is due to reduced oxygen carrying capacity of the blood due to anaemia.
6. Asphyxia (Suffocation)
It is oxygen deficiency and CO2 accumulation in body tissues which results to death.
7. Emphysema
The air pollutants or cigarrette smoke that causes chronic bronchitis may also lead to breakdown the alveoli
of lungs reducing the surface area of gaseous exchange.
8. Asthma
It is an allergic attack of breathlessness associated with bronchial spasm.
9. Anoxia
It is a state during which respiratory centre is inhibited resulting in lack of O2 delivery to tissues.
10. Cyanide poisoning (Histotoxic anaemia)
Causing inactivation of cytochrome oxidase enzyme of mitochondria leading to asphyxia & death
11. CO poisoning
Carbon monoxide affinity for haemoglobin is about 300 times more than O2. It forms a stable carboxy
haemoglobin (chery red in colour) hence decreasing oxygen carrying capacity of Hb

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Additional useful informations
(i) Cessation of breathing is called Apnoea.
(ii) Normal (involuntary) breathing is called Eupnoea.
(iii) Decreased breathing rate is called Hypopnoea.
(iv) Increased breathing rate is called Hyperpnoea.
(v) Difficulty in breathing is called Dysponea.
(vi) Due to deficiency of oxyhaemoglobin skin turns bluish in colour this condition is called Cyanosis.
(vii) Prolong involuntary inspiration due to fall in tension of O2 in blood is called Yawning.
(viii) Sharp inspiratory sound due involuntary contractions in diaphragm is called Hiccup.
(ix) Cough - Forceful expiration to expell an irritant in throat .
(x) Sneeze-Reflex action ; stimulation takes place through the olfactory epithelium of nasal chamber. Air
is expelled out through the mouth & nose both.
(xi) Haemoglobin of foetus has high affinity for oxygen than mother's haemoglobin.
(xiii) Cerebrum initiates impulses for voluntary muscles for forced breathing.
(xiv) Amount of air exchange in breathing can be measured with a Respirometer. Ganong's respirometer
is generally used.
(xv) The partial pressure of O2 which 50% haemoglobin of blood is saturated with oxygen is called p50 value.
Effects of High Altitudes on Respiratory System
As we ascend upwards an mountains above 8000 ft from sea level , the atmosphere become thinner and
& O 2 fall. This causes decrease in Oxygenation of blood with rise in altitude and symptoms like
breathlessness, headache, dizziness, irritability , nausea, vomiting, mental fatigue and bluish tinge on the
skin & lips .This in known as mountain sickness.
A condition of prolonged hypoxia in renal tissue causes Kidney to release a hormone erythropoeitin which
stimulates R.B.C production in bone marrow. Hence longer stays at high altitude result in increased R.B.C.
count of blood (polycythemia) and this also increases the Haemoglobin concentration in blood.
Effects of Depth on Respiratory System or Decompression Sickness
When a diver descends to great depth , his body is subjected to high pressure caused by water to prevent
the collapse of lungs he breathes compressed air. Under compression, N2 gets dissolve in blood and body
fats. This cause the diver to lose his strength and work capacity and feels drowsy. When the diver is
suddenly lifted out of water N2 forms bubbles in blood & tissues due to fall in pressure. Bubbles may block
the blood vessels (Air embolism) and produce serious shortness of breath , itching , local pain , dizziness,

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 BREATHING & EXCHANGE OF GASES

o The process of exchange of O2 from the atmosphere with CO2 produced by the cells is called breathing, commonly
known as respiration.

S.No. Respiratory organs Examples

1. General body surface Sponges, Coelenterates, Flat worms
2. Moist skin Earthworms, Frogs
3. Tracheal tubes Insects
4. Gills Aquatic arthropods, Molluscs, Fishes
5. Lungs Reptiles, Birds, Mammals

o Pharynx is the common passage for food and air.

o In human, path of air is :

External o Nasal o Nasopharynx o Larynx o Trachea o Primary

nostrils chamber Bronchi
Alveoli m Bronchioles m Tertiary m Secondary €
network bronchi Bronchi

o Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric
pressure. Inspiration is initiated by the contraction of diaphragm and external inter costal muscles (EICM). Expira-
tion takes place when the intrapulmonary pressure more than the atmospheric puressure. In this diaphragm and
EICM are relaxed.

o Alveoli are the primary sites of exchange of gases. Exchange of gases also occur between blood and tissues.
o O2 and CO2 are exchanged in these sites by simple diffusion mainly based on pressure/concentration gradient.

o Partial pressures (in mm Hg) of oxygen and carbon dioxide.

Resiratory Gas Atmosheric Air Alveoli Deoxygenated blood Oxygenated blood Tissues
O2 159 104 40 95 40
CO2 0.3 40 45 40 45

S.No. Respiratory volumes and capacities Value

1. Tidal volume (TV) 500 ml
2. Inspiratory reserve volume (IRV) 2500 - 3000 ml
3. Expiratory reserve volume (ERV) 1000 - 1100 ml
4. Residual volume (RV) 1100 - 1200 ml
5. Inspiratory capacity (TV + IRV) 3500 ml
6. Expiratory capacity (TV + ERV) 1600 ml
7. Functional residual capa city (ERV+ RV) 2300 ml
8. Vital capacity (TV + IRV + ERV) 4600 ml
9. Total lung capacity (TV + IRV + ERV + RV) 5800 ml

o Blood transport O2 in the form of oxyhaemoglobin. O2 can bind with heamoglobin in a reversible manner to form
oxyhaemoglobin. Each haemoglobin molecule can carry a maximum of four molecules of O2. Binding of oxygen with
haemoglobin is primarily related to partial pressure of O2.

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o Oxygen dissociation curve is sigmoid.
o High PO2 low PCO2, lesser H+ concentration and lower temperature, the factors are all favourable for the formation
of oxyhaemoglobin.
o Every 100 ml of oxygenated blood can deliver around 5 ml of O2 to the tissues.
o CO2 is transported by blood in three forms :
(i) Carbamino - haemoglobin (about 20-25%)
(ii) Bicarbonate - (about 70%)
(iii) Dissolved in plasma (about 7%)
o Every 100 ml of deoxygenated blood delivers approximately 4 ml of CO2 to the alveoli.
o Respiratory rhythm centre present in the medulla region and pneumotaxic centre present in the pons region.
o Asthma is due to inflammation of bronchi and bronchioles.
o In Emphysema alveolar wall are damaged so respiratory surface is decreased.

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SOLVED EXAMPLE
Ex.1 Respiratory pigment in cockroach is
(A) Haemozoin (B) Haemocyanin
(C) Haemoglobin (D) Absent
Sol. (D) : Haemolymph is found in insect blood which is
colourless.

Ex.2 Carbon dioxide is transported via blood to lungs

mostly
(A) As carbaminohaemoglobin and as carbonic acid
(B) In the form of carbonic acid only
(A) D – Lower end of lungs – diaphragm pulls it
(C) In combination with haemoglobin only down during inspiration
(D) Dissolved in blood plasma (B) A – Trachea – long tube supported by complete
cartilaginous rings for conducting inspired air
Sol. (A)
(C) B – Pleural membrane – surround ribs on both
sides to provide cushions against rubbing
Ex.3 The diagram represents the human larynx. Choose
(D) C – Alveoli – thin walled vascular bag like
the correct combination of labelling from the option structures for exchange of gases
given : Sol. (D)
Ex.5 What is vital capacity of our lungs
(A) Inspiratory reserve volume plus expiratory
reserve volume
(B) Total lung capacity minus residual volume
(C) Inspiratory reserve volume plus tidal volume
(D) Total lung capacity minus expiratory reserve
volume
Sol. (B)
(A) A - Larynx, B - Parathyroid, C - Tracheal cartilage,
D - Trachea Ex.6 The largest quantity of air that can be expired after a
maximum inspiratory effort is
(B) A - Naso Larynx, B - Thyroid, C - Tracheal
(A) Residual volume (B) Tidal volume
cartilage, D - Trachea (C) Vital capacity of lungs (D) Lung volume
(C) A - Trachea, B - Thyroid, C - Bronchiole, D - Sol. (C) : Vital capacity of lungs to expire maximum volume
Tracheal cartilage of air after a deep inspiration. The largest qunatity
of air that can be expired after a maximal inspiratory.
(D) A - Epiglottis, B - Thyroid, C - Tracheal cartilage, Vital capacity is equal the sum of the tidal
D - Trachea complemental and supplemental air (500 + 3100 +
(E) A - Epiglottis, B - Parathyroid, C - Trachea, D - 1200 = 4800 ml).

Tracheal cartilage Ex.7 The volume of air which remains in the conducting
airways and is not available for gas exchange is
Sol. (D)
called
Ex.4 The figure shows a diagrammatic view of human (A) Vital capacity
(B) Functional residual capacity
respiratory system with labels A, B, C and D. Select
(C) Forced expiratory volume
the option which gives correct identification and (D) Anatomic dead space
main function and/or characteristic. Sol. (D)

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BIOLOGY FOR NEET & AIIMS
Ex.8 How much amount of volume of air is in lung FRC Sol. (C)
(A) 1500 ml to 1600 ml (B) 2100 ml to 2500 ml
Ex.15 The major fraction of CO2 released during cellular
(C) 2500 ml to 3000 ml (D) 1600 ml to 2100 ml
respiration is transported by the blood to the lungs
Sol. (B)
capillaries
Ex.9 The enzyme essential for the transport of CO2 as Or
bicarbonate in blood is Approximately seventy percent of carbon-dioxide
(A) Carboxypeptidase absorbed by the blood will be trasnsported to the
(B) Succinic dehydrogenase lungs
(C) Carbonic anhydrase (A) In combination with haemoglobin
(D) Thrombokinase (B) As free CO2
(E) Lactase (C) As carbonic acid or H2CO3
Sol. (C) (D) In the form of bicarbonate ions
Ex.10 Vital capacity of the lung includes Sol. (D) : Nearly 20-25 percent of CO2 is transported by
Or RBCs, whereas , 70 percent of it is carried as
After forceful inspiration, the amount of air that can bicarbonates. About 7 percent of CO2 is carried as
be breathed out by maximum forced expiration is dissolved state in plasma.
equal to
Ex.16 In humans, which among these is not a step in
(A) IRV + TV +ERV (B) ERV + RV
respiration
(C) ERV + TV (D) IRV + TV
(A) Pulmonary ventilation
Sol. (A)
(B) Alveolar diffusion of O2 and CO2
Ex.11 The volume of anatomical dead space' air is normally (C) Transport of gases by blood
(A) 230 ml (B) 210 ml (D) Diffusion of O2 and CO2 between blood and
(C) 190 ml (D) 150 ml tissue
Sol. (D) (E) Utilization of CO2 by cells for catabolic reactions
Ex.12 The urge to inhale in humans results from Sol. (E)
(A) Rising PCO2 (B) Rising PO2 Ex.17 Which one of the following is a possibility for most
(C) Falling PCO2 (D) Falling PO2 of us in regards to breathing, by making a conscious
Sol. (A) effort
Ex.13 The exchange of gases in the alveoli of the lungs (A) One can consciously breathe in and breathe out
takes place by moving the diaphragm alone, without
moving the ribs at all
(A) Osmosis (B) Simple diffusion
(C) Passive transport (D) Active transport (B) The lungs can be made fully empty by forcefully
breathing out all air from them
Sol. (B) : The gaseous exchange is the simple diffusion
of oxygen from alveolar air into the blood and (C) One can breathe out air totally without oxygen
diffusion of oxygen from alveolar air into the blood (D) One can breathe out air through eustachian
diffusion of CO2 from blood to alveolar air. tubes by closing both nose and the mouth
Sol. (D)
Ex.14 Choose the right sequential phenomena among the
following during the delivery of O2 from blood to Ex.18 O2 dissociation curve is
tissue (A) Sigmoid (B) Slope
P. Absorption of CO2 by the blood (C) Straight line (D) Parabola
Q. Reaction of absorbed CO2 with H2O to form Sol. (A)
H2CO3 within RBC and its conversion into H+
and HCO–3 ions Ex.19 The factor which does not affect the rate of alveolar
R. Reaction of absorbed CO2 with H2O in plasma diffusion is
to form H2CO3 and its conversion into H+ and (A) Solubility of gases
HCO–3 ions (B) Thickness of the membranes
S. Combination of H+ with haem portion of HbO2 (C) Pressure gradient
to form reduced haemoglobin and release of O2 (D) Carboxyhaemoglobin
(A) P, Q, T (B) P, R, S (E) Reactivity of the gases
(C) P, Q, S (D) P, R, T Sol. (E)

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 BREATHING & EXCHANGE OF GASES
Ex.20 The figure given below shows a small part of human Ex.23 The respiratory centre in brain which controls
lung where exchange of gases takes place. In which inspiration and expiration is situated in
one of the option given below, the one part A, B, C Or
or D is correctly identified along with its functions Respiratory and vomitting centres are located in
(A) Medulla oblongata (B) Cerebellum
(C) Hypothalamus (D) Pericardium
Sol. (A) : Breathing is controlled by pneumotaxic and
apneustic centres is pons varoli and expiratory and
inspiratory centres in medulla oblongata.
Ex.24 A substance that prevents or delays oxidation is
(A) Bacterial (B) Hormone
(C) Antioxidant (D) Enzymes
Sol. (C)
Options : Ex.25 Increased asthmatic attacks in certain seasons are
(A) B : Red blood cell – transport of CO2 mainly related to
(B) C : Arterial capillary – passes oxygen to tissues (A) Hot and humid environment
(C) A : alveolar cavity – main site of exchange of (B) Eating fruits preserved in tin containers
respiratory gases (C) Inhalation of seasonal pollen
(D) D : Capillary wall – exchange of O2 and CO2 (D) Low temperature
takes place here Sol. (C) : Because plants release pollen grain a fix time
Sol. (C) : A is the alveolar cavity which is the main site of and it is generally March-April or Aug.-Sep.
exchange of respiratory gases. Ex.26 When O 2 is inadequate during respiration, the
condition is called
Ex.21 When you hold your breath, which of the following
(A) Anoxia (B) Pleurisy
gas changes in blood would first lead to the urge to
(C) Asphyxia (D) Hypoxia
breathe
Sol. (D)
(A) Rising CO2 concentration
(B) Falling CO2 concentration Ex.27 Asthma is characterised by
(C) Rising CO2 and falling O2 concentration (A) Spasm in bronchial muscle
(D) Falling O2 concentration (B) Alveolar wall degradation
Sol. (A) : Rise in CO2 concentration is detected by (C) Pain in lungs
chemosensitive area activates inspiratory centre in (D) Damage in diaphragm
Medulla oblongata, which lead to urge of breathing Sol. (A)
. Role of O2 concentration is non significant. Ex.28 State the volume of air remaining in the lungs after a
normal breathing.
Ex.22 The function of surfactant is/are
Sol. The volume of air remaining in the lungs after a
(A) Facilitating lung expansion
normal expiration is known as functional residual
(B) Maintaining the stable size of the alveoli capacity (FRC). It includes expiratory reserve volume
(C) To reduce the surface tension on the alveoli (ERV) and residual volume (RV). ERV is the maximum
(D) All of the above volume of air that can be exhaled after a normal
expiration. It is about 1000 mL to 1500 mL. RV is the
Sol. (D) : Surfactant is a liprotein secreted by surfactant volume of air remaining in the lungs after maximum
secreting cells, which form part of alveolar expiration. It is about 1100 mL to 1500 mL.
epithelium. This tends to reduce the surface tension FRC = ERV + RV
of fluid lining the alveoli and thus facilitates lung 1500 + 1500
expansion and also maintains the stable size of the 3000 mL
alveoli. Functional residual capacity of the human lungs is
about 2500 – 3000 mL.

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BIOLOGY FOR NEET & AIIMS
Ex.29 What are the major transport mechanisms for CO2? contraction of the external intercostal muscles. This
Explain. causes the ribs and the sternum to move out, thereby
increasing the volume of the thoracic chamber in
Sol. Plasma and red blood cells transport carbon dioxide. the dorsoventral axis. The overall increase in the
This is because they are readily soluble in water. thoracic volume leads to a similar increase in the
(1) Through plasma: pulmonary volume. Now, as a result of this increase,
About 7% of CO2 is carried in a dissolved state the intra-pulmonary pressure becomes lesser than
through plasma. Carbon dioxide combines with water the atmospheric pressure. This causes the air from
and forms carbonic acid. outside the body to move into the lungs.
CO2 + H2O o H2CO3
Ex.31 What happens to the respiratory process in a man
(carbonic acid)
going up a hill?
Since the process of forming carbonic acid is slow,
only a small amount of carbon dioxide is carried this Sol. As altitude increases, the oxygen level in the
way. atmosphere decreases. Therefore, as a man goes
(2) Through RBCs: uphill, he gets less oxygen with each breath. This
About 20 – 25% of CO2 is transported by the red causes the amount of oxygen in the blood to decline.
blood cells as carbaminohaemoglobin. Carbon The respiratory rate increases in response to the
dioxide binds to the amino groups on the decrease in the oxygen content of blood.
polypeptide chains of haemoglobin and forms a Simultaneously, the rate of heart beat increases to
compound known as carbaminohaemoglobin. increase the supply of oxygen to blood.
(3) Through sodium bicarbonate: Ex.32 Have you heard about hypoxia? Try to gather
About 70% of carbon dioxide is transported as information about it, and discuss with your friends.
sodium bicarbonate. As CO2 diffuses into the blood
plasma, a large part of it combines with water to Sol. Hypoxia is a condition characterised by an
form carbonic acid in the presence of the enzyme inadequate or decreased supply of oxygen to the
carbonic anhydrase. Carbonic anhydrase is a zinc lungs. It is caused by several extrinsic factors such
enzyme that speeds up the formation of carbonic as reduction in pO2, inadequate oxygen, etc. The
acid. This carbonic acid dissociates into bicarbonate different types of hypoxia are discussed below.
(HCO3–) and hydrogen ions (H+). (i)Hypoxemic hypoxia
CO2 + H2O o H2CO3 In this condition, there is a reduction in the oxygen
H2CO3 o HCO–3 + H+ content of blood as a result of the low partial
pressure of oxygen in the arterial blood.
Ex.30 Explain the process of inspiration under normal (ii)Anaemic hypoxia
conditions.
In this condition, there is a reduction in the
concentration of haemoglobin.
(iii)Stagnant or ischemic hypoxia
In this condition, there is a deficiency in the oxygen
content of blood because of poor blood circulation.
It occurs when a person is exposed to cold
temperature for a prolonged period of time.
(iv)Histotoxic hypoxia
In this condition, tissues are unable to use oxygen.
This occurs during carbon monoxide or cyanide
Sol. Inspiration or inhalation is the process of bringing poisoning.
air from outside the body into the lungs. It is carried
out by creating a pressure gradient between the
lungs and the atmosphere. When air enters the
lungs, the diaphragm expands toward the abdominal
cavity, thereby increasing the space in the thoracic
cavity for accommodating the inhaled air.
The volume of the thoracic chamber in the
anteroposterior axis increases with the simultaneous

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BIOLOGY FOR NEET & AIIMS

Exercise PART - 1 PREVIOUS YEAR (NEET/AIPMT)

1. People living at sea level have around 5 million RBC 4. Inspiratory capacity 4500 mL
per cubic millimeter of their blood whereas those Which one of the following is the correct matching
living at an altitude of 5400 metres have around 8 of two capacities and volumes?
million. This is because at high altitude- (A) (2) 2500 mL, (3) 4500 mL
[CBSE AIPMT 2006] (B) (3) 1200 mL, (4) 2500 mL
(A) Atmospheric O2 level is less and hence more (C) (4) 3500 mL, (1) 1200 mL
RBCs are needed to absorb the required amount (D) (1) 4500 mL, (2) 3500 mL
of O2 to survive.
(B) There is more UV radiation which enhances 6. The figure given below shows a small part of human
RBC production lung where exchange of gases takes place. In which
one of the options given below, the one part A, B, C
(C) People eat more nutritive food, therefore more or D is correctly identified along with its function?
RBCs are formed [CBSE AIPMT 2011]
(D) People get pollution-free air to breathe and more
oxygen is available
2. What is vital capacity of our lungs?
[CBSE AIPMT 2008]
(A) Inspiratory reserve volume plus tidal volume
(B) Total lung capacity minus expiratory reserve
volume (A) A – Alveolar cavity – main site of exchange
(C) Inspiratory reserve volume plus expiratory re- of respiratory gases
serve volume (B) D – Capillary wall – exchange of gases
(D) Total lung capacity minus residual volume takes place here
3. The haemoglobin of a human foetus: (C) B– Red blood cell – transport of mainly
[CBSE AIPMT 2008] haemoglobin
(A) has a lower affinity for oxygen than that of an (D) C– Arterial capillary – passes oxygen to
adult
tissues
(B) its affinity for oxygen is the same as that of an
adult 7. Two friends are eating together on a dining table.
(C) has only 2 protein subunits instead of 4 One of them suddenly starts coughing while swal-
(D) has a higher affinity for oxygen than that of an lowing some food. This coughing would have been
adult due to improper movement of
[CBSE AIPMT 2011]
4. Which two of the following changes (1-4) usually (A) Diaphragm (B) Neck
tend to occur in the plain dwellers when they move (C) Tongue (D) Epiglottis
to high altitudes (3,500 m or more) ?
[CBSE AIPMT 2010] 8. People who have migrated from the planes to an
1. Increase in red blood cell size area adjoining Rohtang Pass about six months back
2. Increase in red blood cell production : [CBSE AIPMT 2012]
3. Increased breathing rate (A) Have more RBCs and their haemoglobin has a
4. Increase in thrombocyte count lower binding affinity to O2
Changes occurring are ? (B) Are not physically fit to play games like foot-
ball
(A) (2) and (3) (B) (3) and (4)
(C) (1) and (4) (D) (1) and (2) (C) Suffer from altitude sickness with symptons like
nausea, fatigue, etc.
5. Listed below are four respiratory capacities (1-4) (D) Have the usual RBC count but their haemoglo-
and four jumbled respiratory volumes of a normal bin has very high binding affinity to O2.
human adult: [CBSE AIPMT 2010]
Respiratory Respiratory 9. Which one of the following is the correct statement
capacities volumes for respiration in humans ? [CBSE AIPMT 2012]
1. Residual volume 2500 mL. (A) Cigarette smoking may lead to inflammation of
2. Vital capacity 3500 mL bronchi
3. Inspiratory reserve volume1200 mL

185
 BREATHING & EXCHANGE OF GASES
(B) Neural signals from pneumotoxic centre in pons (C) There is a positive intrapleural pressure
region of brain can increase the duration of (D) Pressure in the lungs is higher than the atmo-
(C) Workers in grinding and stone-breaking indus- spheric pressure
tries may suffer, from lung fibrosis
15. Reduction in pH of blood will [NEET 2016]
(D) About 90% of carbon dioxide (CO2) is carried
by haemoglobin as carbamino haemoglobin in- (A) Reduce the blood supply to the brain
spiration (B) Decrease the affinity of hemoglobin with oxy-
gen
10. The figure shows a diagrammatic view of human (C) Release bicarbonate ions by the liver
respiratory system with labels A, B, C and D. Select (D) Reduce the rate of heart beat
the option which gives correct identification and
main function and/or characteristic :-[NEET 2013] 16. Name the chronic respiratory disorder caused
mainly by cigarette smoking [NEET 2016]
(A) Asthma
(B) Respiratory acidosis
(C) Respiratory alkalosis
(D) Emphysema
17. Lungs are made up of air-filled sacs the alveoli. They
do not collapse even after forceful expiration, be-
cause of : [NEET 2017]
(A) Residual Volume (RV)
(A) A – trachea - long tube supported by complete (B) Inspiratory Reserve Volume (IRV)
cartilaginous rings for conducting inspired air
(C) Tidal Volume(TV)
(B) B – pleural membrane - surround ribs on both
sides to provide cushion against rubbing (D) Expiratory Reserve Volume (ERV)
(C) C – Alveoli - thin walled vascular bag like struc-
tures for exchange of gases 18. Match the items given in Column I with those in
(D) D – Lower end of lungs – diaphragm pulls it Column II and select the correct option given be-
down during inspiration low : [NEET 2018]
Column I Column II
11. Approximately seventy percent of carbon-dioxide a. Tidal volume i. 2500-3000 mL
absorbed by the blood will be transported to the b. Inspiratory Reserve volume ii. 1100-1200 mL
lungs [CBSE AIPMT 2014] c. Expiratory Reserve volume iii. 500 – 550 mL
(A) As bicarbonate ions d. Residual volume iv. 1000 – 1100 mL
(B) In the form of dissolved gas molecules a b c d
(C) By binding to R.B.C.
(A) i iv ii iii
(D) As carbamino-haemoglobin (B) iii i iv ii
12. Name the pulmonary disease in which alveolar sur- (C) iii ii i iv
face area involved in gas exchange is drastically (D) iv iii ii i
reduced due to damage in the alveolar walls :
[CBSE AIPMT 2015] 19. Which of the following options correctly represents
(A) Pleurisy (B) Emphysema the lung conditions in asthma and emphysema, re-
(C) Pneumonia (D) Asthma spectively ? [NEET 2018]
(A) Increased respiratory surface ; Inflammation
13. The partial pressure of oxygen in the alveoli of the of bronchioles
lungs is [NEET 2016] (B) Increased number of bronchioles; Increased
(A) Equal to that in the blood respiratory surface
(B) More than that in the blood (C) Inflammation of bronchioles; Decreased
(C) Less than that in the blood respiratory surface
(D) Less than that of carbon dioxide (D) Decreased respiratory surface; Inflammation
of bronchioles
14. Lungs do not collapse between breaths and some
air always remains in the lungs which can never be 20. Which of the following is an occupational respira-
expelled because [NEET 2016] tory disorder ? [NEET 2018]
(A) There is a negative pressure in the lungs (A) Botulism (B) Silicosis
(B) There is a negative intrapleural pressure pull-
(C) Anthracis (D) Emphysema
ing at the lung walls

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Exercise PART - 2 PREVIOUS YEAR (AIIMS)

1. Severe Acute Repiratory Syndrome (SARS)[2004] 6. Oxygen binding to haemoglobin in blood is[2012]

(A) is caused by a variant of Pneumococcus (A) directly proportional to the concentration of CO2
in the medium
pneumoniae
(B) inversely proportional to the concentration of
(B) is caused by a variant of the common cold virus
CO2 in the medium
(corona virus)
(C) directly proportional to the concentration of CO
(C) is an acute form of asthma
in the medium
(D) affects non-vegetarians much faster than the
(D) independent of the concentration of CO in the
vegetarians. medium.

2. Which of the following match is correct ? [2007] 7. What is the oxidation state of iron in haemoglobin ?
(A) Emphysema : reduction of surface area of al- [2013]
veoli and bronchi (A) Fe –
(B) Fe 2+

(B) Pneumonia : occupational disease with asbes- (C) Fe 3+

(D) Fe4+
tos
8. Carbon dioxide (CO2) diffuses into blood from tis-
(C) Silicosis : inflammation of alveoli sue site and passes to alveolar site in the form of
(D) Asthma : excessive secretion of bronchial mu- [2013]
cus (A) bicarbonate; 70%
(B) bicarbonate; 20 – 25%
3. When a man inhales air containing normal concen-
(C) carbaminohaemoglobin; 60 – 70%
tration of O2 as well as CO he suffers from suffoca-
tion because [2008] (D) carbaminohaemoglobin; 7%

(A) Co reacts with O2 reducing its percentage in air 9. Hiccups can be best described as [2015]
(B) haemoglobin combines with CO instead of O2 (A) forceful sudden expiration.
and forms carboxyhaemoglobin (B) forceful contraction of intercostal muscles dur-
(C) CO affects diaphragm and intercostal muscles ing deep breathing.
(D) CO affects the nerves of the lungs. (C) vibration of the soft palate during breathing while
sleeping.
4. Respiration is controlled by [2009] (D) jerky incomplete inspiration.
(A) medulla oblongata (B) cerebellum
(C) hypothalamus (D) cerebrum 10. The volume of ‘anatomical dead space’ air is nor-
mally [2016]
5. Chemosensitive area of respiratory centre in me- (A) 230 mL (B) 210 mL
dulla is affected by [2010]
(C) 190 mL (D) 150 mL
(A) less CO2 and H+ ions
(B) less O2 and H+ ions
11. O2 dissociation curve is plotted between pO2 and
(C) excess CO2 and H+ ions [2018]
(D) excess O2 and H+ ions. (A) % Hb saturation (B) pCO2
(C) Hb concentration (D) RBC / mm3 of blood

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 BREATHING & EXCHANGE OF GASES
Statement based question : - 15. Assertion : Extra oxygen consumption in human
Each of the questions given below consist of body is known as oxygen debt. [2012]
Assertion and Reason. Use the following Key to Reason : The extra oxygen is required by the body
choose the appropriate answer. to oxidise the accumulated lactic acid produced dur-
(A) If both Assertion and Reason are correct, and ing strenuous exercise.
Reason is the correct explanation of Assertion.
(B) If both Assertion and Reason are correct but Reason 16. Assertion :O2 easily diffuses from alveoli to tissues
is not the correct explanation of Assertion. and CO2 from tissue to alveoli. [2018]
Reason : Alveoli is 2-celled thick and capillaries are
(C) If Assertion is correct but Reason is incorrect. thin walled.
(D) If Assertion is false but Reason is correct.

12. Assertion : Many visitors to the hills suffer from

skin and respiratory allergy problems. [2003]
Reason : Conifer trees produce a large quantity of
wind-borne pollen grains.
13. Assertion : Ciliated epithelium is present in the in-
ner lining of trachea and large bronchi. [2008]
Reason : Ciliary movement propel the mucus and
foreign particle towards the larynx. ,

14. Assertion : Emphysema is a chronic disorder in

which alveolar walls ar damaged. [2010]
Reason : Emphysema is closely related to cigarette
smoking.

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 BREATHING & EXCHANGE OF GASES

ANSWER KEY

EXERCISE : PART - 1
1. A 2. D 3. D 4. A 5. C 6. A 7. D 8. A 9. C 10. C 11. A 12. B 13. B
14. B 15. B 16. D 17. A 18. B 19. C 20. B

PART - 2
1. B 2. A 3. B 4. A 5. C 6. B 7. B 8. A 9. D 10. D 11. A 12. A 13. A
14. A 15. A 16. C

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BIOLOGY FOR NEET & AIIMS

HINTS & SOLUTIONS

EXERCISE
P-1 (NEET/AIPMT)
1. (A) 5. (C) Inspiratory capacity (IC) is the maximum amount
of air that can be inspired after a normal expiration,
2. (D) Vital capacity is the sum of inspiratory reserve IC = TV + IRV. It is 3500 mL in adult male and 2400
volume, tidal volume and expiratory reserve vol- mL in adult female.
ume. It is about 4800 mL. Residual Volume (RV) is the amount of air remaining
Total lung capacity is the sum of cital capacity and in the lungs after a forced exhalation. Its average
residual volume, i.e., vital capacity of our lungs is value is 1200 mL and 1100 mL in adult male and
total lung capacity minus residual volume. female respectively.
Tidal volume is the amount of air which normally
passes into and out of the lungs during each cycle 6. (A) Option (a) is correctly mentioned as alveoli which
of quite breathing. It is about 800 mL in adult per- are the primary sites of exchange of gases. The ex-
son. change of gases (O2 and CO2) between the alveoli
and the blood occurs by simple diffusion.
3. (D) Haemoglobin is the protein that makes red blood
corpuscles appear red, binds easily and reversibly 7. (D) The epiglottis is a flap that is made of elastic
with oxygen. Normal values for haemoglobin are cartilage tissue covered with a mucous membrane
14-20 g/100 mL of blood in infants, 13 - 18 g /100 mL
in adult male and 12-16 g/100 mL in adult females.
Foetal red blood cells are not sickle-shaped even in
that destined to have sickle-cell anaemia, i.e. hae-
moglobin of foetus has higher affinity of oxygen
that that an adult.
4. (A) When a person moves to higher altitudes, the
pO2 and total atmospheric pressure decrease. Hy-
poxia stimulates the Juxtaglomerular cells of the kid-
ney to release erythropoeitin hormone which stimu-
lates erythropoesis in bone marrow causing poly-
cythemia (increase in RCBs production). Hypoxia
will also increase breathing rate. Initially the size of
RBCs will also increase but with increase in number
of RBCs, the size of RBCs becomes normal.

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BIOLOGY FOR NEET & AIIMS
attached to the entrance of the larynx. It prevents This difference allows passive diffusion of O2 from
the entry of food into the larynx and directs it to the air filled in the lungs to the blood vessels of lung
oesophagus. alveoli.
Due to the improper movement of epiglottis, one
14. (C)Lungs do not collapse breaths and some air al-
may suddenly start coughing while swallowing
ways remains in the lungs which can be never ex-
some food.
pelled because there is a negative intrapleural pres-
8. (A) As a person moves up a hill the pO2 and total sure pulling at the lung walls. Alveoli are basic func-
atmospheric pressure decreases. Decrease in pO2 tional unit of lungs. The outer alveolar wall surface
due to the increasing altitude, stimulates the Juxta- has cells which DPPC also called as lipid surfac-
glomerular cells of kidney to secrete erythropoeitin tant.
hormone which increases the number of RBCs (poly- The surfactant expands the alveoli due to which
cythemia) to compensate the supply of O2. At higher the negative pressure inside the alveoli increases.
altitude, haemoglobin has lower binding affinity to This prevents the alveoli from collapsing. Since, in
O2 because the primary factor responsible for bind- this questionboth options (a) and (b) are correct
ing is pO2 which decreases at higher altitude. and option (b) provides more appropriate explana-
tion therefore, it must be chosen.
9. (C) Irritating gases, fumes, dusts, etc., present in
the work place result in lung disorders. This is be- 15. (B) Reduction in pH blood, i.e. increase in acidity
cause the defence mechanism of the body cannot favours the dissociation of oxyhaemoglobin thereby
fully cope with this situation of so much dust. Long giving upmore O2. When this phenomenon occurs
exposure can give rise to inflamation leading to fi- due to increase in CO2 concentration then it is called
brosis (proliferation of fibrous tissue) and thus caus- Bohr effect.
ing serious lung damage.
16. (D) Emphysema is characterised by inflation or dis-
10. (C) C-Alveoli are thin-walled vascular bag-like struc- tension of alveoli by dissolution of wall of the two
tures for exchange of gases. A - trachea or wind adjacent lung alveoli. It generally occurs due to
pipe is an air conducting tube through which trans- chronic cigarette smoking.
port of gases takes place B - pleural membrane is
double layered which reduces friction on the lung 17. (A) In lungs, even after the most forceful expiration,
surface. D-diaphragm is involved in the inspiration some of the volume of air remains. This volume is
and expiration process of breathing. termed Residual Volume(RV). Due to this, lungs do
not collapse even after the most forceful expiration.
11. (A) This largest fraction of carbon dioxide, i.e. about RV is about 1100 mL - 1200 mL.
70% is converted to bicarbonates (HCO3–) and trans- 18. (B) Tidal volume = 500 ml
ported in the plasma. Inspiratory Reserve Volume = 2500 - 3000 ml
Carbonic Carbonic
ZZZZZX
CO 2  H 2O YZZZZZ ZZZZZX
H 2 CO3 YZZZZZ HCO3  H  Expiratory Reserve Volume = 1000 - 1100 ml
Anhydrase Anhydrase
Residual Volume = 1100 -1200 ml
About –23% of CO2 is carried by haemoglobin as
carbamiohaemoglobin 19. (C) Asthma is difficulty in breathing due to inflam-
CO2 + Hb (haemoglobin) U HbCO3 mation of bronchi and bronchioles.
Carbo amino haemoglobin In Emphysema, alveolar walls are damaged due to
which respiratory surface is decreased.
12. (B) Empysema is a chronic respiratory disease
20. (B) Silicosis is an occupational Respiratory disor-
where there is over-inflation of the air sacs (alveoli)
der (due to prolonged inhalation of silica dust), lead-
in the lung, causing a decrease in lung function and
ing to fibrosis.
often, breathlessness in the disease, the alveolar
walls are damaged leading to drastic reduction in
gas exchange.

13. (B) The partial pressureof oxygen (pO2) in alveoli

of lungs is 104 mm Hg, which is more than that of
blood in the blood capillaries of lung alveoli (40 mm
Hg).

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 BREATHING & EXCHANGE OF GASES
EXERCISE
for this regulation. A chemosensitive area is situ-
P-2 (AIIMS) ated adjacent to the rhythm centre which is highly
sensitive to CO2 and hydrogen ions. Increase in
1. (B) SARS is caused by a human coronavirus. It is a these substances can activate this centre, which in
new member of influenza virus family which is con- turn can signal the rhythm centre to make neces-
sidered as a mutant form of influenza virus. It spread sary adjustments in the respiratory process by
through contact, respiratory secretions & cock- which these substances can be eliminated.
roaches. Symptoms include cold dry cough, head-
ache, loss of appetite, high temperature, fever and 6. (B) Bohr effect is the phenomenon whereby the
hypoxia at later stage followed by muscular stiff- affinity of the respiratory pigment of the blood for
ness, malaise (feeling of bodily discomfort, but with- oxygen is reduced, and the level of carbon dioxide
out clear signs of a particular illness). is increased. This facilitates gaseous exchange,
because more oxygen is released in the tissues
2. (A) Emphysema means air in the tissues. In pulmo- where the amount of carbon dioxide is rising due to
nary emphysema the air sacs (alveoli) of the lungs metabolic activity. At the same time, more oxygen is
are enlarged and damaged, which reduces the sur- taken up at the lungs where the amount of carbon
face area for the exchange of oxygen and carbon dioxide is low.
dioxide. Severe emphysema causes breathlessness,
7. (B) RBCs contain haemoglobin. It has four polypep-
which is made worse by infections. Major causes
tide chains and four haem groups attached to it or 4
are cigarette smoking and the inhalation of other
atoms of iron in ferrous form (Fe2+), thus it can react
smoke or toxic substances over a period of time.
with 4 molecules of oxygen to form oxyhaemoglobin.
Pneumonia is inflammation of the lung caused by
bacteria, in which the air sacs (alveoli) become filled 8. (A) During transport, most of CO2 is passed into
with inflammatory cells and the lung becomes solid. erythrocytes. A major part (nearly 70%) forms car-
The symptoms include those of any infection (fe- bonic acid on reacting with water in erythrocytes
ver, malaise, headaches, etc.), together with cough and then form bicarbonate.
and chest pain. Silicosis, a lung disease, is a form of
pneumoconiosis produced by inhaling silica dust
particles. It affects workers in hard-rock mining and
A seizable portion of bicarbonate passes out into
tunnelling, quarrying, stone dressing, sand blast-
the plasma and changes ionic balance between the
ing, and boiler scaling. Silica stimulates fibrosis of
plasma & the erythrocytes. To restore the ionic bal-
lung tissue, which produces progressive breath-
ance, the chloride ions diffuse from the plasma into
lessness and considerably increases susceptibility
the erythrocytes. This movement of chloride ions
to tuberculosis. Asthma is the condition of sub-
is known as Hamburger’s phenomenon.
jects with widespread narrowing of the bronchial
airways, which changes in severity over short peri- 9. (D) A hiccup can be described as a jerky incomplete
ods of time (either spontaneously or under treat- inspiration. It is an involuntary contraction of the
ment) and leads to cough, wheezing, and difficulty diaphragm that may repeat several times per minute.
in breathing. In medical terms, it is known as synchronous dia-
phragmatic flutter (SDF).
3. (B) Affinity of carbon monoxide for haemoglobin is 10. (D)
200 times more than oxygen. At 0.5 partial pressure,
CO combines with 50% of haemoglobin. It pro-
duces a relatively stable compound called carboxy-
haemoglobin. This cause low supply of oxygen to
the body which is characterised by headache, dizzi-
ness, nausea, etc.
4. (A)
5. (C) Human beings have a significant ability to main- 11.
tain and moderate the respiratory rhythm to suit the
demands of the body tissues. A specialised centre
present in the medulla region of the brain called
respiratory rhythm centre is primarily responsible

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BIOLOGY FOR NEET & AIIMS

12. (A) Some trees of hills like oak, ash, elm, hickory,
pecan and mountain cedar produce allergic pollen
grains which cause allergy to people visiting the
hills and thus they suffer from respiratory and skin
allergy problems. The signs and symptoms of pol-
len allergy are
– sneezing
– itching eyes, nose and throat
– dark circles under the eyes caused by restricted
blood flow near the sinuses
– watering eyes
– conjunctivities
Conifer trees produce a large quantity of wind borne
pollen grains because many pollen grains are de-
stroyed in the process of pollination done by wind.

13. (A) Trachea and large bronchi are lined by

pseudostratified ciliated columnar epithelium bear-
ing glandular cells (mucous gland). The secretion
of mucous glands keeps the walls of trachea and
large bronchi moist and traps dust particles which
enter with the air. The vibratile cilia of the epithe-
lium then carry the mucous containing dust par-
ticles upto the larynx where they can be spitted out.

14. (A) Affinity of carbon monoxide for haemoglobin is

200 times more than oxygen. At 0.5 partial pressure,
CO combines with 50% of haemoglobin. It pro-
duces a relatively stable compound called carboxy-
haemoglobin. This cause low supply of oxygen to
the body which is characterised by headache, dizzi-
ness, nausea, etc.

15. (A) During strenous exercise, the muscle does not

get sufficient oxygen to meet its energy needs im-
mediately. So, it contracts anaerobically and accu-
mulates lactic acid. During recovery, the oxygen
consumption of the muscle far exceeds than that in
the resting state. The extra oxygen consumed dur-
ing recovery is called oxygen debt of the muscle.
16. (C)

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3PVHI
8PSL
3PVHI
8PSL
3PVHI
8PSL