CGP Digestion and Absorption

Question 1

Why are large biological molecules broken down during digestion?

Answer 1

Certain biological molecules are too large to cross cell membranes, meaning they can’t be absorbed from the gut into the blood.
During digestion, when these molecules are broken down into smaller ones, which can easily cross membranes, they can easily be transported around the body for use by body cells.

Question 2

How are most large biological molecules broken down?

Answer 2

Most large biological molecules are polymers which can be broken down into monomers using hydrolysis reactions (adding water).

Question 3

Large biological molecules are broken down in hydrolysis reactions to create monomers. What happens in these reactions?

Answer 3

During hydrolysis, carbohydrates are broken down into disaccharides then disaccharides.

Fats are broken down into fatty acids and monoglycerides.

Proteins are broken down into amino acids.

Question 4

Carbohydrates are broken down by…

Answer 4

Amylase and also membrane bound disaccharides

Question 5

What is starch?

Answer 5

A digestive enzyme that catalyses the conversion of starch (polysaccharide) into maltose (smaller, a disaccharide).

This involves the hydrolysis of the glycosidic bonds in starch.

Question 6

What are membrane bound disaccharides?

Answer 6

Enzymes that are attached to the cell membranes of epithelial cells lining the ilium (in small intestine).

These help to break down disaccharides into monosaccharides.
This involves the hydrolysis of glycosidic bonds.

Question 7

In what way are monosaccharides transported across the cell membrane?

Answer 7

Using transport proteins.

Question 8

Lipids are broken down by…

Answer 8

Lipase (using bile salts).

Question 9

What is a monosaccharide?

Answer 9

A glycerol molecule with one fatty acid attached.

Question 10

Outline how lipids are broken down.

Answer 10

1. Lipase enzymes catalyse the breakdown of lipids into monoglycerides and fatty acids. This involves the hydrolysis of the ester bonds in lipids.
2. Bile salts are produced by the liver and emulsify lipids - meaning they cause the lipids to form small droplets.
3. Once the lipid has been broken down, the monoglicerides and fatty acids stick with the bile salts to form micelles.

Question 11

How are proteins broken down?

Answer 11

By a combination of processes. By endopeptidases and exopeptidases.

Question 12

Outline what endopeptidases do.

Answer 12

Endopeptidases hydrolyse peptide bonds within a protein.

Question 13

What do exopeptidases do?

Answer 13

Exopeptidases hydrolyse protein bonds at the ends of protein molecules.

Question 14

Monosaccharides are a product of digestion. How are they transported across cell membranes and absorbed in digestion?

Answer 14

Glucose and galactose are absorbed by active transport with sodium ions via a co-transporter protein.
Fructose is absorbed via facilitated diffusion through a different transported protein.

Question 15

Monoglycerides and fatty acids are products of digestion. How are these absorbed in digestion?

Answer 15

Micelles help to move monoglycerides and fatty acids towards the epithelium.
Because micelles constantly break up and reform, they can release monoglycerides and fatty acids, allowing them to be absorbed.

Question 16

Amino acids are a product of digestion. How are these transported across the cell membrane and absorbed?

Answer 16

Sodium ions are actively transported out of the epithelial cells into the ilium itself.
They then diffuse back into the cells through sodium dependent transported proteins in the epithelial cell membranes, carrying the amino acids with them.