Cells: Exchange across cell membranes - active transport

Question 1

What is active transport

Answer 1

The movement of molecules against a concentration gradient, from a region of low concentration to a region of high concentration

Question 2

What are the two types of active transport

Answer 2

• Direct active transport
• Co-transport

Question 3

Is active transport a passive process

Answer 3

No - its an active process that uses ATP

Question 4

How do carrier proteins enable active transport to occur within the membrane

Answer 4

• A molecule attaches to the receptor of the carrier protein, and so the protein changes shape and moves the molecule across the membrane
• Then a molecule of ATP binds to the carrier protein and undergoes hydrolysis, producing Pi and ADP
• The phosphate then attached to the carrier protein causing it to change shape - transporting the molecule across the membrane
• Phosphate then unattaches - leaving the carrier protein to return to its normal shape

Question 5

What are the factors that affect the rate of active transport

Answer 5

• Surface area of cell membranes
• The number of carrier proteins in cell membranes

Question 6

How does the surface area of cell membrane affect active transport

Answer 6

The higher the surface area the faster the rate of diffusion

Question 7

How does the number of carrier proteins in cell membranes affect the rate of diffusion

Answer 7

The higher the number of carrier proteins the higher the rate of active transport

Question 7

How does the number of carrier proteins in cell membranes affect the rate of diffusion

Answer 7

The higher the number of carrier proteins the higher the rate of active transport

Question 8

What are co-transporters

Answer 8

They are a type of carrier protein that bind two molecules at a time

Question 9

What is co-transport

Answer 9

Co-transport is the coupled movement of substances across a cell membrane via a carrier protein

Question 10

Carrier proteins move molecules and ions in and out of the cell, but always against the concentration gradient, what transport process does this include

Answer 10

• Active transport
• Co-transport

Question 11

Outline the steps in the co-transport and the absorption of glucose

Answer 11

• Sodium ions are transported out of the epithelial cells in the ileum unto the blood using ATP - creating a concentration gradient as Na+ ion concentration decreases in the cell
• Na+ ions then diffuse from the lumen of the ileum into the epithelial cell down the concentration gradient alongside glucose through co-transporter protein
• Glucose then moves out of the cell through down its concentration gradient facilitated diffusion through a channel protein

Question 12

State are the factors affecting the rate of active transport and how they impact the rate

Answer 12

• The speed of individual carrier proteins - the faster they work, the faster the rate of active transport
• The number of carrier proteins present - the more proteins there are, the faster the rate
• The rate of respiration in the call and the availability of ATP - If respiration is inhibited, active transport cant take place