Page 139 - Biology Form Two

Biology for Secondary Schools

Table 6.4: Differences between inhalation and exhalation
Inhalation Exhalation
(i) External intercostal muscles contract (i) External intercostal muscles relax
(ii) Internal intercostal muscles relax (ii) Internal intercostal muscles contract
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(iii) The ribcage moves outward and (iii) The ribcage moves inward and
upward downward
(iv) The diaphragm contracts and flattens (iv) The diaphragm relaxes and becomes
dome-shaped
(v) The volume of the thoracic cavity (v) The volume of the thoracic cavity
increases as the pressure decreases. decreases as pressure increases. This
This allows air to enter the lungs forces air out of the lungs
(vi) Air enters the alveoli through the (vi) Air leaves the alveoli through
nostrils, pharynx, glottis, trachea, the bronchioles, trachea, glottis,
bronchioles, and finally alveoli pharynx, and finally nostrils

Activity 6.3: Demonstrate breathing in
and out Lid
Y-shaped tube

Materials Balloon

Bell jar or large empty plastic water Plastic bottle
bottle, rubber sheet or cellophane Rubber sheet
material, rubber stopper, Y-shaped glass String
or plastic tube, two balloons, petroleum Figure 6.4: Experimental set-up to

jelly, knife, scissors or razor blade, and demonstrate the breathing process
a string 2. Push the rubber sheet inward
as shown in Figure 6.5. What
Procedure happens to the balloon?

1. Set up the materials as shown in
Figure 6.4. Make sure the jar is
airtight by filling the gaps using

petroleum jelly.

Figure 6. 5:Pushing the rubber sheet inward

Student’s Book - Form Two 133

05/10/2024 15:36:43
BIOLOGY FORM 2 NEW.indd 133
BIOLOGY FORM 2 NEW.indd 133 05/10/2024 15:36:43