Active Transport & Bulk Transport

Definition : active transport is the movement of particles against the concentration gradient from an area of lower concentration to higher concentration using ATP as an energy source.
To do this, it uses carrier proteins.

1. Particle bonds to carrier protein (on the lower concentration side) as it is complementary in shape.

2 ATP is used to give energy to change the shape of the carrier protein.

3. Particle released in the higher concentration side of the membrane.

This transport method moves molecules that can’t be transported across the cell surface membrane by passive processes. It requires metabolic energy/ATP.

There are 2 processes :

• Endocytosis : taking large molecules (macromolecules) into the cell, internalising contents into a vesicle.
• Exocytosis : large molecules leave the cell using vesicles.

Both processes use vesicles to transport molecules.

• Vesicles are small cellular structure made of lipid bilayer, filled with fluid.

1. Large molecules to internalise are outside of the cell.

2. Cell surface membrane surrounds molecules.

3. Eventually CSM fuse together and contents are in a vesicle.

1. Contents to be released are in a vesicle.

2. Vesicle fumes with the CSM.

3. Contents are released.

Active :

• (similarity) both require ATP
• (difference) carrier proteins -> active transport
• (difference) move one way against the concentration gradient

Bulk :

• (similarity) both require ATP
• (difference) uses vesicles -> bulk transport
• (difference) move either way against the concentration gradient
• (difference) move larger molecules