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4.5 Movement of substances across membranes - Coggle Diagram
4.5 Movement of substances across membranes
Simple diffusion
The net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient
All small substances can pass through membranes
Hydrophobic substances can pass through membranes because interior of phospholipid bilayer is also hydrophobic
Many different factors
Steepness of concentration gradient
Temperature
Size/polarity of substance
Surface area
Facilitated diffusion
Diffusion of particles through transport proteins
Allows large or polar substances to pass
Transport proteins move substances often passively
Carrier protein
Undergoes conformational shape change
Uniporter - 1 substance 1 direction
Symporter - 2 substances 1 direction
Cotransport - both substances needed
Antiporter - 2 substances 2 directions
3 sodium out, 2 potassium in
Channel protein
Fluid-filled pore for diffusion
Ion channels - hydrophilic channel proteins allowing ions to pass
Often gated - default state is closed. Opens when stimulus is present
Stimulus can be a molecule (ligand-gated) or electrical charge from ions (voltage-gated)
Does not change shape
Rate is affected by how many transport proteins are present and how many are open
Osmosis
The net diffusion of water particles from a region of high water potential to a region of low water potential through a partially permeable membrane
Rate is affected by water potential difference and pressure applied
The point where a plant cell's protoplast is no longer exerting pressure on the cell wall and is about to peel away is called 'incipient plasmolysis'
Plasmolysis is about to occur
Active transport
Transport of particles across a membrane against a concentration gradient using energy
Primary active transport - direct hydrolysis of ATP to ADP + phosphate + energy
Secondary active transport - energy from ion concentration gradient established using primary active transport
Ions are pumped out of cell and then diffuse back in, cotransporting desired molecule
Bulk transport
Exocytosis
Used in secretion of proteins such as enzymes/hormones
Reverse of endocytosis
Endocytosis
Material outside of cell trapped in depression of cell surface membrane
Vesicle forms and pinches off of membrane, forming internal vesicle
Vesicle lyses, releasing contents into cell
Phagocytosis - solid particles consumed
Pinocytosis - liquids consumed