Topic 3: Digestion & Absorption

Question 1

Define digestion

Answer 1

Large biological molecules are hydrolysed into smaller molecules thay 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. Name: amylase
   Location: pancreas and salivary glands
   Products: hydrolyses polysaccharides into the dissaccharide maltose by breaking the gylcosidic bonds
2. Name: membrane bound dissacharides
   Location: small intestines
   Products: sucrase and lactase are membrane bound enzymes that hydrolysed 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

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

Answer 6

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 7

Describe the digestion of lipids:

Answer 7

Lipase is produced in the pancreas and it can hydrolyse the ester bond 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.
The increases the surface area for lipase to act on

Question 8

What is the difference between the physical and chemical digestion of lipids?

Answer 8

Physical is emulsfication & micelles formation whereas chemical us the lipase hydrolysising lipids into glycerol and fatty acids (some monoglycerides)

Question 9

Which two molecules are absorbed by co-transport?

Answer 9

1. Glucose
2. Amino acids

Question 10

How is the ileum adapted to maximise absorption?

Answer 10

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

Question 11

Describe co transport in absorption

Answer 11

• sodium ions are actively transported out of the epithelial cell into the blood in the capillary.
• this reduces the sodium ions concentration in the epithelial cell
• sodium ions can then diffuse from the lumen down their concentration gradient into the epithelial cell
• the protein the sodium ions diffuse through is a co transporter protein, so either glucose or amino acids also attach and are transported into the epithelial cell against their concentration gradient.
• glucose or amino acids then move by facilitated diffusion from the epithelial cell to the blood

Question 12

What are micelles?

Answer 12

Water soluble vesicles formed of fatty acids, glycerol, monoglycerides and bile salts

Question 13

Why can micelles simply diffuse across the cell surface membrane?

Answer 13

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

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.