Chapter 6 Intext Questions

Page Number: 95

Question 1Why is diffusion insufficient to meet the oxygen requirements of

multicellular organisms like humans ?
Answer: In multicellular organisms like humans, all the body cells are not in direct
contact with the surrounding environment. Therefore, every cell of the body will not
get oxygen as per need by the process of diffusion from the environment. Therefore
diffusion is insufficient to meet the oxygen requirements of multicellular organisms.

Question 2 What criteria do we use to decide whether something is alive ?

Answer: The main criteria used to decide whether something is alive are breathing
and respiration. However, living beings also show growth and movement.

Question 3 What are outside raw materials used by an organism ?

Answer: Any organism uses organic molecules as raw material. Heteroptrophs use
food and autotrophs use carbon dioxide, minerals, water and all organisms use
oxygen (for respiration) as raw materials.

Question 4 What processes would you consider essential for maintaining life ?
Answer: Processes essential for maintaining life are :
(i) Nutrition (ii) Respiration (iii) Transportation (iv) Excretion

Page Number: 101

Question 1 What are the differences between autotrophic nutrition and

heterotrophic nutrition ?
Answer:

Autotrophic nutrition Heterotrophic nutrition

(i) In this mode of nutrition an organism (i) In this mode of nutrition an organism

makes or synthesizes its own food. cannot make or synthesize its own food

Organisms use simple inorganic

(ii) Organisms cannot make their own food
materials like carbon dioxide and water
from simple inorganic matter and depend
and synthesise their food in presence of
on other organisms for their food.
sunlight.
(iii) All green plants and some algae (iii) All the animals, most bacteria and

undergo this mode of nutrition. fungi undergo this mode of nutrition.

Question 2 Where do plants get each of the raw materials required for
photosynthesis ?
Answer: (i) Carbon dioxide : Plants get carbon dioxide from the
environment/atmosphere through stomata.
(ii) Water : Plants absorb water from the soil through roots and transport to leaves.
(iii) Sunlight : Plants get sunlight from the sun.
(iv) Chlorophyll : It is present in chloroplast found in green leaves and green parts of
plants.

Question 3 What is the role of the acid in our stomach ?

Answer: Role of acid in our stomach is :
(i) To make acidic medium which is necessary for the activation of the enzyme
pepsin.
(ii) To kill bacteria which the food may contain.

Question 4 What is the function of digestive enzymes ?

Answer: The food we eat is complex in nature, i.e., it contains complex molecules.
Digestive enzymes break down these complex molecules into smaller simpler
molecules so that they can be absorbed by the walls of the intestine.

Question 5 How is the small intestine designed to absorb digested food ?

Answer: The small intestine is designed to provide maximum area for absorption of
digested food and its transfer into the blood for its circulation into the body. For this
the inner lining of the small intestine has numerous finger-like projections called
villi. The villi are richly supplied with blood vessels which take the absorbed food to
each and every cell of the body

Page Number: 105

Question 1 What advantage over an aquatic organism does a terrestrial organism

have with regard to obtaining oxygen for respiration ?
Answer: Aquatic organisms use oxygen dissolved in surrounding water. Since air
dissolved in water has fairly low concentration of oxygen, the aquatic organisms
have much faster rate of breathing.
Terrestrial organisms take oxygen from the oxygen-rich atmosphere through
respiratory organs. Hence, they have much less breathing rate than aquatic
organisms.

Question 2 What are the different ways in which glucose is oxidised to provide
energy in various organisms ?
Answer: First step of breakdown of glucose (6 carbon molecules) takes place in the
cytoplasm of cells of all organisms. This process yields a three carbon molecule
compound called pyruvate.
Further break down of pyruvate takes place in different ways in different organisms.

(i) Anaerobic respiration : The anaerobic respiration in plants (like yeast) produces
ethanol and carbon dioxide as end products.
(ii) Aerobic respiration : In aerobic respiration break down of pyruvate takes place in
presence of oxygen to give rise three molecules of carbon dioxide and water. The
release of energy in aerobic respiration is much more than in anaerobic respiration.
(iii) Lack of oxygen : Sometimes, when there is lack of oxygen especially during
physical exercise, in our muscles, pyruvate is converted into lactic acid (3 carbon
molecule compound). Formation of lactic acid in muscles causes cramp.

Question 3 How is oxygen and carbon dioxide transported in human beings ?

Answer: (i) Transport of oxygen : Haemoglobin present in the blood takes up the
oxygen from the air in the lungs. It carries the oxygen to tissues which are deficient
in oxygen before releasing it.
(ii) Transport of carbon dioxide : Carbon dioxide is more soluble in water. Therefore,
it is mostly transported from body tissues in the dissolved form in our blood plasma
to lungs. Here it diffuses from blood to air in the lungs.

Question 4 How are the lungs designed in human beings to maximise the area for
exchange of gases ?
Answer: Within the lungs, the air passage divides into smaller and smaller tubes,
called bronchi which in turn form bronchioles. The bronchioles terminate in balloon-
like structures, called alveoli. The alveoli present in the lungs provide maximum
surface for exchange of gases. The alveoli have vary thin walls and contain an
extensive network of blood vessels to facilitate exchange of gases.

Page Number: 110

Question 1 What are the components of the transport system in human beings ?
What are the functions of these components ?
Answer: The transport system (circulatory system) in human beings mainly consists
of heart, blood and blood vessels.

(i) Function of heart : The heart receives deoxygenated blood from the body parts
and pumps it to lungs for enriching with oxygen. It receives purified blood from
lungs and pumps it around the body.
(ii) Function of blood : Blood transports oxygen, carbon dioxide, digested food,
hormones and nitrogeneous waste like urea. It also protects the body from diseases
and regulates the body temperature.
(iii) Function of blood vessels : The blood pushed by the heart flows through the
blood vessels (arteries, veins and capillaries) and also comes back to the heart
through them.

Question 2 Why is it necessary to separate oxygenated and deoxygenated blood in

mammals and birds ?
Answer: Separation of oxygenated and deoxygenated blood allows good supply of
oxygen to the body. This system is useful in animals that have high energy
requirement. Mammals and birds constantly need oxygen to get energy to maintain
their body temperature constant.

Question 3 What are the components of the transport system in highly organised
plants?
Answer: In highly organised plants there are two conducting tissues xylem and
phloem.
Xylem consists of vessels, tracheids and other xylem tissues. The interconnected
vessels and tracheids form a continuous system of water conducting channels
reaching all parts of the plant. Xylem carries water and minerals.
Phloem conducts soluble products of photosynthesis from leaves to different parts
of the plant body.

Question 4 How are water and minerals transport in plants ? [AICBSE 2015]
Answer: The roots of a plant have hair called root hair.
The root hair are directly in contact with the film of water in between the soil
particles. Water and dissolved minerals get into the root hair by the process of
diffusion. The water and minerals absorbed by the root hair from the soil pass from
cell to cell by osmosis through the epidermis, root cortex, endodermis and reach the
root xylem.
The xylem vessels of the root of the plant are connected to the xylem vessels of its
stem.
Therefore the water containing dissolved minerals enters the root xylem vessels into
stem xylem vessels. The xylem vessels of the stem branch into the leaves of the
plants. So, the water and minerals carried by the xylem vessels in the stem reach the
leaves through the branched xylem vessels which enter from the petiole (stalk of the
leaf) into each and every part of the leaf. Thus the water and minerals from the soil
reach through the root and stem to the leaves of the plants. Evaporation of water
molecules from the cells of a leaf creates a suction which pulls water from the
xylem cells of roots. The loss of water in the form of vapour from the aerial parts of
the plant is known as transpiration.

Question 5 How is food transported in plants ?

Answer: The movement of food in phloem (or translocation) takes place by utilizing
energy. The sugar (food) made in leaves is loaded into the sieve tubes of phloem
tissue by using energy from ATR Water now enters the sieve tubes containing sugar
by the process of osmosis due to which the pressure in the phloem tissue rises.
This high pressure produced in the phloem tissue moves the food to all parts of the
plant having less pressure in their tissues. This allows the phloem to transport food
according to the needs of the plant.

Page Number: 112

Question 1 Describe the structure and functions of nephrons.

Answer: Structure of nephron : Each nephron is composed of two parts. First one is
a cup-shaped bag at its upper end which is called Bowman’s capsule.
The Bowman’s capsule contains a bundle of blood capillaries which is called
glomerulus. One end of the glomerulus is attached to the renal artery which brings
the impure blood containing the urea waste into it. These impurities are filtered. The
other part of the nephron is coiled. In this part, the substances like sugar (glucose),
amino acid, ions and excess water which are required by the body, are reabsorbed.
The substance remained in the nephron is mainly urine containing dissolved urea in
water which is expelled from the body through urethra from time to time.

Functions of nephron : Filtration of blood takes place in Bowman’s capsule from the
capillaries of glomerulus. The filtrate passes into the tubular part of the nephron.
This filtrate contains glucose, amino acids, urea, uric acid, salts and water.
Reabsorption : As the filtrate flows along the tubule, useful substances such as
glucose, amino acids, salts and water are selectively reabsorbed into the blood by
capillaries surrounding the nephron tubule.
Urine : The filtrate which remained after reabsorption is called urine. Urine contains
dissolved nitrogenous waste like urea and uric acid, excess salts and water. Urine is
collected from nephrons to carry it to the ureter from where it passes into urinary
bladder.

Question 2 What are the methods used by plants to get rid of excretory products ?
Answer:
(i) The plants get rid of gaseous products-through stomata in leaves and lenticels in
stems.
(ii) The plants get rid of stored solid and liquid waste by the shedding off leaves,
peeling off bark and felling off fruits.
(iii) The plants get rid of wastes by secreting them in the form of gums and resins.
(iv) Plants also excrete some waste substances into the soil around them.

Question 3 How is the amount of urine produced regulated ?

Answer: The amount of urine is regulated by kidney. It depends on the quantity of
excess water and wastes dissolved in water.

(i) Quantity of water : When water is abundant in the body tissues, large quantities of
dilute urine is excreted out. When water is less in quantity in the body tissues, a
small quantity of concentrate urine is excreted.
(ii) Quantity of dissolved wastes : Dissolved wastes, especially nitrogenous wastes,
like urea and uric acid and salts are excreted from the body. When there is more
quantity of dissolved wastes in the body, more quantity of water is required to
excrete them. Therefore, the amount of urine produced increases.
(iii) Hormones : The amount of urine produced is also regulated by certain
hormones which control the movement of water and Na+ ions in and out of the
nephrons.

Chapter 6 Textbook Chapter End Questions

Question 1 The kidneys in human beings are a part of the system for
(i) nutrition (ii) respiration (iii) excretion (iv) transportation
Answer:
(iii) Excretion

Question 2 The xylem in plants are responsible for

(i) transport of water (ii) transport of food (iii) transport of amino acids (iv) transport
of oxygen
Answer: (i) Transport of water

Question 3 The autotrophic mode of nutrition requires

(i) carbon dioxide and water (ii) chlorophyll (iii) sunlight (iv) all of the above
Answer: (iv) All of the above

Question 4 The breakdown of pyruvate to give carbon dioxide, water and energy
takes place in
(i) cytoplasm (ii) mitochondria (iii) chloroplast (iv) nucleus
Answer: (ii) Mitochondria

Question 5 How are fats digested in our bodies ? Where does this process take
place ?
Answer: Digestion of fats takes place in the small intestine.
Bile juice secreted by the liver poured in the intestine along with pancreatic juice.
The bile salts present in the bile juice emulsify fhe large globules of fats. Therefore,
by enulsification large globules break down into fine globules to provide larger
surface area to act upon by the enzymes.
Lipase enzyme present in the pancreatic juice causes break down of emulsified fats.
Glands present in the wall of small intestine secrete intestinal juice which contains
lipase enzyme that converts fats into fatty acids and glycerol.

Question 6 What is the role of saliva in the digestion of food ?

Answer: Saliva contains salivary amylase enzyme that breaks down starch into
sugars like maltose.
Saliva keeps the mouth cavity clean and moistens the food that help in chewing and
breaking down the big pieces of food into smaller ones.

Question 7 What are the necessary conditions for autotrophic nutrition and what are
its by-products ?
Answer: Necessary conditions for autotrophic nutrition :
(i) Presence of chlorophyll in the living cells.
(if) Provision of supply of water to green plants or cells of the plant.
(iii) Sufficient sunlight.
(iv) Sufficient supply of carbon dioxide.
By-product of auto tropic nutrition is oxygen.

Question 8 What are the differences between aerobic and anaerobic respiration ?
Name some organisms that use the anaerobic mode of respiration.
Answer:

Aerobic respiration Anaerobic respiration

1. It takes place in the presence of

1. It takes place in the absence of oxygen.
oxygen.

2. Complete breakdown of food 2. Partial breakdown of food occurs in

occurs in aerobic respiration. anaerobic respiration.

3. The end products in anaerobic respiration

3. The end products in aerobic
may be ethanol and carbon dioxide (as in
respiration are carbon dioxide and
yeast plants) or lactic acid (as in animal
water.
muscles).

4. Aerobic respiration produces a 4. Much less energy is produced in anaerobic

considerable amount of energy. respiration.

Some organisms which use anaerobic respiration are yeast, bacteria etc.

Question 9 How are the alveoli designed to maximise the exchange of gases ?
Answer: (i) The alveoli are thin walled and richly supplied with a network of blood
vessels to facilitate exchange of gases between blood and the air filled in alveoli.
(ii) Alveoli have balloon-like structure. Hence, provide maximum surface for
exchange of gases.

Question 10 What would be the consequences of a deficiency of haemoglobin in our

bodies?
Answer: Due to the deficiency of haemoglobin in blood, its oxygen carrying capacity
decreases. As a result the production of energy by oxidation will become slower.
Therefore, one would fall sick and would feel fatigue most of the time.

Question 11 Describe double circulation of blood in human beings. Why is it

necessary ?
Answer: In our heart blood enters twice and also pumped out twice from the heart.
The deoxygenated blood from the body is brought to the right atrium through vena
cava from where it is sent to right ventricle. From right ventricle, the blood is
pumped to the lungs for oxygenation through pulmonary artery. The oxygenated
blood from lungs again enters the left atrium of the heart through pulmonary veins.
From left atrium it is send to left ventricle, from where this oxygenated blood is
pumped to different parts of body through the arteries. In this way the blood flows
through the heart twice, that’s why it is called ‘double circulation’.

Necessity of double circulation: The right side and the left side of the human heart
are useful to keep deoxygenated and oxygenated blood from mixing. This type of
separation of oxygenated and deoxygenated blood ensures a highly efficient supply
of oxygen to the body. This is useful in case of humans who constantly need energy
to maintain their body temperature.

Question 12 What are the differences between the transport of materials in xylem
and phloem ?
Answer:

Xylem Phloem

1. Xylem conducts water and dissolved 1. Phloem conducts prepared food

minerals from roots to leaves and other material from leaves to other parts of

parts. plant in dissolved form.

2. In xylem, the transport of material takes 2. In phloem, transport of material takes

place through vessels and tracheids place through sieve tubes with the help of

which are dead tissues. companion cells, which are living cells.
3. In xylem upward movement of water 3. In translocation, material is transferred

and dissolved minerals is mainly achieved into phloem tissue using energy from

by transpiration pull. It is caused due to ATP. This increases the osmotic pressure

suction created by evaporation of water that moves the material in the phloem to

molecules from the cells of a leaf. tissues which have less pressure

Question 13 Compare the functioning of alveoli in the lungs and nephrons in the
kidneys with respect to their structure and functioning.
Answer:

Alveoli Nephron

1. Alveoli are functional unit of lungs. 1. Nephrons are functional unit of kidney.

2. A mature lung has about 30 crore

2. A kidney has about 10 lakh nephrons.
alveoli.

3. Alveoli provide a wide surface for 3. The surface area of a nephron is not

gaseous exchange. much more.

4. The exchange of O2 and CO2 takes 4. The Bowman’s capsule in nephron

place through the network of capillaries in regulates the concentration of water and

alveoli. salts.

Question 1 How are fats digested in our bodies? Where does this process take
place?
Solution: The small intestine is the site of the complete digestion of carbohydrates,
proteins and fats. It receives the secretions of the liver and pancreas for this
purpose. The food coming from the stomach is acidic and has to be made alkaline
for the pancreatic enzymes to act. Bile juice from the liver accomplishes this in
addition to acting on fats. Fats are present in the intestine in the form of large
globules, which make it difficult for enzymes to act on them. Bile salts break them
down into smaller globules increasing the efficiency of enzyme action. The
pancreas secretes pancreatic juice, which contains enzymes like trypsin for
digesting proteins and lipase for breaking down emulsified fats. The walls of the
small intestine contain glands, which secrete intestinal juice. The enzymes present
in it finally convert the proteins to amino acids, complex carbohydrates into glucose
and fats into fatty acids and glycerol.

Question 2 What is the role of saliva in the digestion of food?

Solution: When we eat something we like, our mouth ‘waters’. This is actually not
only water, but also a fluid called saliva secreted by the salivary glands. Another
aspect of the food we ingest is its complex nature. If it is to be absorbed from the
alimentary canal, it has to be broken into smaller molecules. This is done with the
help of biological catalysts called enzymes. The saliva contains an enzyme called
salivary amylase that breaks down starch, which is a complex molecule to give
sugar. The food is mixed thoroughly with saliva and moved around the mouth while
chewing by the muscular tongue.

Question 3 What are the necessary conditions for autotrophic nutrition and what are
its byproducts?
Solution: Carbon and energy requirements of the autotrophic organism are fulfilled
by photosynthesis. It is the process by which autotrophs take in substances from
the outside and convert them into stored forms of energy. This material is taken in
the form of carbon dioxide and water, which is converted into carbohydrates in the
presence of sunlight and chlorophyll. Carbohydrates are utilised for providing energy
to the plant. The carbohydrates, which are not used immediately, are stored in the
form of starch, which serves as the internal energy reserve to be used as and when
required by the plant.

Question 4 What are the differences between aerobic and anaerobic respiration?
Name some organisms that use the anaerobic mode of respiration.
Solution: The food material taken in during the process of nutrition is used in cells
to provide energy for various life processes. Diverse organisms do this in different
ways – some use oxygen to breakdown glucose completely into carbon dioxide and
water; some use other pathways that do not involve oxygen. In all cases, the first
step is the breakdown of glucose, a six-carbon molecule, into a three-carbon
molecule called pyruvate. This process takes place in the cytoplasm. Further, the
pyruvate may be converted into ethanol and carbon dioxide. This process takes
place in yeast during fermentation. Since this process takes place in the absence of
air (oxygen), it is called anaerobic respiration. Breakdown of pyruvate using oxygen
takes place in the mitochondria. This process breaks up the three-carbon pyruvate
molecule to give three molecules of carbon dioxide. The other product is water.
Since this process takes place in the presence of air (oxygen), it is called aerobic
respiration. The release of energy in this aerobic process is a lot greater than in the
anaerobic process.
Question 5 How are the alveoli designed to maximise the exchange of gases?
Solution: Within the lungs, the passage divides into smaller and smaller tubes, which
finally terminate in balloon-like structures, which are called alveoli. The alveoli
provide a surface where the exchange of gases can take place. The walls of the
alveoli contain an extensive network of blood vessels. As we have seen in earlier
years, when we breathe in, we lift our ribs and flatten our diaphragm, and the chest
cavity becomes larger as a result. Because of this, air is sucked into the lungs and
fills the expanded alveoli. The blood brings carbon dioxide from the rest of the body
for release into the alveoli, and the oxygen in the alveolar air is taken up by blood in
the alveolar blood vessels to be transported to all the cells in the body. During the
breathing cycle, when air is taken in and let out, the lungs always contain a residual
volume of air so that there is sufficient time for oxygen to be absorbed and for the
carbon dioxide to be released.

Question 6 Describe double circulation in human beings. Why is it necessary?

Solution: The double circulatory system of blood flow refers to the separate
systems of pulmonary circulation and the systemic circulation.
The adult human heart consists of two separated pumps, the right side with the
right atrium and ventricle which pumps deoxygenated blood into the pulmonary
circulation.
The oxygenated blood re-enters the left side of the heart through the pulmonary vein
into the left atrium and passes to the left ventricle where it is pumped to the rest of
the body. This part of the circulation is called as systemic circulation. This type of
circulation is called double circulation. The advantage of a double circulatory
system is that blood can be pumped to the rest of the body at a higher pressure.

Multiple Choice Questions (MCQs) [1 Mark each]

Question 1. Yeast respires anaerobically using sugar as a substrate. Out of the

options given below, choose the correct combination of condition and product?

Condition Product

(a) Aerobic Alcohol

(b) Aerobic Lactic acid

(c) Anaerobic Alcohol

(d) Anaerobic Lactic acid

Answer: (c) Under an aerobic condition, yeast respires and converts glucose to
alcohol and CO2.
Question 2. The table shows the percentage composition of four samples of air.
Which sample could have been breathed out by a person after vigorous exercise?

Water
Samples Oxygen Carbondioxide
Vapour

(a) 16 0.3 Saturated

(b) 16 4 Saturated

(c) 21 0.03 Trace

(d) 21 3 Trace

Answer: (b) This is because rapid aerobic respiration occurs – during vigorous
exercise in order to obtain more energy.

Question 3. Cramps caused during sudden activities are due to the formation of
(a) lactic acid (b) acetic acid (c) excess of water (d) ethanol
Answer: (a) Lactic acid is formed by the breakdown of pyruvate when oxygen is
insufficient in muscles instead of forming C02 and water. Accumulation of excess
lactic acid in the muscles causes cramps.

Question 4. Which of the following plays nose like function in plants?

(a) Flower (b) Phloem (c) Stomata (d) Chlorophyll
Answer: (c) Stomata are pores which help in the passage of air in the plants.

Question 5. Which changes occur when a person breathe in deeply?

Diaphragm External Intercostal

Muscle Muscles

(a) Contracts Contract

(b) Contracts No change

(c) Relaxes Contract

(d) Relaxes Relax

Answer: (a) When a person breathes deeply the external intercostal muscles
contract causing the rib cage to swing up and out. Also, the diaphragm contracts
and flattens causing the thoracic cavity to increase in volume and decrease in
pressure.

Question 6. The diagram given above shows part of the lining of the human trachea.
What is the function of X?
(a) Gaseous exchange (b) Mucus removal (c) Phagocytosis (d) Secretion of mucus
Answer: (b) The cilia (X) of the cells lining the air passages move in a sweeping
motion to keep the air passages clean. The constant action of these cilia carry
mucus and debris upward into the pharynx where they are swallowed.

Question 7. The table given below shows the percentage composition of a gas in
inspired and in expired air.

%Composition

Inspired Air Expired Air

21.0 16.0

What is the gas?

(a) Carbon dioxide (b) Nitrogen (c) Oxygen (d) Water vapour
Answer: (c) The gas is oxygen as atmospheric air has approximately 21% of oxygen