Active Transport
Active Transport:
- Active transport is the movement of particles against a concentration gradient (from an area of low concentration to an area of high concentration) at a rate faster than diffusion.
- It requires energy in the form of ATP.
- It is a selective process, as certain molecules can only be transported by certain proteins.
- Molecule binds to carrier protein, on one side of the membrane.
- ATP is hydrolysed into ADP and P. The phosphate binds to carrier protein on the other side of the membrane, causing the carrier protein to change shape.
- Molecule travels through the newly-opened channel in the cell.
- Phosphate molecule is released and recombines with ATP.
- Carrier protein returns to original shape.
Bulk Transport:
- Endocytosis is bulk transport of material into cells.
- Phagocytosis is the endocytosis of solids.
- Pinocytosis is the endocytosis of liquids.
- Cell surface bends inwards as it comes into contact with the material to be transported.
- Eventually the membrane touches, fusing to form a vesicle known as an endosome.
- The vesicle moves into the cytoplasm, the movement is controlled by microfilaments.
- Exocytosis is the bulk transport of materials out of cells.
- Vesicles move towards the cell membrane, and fuse with it.
- As the membrane fuses, the contents are released out of the cell.
- ATP is required for the movement of vesicles through the cytoplasm brought about by the cytoskeleton, so is an active process.