2.5 Biological membranes Flashcards
Name 4 roles of cell surface membranes
- Separates the cell components from the external environment
- Regulates transport of materials into and out of the cell
- May contain enzymes
- Has antigens so the organisms immune system can recognise the cell as being ‘self’ and not attack it
- May release chemical signals to other cells
2 examples of roles of membranes within cells
- Mitochondria cristae= large surface area to localize enzymes needed for respiration
- Thylakoid membranes house chlorophyll and on these membranes some photosynthesis reactions occur
Why is it called the fluid mosaic model? (2)
The proteins floating in the lipid bilayer look like a mosaic pattern.
Its fluid- cholesterol-maintains stability/fluidity
Which proteins embedded in the phospholipid bilayer require ATP to actively pump large ions across a membrane?
Carrier proteins
How do fat soluble molecules cross a membrane?
Dissolve in the lipid bilayer so can diffuse across
Define osmosis
The net movement of water molecules down their water potential gradient across a partially permeable membrane.
Name the 5 factors affecting simple diffusion
What affects simple diffusion?
- Temperature- temperature ^, diffusion ^
- Distance- distance ^, diffusion decrease
- Surface area- SA ^, diffusion increase
- Size of molecule- size ^, diffusion decrease
- Concentration gradient - gradient ^, diffusion ^
What happens to an animal cell when in solution of high water potential? (2)
water moves in down WP gradient
its cytolysed
What happens to a plant cell when in solution of high water potential? (2)
water moves in down WP gradient
it is turgid
What happens to a plant cell when in a concentrated sugar solution (i.e. low water potential)? (2)
Water moves out down WP gradient
Plant cell membrane pulls away from cell wall, it is PLASMOLYSED
What happens to an animal cell in an concentrated sugar solution (i.e. low water potential)? (2)
Water moves out down WP gradient
Cell is crenated
Define active transport
Active transport- movement of water against a concentration gradient (from high to low concentration) across a cell membrane using ATP and carrier proteins
Why is ATP required for endocytosis?
Energy to form vesicles and move them using motor proteins along cytoskeleton threads into the cell interior
How and why does increase in temperature affect membrane permeability?
increasing temperature-phospholipids kinitic energy so move, permeability increases, effects membrane proteins position may not work/may denature
How does decrease in temperature affect membrane permeability?
Saturated fatty acids become compressed
unsaturated fatty acids become compressed and their tails push adjacent phospholipid molecules away, maintaining membrane fluidity
