Biological termModerate0.5 marks
4(b)
Give appropriate biological or technical terms for the following:
Movement of molecules of a substance from their higher concentration to lower concentration when they are in direct contact.
Topic: Diffusion
Previous-year question practice database
Answer
Exam answer
DIFFUSION.
Explanation
Diffusion needs NO energy and NO membrane — molecules simply spread out until evenly distributed.
Distinguish it from the two processes it is asked alongside: OSMOSIS — also passive and down a gradient, but concerns the SOLVENT (water) only and REQUIRES a selectively permeable membrane ACTIVE TRANSPORT — moves substances AGAINST the gradient and therefore REQUIRES energy from ATP
Diffusion is how gases are exchanged in the alveoli and through the stomata of a leaf.
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