Summative Practice Chapter 8 – Question 6 & 7 (Form 4 Biology Textbook Exercise and Answer)

Question 6:
One of the effects of emphysema is the loss of elasticity in the alveolus. Explain the effect of this on gaseous exchange.

Less air is inhaled and exhaled, making breathing difficult. Air trapped in the alveoli may cause the alveoli to burst, producing a large air space in the alveoli. This means less total surface area for gaseous exchange.

Question 7:
(a) Name structures P and Q that help humans and fish, respectively in gaseous exchange.

(b) Explain the breathing mechanism of fish.

(C) Describe two similarities of structure P and Q that has been adapted to help P and Q function effectively.

(d) Give two reasons why the rate of oxygen supply to human cells is faster than the rate of oxygen supply to fish cells if both are of the same size.

(a) P: alveoli/lung, Q: gills

• When the mouth opens, the floor of the mouth cavity is lowered. At the same time, the operculum cavity enlarges and the operculum closes. This reduces the pressure in the mouth cavity. Water containing dissolved oxygen from outside enters the mouth.

• When the mouth closes, the floor of the mouth cavity is raised up. Water flows through the gill’s lamellae and gaseous exchange occurs between the blood and water by diffusion. At the same time, the operculum muscles relax and the operculum cavity becomes smaller. The volume of the mouth cavity is reduced resulting in a higher pressure in the mouth cavity compared to the pressure outside. The high pressure forces water to flow out through the opening of the operculum.

The surface of P and Q is always moist because they are covered in a film of fluid that helps respiratory gases to dissolve. The large number of respiratory structures provides a large total surface area to volume ratio for respiratory gaseous exchange.

The rate of oxygen supply to all cells in the human body is high because humans have diaphragm and intercostal muscles to aid in the breathing mechanism. These are not found in fish. Besides, humans have a muscular heart that is able to pump oxygenated blood to the whole body faster.

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