Formative Practice 8.2 (Form 4 Biology Textbook Exercise and Answer)

Question 1:
State the function of the spiracle in the breathing mechanism of insects.

Spiracles are air pores that connect the respiratory structure of insects with the external environment.

Question 2:
How do abdominal muscles help insects to breathe?

• During inhalation, the abdominal muscles relax and the spiracle valves open. This reduces the internal pressure of the trachea causing air to be drawn into the trachea through the spiracle.

• During exhalation, the abdominal muscles contract. This increases the internal pressure of the trachea forcing air out through the spiracle.

Question 3:
State the two differences between the respiratory mechanisms of fish and humans.

• Fishes have filaments and gills as their respiratory structures while humans have alveoli.

• The respiratory tract/opening of fish is the mouth and operculum while in humans, it is the nose.

Question 4:
Explain the mechanism of inhalation in humans.

• The external intercostal muscles contract, the internal intercostal muscles relax.

• The action causes the rib cage to move upwards and outwards.

• At the same time, the diaphragm muscles contract and the diaphragm is lowered and flattened.

• Both movements cause the volume of the thoracic cavity to increase and its pressure to decrease.

• The higher atmospheric pressure outside forces air into the lungs.

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