Active Transport

Question 1

What does active transport do

Answer 1

Uses energy to move molecules and ions across plasma membranes, usually against a concentration gradient.

Question 2

How are carrier proteins used in active transport

Answer 2

A molecule attaches to the carrier protein, the protein changes shape and this moves the molecule across the membrane, releasing it on the other side

Question 3

What are the two main differences between active transport and facilitated diffusion

Answer 3

Active transport usually moves solutes from a low to a high concentration. In facilitated diffusion, they always move from high to low concentration.
Active transport requires energy, facilitated diffusion does not.

Question 4

What source of energy is important for active transport

Answer 4

ATP as it’s a common source of energy in the cell.

Question 5

What are co - transporters and how do they work

Answer 5

A type of carrier protein. They bind two molecules at a time. The concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient.

Question 6

Where is glucose absorbed into the blood

Answer 6

Glucose is absorbed into the bloodstream in the small intestine. In the mammalian ileum (the final part of a mammals small intestine) the concentration of glucose is too low for glucose to diffuse out into the blood. So, glucose is absorbed from the lumen (middle) of the ileum by co - transport.

Question 7

Explain how glucose is absorbed into the blood by co - transport (Step 1)

Answer 7

Sodium ions are actively transported out of the epithelial cells in the ileum, into the blood, by the sodium - potassium pump. This creates a concentration gradient - there’s now a higher concentration of sodium ions in the lumen of the ileum than inside the cell.

Question 8

Explain how glucose is absorbed into the blood by co - transport (Step 2)

Answer 8

Sodium ions diffuse from the lumen of the ileum into the epithelial cells, down their concentration gradient. They do this via the sodium - glucose co - transporter proteins.
The co - transporter carries glucose into the cell with the sodium. As a result, the concentration of glucose inside the cell increases.

Question 9

Explain how glucose is absorbed into the blood by co - transport (Step 3)

Answer 9

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