WEEK TOPIC

1 DIGESTION
2 FEEDING MECHANISM
3 DENTITION
4 CELLULAR RESPIRATION
5 RESPIRATORY SYSTEM
6 EXCRETION
7 EXCRETORY SYSTEM
8 GROWTH
9 CELL REACTION TO ITS
ENVIRONMENT
(IRRITABILITY /SENSITIVITY)
1 REVISION
11 EXAMINATION
12 EXAMINATION
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WEEK ONE
DIGESTIVE SYSTEM
 Digestion is defined as the breaking down of complex food
substances [macromolecules] into simple and absorbable form
[micromolecules] for use by the animals.
Digestion generally involves two phases:
[a] Mechanical phase: This phase involves the use of teeth or
other structures to physically break down large pieces of food
into smaller pieces.
[b] Chemical phase: This phase involves digestive chemicals
called enzymes breaking down individual macromolecules of
food to yield micromolecules that can be absorbed and
distributed throughout the body. These enzymes are secreted
(produced and released) by digestive glands in the body.
The digestive System which consists of series of connected
organs is the system of the animal body that is responsible
for the process of digestion. The digestive system is also
referred to as the alimentary canal or gut and it varies from
one animal to another. Plants produce their own food
through a process called photosynthesis, and as result do not
have digestive system.

MODIFICATION OF ALIMENTARY CANAL

Alimentary canal is a tubular passage between the mouth and
the anus, including the organs through which food passes for
digestion and elimination as waste. Simple unicellular
animals such as amoeba do not have an alimentary canal.
[1] ALIMENTARY CANAL IN TAPEWORM: The tapeworm is
an endoparasite that lives in the intestine of some mammals.
It has no alimentary canal because it absorbs the digested
food from its host by simple diffusion.
[2] ALIMENTARY CANAL IN EARTHWORM: The earthworm
feeds mainly on dry vegetable found in the soil. Its
alimentary canal includes the following parts:
(a) Mouth: This is where the food is ingested (taking-in)
(b) Pharynx: mucus is secreted to lubricate the food particles
(c) Oesophagus transfers the food to the crop.
(d) Crop: store food temporarily
(e) Gizzard: food is grinded by small stones
(f) Intestine: final digestion and food absorption take place.

[3] ALIMENTARY CANAL IN GRASSHOPPER OR COCKROACH:

The grasshopper feeds mainly on green vegetables while the
cockroach feeds on household materials such as paper, food,
cloth, etc. Their alimentary canals include the following
parts:
(a) Mouth: This is surrounded by mouthparts such as
mandibles, maxillae and labium for cutting chewing food.
(b) Salivary glands: Secret enzymes in the mouth for
digestion of food
(c) Oesophagus: Serve as a muscular passage for the
swallowed food to the crop.
(d) Crop: Store food temporarily
(e) Gizzard: A muscular organ where food is grinded.
(f) Mid-gut: Consists of vascularised diverticulum for food
digestion and food absorption.
(g) Hind-gut: Consists of ileum, colon and rectum. It absorbs
water and mineral salt and shape the faeces into pellets.
(h) Anus: Exit point for the faeces out of the body.
[4] ALIMENTARY CANAL IN BIRD: Birds have relatively long
alimentary canal which provides a large surface area for the
digestion and absorption. Their alimentary canals include the
following parts:
(a) Beak: Used for picking the food into the mouth.
(b) Mouth: Birds do not have teeth.
(c) Oesophagus: The passage through which swallowed food
pass through to the crop.
(d) Crop: Store food temporarily, moistened and fermented.
(e) Proventiculus (glandular stomach): Contain glands that
secret digestive enzymes on the food
(f) Gizzard (grindular stomach): A muscular organ where
food is grinded with aid of small stones or grits.
(g) Duodenum: This is where further food digestion and food
absorption take place.
(h) Caeca and rectum: Passage for undigested food
(i) Anus (cloaca): Exit point for the faeces and urine out of
the body.
 SIMILARITES BETWEEN THE ALIMENTARY CANAL
OF GRASSHOPPER AND BIRDS
[a] They both have narrow oesophagus
[b] Crop is present in both organisms
[c] They both have muscular gizzard
[d] They both have caecum

DIFFERENCES BETWEEN THE ALIMENTARY CANAL

OF GRASSHOPPER AND BIRDS
GRASSHOPPER BIRDS
1 Tongue is absent Tongue is present
2 Mouth is modified into Mouth is modified into
mandibles and maxillae beak for picking food
for chewing
3 Absence of duodenum Presence of duodenum
4 Relatively short Relatively long
alimentary canal alimentary canal
5 Pancreas is absent Pancreas is present
[5] ALIMENTARY CANAL IN MAMMALS
A typical mammalian alimentary canal consists of the
following parts namely: mouth, pharynx, oesophagus,
stomach, small intestine, rectum and anus. All these parts can
be found in most vertebrates. However, there are
modifications of the parts of the alimentary canal in various,
animals. In some animals, a structure may be reduced or
enlarged, while in others, some parts may be absent. The
modifications reflect the various modes of feeding and types
of diet. The human alimentary canals include the following
parts:
[a] Mouth: This is where digestion starts. The human
alimentary begins in the mouth which contains the teeth,
tongue ad salivary gland.
(i) Teeth: These are used to cut and chew the food and also
expose the food for the enzyme action.
(ii) Tongue: The tongue tastes the food, aid food movement
in the mouth, allow turning and mixing of the food with
saliva, roll the food into bolus and aids swallowing of food
into the oesophagus.
(iii) Salivary gland: This secret saliva which contains ptyalin.
Ptyalin digest starch into maltose. Saliva lubricates the food,
allows easy chewing or movement of food in the mouth for
swallowing. The chewed food in the mouth is then
swallowed.
[b] Oesophagus/gullet: This is a narrow, straight tube that
connect the mouth to the stomach. The swallowed food
passes through the oesophagus by a wave-like muscular
contraction and relaxation called peristalsis.
[c] Stomach: The stomach is primarily a storage organ. The
stomach is a sac-like structure with strong muscular walls.
The muscular movement of the stomach walls enables the
mixing of the food with digestive juice and also convert the
food into a semi-liquid state called chyme. The gastric glands
in the walls of the stomach secrete gastric juice which
contains hydrochloric acid and two enzymes namely renin
and pepsin. Hydrochloric acid helps to kill some bacteria in
the stomach. Rennin curdles milk, while pepsin breaks down
protein into peptones.
[d] Small intestine: This is where most digestion, as well as
absorption of digested food occur. This narrow twisting tube
is about 6 meters in length. The intestine is divided into three
parts namely the duodenum (first section of the small
intestine) the jejunum, and finally into the ileum (the last
section of the small intestine).
The duodenum contains pancreas which secretes pancreatic
juice that contains three enzymes:
(i) Amylase convert starch to maltose
(ii) Lipase coverts fats and oils to fatty acids and glycerol
(iii) Trypsin converts proteins and peptones to polypeptides
The liver also secretes the bile which help in the digestion of
fats and oils. At the end of digestion in the duodenum, the
liquid food is called chyle.
The last and final food digestion and food absorption take
place in the ileum. The ileum secretes intestinal juice which
contains the following enzymes;
(i) Lipase converts fats and oils into fatty acids and glycerol,
(ii) Erepsin converts polypeptides to amino acids,
(iii) Maltase converts maltose to two units of glucose,
(iv) Sucrase converts sucrose to glucose and fructose,
(v) Lactase converts lactose to glucose and galatose
The small intestine’s capacity for absorption is increased by
millions of finger-like projections called villi, which line the
inner walls of the small intestine. The villi increase the
surface area of the small intestine’s lining by about 150
times, multiplying its capacity for absorption. Beneath the
villi’s single layer of cells are capillaries of the bloodstream.
The digested food passes through the capillaries to enter the
bloodstream from where it is taken to all the cells of the
body. A watery residue of indigestible food and digestive
juices remains unabsorbed. This residue leaves the ileum of
the small intestine and moves into the large intestine.
[e] Caecum and appendix: These two parts of the
alimentary canal do not have any well-known function in
human but the caecum usually contains some bacteria which
aid minor digestion of cellulose.
[f] Large intestine (colon): The large intestine forms an
inverted U over the coils of the small intestine. It starts on the
lower right-hand side of the body and ends on the lower left-
hand side. The large intestine is 1.5 to 1.8 m (5 to 6 ft) long.
The large intestine absorbs water as well as dissolve salts
from the undigested food and turn it into faeces. In addition,
bacteria in the large intestine promote the breakdown of
undigested materials and make several vitamins, notably
vitamin K, which the body needs for blood clotting.
[g] Rectum: This is where the faeces are stored until
elimination.
[h] Anus: This is the last point of the digestive system where
the undigested food is removed from the body.

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WEEK 2
FEEDING MECHANISMS
Living things feed on different type of food in different ways.
There are various modifications in the alimentary systems of
some animals which suggest that the parts are modified
according to the type of food they eat. Based on the
modification on the feeding habits of organisms, we have the
following feeding mechanisms.
[A] Absorbing mechanism: This is commonly found among
organisms that are parasites and are also wallowers. They
have no mouth, alimentary canal and feed on digested food
which is absorbed through its entire body surface from their
host. Example is the tape worm.
[B] Biting (cutting) and chewing mechanism: Organisms
with this mechanism have four different mouth parts
adapted for biting and chewing. These mouth parts include:
(i) Labrum or upper lip prevent food from fall off.
(ii) Labium or lower lip prevent food from falling off
(iii) Mandibles for cutting and chewing
(iv) Maxillae for biting food into smaller pieces
Examples of such organisms are cockroach and grasshopper.
[C] Piercing and sucking: Organisms that possess this
feeding mechanism have different modifications in their
mouth which enables them to adapt to feeding on food
through mechanism of sucking. E.g. mosquito and butterfly
possess proboscis for piercing and sucking. For mosquito, the
mouth parts altogether form a strong Stylet. Housefly
possess labella for sucking. It has the ability to convert solid
food to liquid by secretion of saliva on the solid food.
[D]Trapping and absorbing: This is common among plants
that feed on insects. They are called insectivorous or
carnivorous plants. These plants have body parts that are
modified into traps that they use to catch insects or other
small animals. They are capable of digesting the animals they
capture and absorb protein from them. Examples are
bladderwort, sundew, Venus flytrap, pitcher plant.
[E] Grinding mechanism: This is common among mammals
such as man, cattle, sheep, that which possess teeth that they
use to grind their food before swallowing. They possess
different types of teeth for chewing, grinding or cracking of
food. Mammals feed on a wide range of food such as plants
(herbivores), flesh (carnivores), both plants and flesh
(omnivorous) and dead animals (scavengers).

FEEDING HABITS
Organisms exhibit different types of feeding habits; some
examples are discussed below:
[1] Filter Feeding: This is found in some aquatic organisms
that feed on tiny organisms (planktons) in their habitat. They
use sieve-like structure in their body to take in water
containing suspended planktons which they then filter from
the water and flush out the water. Typical examples of filter
feeders include; duck, mosquito larvae, and molluscs such as
oyster, prawn and mussels. They are also called microphagus
feeders.
[2] Fluid Feeding: This involves organisms that feed only on
soluble or fluid food materials. There are two types of fluid
feeders.
(a) Wallowers: These are organisms that live, rest or wallow
inside their food e.g. tapeworm in the intestine of man. The
tape worm lives within the digested food of its host and
absorbs the food directly into its body.
(b) Suckers: These are mainly insects that feed by sucking
fluid from plants and animals. Examples of suckers are bees,
housefly, mosquito, tsetse fly, and butter fly.
[3] Saprophytic Feeding: These are organisms which obtain
their nutrients from dead and decaying food materials or
dead organic matters. They are mainly non-green plants
which do not have chlorophyll and therefore cannot carry
out photosynthesis. Typical examples include many fungi,
e.g. Mushroom, Mucor or Rhizopus, Penicillum and Yeast as
well as some bacteria. They use their rhizoids to penetrate
into the dead organic matter, and secrete enzymes into it.
The enzyme will cause extracellular digestion to occur
(digestion outside the body). The digested food diffuses into
the plant through their rhizoids
[4] Parasitic feeding: This involves plants and animals
which live and feed on or inside other living organisms and
also causing them harm. Parasites which live outside the
body or the surface of their hosts are called ectoparasites e.g.
tick, mites, lice and fleas. Those parasites which feed and live
inside their hosts are called endoparasites e.g. tapeworm,
roundworm etc. Plant parasites include dodder, mistletoe
and Cassytha.
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 WEEK 3
DENTITION
Dentition is defined as the number, arrangement and
conformation of teeth in the mouth of an animal. Each group of
mammals has a peculiar type of dentition related to its diet
There are two types of dentitions found in vertebrates.
[1] Homodont dentition: In this type of dentition, the organisms
have the same type of teeth with the same shape, size and
perform the function. This type of dentition is found in fishes,
amphibians and reptiles.
[2] Heterodont dentition: In this type of dentition, the
organisms possess teeth of different shapes, sizes and functions.
This type of dentition is found in mammals such as man, rabbit,
cattle, etc.
TYPES OF TEETH
Mammals generally have four different types of teeth.
[a] Incisors: These are flattened, chisel-like with a sharp
edge for cutting and holding onto the food/prey. They are
located in the front of the jaw.
[b] Canines: These have sharp and pointed tips. They are
used for tearing flesh and catching prey. They are next to the
incisors.
[c] Premolars: They are located towards the back of the jaw
next to canines. They have broad ridged surfaces called
cusps. They are used for grinding and chewing food.
[d] Molars – These also have broad, ridged surfaces and are
used for chewing and grinding food. They are found at the
extreme back of the jaws.
 Adult jaws showing the teeth

SET OF TEETH IN MAMMALS

Mammals have two sets of teeth, these are:
[a] Milk teeth: This set of teeth is found in young ones and will
later fall off to be replaced by the permanent teeth. Milk teeth
consist of incisor, canine and premolar.
[b] Permanent teeth: This is the set of teeth possessed by adult
mammals. They usually remain till old age. Permanent teeth
consist of incisor, canine, premolar and molar.

STRUCTURE OF A TOOTH
A typical tooth has three parts; the crown, the neck and the
root. The crown is the part above the gum. The root is
embedded in the jaw and the neck is the narrow junction
between the crown and root.
The incisors and canines have one root each while the
premolars and molars have two or three roots each. In the
centre of the tooth is a pulp cavity which contains blood
vessels and nerves that make extremely sensitive to heat,
cold and pain. The dentine, a hard bone-like material,
encloses the pulp. The enamel, a white, hard material covers
the dentine, protecting it and the pulp within. At the root
region a thin layer of cement covers the dentine. The cement
is surrounded by the periodontal membrane, a fibrous tissue
that fixes the tooth into the jaw bone.

A TYPICAL TOOTH

DENTAL FORMULA
Dental formula refers to the number, type and arrangement
of teeth in one half of each jaw. It is a reflection of special
adaptation of mammalian teeth for feeding.
[1] Dental formula of omnivore e.g. man: Man feeds on both
flesh and plants.
I = 2/2 ; C = 1/1 ; P = 2/2 ; M = 3/3 = 32
[2] Dental formula of carnivore e.g. dog: I = 3/3 ; C = 1/1 ; P =
4
/4 ; M = 2/3 = 42

[3] Dental formula of herbivore e.g. rabbit: I = 2/1 ; C = 0/0 ; P =

3
/2 ; M = 3/3 = 28
 PRACTICE QUESTIONS
1. Define Digestion.
2. Explain the alimentary canal of a named animal
3. List ten parts of the alimentary canal and their functions.
4. Discuss in details the functions of the duodenum.
5. Write two functions of the hydrogen chloride in the stomach
6. Draw annotated diagram of the alimentary canals of man.
7. Write short notes on the following feeding habits:
(a) Filter feeding
(b) Fluid feeding
(c) Saprophytic feeding
(d) Parasitic feeding.
8. Write short note on each of the following;
(a) Herbivores
(b) Carnivores
(c) Omnivores
(d) Scavengers
9. Define the terms (a) dentition (b) dental formula
10. Make a large well labeled drawing of a tooth.
11. State four ways of caring for your teeth
12. Name four types of teeth in mammals or human.
13. What is heterodont dentition?
14. State the two sets of teeth.

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WEEK 4
 CELLULAR RESPIRATION
Cellular respiration can be defined as the series of chemical
activities of the cells in which glucose is broken down by a
series of reactions controlled by enzymes to release energy.
The energy released is stored in adenosine triphosphate
(ATP) which is the form of energy used by all living cells for
their various metabolic processes.
TYPES OF CELLULAR RESPIRATION
There are two types of cellular respiration:
[1] Anaerobic Respiration: This is the type of respiration
which does not require oxygen to release energy. During
anaerobic respiration, glucose is broken down into ethanol,
carbon dioxide and energy (ATP). It can be represented by
the chemical equation below:
C6H12O6 2CO2 + 2C2H5OH + Energy
The breaking down of glucose in the absence of oxygen is
called fermentation which is found in yeast.
[2] Aerobic Respiration: This is the type of respiration
which requires oxygen to break down glucose into water,
carbon dioxide and energy (ATP). It can be represented by
the chemical equation below:
C6H12O6 + 6O2 6CO2 + 6H2O + Energy
The breaking down of glucose in the body passes through
several pathways before it can produce energy. These
pathways are glycolysis and Kreb’s cycle.
(a) Glycolysis: This is the series of chemical reactions which
involve the breaking down and is described as follows:
(i) Glycolysis occurs in the cytoplasm of the cells
(ii) Oxygen is needed at this point
 (iii) It begins with the phosphorylation of glucose to
glucose–6–phosphate
(iv) glucose to glucose–6–phosphate is broken down into 3
carbon compounds
(v) The 3-carbon compound is the converted to pyruvic
acid
(vi) A net formation of 2 ATPs is produced from the
complete oxidation of one glucose molecule during
glycolysis
What happens to pyruvic acid depends on whether oxygen is
available of not. In the absence of oxygen, pyruvic acid is
converted to lactic acid (animal cells) or ethanol (plant cells).
In the presence of oxygen, pyruvic acid will enter into the
mitochondria where it is converted to Acetyl co-enzyme A
(Acetyl CoA) giving off carbon dioxide and hydrogen atoms.
Acetyl CoA is an important intermediate in the breaking
down of sugar because it links glycolysis to the Kreb’s cycle.
It is also formed during the breakdown of proteins and fats.
(b) Kreb’s cycle: This is also known as Citric Acid Cycle or
Tricarboxylic Acid Cycle (TAC). Kreb’s cycle takes place in the
mitochondria of all cells in the presence of oxygen. It involves
series of cyclic reactions during which pyruvic acid combined
with acetyl Co A to form citric acid, oxoglutaric acid and then
oxaloacetic acid. The reaction continues in a cyclic form and
it repeats itself continuously.
At various stages of the Kreb’s cycle, carbon dioxide and
hydrogen are produced. The hydrogen released combines
with oxygen to produce water. Kreb’s cycle produces a net
production of 36 ATPs. The total net production for both
glycolysis and Kreb’s cycle is 38 ATPs.

SIMILARITIES BETWEEN AEROBIC AND ANAEROBIC

RESPIRATION
[a] Both aerobic and anaerobic respiration lead to release of
energy.
[b] Both occur in plant and animal cells
[c] Both give off carbon dioxide as b-product
[d] Both require enzymes to speed up the reactions
[e] Both lead to the generation of heat

DIFFERENCES BETWEEN AEROBIC AND ANAEROBIC

RESPIRATION
AEROBIC RESPIRATION ANAEROBIC RESPIRATION
a Oxygen is required Oxygen is not required
b More energy is released Less energy is released
c Occurs in the mitochonria Occurs in the cytoplasm
d By-products are water By-products are alcohol or
and carbon dioxide lactic acid
e Water is given off as by- Alcohol is given off as by-
product. product.

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 WEEK 5
RESPIRATORY SYSTEM
Respiratory system is the system of the body that helps in
gaseous exchange and also in the break down of glucose to
release energy. Respiration takes place in two phases or
stages.
[1] External respiration (breathing): This is defined as the
exchange of gases between the environment and the
respiratory organs of living organisms. It involves breathing
(inspiration/inhalation) and breathing out
(expiration/exhalation).
[2] Internal (cellular/tissue) respiration: This is defined as
the oxidation of digested food within the cells to release
energy while producing water and carbon dioxide as by-
products.

CONDITIONS NECESSARY FOR RESPIRATION

The following conditions are necessary for efficient
respiration to take place:
[a] Respiratory medium: This is the surroundings of the
organism from which it obtains oxygen. Examples are air
and water.
[b] Respiratory organ: This includes organs like the lungs and
gills for taken in air.
[c] Transport medium: This is the system that moves the
dissolved gases around the body e.g. the blood
[d] Ventilation: This involves the free flow of the respiratory
medium (air or water) over the respiratory surface in one
direction.
[e] Respiratory surface: This refers to the surface of the
respiratory organs where gaseous exchange takes place.
Examples are the surface of the lungs and gills.
CHARACTERISTICS OF RESPIRATORY SURFACE
[1] Respiratory surface must be moist so that gases can easily
diffuse through
[2] Respiratory surface must be permeable to allow gases
pass in and out of them
[3] Respiratory surface must be thin-walled for easier and
faster diffusion
[4] Respiratory surface must have adequate supply of
transport medium e.g. blood
[5] Respiratory surface must be highly vascularised i.e. have
plenty of blood capillaries
[6] Respiratory surface have large surface area to aid easy
diffusion of gases

TYPES OF RESPIRATORY ORGANS/SYSTEMS

ORGANISMS RESPIRATORY ORGANS/SYSTEMS
1 Unicellular Body surface
organisms
2 Hydra and Cell membrane
tapeworm
3 Earthworm Wet skin or body surface
 4 Fishes Gills
5 Arthropod Tracheal system
6 Arachnids Lung books
7 Tadpoles Gills
8 Reptiles, birds Lungs
and mammals
9 Amphibians Mouth, skin and lungs
10 Flowering plants Stomata and lenticels

MECHANISM OF RESPIRATION IN TOAD

The young toad called tadpole uses gills for gaseous
exchange. The gills provide an efficient respiratory surface
for direct diffusion of gases between the tadpole and the
respiratory medium (water). Dissolved oxygen in water can
easily diffuse into the body and carbon dioxide can also
diffuse out of the body by simple diffusion.
The adult toad uses three different respiratory organs or
systems for gaseous exchange namely:
[a] Mouth (buccal respiration) used on land
[b] Skin (cutaneous respiration) used on land and in water
[c] Lungs (pulmonary respiration) used on land
The three respiratory organs have the characteristics of an
efficient respiratory surface.

MECHANISM OF RESPIRATION IN MAN

The respiratory system of man is typical of the respiratory of
mammals. It includes all the parts shown in the diagram
below:

Man like other terrestrial vertebrates such as the reptiles,

birds and mammals use the lungs as their only respiratory
organs. The lung is a pair of reddish, elastic organ located on
each side of the heart within the thoracic cavity of the body
and protected by the 12 pairs of ribs.
The mechanism of breathing in man involves two phases or
stages namely inspiration (inhalation) and expiration
(exhalation). The various processes involved in the two
stages are shown in the table below:
Inspiration/inhalation Expiration/exhalation
1 Thoracic cavity first Thoracic cavity first
increases in volume decreases in volume
2 Diaphragm contract and Diaphragm relaxes and
becomes flattened becomes dome-shaped
3 The intercostal muscles The intercostal muscles
 contract relax
4 The sternum is moved The sternum is moved
forward inward
5 The ribs are moved The ribs are moved
upward and outwards downward and inwards
6 Increase in volume and Decrease in volume and
decrease in pressure of increase in pressure of the
the thoracic cavity thoracic cavity
7 Air rich in oxygen is Air containing carbon
drawn into the lungs or dioxide and water vapour
alveoli through the nose, from the lungs or alveoli are
trachea, bronchi and forced out through the nose,
bronchioles. trachea and bronchioles,
bronchi, trachea and the
nose
8 Consequently, there is an Consequently, there is a
increase in the size of the decrease in the size of the
lungs lungs

During expiration, not all the air in the lungs is removed. The
air left in the lungs is called residual air while the one which
is exchanged with each breathe is called tidal air. The
approximate composition of inhaled or exhaled air is shown
in the table below:
Air component Inhaled air Exhaled air
a Oxygen 21% 16%
b Carbon dioxide 0.03% 4.1%
c Nitrogen 79% 79%
d Water vapour Variable Saturated
 RESPIRATORY SYSTEMS IN PLANTS
Plants do not have special respiratory organs for gaseous
exchange. However, gases move in and out of the plants
through the stomata and lenticels.
[a] Stomata: These are very thin openings found in the
epidermis of leaves and stems of seedlings. Each stoma is
surrounded by two bean-shaped cells called guard cells. The
closing and opening of the stomata are controlled by the
guard cells.
[b] Lenticels: These are breathing pores found in the bark of
older stems.

ASSIGNMENT
EXPLAIN RESPIRATORY SYSTEM IN FISH,INSECT.

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 WEEK 6
EXCRETION
Excretion can be defined as the process by which organisms
get rid of waste products during its metabolism. These
wastes have to be removed from the body because they are
toxic and can be harmful to the body. However, excretion
should not be confused with egestion. Egestion is the removal
of solid undigested food substances which are not by-
products of metabolism e.g. faeces.
IMPORTANCE OF EXCRETION
[a] Excretion helps to maintain water balance in the body
[b] Excretion helps to maintain salt balance in the body
[c] Some of these wastes are poisonous and must not be
allowed to accumulate in the body
[d] These wastes are harmful to the body and so must be
removed.
[e] These wastes can interfere with normal metabolic
activities of the body if not removed.
FORMS OF WASTE MATERIALS
[a] Liquid form: Examples include water, sweat, uric acid,
urea, dissolved mineral salts, latex, gum, etc.
[b] Gaseous form: Examples include carbon dioxide, oxygen,
ammonia gas, etc.
[c] Solid form: Examples include tannis, alkaloids, mucilages
in plants.

EXCRETORY ORGANS
Organisms Excretory organs
a Protozoa e.g. Amoeba Body surface and contractile
vacuole
b Flatworm e.g. tapeworm Flame cells
c Roundworm e.g. Nephridia
earthworm
d Insects Malpighian tubules
e Crustaceans Green glands
f Fishes Kidneys
g Amphibians Kidneys
h Reptiles Kidneys
i Birds Kidneys and lungs
j Mammals Kidneys, skin, liver and lungs
k Flowering plants Stomata and lenticels
 MECHANISM OF EXCRETION IN FLATWORMS
The excretory organ of flatworms is the flame cells. The
waste products in flatworms include carbon dioxide,
ammonia and water. These waste products diffuse from the
surrounding cells into the flame cells. The flagella are then
used to propel the wastes into the tubules and from there
they are passed to the outside.
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WEEK 7
EXCRETION IN MAMMALS
Mammals have four types of excretory organs namely:
[a] Lungs excrete water vapour and carbon dioxide
[b] Skin excretes sweat containing water, salts and urea
[c] Liver excretes bile pigments called bilirubin
[d] Kidneys excrete water, mineral salts, urea, uric acid, etc.
The kidneys are the major excretory organs in mammals. The
longitudinal section of the kidney is shown below:

The mammalian kidney is a bean shaped and reddish-brown

organ located in the posterior end of the abdomen. There are
two kidneys in mammal. The right kidney is slightly lower in
the body than the left kidney. The above diagram of the
kidney shows two distinct regions; an outer cortex and inner
medulla.
There are millions of urinary tubules passing through both
regions. Each kidney is connected to two main blood vessels
namely the renal artery and the renal vein.
MECHANISM OF EXCRETION IN MAMMALS
(URINE FORMATION)
Urine formation occurs in the millions of urinary tubules of
the kidneys. The diagram of the urinary tubule is shown
below.
The process involved in the formation of urine occur in three
phases or stages.
[1] Ultra filtration: This is the process of filtering materials
from the glomerulus into the bowman’s capsule. It begins
with the renal artery bringing blood to the kidney. The blood
circulates through the capillaries of the glomerulus of each
Bowman’s capsule. Materials such as water, urea, mineral
salts, glucose, nitrogenous compounds, plasma solutes are
filtered into the capsule.
[2] Selective reabsorption: This is the process of
reabsorbing useful materials back into the blood. It occurs
when the filtered materials (glomerular filtrate) get to the
proximal convoluted tubule and Henle’s loop. Some water,
glucose, amino acids and salts which are useful to the body
are reabsorbed into the blood.
[3] Hormonal secretion: This involves the secretion of Anti
Diuretic Hormone (ADH). As the fluid gets to the distal
tubule, ADH is used to retain additional water in the body
and urine is finally formed. The urine trickles into the renal
pelvis and is propelled by peristalsis through the ureter into
the urinary bladder. When the bladder is full, it contracts and
discharges the urine through the urethra.

EXCRETION IN FLOWERING PLANTS

Flowering plants do not have any special excretory organ.
They dispose their wastes through various parts of their body
such as the stomata, lenticels, etc.
Plant wastes Point of removal
a Carbon dioxide stomata, lenticels
b Water stomata, lenticels
c Oxygen stomata, lenticels
d Latex Damaged parts
e Tannins, gum, mucilage, Dead tissues like the bark of
crystals, alkaloids and stems, leave and petals that
anthocyanin are shed off periodically.

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 WEEK 8
IRRITABILITY
Irritability (sensitivity) is the ability of living things to detect
and respond to changes (stimulus) in their environment. All
living things are capable of responding to internal and
external stimuli. Irritability is one of the characteristics of
living things.
Generally, plants respond very quickly to external stimuli
while plants respond slowly. Plants also respond to stimuli
using certain parts of the body while animals respond to
stimuli using their whole body
TYPES OF RESPONSES
There are three major types of responses namely tactic,
nastic and tropic movements
[1] Taxis or tactic movements: This is a directional type of
response in which a whole organism moves from one place to
another in response to external stimuli. The movement may
positive (moving towards) or negative (moving away from).
Examples of taxis are listed in the table below:
Types of Stimulus Examples
taxis
a Phototaxis Light Euglena and Chlamydomonas
swim towards light of low
intensity (positive phototaxis)
and away from light of high
intensity (negative phototaxis)
b Hydrotaxis Water Woodlouse moves towards
areas of high humidity
(positive hydrotaxis)
c Chemotaxis Chemical The sperms of Moss plants
s swim towards the chemical
produced by the egg cell
(positive chemotaxis)
d Thermotaxis Tempera Motile bacteria swim from cold
ture regions to warm regions
 (positive thermotaxis)

[2] Nastism or nastic movement: This is a type of non-

directional response in which a part of a plant moves from in
response to non-directional stimuli such as light intensity,
temperature or humidity. Examples of nastic movements are:
(a) Closing of the morning glory flower when the light
intensity is low
(b) The petals of sunflower which open in the light and close
in the dark
(c) The folding of the leaflets of the Mimiosa plant when it is
touched
(d) The closing of the leaflets of the flamboyant tree (sleeping
movements) due to low light intensity.
[3] Tropism or tropic movements: This is a type of
response in which a part of a plant moves in response to a
directional stimulus. The direction of the response is related
to that of the stimulus and may be positive or negative.
Tropisms are very slow growth movements. Examples of
tropisms are shown in the table below:

Types of Stimulus Examples

tropism
a Phototropism Light Shoots of plants bend towards light
(positively phototropic) while roots
 bends away from light (negatively
phototropic).
b Hydrotropism Water Roots of plants bend towards water
(positively hydrotropic) while shoots
bend away from water (negatively
hydrotropic).
c Geotropism Gravity Shoots of plants move away from
gravity (negatively geotropic) while
roots move towards gravity
(positively geotropic).
d Thigmotropism Touch Tendrils of a climbing plant twine
around a support (positively
thigmotropic) while roots grow away
from it (negatively thigmotropic).

COMPARISM AMONG TAXIS, NASTISM AND TROPISM

PARAMETERS TAXIS NASTISM TROPISM
1 Organism Animals and some Plants Plants
involved plants
2 Stimulus Unilateral General Unilateral
3 Response Directional Non-directional Directional
4 Nature of The whole Only part of the Only part of
movement organism moves organism the organism
moves moves
5 Is it growth No Yes Yes
movement

MOVEMENT
Movement is he ability of living things to change their
location or position. Living things move from one place to
another. Reasons why living things move include:
[a] Searching for food
[b] To escape danger
[c] Response to stimuli
[d] For reproduction
All organisms that can move are equipped with various
organelles or organs and mechanisms for movement.
Examples include:
[a] Flagella (flagellum): These are long whip-like projections
on the cell surface. They are usually one or two in number.
They are found in animals such as Euglena, Chlamydomonas,
trypanosome, spermatozoa, etc.

[b] Cillia (cilium): These are short, hair-like structures that

project out of the cell’s surface. They are usually numerous
and packed closely together. They move in a coordinated way
to bring about movement. Cilia are found in paramecium
 CYCLOSIS
Cyclosis is a type of movement that involves the circulation of
protoplasm in cells. It occurs in protozoa like Amoeba
popularly known as amoeboid movement. It is aided by a
mechanism called cytoplasmic streaming which involves the
principle of gel-sol conversion of cytoplasm.
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