Theory question 101
ExcretionSection A
(a) Explain briefly the term excretion.
(b) Name two excretory products each of: (i) mammals; (ii) plants.
(c) Complete the table below.
Table columns: Organism | Excretory structure | Mechanism involved in excretion | Adaptation of the structure for excretion
Rows: Paramecium | ______ | ______ | Thin semi permeable membrane
Planaria | ______ | ______ | ______
Leaf of plant | ______ | Transpiration | ______
Earthworm | ______ | ______ | ______
(d) State three functions of the kidney in humans.
Show the model answer
(a) Excretion is the removal from the body of the waste products of metabolism (e.g. carbon (IV) oxide, urea, excess water and salts) which would be harmful if they built up.
(b)(i) Mammals, any two: carbon (IV) oxide; urea; water; mineral salts; bile pigments. (ii) Plants, any two: oxygen; carbon (IV) oxide; water vapour; tannins; resins; gums; latex; alkaloids.
(c) Paramecium - contractile vacuole / cell membrane - diffusion and osmoregulation (vacuole fills and bursts at the surface) - thin, semi-permeable membrane with large surface.
Planaria - flame cells - beating cilia drive waste into excretory canals and out through pores - many flame cells with cilia, joined to a network of tubules.
Leaf of plant - stomata (lenticels) - transpiration/diffusion of gases - many stomata, thin leaf with large surface and air spaces; guard cells control opening.
Earthworm - nephridia - waste filtered from body fluid through ciliated funnels (nephrostomes) and out through nephridiopores - ciliated funnel, long coiled tubule surrounded by capillaries.
(d) Any three: removes urea and other nitrogenous wastes; regulates water balance (osmoregulation); regulates salt balance and pH of blood; removes drugs/toxins; helps control blood pressure.
Each row of the table needs a structure, a mechanism and an adaptation.