Digestion & absorption

Question 1

Describe the process of starch digestion

Answer 1

Amylase breaks down starch into maltose

Maltase hydrolyses maltose into glucose by breaking the glyosidic bond

Question 2

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels.

Answer 2

1. Micelles contain bile salts and fatty acids/monoglycerides;
2. Make fatty acids/monoglycerides (more) soluble (in water) OR Bring/release/carry fatty acids/monoglycerides to cell/lining (of the iluem) OR Maintain high(er) concentration of fatty acids/monoglycerides to cell/lining (of the ileum);
3. Fatty acids/monoglycerides absorbed by diffusion;
4. Triglycerides (re)formed (in cells);
5. Vesicles move to cell membrane;

Question 3

Describe the role of micelles in the absorption of fats into the cells of the ileum.

Answer 3

1. Micelles include bile salts and fatty acids;
2. Make the fatty acids (more) soluble in water;
3. Bring/release/carry fatty acids to cell/lining (of the ileum);
4. Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
5. Fatty acids (absorbed) by diffusion;

Question 4

Describe the role of enzymes in the digestion of proteins in a mammal.

Answer 4

1. (Reference to) hydrolysis of peptide bonds;
2. Endopeptidase act in the middle of protein/polypeptide OR Endopeptidase produces short(er) polypeptides/ increase number of ends;
3. Exopeptidases act at end of protein/polypeptide OR Exopeptidase produces dipeptides/amino acids;
4. Dipeptidase acts on dipeptide/between two amino acids OR Dipeptidase produces (single) amino acids;

Question 5

Describe the absorption of glucose (Cotransport)

3 marks

Answer 5

Sodium ions actively transported from ileum cell to blood;

Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose);

Glucose enters by facilitated diffusion with sodium ions;

Question 6

Describe protein digestion

4 marks

Answer 6

Proteins/polypeptides are hydrolysed by enzymes called proteases.This process begins in the stomach

Endopeptidases hydrolyse the peptide bonds within the polypeptide chain

This produces many smaller/shorter polypeptide chains and increases the surface area(conc of substrate) for the next enzyme.This makes digestion faster and more efficient.

Exopeptidases hydrolyse peptide bonds at the terminal ends of the of the protein, removing one amino acid at a time.

exopeptidase are specific:one group are complementary to the C end and the other group are complementary to the N end.A.A and amino acids are produced

Question 7

Describe the role of the enzymes of the digestive system in the complete breakdown of starch

Answer 7

1-Salivary/pancreatic amylase hydrolysis starch into maltose
2-By hydrolysing glycosidic bonds
3-Maltose is hydrolysed into glucose
4- By maltase

Question 8

Describe how glucose is absorbed from the ilium into the blood

5 marks

Answer 8

1-Na+ are actively transported out of the epithelial cell into the blood (by sodium potassium pump)
2- this creates a concentration gradient of Na+,
3-Na+ and glucose enter by facilitated diffusion using cotransporter proteins
4-Na+ diffuse into the cell down its concentration Gradient
5-glucose moves into the cell against its concentration gradient/down an electrochemical gradient
6-Glucose moves into the blood by facilitated diffusion

Question 9

What is digestion?

Answer 9

A process in which large molecules are hydrolysed by enzymes into small molecules, which can be absorbed into the blood/ lymph and then assimilated into biological molecules

Question 10

Explain the advantages of lipid droplet and micelle formation

Answer 10

1. Droplets increase surface areas (for lipase /
   enzyme action);
2. (So) faster hydrolysis / digestion (of
   triglycerides / lipids);
3. Micelles carry fatty acids and glycerol /
   monoglycerides to / through membrane / to
   (intestinal epithelial) cell;

Question 11

The name of the process by which fatty acids and glycerol enter the intestinal epithelial cell

Answer 11

Simple diffusion

Question 12

What is the meaning of assimilated?

Answer 12

Absorbed molecules or ions to be used by the body for a function

Question 13

Describe how amino acids are absorbed from the ilium into the blood

5 marks

Answer 13

• Na+ ions actively transported out of epithelial cell into the blood (by sodium potassium pump)
• This creates a concentration gradient of Na+ (between lumen of the ilium and the epithelial cell)
• Na+ and amino acid enter by facilitated diffusion
• Na+ moves into the cell down its concentration gradient
• Amino acids move into the cell against their concentration gradient / down an electrochemical gradient
• Amino acids move into the blood by facilitated diffusion