Digestion & Absorption - key points

Question 1

Describe the process of starch digestion

Answer 1

1. (salivary/pancreatic) Amylase hydrolyses starch into maltose;
2. by hydrolysing glycosidic bonds;
3. maltose is hydrolysed into glucose;
4. by maltase

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 how glucose is absorbed from the ileum into the blood (5 marks) (6)

Answer 5

1. Na+ actively transported out of epithelial cell into the blood
2. Creates concentration gradient of Na+
3. Na+ and glucose enter by facilitated diffusion using co-transport proteins
4. Na+ diffuse into the cell down its concentration gradient
5. Glucose moves into the cells against its concentration gradient
6. Glucose moves into the blood by facilitated diffusion

Question 6

Describe how amino acids are absorbed from the ileum into the blood (5 marks) (6)

Answer 6

1. Na+ actively transported out of epithelial cell into the blood
2. Creates concentration gradient of Na+
3. Na+ and amino acids enter by facilitated diffusion
4. Na+ diffuse into the cell down its concentration gradient
5. Amino acids move into the cells against their concentration gradient
6. Amino acids move into the blood by facilitated diffusion

Question 7

Explain the advantages of lipid droplet and micelle formation (3)

Answer 7

micelles make fatty acids soluble in water and bring fatty acids ad glycerol to surface of membrane
droplets increase surface area of lipids so lipase can hydrolase them quicker