Transport through cell membranes (AQA A-level biology (AS) TOPIC 2 CELLS) A* notes
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Course
Unit 2 - Cells
Institution
AQA
Summarised notes on transport through cell membrane, exploring osmosis, facilitated diffusion etc. Notes on TOPIC 2 of AQA Biology- and the transport through cell membrane chapter. These notes got me an A*.
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transport through cell
membranes
cell membrane
functions:
permit movement of substances by controls entry & exit of substances
endocytosis and exocytosis
barrier to many water-soluble
permit recognition by other cells substances
provide receptors for signalling keep large molecules (e.g.
molecules (e.g. hormones) enzymes) within
allows cell to change shape permeable to small molecules
(e.g. water, oxygen, carbon
transport and packaging within a cell
dioxide)
often extended into microvilli to
permeable to selected molecules
provide a large surface area for
(e.g. glucose, ions)
absorption
structure:
transport through cell membranes 1
, function - green
normal thickness of phospholipid bilayer
is 5-10nm
phospholipids
hydrophilic phosphate heads face
aqueous solution
hydrophobic fatty acid tails face
inwards
why phospholipids form a bilayer:
phospholipids are amphipathic molecules:
phospholipids have a polar phosphate group which is hydrophilic and will face
aq.
the fatty acid tails are non-polar and are hydrophobic will move away from aq.
as both tissue fluid & cytoplasm is aqueous, phospholipids form two layers with the
hydrophobic tails facing inward and phosphate groups outwards interacting with the
aq. environment
phosphate has charge → hydrophilic → interacts with water
allows lipid soluble substances to enter and leave the cell
prevents water-soluble substances entering and leaving cells (due to hydrophobic
fatty acid tails)
makes membrane flexible and self-sealing
cholesterol
a lipid that helps to stabilise membrane by partially immobilising fatty acid
chains by pulling them together
not in bacterial cell membranes
transport through cell membranes 2
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