AQA GCSE Biology Unit 3 (Higher Tier)

All you need to know about Unit 3 as told by the AQA book and my Bio teacher Mrs Moody :D 

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Absorption of Substances by Cells (Diffusion)

  • The movement of particles in a liquid or gas from a high conc'n gradient to a low conc'n gradient, until they are balanced.
  • The greater the difference in conc'n, the faster the rate of diffusion.
  • 2 examples of diffusion through a cell membrane:
    • Oxygen required for respiration diffuses into cells.
    • CO2 produced by respiration diffuses out of cells.
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Absorption of Substances by Cells (Osmosis)

  • The diffusion of water from a dilute conc'n to a higher conc'n through a partially permeable membrane.Until they are balanced.
  • 2 examples of osmosis:
    • Absorption of water by root hair cells in plants.
    • Absorption of water by epithelial cells in the small intestine.
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Absorption of Substances by Cells (Active Transpor

  • The process by which cells absorb substances against a conc'n gradient.
  • The substance transported attaches to large protein molecules in the cell membrane.
  • Energy released through respiration is used to change the shape of the protein.
  • This releases the substance through to the other side of the membrane.
  • Enables cells to absorb substances from very dilute conc'ns.
  • 2 examples:
    • Absorption of mineral ions by root hair cells.
    • Absorption of glucose by epithelial cells in small intestine.
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Gas Exchange in the Lungs

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