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Biology; FORM 5: Chapter 1
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Biology Form 5: Chapter 1
1. Living organisms need to exchange substances such as oxygen, food, carbon dioxide, and other waste products with the environment through diffusion so they can continue to live and grow.
2. The exchange of substances occurs
rapidly if
a. The surface area of organism in
contact with the environment is large.
b. The volume of organism is small.
c. The total surface area/volume
(TSA/V) of organism is large.
d. The distance b/w the source of the
substances and the body cells is near.
e. A high concentration gradient is
maintained b/w the source and the body
cells.
1.1: Importance of having a transport system in some multicelluar organisms
Unicellular organisms
Unicellular organisms
1. Such as Amoeba sp. and Paramecium sp. obtain substances via diffusion
through the cell surface.
2. They do not face any problems in obtaining their cellular
requirements via diffusion because the volume of the body is very
small. As a result, the total surface area/volume ratio is very
high.
3. Therefore, nutrients and oxygen can diffuse through the cell surface
to reach the inside of the cell easily. Similarly, waste products can be
rapidly removed the cell through simple diffusion.
Multicellular Organisms
Multicellular organisms
1. In large multicellular organisms, diffusion alone cannot ensure a constant supply of oxygen and nutrients to the cells because;
(a) The total surface area/volume ratio of the organisms is too small.
(b) The distance between the source of substances and the cells of the organisms is too far
from the environment for a direct exchange to take place effectively.
2. Thus, the multicellular organisms need to overcome the problem of obtaining their
cellular requirements and in getting rid of their waste products
3. They overcome this problem by having a circulatory system to carry out;
(a) The distribution of nutrients and oxygen throughout the body and,
(b)The removal of waste products from the body.
1. The circulatory system;
(a) Delivers nutrients and oxygen in cells.
(b) Carries waste products away from the cells.
(c) Protects the body from infections.
2. The circulatory system has three major
components.
(a) The blood is a type of connective tissue made
up of plasma, blood cells, and platelets. Blood
acts as a medium of transport.
(b) The heart functions as a muscular pump that
circulates the blood throughout the body.
(c) The blood vessels are vessels consisting of
arteries, capillaries, and veins that are
connected to the heart to deliver blood to all
body tissues.
1.2 The Circulatory System
Blood and haemolymph
Blood and haemolymph
1. Blood is the medium of transport in humans and animals.
2. In many invertebrates such as insects, the medium of transport is
called the haemolymph.
3. The haemolymph is a blood-like nutritive fluid which fills the
entire body cavity (haemocoel) and surround all cells.
Functions of blood
1. Blood has three general functions: transportation, regulation, and protection.
2. Blood transports;
(a) oxygen from the lungs to the cells of the whole body and carbon dioxide from the cells to the
lungs.
(b) Nutrients, hormones, and antibodies throughout the body.
(c) Waste products away from the cells to the organs of the excretory system.
3. Blood regulates;v
(a) The pH of body fluids
(b) The body temperature.
(c) The water content of cells.
4. Blood protects us from;
(a) Excessive blood loss in an injury through the mechanism of blood clotting. It helps to heal
wounds.
(b) Diseases and helps fight against infections, for example, white blood cells carry out
phagocytosis and produce antibodies to destroy phatogens which enters the body.
Figures are showing red blood cells
Functions of haemolymph
1. Haemolymph transports water,
inorganic salts, and organic
compounds throughout the haemocoel.
2. Unlike blood, haemolymph does not
transport respiratory gases.
3. In insects, respiratory gases are
transported via the tracheal system.
Figures are showing haemolymph cells