The mechanisms by which substances can move into and out of cells, across cell membranes, needs to be clearly understood by GCSE Biology students. Students need to be able to explain what diffusion is, examples of substances transported in and out of cells by diffusion and the factors that affect the rate of diffusion. Similarly students need to explain how water may move across the cell membrane via osmosis. With active transport students need to explain how substances are moved against a concentration gradient and that this requires energy from respiration. Having an understanding of all three processes should allow students to compare the processes and explain the differences between them.
The transport of substances is often a difficult and abstract concept for students and as such a number of misconceptions occur. As this is a fundamental concept which is then seen in many other GCSE Biology topic areas, it is vital that students understand the mechanisms fully.
Confusion is often seen in terms of the differences between diffusion and osmosis, so it is important to stress this difference clearly, and reinforce and revise it in other topics,ensure that students clearly understand that osmosis is only ever the movement of water.
Similarly students have difficulty understanding the term net movement and concentration gradient, as well as the difference between active and passive movement. Using animations and getting students to do "the voice over" or getting students to give presentations to articulate the processes can help to ensure that misconceptions do not occur.
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