KCSE 2014 Q7 a) HOW DOES EXCRETION TAKE PLACE IN PLANTS. (4 MARKS) b) DESCRIBE THE ROLE OF HUMAN SKIN IN HOMEOSTASIS. (16 MARKS)

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(a) HOW DOES EXCRETION TAKE PLACE IN PLANTS. (4 MARKS) 
  • Diffusion of Carbon (IV) Oxide; and oxygen; through stomata and lenticels;
  • Some wastes are stored in tissues in non-toxic form e.g. calcium oxalate;
  • Some of these tissues or organs drop off from plants e.g. leaves, flowers, fruits and bark containing caffeine, nicotine, quinine;
  • Some wastes are released by transpiration through stomata and lenticels such as water vapour;
  • Others are released by guttation through hydathodes as liquid water;
  • Others are released by exudation. 
(max 4 marks)

(b) DESCRIBE THE ROLE OF HUMAN SKIN IN HOMEOSTASIS. (16 MARKS)
  • When body temperature is lowered below normal;arterioles in the skin constrict; blood is diverted to a shunt system; less blood flows to the skin/less heat is lost;
  • When body temperature is raised above normal; arterioles in the skin dilate; more blood flows to the skin; more heat is lost by convection and radiation;
  • When body temperature is lowered below normal: erector-pilli muscles contract, hair stands erect; more air is trapped, air is a bad conductor;and insulates the body against heat loss;
  • When body temperature is raised above normal: erector-pilli muscles relax, hair lies on skin; less air is trapped, more heat is lost; 
  • When body temperature is lowered below normal: less fluids are absorbed by sweat glands; less sweating, less vaporisation of water;
  • When body temperature is raised above normal: sweat glands are more stimulated and more sweat is produced; water in sweat evaporates and takes up heat from the body; body is cooled/body temperature is lowered;
(18 marks)
(Max 20)

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