Theory question 102
Homeostasis(a) Describe the process of osmoregulation in (i) a named unicellular organism (ii) man
(b) Describe how the mammalian skin can react to regulate the body temperature in a hot room
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(a)(i) Amoeba (freshwater): water enters continuously by osmosis because its cytoplasm is more concentrated than the surroundings; the contractile vacuole collects the excess water, swells, moves to the surface and bursts, expelling the water; this repeats, so the cell does not burst
(ii) Man: osmoreceptors in the hypothalamus detect the water content of blood; if blood is too concentrated the pituitary releases more ADH, the distal tubules and collecting ducts reabsorb more water and little concentrated urine is made; thirst makes the person drink; if blood is too dilute less ADH is released and much dilute urine is passed; salts are also regulated by the kidney (aldosterone)
(b) Vasodilation – skin arterioles widen, more blood flows near the surface and loses heat by radiation; sweat glands produce more sweat, whose evaporation takes latent heat from the skin; hair erector muscles relax so hairs lie flat and trap little air; metabolic rate falls
Name the organism in (a)(i) before describing it.