Page 114 - Biology Form Two

Biology for Secondary Schools

Plasma is also important for distributing Another feature is the lack of a nucleus,
heat to all parts of the body, regulating which increases the total surface area
the pH of body fluids, and maintaining for loading respiratory gases. Their
a normal balance of body fluids. membrane is also very flexible and can
bend in many directions without being
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Red blood cells damaged. This helps them to pass
These are red, round, biconcave cells through the capillaries.
with no nucleus when mature, as shown
in Figure 5.8. They are also called Transport of oxygen: In the lungs,
erythrocytes. One millilitre of blood there is a high concentration of oxygen
has approximately 5 to 6 million red gas. Haemoglobin combines with
blood cells. Erythrocytes are formed in oxygen gas to form oxyhaemoglobin.
the red bone marrow. Their lifespan is This is an unstable compound, which
about 120 days. The liver and the spleen releases oxygen by diffusion when it
destroy old red blood cells and release reaches a tissue fluid that has a low
haemoglobin for the formation of new concentration of oxygen gas. The
cells. Haemoglobin is a red pigment formation of oxyhaemoglobin and the
in the erythrocytes, which gives them release of oxygen gas and haemoglobin
a red colour. Haemoglobin has a high can be shown using the following
affinity to oxygen. equation of a reversible reaction.

Haemoglobin
+ oxyhaemoglobin
oxygen

Oxygen diffuses out of the red blood
cells, through the capillary walls to the
tissue fluid.

Transport of carbon dioxide: This
Figure 5.8: Red blood cell occurs when carbon dioxide combines
Functions of red blood cells with haemoglobin in the red blood
The red blood cells transport oxygen cells to form carbaminohaemoglobin.
from the lungs to the body cells and This combination occurs in the tissue
carbon dioxide from the body cells to fluid where the concentration of carbon
the lungs. The features that facilitate dioxide is high. The formed compound
the adaptation of red blood cells is transported to the lungs where carbon
to its function are the presence of dioxide is released and expelled from
haemoglobin pigment, its biconcave the body through exhalation.
shape, and their large numbers.

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BIOLOGY FORM 2 NEW.indd 108 05/10/2024 15:36:39