Absorption

Question 1

What are disaccharidases?

Answer 1

Membrane-bound enzymes which catalyse the break down of disaccharides
Are secreted by the ileum epithelial cells of the small intestine

Question 2

Describe how the disaccharide maltose is broken down

Answer 2

Maltose is broken down to form 2 alpha glucose
Via the enzyme maltase

Question 3

Describe how the disaccharide lactose is broken down

Answer 3

Lactose is broken down to form alpha glucose and galactose
Via the enzyme lactase

Question 4

Describe how the disaccharide sucrose is broken down

Answer 4

Sucrose is broken down to form alpha glucose and fructose
Via the enzyme sucrase

Question 5

How is glucose and galactose absorbed?

Answer 5

Facilitated diffusion and co-transport

Question 6

How is fructose absorbed?

Answer 6

Only facilitated diffusion

Question 7

Describe the functions of micelles

Answer 7

• Micelles transport the poorly soluble monoglycerides and fatty acids
• to the surface of epithelial cells
• where they can be absorbed

Question 8

Micelles are small enough to fit between microvilli, what does this allow them to do?

Answer 8

• are small enough to fit between microvilli:
• constantly break down and reform
• building up a pool of monoglycerides and fatty acids that are in solution
• only freely dissolved monoglycerides and fatty acids can be absorbed
• not micelles

Question 9

What are the adaptations of the ileum for efficient absorption?

Answer 9

Villi and microvilli - large surface area

Carrier proteins - for facilitated diffusion

Mitochondria - production of ATP for active transport

Good blood supply - maintains steep conc. gradient

Thin walls - short diffusion pathway