Formative Practice 13.1 (Form 4 Biology Textbook Exercise and Answer)

Question 1:
What is the meaning of homeostasis? Explain how homeostasis happens.

Homeostasis is the regulation of the physical and chemical factors of the internal environment within a normal range so that cells can function optimally.

The mechanism of homeostasis occurs by negative feedback:
• A values that exceeds the normal range is reduced back to normal.

• A value that drops below the normal range is raised back to normal.

Question 2:
An employee had to work in hot conditions because the power supply in his office got cut off. Describe the response of the effectors in regulating his body temperature.

Mechanism of homeostasis:
• Vasodilation occurs

• Sweat glands secrete sweat

• Erector muscles relax – body hairs are lowered

• Skeletal muscles contract and relax lesser. Body does not shiver.

• The adrenal and thyroid glands are less stimulated – metabolism rate is lowered

Question 3:
A 40-year-old man was diagnosed by a doctor as unable to produce enough insulin. Describe what has happened to the man.

Excess glucose is not converted into glycogen. The glucose level in the blood rises (hyperglycaemia) and glucose is excreted through the urine (glycosuria). In this condition, the individual is considered as having diabetes mellitus. A diabetic patient is constantly feeling thirsty, exhausted and lethargic and experiences weight loss. If left untreated, it may lead to death.

Question 4:
Ahmad has just finished a 100 m sprint run. Explain how his blood pressure is lowered back to normal range.

• Blood pressure rises. The baroreceptor on the aortic arch and arterial carotid are stimulated.

• The cardiovascular control centre in the medulla oblongata is stimulated.

• The smooth muscles of the artery wall relax (vasodilation), hence reducing resistance to blood flow in the blood vessels.

• The cardiac muscles contract weakly.

• Blood pressure returns to normal.

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