Summative Practice 13 – Question 11 (Form 4 Biology Textbook Exercise and Answer)

Question 11:
(a)(i) Explain the importance of maintaining the body temperature at 37 °C.
(a)(ii) Describe two physical ways in which the body reacts to regulate body temperature after a person bathes with cold water.

(b) In your opinion, what is the effect on urine excretion if the food consumed contains large quantities of protein?

(c) Explain how the pituitary gland regulates blood osmotic pressure when a person drinks too little water.

The optimum temperature for all enzyme-catalysed chemical reactions is 37 °C. If the body temperature rises, enzyme-controlled metabolic reactions will be affected because the enzymes will become denatured.

• The erector muscles of the skin contract, raising body hairs. A layer of air trapped on the skin surface, functions as an insulator.

• When stimulated, skeletal muscles contract and relax more. The body shivers and heat is generated.

• Protein is digested into amino acids.

• Excess amino acids are toxic and cannot be stored.

• Through deamination, the nitrogenous part of amino acids is converted to urea while the non-nitrogenous (carbon chain) part is converted to glycogen or fat for storage.

• Urea is a nitrogenous waste product that needs to be excreted through the urine.

• Since the urea concentration is high in a person who ate too much protein-rich foods, urea needs a lot of water to be excreted.

• Therefore, he/she will pass urine frequently.

• When a person drinks too little water, the blood osmotic pressure will increase above normal levels.

• The osmoreceptor in the hypothalamus is stimulated. Nerve impulses are transmitted to the pituitary gland to secrete more antidiuretic hormone (ADH) into the blood.

• A high concentration of ADH increases the permeability of the distal convoluted tubule and collecting duct walls.

• More water is reabsorbed from the filtrate into the blood.

• Urine becomes more concentrated and only a small amount is excreted.

• As a consequence, blood osmotic pressure drops and returns to the normal range.

• Low osmotic pressure creates a negative feedback mechanism that reduces the activities of the osmoreceptor cells in the hypothalamus.

• This will then cause the pituitary gland to cease secreting more ADH.

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