WAEC Biology 2012 Theory — Question 1

Model answer

(a) Factors affecting diffusion: Temperature — the higher the temperature the higher the rate of diffusion and vice-versa. Surface area — the larger the surface area of the exposed fluid, the faster the diffusion and vice-versa. Size of particles — small particle tends to diffuse faster than big ones. State of matter — diffusion occurs the fastest in gases, intermediate in liquids and slowest in solids. (b)(i) Active transport is simply defined as the movement of molecules against the concentration gradient. (ii) Transpiration is the loss of water in the form of water vapour from the stomata, lenticels or cuticle of a plant. (c) Ways by which plants can reduce the rate of transpiration include: closing of stomata, development of thick cuticle, reduction of leaf size, and the presence of hair on leaves. (d) The disc-like shape of red blood cells (erythrocytes) makes it able to house sufficient amount of oxygen. The haemoglobin in erythrocytes aids the attachment of oxygen.