Exchange Across Cell Membranes - Active Transport

Question 1

What does active transport use?

Answer 1

Active transport uses energy to move molecules or ions across membranes, usually against a concentration gradient

Question 2

What proteins are involved in active transport?

Answer 2

Carrier proteins

Question 3

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

Answer 3

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

Question 4

Give a type of carrier protein

Answer 4

Co-transporters

Question 5

How do co-transporters work?

Answer 5

1. They bind two molecules at a time
2. The concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient

Question 6

Give an example of co-transport

Answer 6

Sodium ions move into the cell down their concentration gradient. This move glucose into the cell too, against its concentration gradient

Question 7

Give three factors which affect the rate of active transport

Answer 7

1. The speed of the individual carrier proteins
2. The number of carrier proteins present
3. The rate of respiration in the cell and the availability of ATP

Question 8

How does the speed of the individual carrier proteins affect the rate of active transport?

Answer 8

The faster the carrier proteins work, the faster the rate of active transport

Question 9

How does the number of carrier proteins present affect the rate of active transport?

Answer 9

The more proteins there are, the faster the rate of active transport

Question 10

How does the rate of respiration and availability of ATP affect the rate of active transport?

Answer 10

If respiration is inhibited, active transport can’t take place

Question 11

Where is glucose absorbed into the bloodstream?

Answer 11

The small intestine

Question 12

Why is glucose absorbed by co-transport?

Answer 12

In the ilium (final part of the small intestine) the concentration of glucose is too low for the glucose to diffuse out into the blood. So glucose is absorbed from the lumen of the ilium by co-transport

Question 13

How is glucose co-transported into the blood from the small intestine?

Answer 13

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

This causes the sodium ions to diffuse from the lumen of the ileum into the epithelial cell, 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

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