transport across the membrane Flashcards
what is diffusion
Diffusion is the movement of molecules from a region of high concentration to a region of low concentration down a concentration gradient. It is a passive process and so requires no energy.
what is simple diffusion
Simple diffusion occurs through the phospholipid bilayer.
Diffusion rate is increased by:
higher concentration gradient
thinner membrane/shorter diffusion distance
larger surface area
smaller molecules
being non-polar or fat soluble
increased temperature.
what is facilitated diffusion
This is the process of diffusion but for polar molecules or ions that cannot pass directly though the phospholipid bilayer.
All the same rules apply as for diffusion, the only difference is that substances enter the cell through protein channels.
The effect of this is shown in the graph below.
A continuing increase in the concentration will eventually lead to a maximum rate being reached due to the limiting effect of the number of channels available.
This is a passive process; therefore, the respiratory inhibitor has no effect.
what is active transport
This moves molecules against a concentration gradient, i.e. from where they are in lower concentration to where they are already at a higher concentration.
This process requires energy in the form of ATP from respiration.
The ATP activates carrier proteins to move molecules across the cell membrane.
As this relies on ATP the addition of a respiratory inhibitor or lack of oxygen will also prevent transport as there will be no ATP available.
what is bulk transport
Endocytosis Two main types
- Phagocytosis - solids enter the cell.
- Pinocytosis - liquids enter the cell.
- Plasma membrane folds inwards
- Plasma membrane engulfs the material.
- Vesicle formed from plasma membrane enters the cell.
Exocytosis
- Vesicle formed from the Golgi moves towards the plasma membrane.
- Vesicle fuses with plasma membrane
- Vesicle contents empty out of cell.
