Digestion and Absorption

Question 1

Describe the role of the enzymes of the digestive system in the complete breakdowm of starch (4)

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

Answer 2

1. Na+ are actively transported out of epithelial cell into the blood (by NaK pump)
2. This creates a concentration gradient of Na+ (between lumen of the ilieum and the epithelial cell)
3. Na+ and glucose enter by facilitated diffusion using complementary cotransporter proteins.
4. Na+ diffuse into the cell down its concentration gradient
5. Glucose moves into the cell against its concentration gradient
6. Glucose moves into the blood by facilitated diffusion

Question 3

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

Answer 3

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; REJECT MICELLES ABSORBED
4) Triglycerides (re)formed (in cells);
5) Vesicles move to cell membrane;

Question 4

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

Answer 4

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 5

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

Answer 5

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 6

Describe the absorption of glucose (Cotransport)

Answer 6

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