B3 - Organsiation and the Digestive System

Question 1

B3 - Explain how the villi are adapted to maximise absorption in the small intestine.

Answer 1

Many microvilli provide a large surface area.

Good blood supply maintains diffusion gradient.

Microvilli have thin walls which provide a short diffusion pathway.

Many mitochondria to allow uptake of nutrients by active transport.

Question 2

B3 - What role does bile play in digestion?

Answer 2

• Neutralises stomach acid.
• Breaks down fats into droplets (emulsification).
• Improves function of lipase enzymes in small intestine.

Question 3

B3 - Describe how different parts of the digestive system help to break down molecules of fat so that they can be absorbed into the body.

Answer 3

• Mechanical breakdown (chewing) in the mouth.
• Bile breaks down fats into droplets.
• This increases the surface area of the fat.
• Lipase enzymes produced by the pancreas and small intestine break down the fat further into fatty acids and glycerol.
• Large surface area of droplets increases the rate of this digestion.

Question 4

B3 - Explain how pH/temperature affect enzyme activity.

Answer 4

• Enzyme activity increases up to an optimum point.
• Past the optimum point the enzyme denatures.
• The active site changes shape.
• The substrate no longer fits

Question 5

B3 - Describe the lock and key mechanism of enzyme action.

Answer 5

• Each enzyme is specific to one substrate, just like a lock and a key.
• The active site of an enzyme fits into a specific substrate.
• If the shape of this active site changes, the enzyme will no longer be able to catalyse the reaction.