Summative Practice 13 – Question 8 – 10 (Form 4 Biology Textbook Exercise and Answer)

Question 8:
Describe how the body temperature of a worker who has been in a cold room for 6 hours is regulated.

• The body temperature of the worker drops after sitting in a cold room for 6 hours.

• The thermoreceptors on the skin receive stimuli and transmit nerve impulses to the temperature control centre in the hypothalamus through afferent nerves.

• A negative feedback mechanism occurs:

– Vasoconstriction takes place. This reduces the flow of blood to the skin surface and hence less heat flows to the surrounding.

– Sweat glands are not stimulated. Therefore, no sweating occurs.

– Erector muscles contract, causing body hairs to rise. A thick layer of air is trapped on the skin surface and acts as a heat insulator that prevents the loss of heat through the skin.

– Body shivers. The skeletal muscles contract and relax, generating heat and increasing body temperature.

– The thyroid gland is stimulated to secrete thyroxine and the adrenal gland is stimulated to secrete adrenaline. Thyroxine increases cell metabolism rate and adrenaline increases glycogen conversion into glucose. Glucose is oxidised to yield heat energy.

Question 9:
Breathing is an involuntary process that is controlled by the respiratory control centre in the medulla oblongata. Explain what happens to a climber’s breathing rate when he is at the peak of a high mountain.

• There is less oxygen in the atmosphere.

• The oxygen partial pressure is low.

• There is less oxygen in the blood.

• This is detected by the peripheral chemoreceptors. Nerve impulses are generated and sent to the respiratory and cardiovascular control centres, and then to the intercostal muscles, diaphragm and cardiac muscles.

The rate of contraction and relaxation of the intercostal muscles and diaphragm increases, hence increasing the breathing (inhale/exhale) rate. Heartbeat also increases.

• More oxygen is brought to the cells and more carbon dioxide is transported to the lungs.

Question 10:
Explain the role of erector muscles, fine hair and sweat glands in maintaining the body temperature on hot days.

• The erector muscles relax, causing the body hairs to lean towards the skin surface.

• Body hairs trap a thin layer of air allowing more heat to be released to the surrounding.

• Sweat glands secrete sweat. When the sweat evaporates, heat is lost to the surrounding.

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