Tj789
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Here's my answer- is it a "model" answer if not please can someone add to it?

Small organisms can exchange substances easily across their outer surface. This is because they have a large surface area to volume ratio, so diffusion alone is adequate as their surface area is large enough to allow molecules to move across quickly to get to the cells , in order for those cells to survive. As well as this in small organisms its cells are quite close to the environment, and substances don’t have to travel a long distance to reach the centre of the cell, so diffusion is fast enough to meet all the cells need as the diffusion distance is low. Also small organisms are generally not as active, so don’t need substances as fast, which again means diffusion is adequate enough.

And of course if it said large organisms, I'll just say how they have a small surface area to volume ratio, so diffusion is now adequate enough to meet the cells needs quickly. How they have a number of layers of cells so diffusion distance is increased. And their higher activity level.


My confusion: does this all apply with transport systems to? If the question was "why do small organisms need transport systems?" Can I use this EXACT same answer and get the marks?
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Tj789
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