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Movement of Substances
Quick questions on Surface area to volume ratio explained: O-Level Biology
6short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What are small organisms?Show answer
A single-celled organism is tiny and has a large surface area to volume ratio. Diffusion across its cell surface membrane alone is fast enough to supply every part of it, so it needs no special exchange surface, and the distance to its centre is short.
What are large organisms?Show answer
A large organism has a small surface area to volume ratio. Diffusion across its outer surface cannot supply all its inner cells, and substances would have too far to travel. It therefore needs:
What is the features of a good exchange surface?Show answer
A good exchange surface has a large surface area, a thin barrier (short diffusion distance), and a good blood supply or ventilation to keep the concentration gradient steep. These are exactly the factors that speed diffusion.
What is q1?Show answer
State the surface area and volume of a cube with sides of , and give the ratio. [2 marks]
What is q2?Show answer
Explain why the surface area to volume ratio falls as an organism gets bigger. [2 marks]
What is q3?Show answer
State two features of an efficient gas exchange surface. [2 marks]
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