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Cell membrane, Osmosis, Exocytosis and Endocytosis, (Phospholipids are…
Cell membrane
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Membrane transport
- The plasma membrane is selectively permeable.
- Allows the passage of some ions and molecules but not others.
- This structure ensures that:
1-Essential molecules enter.
2-Metabolic intermediates remain.
3-Waste products exit.
- Passive transport: (requires no input of energy)
- Active transport: (requires input of energy)
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- Membranes are semifluid.
- Movements of lipids:
1-It can move laterally within the membrane.
2- Lipid movement via flippase. Flippase requires AT transport lipids between leaflets.
Osmosis
Osmosis in animal cells:
- Creation: shrinkage of a cell in a hypertonic solution.
- osmotic lysis: swelling and bursting of a cell in a hypotonic solution.
Osmosis in plant cells:
- A cell wall prevents major changes in cell size.
- Plasmolysis: plants wilting because water leaves plant cells.
- Turgor pressure: pushes plasma membrane against cell wall (Maintains shape and size).
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- (Phospholipids are amphipathic molecules)