AQA · Biology · 8461
GCSE Biology: Diffusion
Cell biology · AQA GCSE Biology (8461), specification point 4.1.3.1. Cards are generated from the exam board's own specification for "Diffusion", and every card links back to the page it came from. Specification © AQA — used with attribution.
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Define diffusion.
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The spreading out of particles of a substance in solution or of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.
Diffusion results in a net movement of particles from an area of higher concentration to an area of ? concentration.
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lower
Which two gases move in and out of cells by diffusion during gas exchange?
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Oxygen and carbon dioxide.
Which waste product diffuses from cells into the blood plasma for excretion in the kidney?
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Urea.
Name the three factors that affect the rate of diffusion.
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The concentration gradient, the temperature, and the surface area of the membrane.
Why can a single-celled organism rely on diffusion alone to meet its needs?
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It has a relatively large surface area to volume ratio, so enough molecules can move in and out of the cell across its surface.
Why do multicellular organisms need specialised exchange surfaces and a transport system?
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Their surface area to volume ratio is too small for diffusion across the outer surface alone to supply enough molecules to all their cells.
Why does a thin membrane make an exchange surface more effective?
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It provides a short diffusion path, so substances cross it faster.
In animals, an exchange surface used for gaseous exchange is more effective when it is ?.
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ventilated
Which feature of an animal's exchange surface maintains a steep concentration gradient by carrying substances away?
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An efficient blood supply.
Which organ in fish is adapted for exchanging materials?
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The gills.
Which two plant organs are adapted for exchanging materials?
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The roots and the leaves.
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