Theory question 101
Cell and Its Environment(a) Explain briefly four factors that affect the diffusion of substances.
(b) Explain the following terms: (i) active transport; (ii) transpiration.
(c) State four ways by which plants can reduce high rate of transpiration.
(d) State the features of red blood cells and how these features adapt the cell to perform its functions.
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(a) Any four, each explained: concentration gradient — the steeper the gradient, the faster the diffusion; temperature — higher temperature makes molecules move faster; size of molecules — small molecules diffuse faster; surface area — a larger area allows more diffusion; distance/thickness of membrane — thinner surface, faster diffusion; medium — faster in gases than in liquids.
(b)(i) Active transport: movement of substances across a living membrane from a region of low concentration to high concentration (against the gradient), using energy (ATP) from respiration.
(ii) Transpiration: loss of water as vapour from the aerial parts of a plant, mainly through the stomata of leaves.
(c) Any four: thick waxy cuticle; sunken stomata; few or small stomata; leaves reduced to spines/needles or small leaves; hairy leaves; rolling of leaves; shedding of leaves in the dry season; closing stomata during the hottest part of the day.
(d) Biconcave disc shape — large surface area for absorbing oxygen; no nucleus — more room for haemoglobin; contains haemoglobin — combines with oxygen to carry it; thin membrane — short diffusion distance for gases; small and flexible — can squeeze through capillaries.
In (d) pair each feature with how it helps the cell carry oxygen.