REVISED SCHEME FOR SS2

BIOLOGY (SECOND TERM)

WEE TOPIC CONTENT

K
1-3 Digestive Types of alimentary tracts.
system Description and functions of parts
of alimentary tracts
Modification of parts to effects
their digestive functions
Feeding habits: categories and
mechanism
Modification in feeding habit
Feeding in protozoa.
4-6 Transport Transport system in large
system organisms
Need for substances to move over
greater distances
Materials for transportation
Structure of artery, vein and
capillary and vascular bundle
Media of transportation
Mechanisms of transportation in
lower animals, higher animals and
plants
7-8 Respiratory Types of respiratory system
system Mechanism of respiratory system
in lower animals, higher animals
and plants
Mechanism of gaseous exchange
through the stomata of plants
9-10 Excretory Excretory systems: contractile
system vacuoles, flame cells, malpigian
tubules…
Excretory mechanism in
 earthworm, insects and mammals
11 Revision
12-13 Exam
 DIGESTIVE SYSTEM
Digestion is the breakdown of large molecules of food
into simple and absorbable form for use by animals.
Digestive system is made up of the alimentary canal
(tract) and the associated glands and organs which
produce some of the enzyme-rich secretions that bring
about digestion.

ALIMENTARY CANAL AND DIGESTION IN

MAN
The alimentary canal of man includes the mouth,
oesophagus, stomach, duodenum, small intestine or
ileum, caecum, appendix, large intestine or colon,
rectum and anus. The description and importance of the
alimentary canal are as follows:

Mouth
The alimentary canal of man starts from the mouth.
Food is ingested in the mouth. The mouth contains the
teeth, salivary gland and tongue.

The Teeth (FUNCTION)

 i. The teeth cut, grind or chew food into smaller
particles.
ii. Teeth expose large area of food for the action of
enzymes.
iii.The teeth cut, grind or chew food into smaller
particles.
iv. Teeth expose large area of food for the action of
enzymes.

Diagram of mammalian tooth

The salivary gland
The salivary gland secretes saliva which contains an
enzyme called ptyalin which acts on cooked starch,
converting it into complex sugar. Saliva is a watery,
slightly alkaline substance secreted by salivary gland.

Functions of the saliva:

i. The saliva allows easy chewing or movement of

food in the mouth for swallowing.
 ii. It ensures moistening of food
Tongue
i. The tongue rolls the food into bolus.
ii. It allows mixing of food with saliva or ptyalin.
iii. It aids swallowing of food into the gullet or
oesophagus.

ALIMENTARY TRACT OF MAN

The mouth opens into a short, wide and muscular
pharynx. The nasal cavity also opens into the pharynx.
The pharynx leads into two tubes. The one in front is
the trachea or windpipe which leads to the lungs.
Behind the trachea is the oesophagus or gullet through
which food passes down to the stomach. During the
swallowing of the food, the entrance to the trachea must
be covered to prevent choking. The epiglottis flaps
down to cover the trachea during swallowing. The food
thus goes into the oesophagus.

Oesophagus or Gullet
It connects the mouth to the stomach. The wall of the
oesophagus is muscular. Bands of muscles contract and
relax alternately to push each bolus of food downwards
slowly. This process is known as peristalsis.

Stomach
Food enters the stomach when the ring of muscles or
pyloric sphincter at the entrance of the stomach relaxes.
The muscular walls of the stomach contract and relax
forcefully, thus churning the food. Small pieces of food
are broken down even more and gastric juice is mixed
into the food. In the stomach, the gastric gland secretes
gastric juice which contains two enzymes pepsin and
renin which are very important as well as dilute
hydrochloric acid. They are produced by special cells
lining the wall of the stomach. Pepsin is a protease; it
digests proteins to polypeptides, which are intermediate
products of protein digestion. Pepsin works best in an
acidic medium. The dilute hydrochloric acid (HCl) is
secreted by the gastric gland. HCl creates an acid
medium for two enzymes to act. HCl also help to kill
some bacteria in the stomach.

Renin causes the coagulation of milk into thick curds. It

does this by acting on the soluble milk protein, , and
converting it into insoluble casein. This action is
important in infants whose main diet is milk. The casein
is then broken down by pepsin. Food is retained in the
stomach for three to four hours. By this time, it is a
thick, creamy fluid called chyme. It moves out through
the sphincter at the bottom of the stomach into the
duodenum.

Duodenum
Duodenum is the first part of the intestine. The middle
and last sections of the small intestine are the jejunum
and ileum respectively. Several substances are secreted
into the duodenum. The pancreas secretes pancreatic
juice, a watery alkaline liquid containing several
digestive enzymes. The liver produces bile which is
stored in the gall bladder. Bile is a greenish alkaline
liquid which does not contain digestive enzymes. When
chyme enters the duodenum, certain hormones
stimulate the pancreas andgall bladder to send their
digestive juices to the duodenum. The duodenum
contains pancreas which secretes pancreatic juice that
contain three enzymes:

These enzymes are:

i. Amylase which breaks down starch to maltose.
ii. Lipase which breaks down fats to fatty acids and
glycerol.
iii. Trypsin which breaks down protein to
polypeptides.

Although bile does not contain digestive enzymes, it is

important for digestion. It contains a high percentage of
water and therefore adds water to chyme. Secondly, its
alkaline (sodium) salt neutralizes the hydrochloric acid
in chyme and allows the enzymes of the pancreas juice
to begin working. Thirdly, bile reduces the surface
tension of fats and emulsifies them. This means that
large fat and oil drops are broken up into tiny droplets,
thus providing a larger surface area for enzyme action.
At the end of digestion in the duodenum, the food now
in liquid form called chyle passes to the ileum or small
intestine.

Small intestine
Small intestine is found between the duodenum and the
large intestine. Two major events take place in the small
intestine. These events are

a. Digestion
b. Absorption of the digested food.
 Digestion: Digestion of food also takes place in the
small intestine or ileum.

 Absorption of digested food: Glucose, amino

acids, fatty or carboxylic acids and glycerol as
wellas vitamins and mineral salts are absorbed in
the small intestine. The walls of the small intestine
have tiny fingerlike structures called villi (singular
villus) which helps in absorption.
DIAGRAM OF HUMAN VILLUS
The inner surface layer or epithelium of each villus is
thin this allows the absorption of the end-products by
either diffusion or active transport. There is a rich
supply of blood vessels and lymphatic vessels
containing blood and lymph respectively. The
lymphatic vessels eventually empty their contents into
the blood vessels near the heart. The blood then carries
the nutrient to where they are needed and are
assimilated.

Caecum and Appendix

In man, the functions of caecum and appendix are not
well known but the caecum usually contains some
bacteria which aid minor digestion of cellulose. Some
vitamins K and B-complex are partially synthesized in
this region.
Large Intestine
Undigested food passes into the colon or large
intestine. Here water is absorbed. This absorption of
water concentrates the waste products and makes them
into faeces. Faeces pass into the rectum and out of the
body through the anus. Movements of the faeces are
facilitated by dietary fibres or roughage which gives
the gut muscles something to squeeze against.
Insufficient roughage in the diet will result in
constipation. i.e difficulty in moving the bowels.

SUMMARY OF DIGESTION IN HUMAN ALIMENTARY

CANAL (Not to be drawn)

ENZYME SOURCE SITE OF SUBSTRATE PRODUCT

ACTION ACTED UPON
1. Ptyalin Saliva Mouth Starch Maltose
2. Pepsin Gastric Juice Stomach Proteins Peptones
3. Rennin Gastric juice Stomach Proteins Curdles milk
4. Pancreatic lipase Pancreatic Juice Duodenum Fats and oils Fatty acid and
glycerol
5. Trypsin Pancreatic juice Duodenum Proteins/peptonesPeptones/
polypeptides
6. Amylase Pancreatic juice Duodenum Starch Maltose
7. Erepsin Succusentericus Small Polypeptides Amino acids
intestine
8. Lipase Succusentericus Small Fats and oils Fatty acid and
intestine glycerol
9. Lactase Succusentericus Small Lactose Glucose and
intestine galactose
10. Maltose Succusentericus Small Maltose Glucose
intestine
11. Sucrase Succusentericus Small Sucrose Glucose and
intestine fructose
ALIMENTARY CANAL AND DIGESTION IN
EARTHWORM
The alimentary tract of the earthworm is a tube with
two openings: the mouth through which food enters
and the anus through which undigested food leaves the
body.

The alimentary canal of the earthworm includes the

following parts: mouth (bucal cavity), pharynx,
oesophagus, crop, gizzard, intestine, caecum, rectum
and anus.

ALIMENTARY TRACT OF EARTHWORM

An earthworm feeds mainly on the vegetable matter

found in the soil that it swallows as it burrows. The
digested food diffuses through the intestinal wall into
the surrounding blood capillaries. The blood then
transports the food to all parts of the body. The
undigested food materials are then removed through the
caecum, the rectum and finally to the anus.

ALIMENTARY CANAL AND DIGESTION IN

GRASSHOPPER OR COCKROACH
The grasshopper feeds on green vegetables while the
cockroach feeds on household materials like books,
sugar, food, etc. The alimentary canal of grasshopper or
cockroach includes the mouth (mandible), salivary
gland, oesophagus, crop, gizzard, mid-gut, caecum,
ileum, rectum, hind gut, malpighian tubules and anus.
The mouth is surrounded by mouth parts such as
maxillae, mandibles and labium with sharp cutting
edges for the cutting and grinding of food.

A pair of salivary gland opens into the mouth which

secretes enzymes for the digestion of food. The food is
then swallowed through the muscular oesophagus into
the crop. The crop is where the food is stored. The food
is later taken to a muscular gizzard for grinding. The
short mid-gut has six fleshy vascularized tube or mid-
gut. The hind-gut consisting of ileum, colon and rectum
shapes the feaces in pellets and absorbs water and
mineral salts. The faeces are later passed out through
the anus.

ALIMENTARY TRACT OF COCKROACH

ALIMENTARY CANAL AND DIGESTION IN BIRDS

In birds, the jaws are drawn out to form a horny
beak which does not have teeth. Birds use their beaks
for feeding. The beak shows adaptation according to the
types of food the birds eat. The digestive system of the
bird includes the beak, mouth, pharynx, oesophagus,
crop, proventiculus, gizzard, intestine, caecum, rectum
and anus (cloaca).
 When birds pick up foods such as fruits or grain by
their beak, the food moves from the mouth through the
oesophagus to the crop where it is temporarily stored,
moistened and fermented by some bacteria. From there,
the food now passes on to proventiculus called
glandular stomach because it has glands which secretes
digestive enzymes e.g. pepsin, amylase and lactase on
the food. The food moves to the gizzard. The action of
the muscles of the gizzard and the gastric juice churns
and breaks up the food into small pieces. Small stones
(which the bird swallows from time to time) in the
gizzard also helps to grind the food. Chemical digestion
also begins here. Digestion is completed in the small
intestine by the action of the pancreatic juice and
intestinal secretions. Absorption also takes place here.
In the rectum, most of the water is reabsorbed. Solid
waste, Body waste from the kidneys, eggs and sperms is
ejected through the anus into the cloaca and out of the
body.

Note: that birds just like other herbivores have a

relatively long alimentary canal than other animals. The
reason for this long alimentary canal is to produce a
large surface area for the digestion and absorption of
food.

Diagram of alimentary tract of bird

SIMILARITIES AND DIFFERENCE BETWEEN THE ALIMENTARY

CANAL OF A BIRD AND THAT OF GRASSHOPPER

Similarities

Both organisms have narrow oesophagus, Crop,

Muscular gizzard, presence of caecum and mid-gut.

DIFFERENCES BETWEEN THE ALIMENTARY

CANAL OF A BIRD AND GRASSHOPPER

BIRD GRASSHOPPER
i. There is presence of Tongue, duodenum and
tongue, duodenum, and pancreas is absent
pancreas.
ii. Mouth is modified into Mouth is modified into
beak mandible and maxillae for
Chewing and grinding.
iii. It has a long alimentary It has relatively short
canal alimentary canal
iv. The hind gut ends in Hind gut ends in anus
cloaca distinct from the reproductive
tract
v. Malphigian tubule are Malphigian tubules are
absent attached to the alimentary
canal.

MODIFICATIONS AND MECHANISM OF

FEEDING IN SOME ANIMALS
There are five modifications and mechanisms of
feeding associated with some organisms. These
feeding mechanisms include:

1. Absorbing mechanisms: e.g. tapeworm: the

tapeworm is an endoparasite which carries
outparasitic feeding on its host i.e. man. It has no
mouth but absorbs digested food from the intestine
of its host.
2. Biting and chewing mechanism: e.g. grasshopper
or cockroach. The grasshopper or cockroachhas mouth
parts adapted for biting and chewing. These insects
have four different mouth parts which are modified and
adapted for biting or chewing food. These mouth parts
are;

i. Labrum or upper lip: the grasshopper has

labrum or upper lip which prevents the
foodfrom falling off the mouth.

ii. Mandibles: it possess a pair of mandible

which are heavy, toothed and jaw-likestructure
used for cutting and chewing food materials.

iii. Maxillae: the grasshopper also has a pair of

maxillae which is also a biting blade.
Thisbreaks down the food which the mandible
has chewed into smaller particles.

iv. Labium: the labium (lower lip) prevents

the wastage of food from the mouth.
3. Sucking mechanism: there are three popular
organisms which exhibits sucking mechanism.These are
mosquito, housefly and butterfly. These insects have
different modifications of mouth parts adapted for
feeding on food through the mechanism of sucking.

4. Grinding mechanism: grinding is common among

mammals e.g. man, cattle, sheep, goat, etc.These
animals are capable of grinding the food before
swallowing. This grinding is aided by the presence of
hard and strong teeth made of enamel and dentine. The
animals are adapted to the grinding mechanism by the
following features:

 They possess different sets and types of teeth to

process food.

 The teeth are hard and strong to withstand biting,

chewing or grinding or cracking food.
 The absence of front teeth (incisors) in sheep
(herbivore) is a special adaptation as it helps to bite
the grasses during feeding the animal.

5. Trapping and absorbing mechanism: trapping and

absorbing mechanism are common amongthe
insectivorous or carnivorous plants such as bladderwort
and sundew.
 FEEDING HABITS
Organisms exhibit different feeding habits. These are:
1. FILTER FEEDING
Filter feeders are also called microphagus feeders
which feed on very tiny organisms which cannot be
easily picked to the satisfaction of the feeder. Filter
feeders are mainly aquatic animals and they have to
wallow in water through sieve-like structure in their
body in order to collect reasonable quantity of their
prey or food. Examples of filter feeders are mosquito
larva, mussel, ducks, prawns, etc.

2. FLUID FEEDERS
Animals which feed on any fluid materials are classified
as fluid feeders. There are two major groups of fluid
feeders. These are:

 Wallowers: these organisms rest within or wallow

in their food e.g. tapeworm in the intestine ofman.
It has no alimentary canal and it uses its entire
body surface to absorb directly digested food of the
host.
  Suckers: suckers are organisms mainly insects
which feed by sucking fluids from plants
andanimals. Examples of suckers are bug,
mosquito, butterfly, aphid, tsetse fly and housefly.
The fluid feeding mechanism of mosquito, housefly
and butterfly.

3. INSECT FEEDERS

Insectivorous plants: they are plants which entrap and

feed on some insects to obtain mineral/nitrogenous
substances. Examples are sundew (Drosera),
bladderwort (Utricularia).

4. PARASITIC AND SAPROPHYTIC FEEDERS

Parasitic feeding is found in both plants and animals.
Animal parasites are tapeworm, roundworm, liver fluke,
louse, tick and guinea worm while plant parasites are
cassytha, dodder and mistletoe.

5. Saprophytes are mainly non-green plants which do

not have chloroplasts and therefore cannot manufacture
their own food. They then feed on dead and decaying
organic matter from which they derive their food.
Examples of saprophytes are rhizopus, mushroom and
mucor.

PROCESS OF FEEDING IN PROTOZOA (AMOEBA)

AND HYDRA
Feeding in Amoeba
Protozoa like Amoeba exhibits holozoic mode of
nutrition. Amoeba feeds on micro-organisms like
diatoms or other organic particles. It engulfs the food
particles by putting out its pseudopodia which
surrounds the food particles by forming a cup-shape
when the two ends of the pseudopodia touch and fuses
enclosing the food into the body with little drops of
water, these forms a food vacuole. The food is digested
inside the food vacuole.

NB; Diagram of the mechanism of feeding in amoeba)

Feeding in hydra
Hydra feeds mainly on small crustaceans or other
smaller aquatic organisms. The food is captured by the
actions of nematocysts borne on the tentacle. The food
is carried into the wide mouth by the tentacles.
Enzymes are secreted into the enteron by the gland
cells. Here digestion takes place intracellularly i.e.
inside the body cells. The digested food is absorbed into
the body while the undigested parts are sent back into
the enteron and forced out through the mouth.

NB; Diagram of the mechanism of feeding in hydra

TRANSPORT SYSTEMS
The transfer of organic food and inorganic substances
from one part of the body to another in a living
organism is known as the transportation or
translocation. To transport these substances, every
living organism is equipped with a special transport
system.

Materials that are transported in animals include;

digested food nutrients, water, oxygen,
hormones ,enzymes, antibodies, waste products such as
carbondioxide, urea, salt. Amino acids glucose, fatty
acid and glycerol etc.
Materials transported in plants include; manufactured
food, Water, Excretory products, Nitrogenous waste
products, Oxygen, Glucose, Lipids, Latex, Auxins or
hormones, Amino acid, Mineral salts.
NEED FOR TRANSPORTATION
1. It is needed for the waste products of metabolism
to be executed out so that they will not harm or
form to poisonous (toxic) materials.

2. Transport of essential materials (nutrients,

oxygen, water, etc) is necessary for every cell of
the organism.

3. In plants, transport is necessary to move glucose

from the leaves to other parts and mineral salts and
water from the roots to the stem and leaves.

In organisms where the surface area to volume ration

(SA/V) is large, diffusion is the adequate means of
exchange (transport) of materials. Such organisms
are; unicellular – Amoeba, Paramecium,
Chlamydomonas and Euglena and in simple
multicellular animals – tapeworms. Whereas in large
organisms, an efficient transport system is necessary.
MATERIAL TRANSPORTED IN ANIMALS ( Not
to be drawn)

Location
TRANSPO FROM TO FINAL
RTED USE/FATE
MATERIA
L
1. Oxygen Lungs Living cells Respiration
2. Water Cells Kidney, skin Excretion
and lungs
3. Carbon (iv) Living cells Lungs, gills, Excretion
oxide trachea
4. Nitrogenous Living cells Liver, kidney Excretion
waste
products
5. Amino acids Gut or small Living cells Growth and
intestine repair
6. Excess salts Cells Skin and kidney Excretion
7. Vitamins Small intestine Cells Digestion
8. Glucose Gut or ileum Living cells Respiration
9. Lipids Gut Living cells Respiration
10. Hormones Endocrine Organs or tissue
glands
11 Antibodies White blood All part of the
cells body

MEDIA OF TRANSPORTATION
Materials move round the body of organisms carried in
fluid media i.e. a liquid or fluid is the medium of
transportation of materials. There are four major media
of transportation:

 Cytoplasm: materials are circulated in the

cytoplasm of unicellular organisms, algae, fungi
andcoelenterates.

 Cell sap or latex: is used as the medium of

transportation of material in plants.

 Blood: blood is theliquid medium in which

materials are carried to all cells of the animal’s
bodyespecially the vertebrates. Blood is carried in
the circulatory system which may be opened or
closed.

 Lymph: is one of the media of transportation in

higher animals. It is a fluid similar incomposition
to tissue fluid. Examples of lymph vessel is the
lateal which transmits fatty acids and glycerol

TRANSPORT SYSTEM IN MAMMALS

In mammals, blood and lymph are the media of
transportation. The blood is a tissue in a fluid form.

COMPOSITION OF BLOOD
Mammalian blood comprises of four main components:
  Red blood cells (Erythrocytes).
 White blood cells (Leucocytes).
 Platelets (Thrombocytes)
 Plasma.

DIAGRAM SHOWING THE CONSTITUENTS OF MAMMALIAN

BLOOD (Not to be drawn)

RED BLOOD CELLS (ERYTHROCTYES)

They are small, biconcave, and disc-like in shape. They
are without nucleus. They contain a red pigment called
haemoglobin a protein which contains iron and is
responsible for circullation of oxygen in the blood.
They live for about four months before they are
destroyed in the liver. They are synthesized in the red
bone marrow of the sternum, ribs and vertebrae.

Function:
The haemoglobin (pigment) in the red blood cells helps
to transport oxygen from the lungs to the body cells.

1. Haemoglobin combines with oxygen to form

oxyhaemoglobin in the lungs.

WHITE BLOOD CELLS

They are irregular in shape (phagocytes) and large

with lobed nuclei. All the white blood cells have
nuclei. They are made in the red bone marrow and
the lymph nodes or the spleen. They live for many
months.

Types of white blood cells

1. Phagocytes can be found in the lymphatic system
where they ingest bacteria, viruses and dead cells
and help in preventing diseases. The ingestion of
materials is called phagocytosis and hence such
white corpuscles are called phagocytes.

2. Lymphocytes: is another type of white corpuscles

which produce antibodies and are produced in the
lymph glands.

Functions of WBC
 1. Lymphocytes produce chemicals called antibodies
which stick to the surface of germs and kill them.

2. They help to defend the body against diseases by

ingesting the bacteria and virus that cause diseases.

3. The white blood cells also produce antitoxins

which neutralize the toxin produced by pathogenic
agents thereby making them harmless.

PLATELETS (THROMBOCYTES)

They are tiny, irregular cell fragment without nucleus.

They are formed in the red bone marrow. They are
fewer and smaller than red blood cells.

Functions: it aids in the clotting of blood i.e.

preventing further bleeding and stops bacteria from
entering the body through the wound.

PROCESS OF BLOOD CLOTTING

When a capillary (blood cell) is damaged and blood is
exposed to the air, the blood platelets break-up to
release an enzyme (thromboplastin) which starts a
chain of reactions that cause the protein fibrinogen to
be converted to fibrin. The fibrin forms a mesh of
threads in which blood cells are caught thus forming a
clot. Naturally, some people possess blood which is
unable to clot. These people suffer from a disease called
haemophilia.

GENERAL FUNCTIONS OF BLOOD

The mammalian blood performs a number of functions
under three groups: transport, protection and body
regulation.

1. It transports oxygen from the lungs to the tissues

and carbon(iv)oxide from the tissues to the lungs
for excretion.

2. It transports nitrogenous wastes products from the

tissues to the kidneys.
3. It transports digested foods from the small intestine
(villus) to the various parts of the body.
4. It transports hormones and antibodies from one part
of the body to another.
5. It protects the body from attacks of germs which
cause diseases by killing the germs.
6. It protects the body from excessive bleeding by
initiating the process of blood clotting when an
injury is sustained.
7. It helps to keep the body temperature fairly
constant by distributing heat uniformly around the
body.
 8. It helps to regulate the quantity of water and
various chemical materials in the tissue.

CIRCULATORY SYSTEMS IN MAMMALS

It is the continuous flow or movement of blood round
the body, heart and blood vessels.
Types of circulatory system
i. Closed and opened circulatory systems.
ii. Simple and double circulatory systems.
iii. Pulmonary and systemic circulatory systems.
Closed circulatory system
This is the circulating blood enclosed in blood vessels.
Blood vessels (arteries) carrying blood away from the
heart branch into smaller vessels (arterioles) which
branch and re-branch into finer-vessels called
capillaries. The cells of the body are in contact with the
capillaries. Capillaries eventually join up with other
vessels called veins that are connected to the heart. In
this system, arteries carry blood away from the heart
and veins bring blood back to the earth. Some
invertebrates like annelids and all the vertebrates have
closed circulatory systems.
SCHEME OF CLOSED CIRCULATION (To be
drawn)
Opened circulatory system
In this system, heart pumps blood out into a blood
vessel. The vessel branches and opens into spaces in the
body cavity called haemocoels. In these spaces, the
blood comes into direct contact with the cells after
which it is returned to the heart. It is found in some
animals, roundworms, insects and molluscs.

Single and double circulatory systems

1 Single circulatory system: in this system, the
blood only passes through the heart once
andovertime it makes one complete movement
round the body. This system is common in fish.
Fish has only two-chambered heart – one ventricle
and one auricle.
 2 Double circulatory system: in this system, the
blood passes through the heart twice every timeit
makes one complete movement round the body.
This is found in mammals.

Pulmonary and systemic Circulation

Pulmonary circulation: this system involves the
movement of blood from the heart to the lungsfor
oxygenation.

Systemic circulation: this system involves the

movement of blood between the heart and allother parts
of the body besides the lungs.

Blood vessels
They are the tubes within the body through which the
blood flows away or to the heart. They are
i. Arteries
ii. Veins and
iii. Capillaries
Arteries
ii. They carry blood away from the heart to the body.
 iii. They have elastic and thick muscular walls with
small lumen (canal) to withstand high blood
pressure coming from the heart

Veins
They carry blood to the heart from the body. They have
thin and non-elastic muscular walls with large lumen.

Capillaries
They are tiny blood vessels joining the arteries to the
veins. They are found at the junction between arteries
and veins around tissues and organs of the body. They
have tiny, thin walls. Arteries divide and become
smaller to form arterioles as they leave the heart. At the
same time, the smaller veins from capillaries which join
to form bigger veins called venules.
DIRECTION OF BLOOD FLOW IN THE BODY
(May be drawn)

***Assignment; State five differences between artery

and vein***

DIFFERENCES BETWEEN ARTERY AND VEIN

ARTERY VEIN

It has thick muscular

1. wall It has thin/less muscular wall

2. It has elastic wall It has non-elastic wall

It carries blood away

3. from the heart It carries blood to the heart

It carries oxygenated It carries deoxygenated

4. blood except the blood, except the
pulmonary artery pulmonary vein.

5. It has small lumen It has large lumen

Blood in it is pink or
6. bright red in colour Blood is dark-red in colour.
 Blood flows at high
7. pressure Blood flows at low pressure

It is deeply situated in
8. the muscles It is superficially located

It has valve

No valve except aorta Pulse is not readily

9. and pulmonary detectable
Arteries
10. Pulse is readily
detectable

HEART
The heart is the pumping station of the circulatory
system. It is muscular and the most powerful organ
responsible for the pumping of blood round the body.
The heart is found behind the breast bone (sternum) and
in between the two lobes of lungs within the chest or
thoracic cavity. Heart beat means each pumping action
of the heart. Man has an average of 72 heartbeats per
minute when at rest.
Heart is reddish in colour and made-up of special
muscles called the cardiac muscles. Covering the heart
is a tough bag, the pericardium. The space between the
two layers is filled with pericardial fluid which reduces
the friction caused by the pumping movements of the
heart.

Structure of the mammalian heart

Mammalian heart is divided into four chambers: the
right and left auricles or atria(singular-atrium) and the
right and left ventricles. The walls of the ventricles are
normally thicker and more muscular than that of the
right ventricle. This is because it is through it that blood
is pumped to all the body parts. There is a central wall
in the heart called the septum which divides it into a
right and left half. Between the right auricle and right
ventricle is the three flapped tricuspid valve, while the
two-flapped mitral or biscupid valve is between the left
auricle and left ventricle. The two valves allow the flow
of blood from the right or left auricle to the right or left
ventricle.
Longitudinal section of the mammalian heart
A complete heartbeat takes place in two phases: the
diastolic and the systolic phase.
The diastolic phase: this is the phase in which the
ventricles fill out. First, the ventricles relax andexpand,
then blood flows into the expanded ventricles helped by
contraction of the auricles.

The systolic phase: in this phase, the ventricles

contract forcing blood under pressure into the aorta
andpulmonary artery; and the auricles expand and fill
out with blood.
DIASTOLE AND SYSTOLE

MECHANISM OF TRANSPORTATION IN
UNICELLULAR/LOWER ORGANISM
In unicellular organism, the surface area to volume ratio
(SA\V) of the body is large and as such the materials
such as food, oxygen, water, carbondioxide, etc are
transported from one part of the body to another by
diffusion. Examples are found in amoeba, paramecium,
hydra and flatworms. In amoeba, the cytoplasm rotates
from the back to the front along the direction of its
movement as it changes its shapes. In hydra, the
movement of the gut wall draws water into the gut and
cause digested food and other materials to circulate
within the circulate and allow the cells lining of the gut
to absorb the materials. Some cells possesflagellae and
enhance the circulation of materials in the gut.
Insects and molluscsposses open circulatory system for
transportation of materials within the body. The heart
pumps blood into a blood vessel with branches opening
into all the body cavity called haemocoels. The
materials are exchanged between the body cells and the
blood and the blood in the spaces eventually flows into
the vessels leading to the heart in one direction through
the valves. In this system of the organisms (insects and
molluscs), the distribution of blood to the body parts is
poorly controlled.

MECHANISM OF TRANSPORTATION /
TRANSLOCATION IN HIGHER PLANTS.
Plants need sufficient quantities of many materials
which are transported in them. In aquatic, unicellular
and simple, multicellular plants, gas enter and leave
their cells by diffusion. Water enters the cells of these
plants by osmosis, while manufactured foods and
wastes are transported by diffusion.

In flowering plants, the gases are absorbed mainly

through the stomata in the leaves and lenticels in the
stems while mineral salts are absorbed through the root
system. Inside the plants, gases move by diffusion.
They always dissolve in the water of the moist cell
walls before entering the cells. Water, mineral salts and
soluble foods are transported in vascular tissues. The
vascular tissues of plants are made up of a network of
long tubes called vascular bundles. They are called
veins in the leaves. A vascular bundle consists mainly
of the xylem and the phloem tissues. But in the roots
and stems of dicotyledons, a layer of cambium cells
exists between the xylem and phloem tissues. Vascular
bundles are found in the roots, stems and leaves of
flowering plants.

1.Phloem tissues
The phloem tissue consists of thin-walled, living cells,
with dense cytoplasm which have perforated cross-
walls. It conducts manufactured foods from the leaves
and storage organs to the other parts of the plant.

2.The xylem tissues

The xylem tissue consists mainly of dead cells with

lignified cell walls and perforated end walls which may
be absent. It transports water and mineral salts from the
roots to other plant parts and also gives support to the
plant.
 3.The cambium
It is made up of narrow, living cells with thin walls
and dense cytoplasm. They are able to divide and
multiply, thereby enabling the plant to produce
secondary xylem and phloem.

DISTRIBUTION OF VASCULAR BUNDLES IN

ROOT
DISTRIBUTION OF VASCULAR BUNDLES IN
STEM

DISTRIBUTION OF VASCULAR BUNDLES IN

LEAF

Root pressure and suction presence

Root pressure and suction pressure are considered to be
the two important forces which contribute to the upward
movement of water. Suction pressure is also known
transpiration pull.

Root pressures: when soil water reaches the xylem

cells of the root, it is transported upwards to thexylem
cells of the stem. This needs a certain amount of
pressure in the root system. This pressure is known as
root pressure.
Suction pressure or transpiration pull: it is the total
force, pull or suction by which the cells absorbwater
from its surroundings. The pressure is normally created
when water is lost in the form of transpiration through
the stomata of the leaves or transpiration is the process
by which water evaporates from the aerial parts of a
plant mainly through the stomata in the leaves. The
cells of the spongy mesophyll lose water to the
intercellular spaces of the leaf and finally to the
atmosphere.

CONDITIONS AFFECTING THE RATE OF

TRANSPIRATION
There are many factors which affect the rate at which
water vapour is lost by plants. These include:
i. The size of the stomata pores: for transpiration to
occur in a leaf, the stomata pores must beopen but
the rate of transpiration depends on how wide each
stomata opening. While flaccidity of the cells
causes the guard cells to close.
 ii. Temperature: low temperature gives rise to low
rate of transpiration while increase intemperature
gives rise to high rate of transpiration.

iii. Soil water: when the level of soil water is higher

than the rate of absorption (rate oftranspiration)
will be higher and vice –versa.

iv. Humidity: the higher the humanity of the

atmosphere, the slower the rate of transpiration
andvice versa.

v. Wind: the higher the speed of wind, the higher the

rate of transpiration and vice-versa
vi. Light: high light intensity leads rate of
transpiration in vice-versa.
Advantages of transpiration to plants
a. It helps plants to absorb water and mineral salts
from the soil
b. It removes excess water from the plant.
c. Transpiration cools the plants through evaporation
of water.

d. It takes part in the movement of soil water.

TRANSLOCATION
It is the process by which manufactured food substances
are transported from where they are manufactured to the
tissues where they are needed or stored through the
phloem vessels/tissues.

Materials commonly transported in plants are sugar,

glucose or carbohydrates, oil, resins, proteins or amino
acids, alkaloids and hormones.

SIMILARITIES AND DIFFERENCES BETWEEN

TRANSPORT IN ANIMALS AND PLANTS
Similarities
i. In both, liquid medium is required for
transportation in plants and animals.
ii. Diffusion plays a major role in both.
iii. Tubular or cylindrical vessels are necessary in
both.
iv. Materials and hormones are transported in
dissolved form.
Differences between transport in plants and animals
Plants Animals
i. Cell sap is the Blood is the medium
medium
ii. Material (water Materials are transported in
 and food) are the same vessel
transported
through different
vessels force for
pull
III. Transport medium Transport medium is made
is not tissue up of different tissues.

RESPIRATORY SYSTEMS
Respiration can be defined as the oxidation of food to
release energy for use by living organisms for various
life activities. Respiratory system involves the
exchange of gases i.e. oxygen and
carbondioxidebetween organisms and its environment
using specialized organs called respiratory organs.

STAGES OF RESPIRATION

Respiration occurs in two stages, these are:

 External respiration or gaseous exchange:
This is the exchange of gases between
therespiratory organs of an organism and its
environment. For animals, this process involves
the breathing in of oxygen into the respiratory
 organs and the breathing out of carbondioxide
and water vapour. The intake of oxygen is called
inhalation or inspiration while the release of
carbondioxide and water from the respiratory
organ is called exhalation or expiration.

 Internal or tissue (cellular) respiration: This is

the oxidation of food consumed by theorganisms
to release energy, carbondioxide and water. It is
also called cellular respiration and can be
represented by the equation:

CONDITIONS NECESSARY FOR RESPIRATION

Some conditions must be met for respiration to occur,
these are:
 Presence of respiratory organs

 Presence of respiratory medium

 Presence of respiratory surface

 Transport medium

RESPIRATORY SURFACE (Characteristics)

  Respiratory surface must possess large surface area
to aid quick diffusion of gases.
 It must possess a thin-walled membrane to reduce
diffusion distance.

 It must possess a moist or wet area for dissolved

gases to pass.

 It must possess a permeable structure to allow the

exchange of gases.

 It must possess different gas concentration

gradient to facilitate the exchange of gases by
diffusion.

 It must possess vascularised structures equipped

with capillaries for easy exchange of gases.
 It must possess adequate supply of transport
medium like blood.
ORGANISMS AND THEIR RESPIRATORY
SURFACES

RESPIRATORY
ORGANISM STRUCTURE/ORGAN

i. Unicellular Organisms Plasma membrane or cell

 membrane

Simple multicellular Cell membrane and body

ii. organism (hydra, surface.
earthworm, tapeworm)

iii. Mollusc (Aquatic Snail) Gills

iv. Fish and tadpoles Gills

v. Insects (Cockroach) Trachea

vi. Arachnids (Spider) Lung books

vii. Reptiles (Lizards) Lungs

viii.Amphibians (Toad) Mouth, skin and lungs

ix. Birds Lungs

x. Mammals (Rat, dog, Lungs

 man)

Flowering plants
xi. (maize, plant) Stomata and lenticels

RESPIRATORY MECHANISMS AND GASEOUS

EXCHANGE
UNICELLULAR ORGANISM
The mechanism involved in the diffusion of oxygen into
the body and removal of carbondioxide from the body.
The respiratory system in unicellular organism is
through the entire body surface or plasma/cell
membrane via diffusion. This occurs when the surface
area to the volume of oxygen required is large (surface
area to volume ratio).

ARTHROPODS (INSECT – COCKROACH)

The respiratory system in arthropods is the tracheal

system. Gaseous exchange occurs through the tiny holes
on the abdominal segments of the insects called
spiracles, which are connected to certain tubes called
tracheae. The tracheae further splits into tracheoles
linking the body tissues and cells.

DIAGRAM SHOWING THE POSITION OF

SPIRACLES IN INSECTS
DIAGRAM SHOWING THE STRUCTURE OF
THE TRACHEAL SYSTEM OF INSECT
RESPIRATION HIGHER ORGANISMS AND
VERTEBRATES

Fish (Tilapia) and tadpole

The respiratory organ for gaseous exchange in fish and

tadpole is gills. Basically, gills are offshoots from the
body which projects into the external environment and
linked with the circulatory system in the body. Gills are
found in the head region in group of three or four
located in the chamber covered with operculum.

The structures of the gills are as follows

 Gill filament: the place where gaseous exchange

occurs.

 Gill raker: it helps to stop food particles from

entering the gill chamber.

 Gill arch: it bears the gill filaments.

 Gill chamber: it is the compartment in which the

gills are located.
DIAGRAM SHOWING THE GILLS OF A BONY
FISH

In tadpole (young toad), gaseous exchange occurs in the

gills. At the early stage, it breathes in and out by
external gills by simple diffusion of gases between the
tadpole and the surrounding water.

Later, the tadpole develops internal gills under the spout

(operculum) for gaseous exchange similar to the type in
fish.
DIAGRAM OF YOUNG TADPOLE WITH
EXTERNAL GILLS

Toad

In amphibians such as toad and frog, gaseous exchange

takes place in three different organs. These are:

 Mouth (mouth or buccal respiration)

 Skin (skin or cutaneous respiration)

 Lung (lung or pulmonary respiration)

DIAGRAM OF RESPIRATION IN TOAD (for
explanation)

Mouth or buccal respiration:

In mouth, the toad carries out the exchange of gases

through the mouth when on land. Buccal respiration
takes place in toad as follows:

1. To breathe in, the toad closes its mouth, opens

its nostrils and lowers the floor of the mouth.

2. The air pressure in the mouth is reduced

making air to draw into the nostrils.

3. Then, the nostrils and glottis are closed and the

gases are exchanged in the buccal cavity
between the blood in the capillaries and the
inhaled air.
 4. To breathe out i.e. remove carbondioxide, the
toad raises the floor of the mouth.

5. The air pressure in the buccal cavity then

increases, thus the nostrils are opened and
carbondioxide is forced out to the surrounding.

Skin (cutaneous) respiration:

At adult stage, the toad is able to carry out respiration

by using its skin which is moist, rich in blood
capillaries and larger in surface area with continuous
secretions from the mucus glands.

 In water or land, oxygen diffuses directly through

the entire body (skin) into the blood of the
capillaries in the skin.

 Blood rich in dissolved oxygen is transported to the

cell and tissues within the body and exchange of
gases occurs.

 Carbondioxide from the body cell diffuses out from

the blood in the capillaries through the skin surface.
Lung (pulmonary) respiration:

Under normal condition, the toad lives on cutaneous

and buccal respiration but during increased body
activities, lungs respiration is involved. Lung
respiration occurs majorly on land and its mechanism
resembles that of buccal respiration.

MAMMALS

The organ of respiration in mammals is the lung

alongside with vertebrates such as lizards and birds
which live outside the aquatic environment. The lung is
a paired organ with one on each side of theheart of a
mammal and is located within the thoracic cavity of the
body.
Diagram on the respiratory system of man

The respiratory system in mammals such as humans

consists of the nasal passages (nostrils), pharynx, larynx
(voice box), trachea (wind pipe), bronchus, bronchioles
and the alveoli, with epiglottis (a flat piece of tissue)
covering the entrance of the larynx to prevent food
particles from entering the respiratory tract. The trachea
splits into bronchi and have rings of cartilage which
strengthen them and prevent their collapse under low
pressure while the bronchi break into small holes called
bronchioles linking the several sacks called alveoli. The
alveoli are rich in blood capillaries for gaseous
exchange to take place.
DIAGRAM OF ALVEOLI AND BLOOD SUPPLIES
MECHANISMS OF RESPIRATION IN MAMMALS

This include the two stages, namely:

the external and

the internal or tissue/cellular respiration

External respiration (gaseous exchange)

This is the exchange of gases (oxygen and carbondioxide)

between respiratory organs of living organisms and their
environment. External respiration involves two processes,
these are

c. Inspiration or inhalation and

d. Expiration or exhalation

Inspiration or inhalation: this is the breathing in of

oxygen into the lungs.

Processes involved in inspiration

The thoracic cavity increases in volume.

1. The diaphragm contracts, flattens downwards.

2. The intercostal muscles contract.

3. The ribs move upwards and outwards.

4. The sternum (breast bone) moves upwards and

outwards.

5. The thoracic volume increases

Expiration or exhalation: this is the breathing out of

carbondioxide and water vapour out of thelungs in the
body into the environment (air or water).

Processes involved in expiration

 The thoracic cavity decreases in volume.

 The diaphragm and intercostals muscles relax.

 The sternum moves upwards.

  The ribs move downwards and inwards.

 The thoracic cavity volume decreases.

GASEOUS EXCHANGE

The process of inspiration is followed by gaseous

exchange, the air rich in oxygen dissolves in the thin
water coverings of the alveolar wall before diffusing into
the blood.

GASEOUS COMPOSITION OF INHALED AND

EXHALED AIR

Air Component Inhaled Air Exhaled Air

Oxygen 21% 16%

Carbondioxide 0.003% 4%

Nitrogen 79% 79%

 Water vapour Variable Saturated

During normal breathing, about 500cm3 of air moves in

and out of the lungs, this amount is called tidal air. The
remaining or left over in the lungs which can never be
expelled is called the residual air while the total
amount of air the lungs are capable of holding up is
called total lung capacity.

GASEOUS EXCHANGE IN PLANTS

Gaseous exchange occurs in plants in two main processes.

These are

a. Photosynthesis and

b. Respiration
The differences between the process of photosynthesis
and respiration are highlighted below:
Photosynthesis Respiration
1. It occurs in It is carried out by a
green plants plant cells
2. It occurs during the It occurs at all times.
day (in sunlight)
3. It is a fast and It is slow due to
vigorous process inactive nature of
plants.
4. Carbondioxide is Oxygen is taken in and
taken in and Oxygen Carbondioxide is given
out
is given out
5. Photosynthesis Respiration releases
absorbs solar energy energy as ATP
6. It involves the It involves break down
production of of food to release
organic food energy
(glucose)

Gases move in and out of plants through tiny openings of:

  Leaves – stomata

 Stems – lenticels

 Root hairs in young roots.

Stomata

Stomata are thin openings found in the epidermal layer of

leaves and stems of seedlings. They occur mainly on the
lower surface of dicotyledonous leaves (cowpea) while on
monocotyledonous leaves (maize) they are found on both
sides. Each stoma (singular) is surrounded by two bean
shaped cells called guard cells which control the opening
and closing of the stomata.
Diagram illustrating the opening and closing of stoma

Opening and closing of the stomata

The opening and closing of stomata controls the
movement of gases in and out of the leaves. Normally,
stomata open during the day and closes at night. Changes
in the solute concentration of the guard cells cause water
to flow in and out of them by osmosis. During high solute
concentration, water flows into the guard cells causing
turgidity and thin walls stretch more than thicker walls to
make the stoma open. During low concentration of solute,
water flows out of the guard cells, the turgidity and
volume decrease and they become flaccid, so the walls
(thin and elastic) return to their original position, causing
the guard cells to straighten up and close. The solute
concentration include sugar and ions like potassium (K)
and energy is required in the movement of the ions.

Lenticels

They are tiny pores or air slits found as scars on the stems
and roots that exhibit secondary thickening. A lenticel
consists of a loose mass of small thin-walled cells which
permits easy diffusion of gases in and out of the stem. As
the cortices increase in number and size, the epidermis
ruptures to form an opening (lenticels) for gaseous
exchange
Diagram of the structure of a lenticel
Root hairs

Root hairs provide a large surface area for the gaseous

exchange between the cells and its environment (oxygen
dissolved in the moist soil). The root hairs absorb water,
mineral salts and oxygen by diffusion while
carbondioxide produced by the root cells during cellular
respiration diffuses out into the soil through the root hairs.

EXCRETORY SYSTEM

Excretion is defined as the process by which waste

products of metabolism are removed from the body of
living things.

Egestion is the removal of solid undigested food

substances which are not by-products of metabolism e.g.
the removal of faeces from anus.
Secretion on the other is the production of useful
substances such as enzymes and hormones by metabolic
processes in the body.

IMPORTANCE OF EXCRETION
1. Excretion helps to remove poisonous/ toxic or
unwanted substances.

2. It helps in controlling body temperature.

3. Excretion helps to maintain water balance in the

body.

4. Excretion also helps to maintain salt balance i.e.

homeostasis in the body.

5. Waste products when not removed can interfere

with normal metabolic activities of the body.

6. Regulation of hydrogen ion concentration of the

body.
EXCRETORY SYSTEMS OR ORGANS OF SOME
ORGANISMS

ORGANIS EXCRETORY Waste products

M SYSTEM/ORGAN excreted
S
i. Protozoa e.g. Contractile vacuole Carbon dioxide,
amoeba by diffusion ammonia and
water
ii. Flatworms Flame cells Carbon dioxide,
e.g. ammonia and
tapeworm water
iii. Annelids e.g. Nephridia Water, urea,
earthworm carbondioxide
and nitrogenous
iv. Insects Malphighian tubules Water,
carbondioxide and
uric acid
v. Crustaceans Green glands. Water, urea,
carbondioxide and
ammonia salts.
vi. Fishes Kidneys Urine containing
urea, salts, water,
Amphibian
hormones and uric
Reptiles acid
 Birds,
mammals
lungs Carbondioxide
and water vapour
Liver Bile salts, water
and urea
x. Mammals Skin Sweat containing
urea, salts and
water
xi. Flowering Stomata and Water,
plants lenticels. carbondioxide and
oxygen
Flowering Back of trees Tannins,
plants mucilage, bum,
crystals,
anthocyanin,
alkaloid, resin, oil
and latex

EXCTRETORY SYSTEM IN EARTHWORM

The nephridia are the excretory organs of the
earthworm. Each nephridium is surrounded by a
capillary network. The waste products, mainly urea are
excreted from the blood capillaries surrounding the
nephridia. Waste products are also removed from the
fluid into the body cavity and passed into the funnel.
Fluid containing waste products moves through the long
tubes of the nephridia. Along the way, salts and other
substances that are useful to the body are reabsorbed
through the walls of the tubes. The unabsorbed
substances including water, is collected in the muscular
tube as urine. The excretory pore relaxes to allow the
urine to escape to the exterior. Earthworm gets rid of
carbondioxide during gaseous exchange through the
moist body surface or skin.
DIAGRAM OF nephridia(Excretory System of
Earthworm)

EXCTRETORY SYSTEM & MECHANISM IN

INSECTS

The organs responsible for excretion in insects are the

malpighian tubules. These are outgrowths from the
exterior portion of the small intestine. They are fine, long
and slender, found floating between glands and organs in
most parts of the thorax and abdomen.
Nitrogenous waste products and water which are liberated
into the haemocoel are absorbed at the distal end of the
malphighian tubules. The nitrogenous wastes are
converted to uric acid as it passes along the malpighian
tubule towards the gut. A lot of water is also reabsorbed
so that by the time the uric acid reaches the proximal end
of the tubules, it is changed into solid crystals. In the hind
gut, more water is reabsorbed by the rectal glands. Thus,
the urine with faeceswhich eventually leaves the body is
very concentrated i.e. almost a dry solid.
EXTERNAL FEATURES OF MALPHIGHIAN
TUBULE

LONGITUDINAL SECTION OF MALPIGHIAN

TUBULE
FLATWORMS
The excretory organs of the flatworms especially the free
living planarian are the flame cells. In these animals, there
are two longitudinal excretory canals with a number of
openings to the exterior on the body surface. The canals
consist of numerous branched tubules. The fine end of the
tubules end in a specially hollow structure called flame
cells. In a flame cell, the nucleus is displaced to one side
of the cell and the cytoplasm has a large hollow called the
cell lumen. The lumen is continuous with the fine tubules.

The waste products especially water, ammonia and

carbondioxide diffuse from the surrounding cell into the
flame cells. With the aid of the flagella, the fluid
containing the waste products is propelled into the
tubules. From there, the fluid passes into the exterior.
Diagram of flame cell

EXCRETION IN MAMMALS

STRUCTURE OF THE KIDNEY

The mammalian kidney is a bean shaped and reddish
brown organ located in the posterior end of the abdomen.
In a longitudinal section, the kidney has two distinct
regions – an outer cortex and an inner medulla.
LONGITUDINAL SECTION OF THE KIDNEY
THE EXCRETORY SYSTEM OF MAMMALS

The kidney is supplied with blood vessels. The renal

artery supply blood to the kidney while the renal vein
takes away blood from the kidney. A long narrow tube
called the ureter connects the kidney to the urinary
bladder where urine is stored temporarily. The urinary
bladder leads to the urethra which opens to the exterior
from which urine is finally passed out.

THE STRUCTURE OF THE URINARY TUBULE

The urinary tubule or nephron is the functional unit of the

kidney. Each tubule starts in the cortex as a cup-shaped
structure called the Bowman’s capsule. The capsule opens
into a short coiled tube referred to as the proximal
convoluted tubule. Then it straightens out as it passes into
the medulla where it makes a u-shaped loop called the
Henle’s loop before re-entering the cortex.

URINARY TUBULE
MECHANISM OF EXCRETION IN MAMMALS
(URINE FORMATION)

The process involved in the formation of urine occur in

three phases which are

 Ultra filtration

 Selective re-absorption

 Hormonal secretion

Ultra filtration: in the first phase, blood is brought

to the kidney by renal arteries. As it circulatesthrough
the capillaries or glomerulus of each Bowman’s
capsule, water, urea, nitrogenous compounds, mineral
salts, sugar, glucose and plasma solutes are filtered
into the capsules. This process of filtering materials
from the glomerulus into the Bowman’s capsule is
called ultra filtration.
Selective re-absorption: the fluid in the capsule or
glomerular filtrate now flows down thetubule. At the
proximal convoluted tubule and Henle’s loop, some
water, sugars, amino acids which are re-absorbed into
the blood capillaries against concentration gradient or
by active transport. This process of re-absorbing
useful materials back into the blood is called
selective re-absorption.

Hormonal secretion: the fluid in the tubule becomes

more concentrated as it flows through thedistal tubule
where more water is re-absorbed by the action of
Anti-Diuretic Hormone (ADH) and urine is finally
formed. The urine gradually trickles into the renal
pelvis and 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

The main excretory organs of flowering plants are the

stomata in the leaves and lenticels in the stem. Some of
the excretory products in plants are:

Carbon dioxide which is excreted by diffusion

through the stomata or lenticels.

Water: water is excreted by diffusion out of the

stomata or lenticels and through guttation
ortranspiration.

Oxygen: oxygen produced during photosynthesis is

removed or eliminated by diffusion throughthe
stomata or lenticels.

Oils and resins: these are stored in the cell

cytoplasm where they are kept from the system
untilthey can be eliminated.
Latex: latex is stored in tube-like system in tissues
and kept harmless until they ooze out of theplant
when part of it is damaged.

Tannins, mucilage, gum, crystals, alkaloids and

anthocyanin: these pigments are converted into
insoluble compounds and deposited in dead tissues
like the bark of stems, leaves and petals which are
shed periodically.