Biology AS - Biological Membranes

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Phospholipid Bilayer

Structure:

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Limiting Factors

- Solvent: increasing concentration results in increased membrane permeability - Causes lipids to dissolve which causes the membrane to unravel

- Temperature below 0 degrees: Phospholipids have little energy which causes the channel proteins and protein carriers to denature

- Temperature between 0 degrees and 45 degrees: Phospholipids move which allows partially permeability

- Temperature over 45 degrees: Phospholipids break down, water expands and puts pressure on the membrane – this causes the proteins and bilayer to denature

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Osmosis - Passive Process (No ATP)

Factors: 

Concentration gradient – higher = faster

Thickness of exchange surface- thinner = faster rate

Surface area – larger = faster

Temperature – warmer = faster rate

Area of High Water Potential to a area of Low Water Potential

   - Down a water potential gradient

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Diffusion - Passive Process (No ATP)

Factors: 

Concentration gradient – higher = faster

Thickness of exchange surface- thinner = faster rate

Surface area – larger = faster

Temperature – warmer = faster rate

Area of High Water Potential to a area of Low Water Potential

   - Down a water potential gradient

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Water Potential

-Pure water has water potential of zero –solutes decrease this score (so a solution is always negative)     - the more negative it is, the higher the concentration of solutes

- Isotonic Solutions - have same water potential –won’t lose or gain water

- Hypotonic Solutions - outside solution has higher water potential (Animal cell will burst, but Plant cell will go turgid)

- Hypertonic Solutions - outside solution has lower water potential (Animal will shrink, and plant will turn flaccid

- Plasmolysis: Plasma membrane will pull away from Cell wall

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Active Transport - Active process (ATP)

- Move molecules and ions across Plasma Membrane – against concentration gradient

- Large molecules bind to a Binding Site at one side of the Carrier Protein. Using ATP, the Protein changes shape and allows the molecules to release into the other side

- Endocytosis: Cell surrounds substance in a Vesicle and ingests it – e.g. White Blood Cells (Uses ATP)

- Exocytosis: Vesicles transport substances from Golgi Apparatus – fuses with Plasma Membrane and releases contents (Uses ATP)

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Facilitated Diffusion - Passive process (No ATP)

Facilitated Diffusion:

- Large or charged molecules diffuse through carrier proteins or channel proteins

- Passive process –doesn’t use energy

- Down a concentration gradient - high to low concentration

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