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Summary 3.2.3 Plasma Membranes & Transport

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Summary for the entire of 3.2.3 for AQA A-level Biology

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3.2.3


Plasma Membranes
Structure
• eukaryotes
• selectively permeable
• phospholipid bilayer w. embedded proteins
• uid mosaic model: dif phospholipids + proteins & moving




Function
• Phospholipids
- allow lipid soluble subs enter + leave cell
- prevent H₂O soluble subs enter + leave cell
- make exible + ‘self healing’
• Proteins
- structural support
- act as receptors (e.g. hormones)
• Channel Proteins
- pores in membrane
- allow H₂O soluble ions di use across
- speci c
• Carrier Proteins
- bind to large molecules (e.g. glucose + amino acids) & change shape :. move across
• Glycoproteins + Glycolipids
- recognition sites
- help cells attach to one another
• Cholesterols
- bind to hydrophobic tails :. closer :. restrict movt :. less uid, more rigid



Transport
Diffusion
• net movt of molecules/ions from area of ↑ conc to ↓ conc, until molecules evenly distributed
• factors a ect rate:
- conc grad
- area of exchange surface
- thickness of exchange surface
• Fick’s Law: di usion proportional to:

surface area x conc di erence
length of di usion pathway



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Browse related subjects

Subjects

  • plasma membrane
  • phospholipid
  • bilayer
  • fluid mosaic model
  • hydrophilic
  • hydrophobic
  • lipids
  • diffusion
  • active transport
  • osmosis
  • co transport

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