Topic 3: Digestion And Absorption

Question 1

Define digestion

Answer 1

Large biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes

Question 2

Name the three locations carbohydrates are digested

Answer 2

1. Mouth
2. Duodenum
3. Ileum

Question 3

Which two enzymes hydrolyse carbohydrates, where are they produced and what are the products?

Answer 3

1. Amylases- pancreas and salivary glands- hydrolyses polysaccharides into the disaccharide maltose by break glycosidic bond
2. Membrane bound disaccharidases- small intestine- sucrase and lactase are membrane bound enzymes that hydrolyse sucrose and lactose into monosaccharides

Question 4

Which two molecules are needed to digest lipids?

Answer 4

1. Lipase
2. Bile salts

Question 5

Where does protein digestion occur?

Answer 5

Digestion starts in the stomach continues in the duodenum and is fully digested in the ileum

Question 6

Describe the digestion of lipids

Answer 6

Lipase is produced in the pancreas and it can hydrolyse the ester in triglycerides to form monoglycerides and fatty acids. Bile salts are produced in the liver and can emulsify lipids to form tiny droplets and micelles. This increases the surface area for lipase to act on

Question 7

What’s the difference between the physical and chemical digestion of lipids?

Answer 7

Physical is emulsification and Micelle formation whereas chemical is the lipase hydrolysing lipids into glycerol and fatty acids

Question 8

Three enzymes are involved in digesting proteins. Describe the role of each.

Answer 8

• endopeptidases: hydrolyse peptide bonds between amino acids in the middle of a polymer chain
• exopeptidases: hydrolyse peptide bonds between amino acids at the end of a polymer chain.
• membrane bound dipeptidases: hydrolyse peptide bonds between two amino acids

Question 9

How is the ileum adapted for absorption?

Answer 9

The ileum wall is covered in villi, which have thin walls surrounded by a network of capillaries and epithelial cells have even smaller microvilli.
These features maximise absorption by increasing the surface area, decreasing the diffusion distance and maintaining a concentration gradient.

Question 10

Which two molecules are absorbed by co-transport?

Answer 10

1. Glucose
2. Amino acids

Question 11

Write out a description of co-transport for absorption.

Answer 11

-Sodium ions are actively transported out of epithelial cell into the blood in the capillary
-This reduces the sodium ion concentration in the epithelial cell
- Sodium ions cab then diffuse from the lumen down their concentration gradient into the epithelial cell
- the protein the sodium ions diffuse through us a co-transporter protein. So either glucose or amino acids also attach and are transported into the epithelial cells against their concentration gradient
- glucose or amino acids then move by facilitated diffusion from the epithelial cell into the blood

Question 12

What are micelles?

Answer 12

Micelles are water-soluble vesicles formed of fatty acids, glycerol, monoglycerides and bile salts.

Question 13

Why can micelles simply diffuse across the cells surface membrane?

Answer 13

When the micelles encounter the ileum epithelial cells, due to the non-polar nature of the fatty acids and monoglycerides, they can simply diffuse across the cell surface membrane to enter the cells of the epithelial cells

Question 14

What happens to the micelles once they have been absorbed into the cells?

Answer 14

Once in the cell, these will be modified back into triglycerides inside of the endoplasmic reticulum and Golgi body