Digestion & Absorption 3.3

Question 1

Definition of Digestion (1)

Answer 1

Digestion is the hydrolytic breakdown of large, insoluble molecules into smaller soluble molecules
(to be assimilated (absorbed) for metabolic reactions.)

Question 2

Name the products of the digestive hydrolysis of:

a) Proteins
b) Carbohydrates
c) Lipids
d) Disaccharides

Answer 2

a) Amino acids
b) Disaccharides
c) Fatty acids + monoglycerides
d) Monosaccharides

Question 3

Where is the enzyme maltase found? (1)

Answer 3

Embedded in micro-villi of ileum (in small intestine)

Question 4

Where does protein digestion occur? (1)

Answer 4

In the stomach (proteases) and small intestine (ileum - endo/exopeptidases)

Question 5

Give two examples of endopeptidases in the small intestine.

Answer 5

Trypsin & Pepsin

Question 6

Describe the processes involved in the absorption of the products of starch digestion (5)

Answer 6

1. Glucose moves in with sodium (into epithelial cell)
2. Via (carrier/channel) protein symport;
3. Sodium removed (from epithelial cell) by active transport/sodium potassium pump - into blood;
4. Maintaining low concentration of sodium (in epithelial cell) / sodium concentration gradient (between lumen and epithelial cell);
5. Glucose moves into blood by facilitated diffusion.

Question 7

Describe the role of micelles in the absorption of fats into the cells of the ileum [5]

Answer 7

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

Question 8

Describe the process of starch digestion:

Answer 8

Salivary/pancreatic Amylase hydrolyses starch (insoluble polysaccharide) –> Maltose
Maltase hydrolyses maltose (disaccharide) –> Glucose (monosaccharides)
- Must say hydrolysis of glyosidic bonds

Question 9

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

Answer 9

1. Micelles contain bile salts (from liver) and fatty acids/monoglycerides;
2. Make fatty acids/monoglycerides MORE soluble in water, bring fatty acids to lining of ileum;
   OR maintain higher concentration of fatty acids/monoglycerides to lining of ileum;
3. Fatty acids absorbed by diffusion;
4. Triglycerides reformed (in cells);
5. Vesicles move to cell membrane.

Question 10

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

Answer 10

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 ileum);
4. Maintain higher concentration of fatty acids to cell/lining (of ileum);
5. Fatty acids absorbed by diffusion.

Question 11

Describe the role of enzymes in the digestion of proteins in a mammal (4)

Answer 11

1. Hydrolysis of peptide bonds;
2. Endopeptidase acts in middle of protein/polypeptide/produces shorter polypeptides;
3. Exopeptidases act at end of protein/polypeptide/produces dipeptides/amino acids;
4. Dipeptidase hydrolyses into single amino acids.

Question 12

Describe the absorption of glucose (Co-transport) (3)

Answer 12

1. Sodium ions actively transported from ileum cell to blood;
2. Maintains/forms diffusion gradient for sodium to enter cells from gut (with glucose);
3. Glucose enters with sodium ions by facilitated diffusion.