4. Active Transport

Active transport def:

Uses energy to move molecules and ions across plasma membranes, usually against a concentration gradient. Carrier proteins and co-transporters are involved in active transport.

What are co transporters

A type of carrier protein which binds two molecules at a time.

The concentration of the carrier protein is used to move another molecule against it’s own concentration gradient.

Describe the process of the co-transport and absorption of glucose:

1. Sodium ions are actively transported out of the epithelial cells in the ileum, into the blood, by the sodium-potassium pump. This creates a steep concentration gradient.

2. This causes sodium ions to diffuse from the lumen in the ileum into the epithelial cell down their concentration gradient via the sodium-glucose co-transporter proteins.

3. The co transporter carries glucose with it.

4. Glucose diffuses out of the cell, into the blood, down its concentration gradient through a protein channel, by facilitated diffusion.

Factors affecting the rate of active transport - 3

• The speed of individual carrier proteins

• The number of carrier proteins present

• The rate of respiration in the cell and the availability of ATP.