Page 141 - Biology Form Two

Biology for Secondary Schools

When we breathe in, air accumulates in the blood increases the rate of gas
in the alveoli. This brings higher exchange. The increase in the rate of
concentration of oxygen in the alveoli gas exchange provides the cells with an
than in the blood capillaries. Therefore, adequate concentration of oxygen and
oxygen diffuses from the alveoli into lower concentration of carbon dioxide
FOR ONLINE READING ONLY
the blood capillaries. It combines with in the blood.
haemoglobin to form oxyhaemoglobin. Haemoglobin concentration

Haemoglobin is a reddish protein
The oxygen gas is then transported to
the body cells. Once in the body cells, molecule containing an iron atom,
which is responsible for transporting
oxyhaemoglobin breaks down to release oxygen and carbon dioxide in the blood
oxygen and haemoglobin. The cells use of vertebrates. Haemoglobin transports
oxygen for respiration, whereby carbon oxygen gas from the lungs to the body
dioxide is produced as the by-product. cells and carbon dioxide from the body
This causes the levels of carbon dioxide cells to the lungs. Efficient transport of

to become higher in the cells than in gases takes place when the body has an
the blood. As a result, carbon dioxide adequate concentration of haemoglobin.
diffuses into the blood capillaries When a person is anaemic, the body has
and combines with haemoglobin to a low concentration of haemoglobin.
form carbaminohaemoglobin. Blood Therefore, a low level of oxygen can
transports carbon dioxide in this form to be transported at a time. This situation
the alveoli. This process leads to a higher results in the increase of the rate of gas
concentration of carbon dioxide in the exchange so that the cells can get enough
blood capillaries than in the alveoli. oxygen.
Therefore, carbon dioxide diffuses from Physical activity
the capillaries into the alveoli. It is then A more active body requires more
transported through the bronchioles, oxygen than a less active body. During
trachea, glottis, pharynx and finally physical exercise the muscle cells
nostrils into the atmosphere. respire more than when the body is at

Factors affecting the rate of gas rest. Therefore, the rate and depth of
exchange in mammals breathing increases. This ensures that
Gas exchange is affected by many more oxygen is absorbed into the blood,
factors, including the following: and more carbon dioxide is removed.
As a result, the rate of gas exchange
Carbon dioxide concentration increases when there is increased body
A high concentration of carbon dioxide activity.

Student’s Book - Form Two 135

05/10/2024 15:36:44
BIOLOGY FORM 2 NEW.indd 135 05/10/2024 15:36:44
BIOLOGY FORM 2 NEW.indd 135