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QLDBiologyQuick questions
Unit 1: Cells and multicellular organisms
Quick questions on Surface area to volume ratio and limits on cell size (QCE Biology Unit 1)
7short 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 is calculating SA?Show answer
For a cube of side length L: - Surface area = 6 L squared. - Volume = L cubed. - SA:V = 6 / L.
What is why this limits cell size?Show answer
Diffusion supplies oxygen, nutrients and the removal of waste from the surface. The rate of supply scales with surface area; the rate of demand scales with volume. If the cell is too large:
What is cell strategies for keeping SA?Show answer
Cells use three strategies to maintain a workable SA:V:
What is exchange surfaces?Show answer
When organisms are too large for diffusion through the body surface, they evolve specialised exchange surfaces. These maximise surface area and minimise diffusion distance:
What is forgetting the units?Show answer
A ratio of 6 means 6 area units per 1 volume unit. Always keep the units consistent.
What is treating SA:V as a yes-or-no test?Show answer
It is a continuous quantity. Cells balance their size against their metabolic demand; very active cells (liver hepatocytes, kidney tubule cells) keep SA:V high with microvilli or membrane folds.
What is saying surface area equals volume?Show answer
They scale differently. A cell that doubles in linear dimensions gains 8x volume but only 4x surface area; SA:V halves.
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