The topic Movement of Substances is likely to be covered in Secondary 3. Students will need to know what is meant by the terms diffusion, osmosis and active transport. In addition, students also need to know the application of these processes.
Diffusion is the movement of substance from a region of higher concentration to a region of lower concentration, down the concentration gradient. Another process, osmosis, is also similar, with the exception of three differences
- it is the movement of water, not substances
- from a region of higher water potential to that of lower water potential (not concentration)
- through a partially-permeable membrane.
Take note that diffusion and osmosis do not need energy (hence known as passive transport), but active transport requires energy. Active transport is the movement of substances from a region of lower concentration to a region of higher concentration, against the concentration gradient.
Students may find this easy, and it will be a bonus if this question come out, as a definition question, in Free Response Question. If question of this topic really come out, do expect some applications that you may not have seen in your textbook (e.g. transdermal patch).
Try this question: Describe what will happen to a red blood cell when it is placed in a beaker of (a) distilled water; (b) 50% glucose solution.
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