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The Role of the Cell Membrane in Transport (Concentration Gradient…
The Role of the Cell Membrane in Transport
Passive Transport
Facilitated Diffusion
Channel Proteins
A protein in the cell membrane that forms a passageway through which specific solutes can pass through via diffusion
Some channels open and close in response to the binding of specific molecules
Carrier Proteins
A protein present in a cell membrane that binds to a specific molecule and allows it to pass through the membrane
Material transport that still doesn't require energy (follows the high to low concentration gradient) but requires the use of a protein to aid diffusion
Does
NOT
require energy
Think about sliding down a slide!
Diffusion
The natural flow of particles from a high concentration to low :
Examples
Smelling a scent
Water going into the roots of plants
Food colouring spreading in water
Keeps occurring until
equilibrium
is reached
Equilibrium can be thought of as a perfect balance
Osmosis
The diffusion of water
Active Transport
Active transport is the movement of molecules across a cell membrane going from a low to high concentration (ie, against the concentraion gradient)
It is similar to climbing a slide (it takes additional energy)
Requires energy
ATP (adenosine triphosphate)
Useful for when you need to bring in something that you already have more of than the environment
A plant that already has a lot of nitrogen but needs more will need to use active transport to go against the concentration gradient
Tonicity
Concentration of a solution compared to another
Hypertonic solution
'Hyper' means 'over'
If a cell is placed in a hypertonic solution, water will flow out of the cell in an attempt to reach equilibrium
The cell will shrivel up as water exits, leaving the cell
plasmolyzed
Hypotonic solution
'Hypo' is 'under'
If a cell is placed in a hypotonic solution, water will flow into the cell in an attempt to reach equilibrium
The cell will swell up with water and either burst (animal cell) or become
turgid
(plant cell)
Plants can survive this increase in water because of their large vacuole (storage) and their cell wall (additional strength)
Isotonic solution
Describes as solution that has the same concentration as another (ie, it is already in equilibrium!)
'Iso' means 'equal'
If a cell is placed in an isotonic solution, water will flow in and out but concentration levels will not be affected
Concentration Gradient
Different ions or molecules move along the gradient independently of one another (ie, they each have their own concentration gradient)
Involves molecules or ions of a single type
Drives diffusion
In cells, different concentrations may be separated by a membrane
Must involve different concentrations (ie, must not already be at equilibrium)
Cell Membranes
Selectively-Permeable Membrane
Allows certain particles to pass through, excludes others
To pass through a cell membrane a particle must: soluble in lipids and small enough to pass through
Made up of a phospholipid bilayer with proteins attached
Cell organelle