Digestion and Absorption

Question 1

Describe the process of starch digestion. (3)

Answer 1

1. Amylase hydrolyses starch into maltose
2. Hydrolysing glycosidic bonds
3. Maltase hydrolyses maltose into glucose

Question 2

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

Answer 2

1. Na+ is actively transported out of epithelial cell into the blood
2. 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
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 the lymph vessels (5)

Answer 3

1. Micelles contain bile salts and fatty acids
2. Make fatty acids soluble in water OR brings fatty acids to cell surface
3. Fatty acids absorbed by diffusion
4. Triglycerides re-formed in cells to form chylomicrons
5. Vesicles move to cell membrane - chylomicrons transported into lymph vessel by exocytosis

Question 4

Describe the role of micelles in the absorption of fats into the cells of the ileum (5)

Answer 4

1. Micelles contain bile salts and fatty acids
2. Make fatty acids soluble in water
3. Brings fatty acids to cell surface
4. Maintain higher concentration of fatty acids to cell
5. Fatty acids absorbed by diffusion

Question 5

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

Answer 5

1. Hydrolysis of peptide bonds
2. Endopeptidase act in middle of polypeptide OR endopeptidase increase number of ends on polypeptide
3. Exopeptidases act at end of polypeptide OR exopeptidase produces dipeptides / amino acids
4. Dipeptidase acts on dipeptide / between two amino acids

Question 6

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

Answer 6

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

Question 7

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

Answer 7

1. Lipid droplets increase surface area
2. Faster diffusion / hydrolysis
3. Micelles carry fatty acids to cell membrane of epithelial cell

Question 8

Describe and explain two features you would expect to find in a cell specialised for absorption (2)

Answer 8

1. Folded membrane SO large surface area
2. Large number of co-transport proteins SO fast rate of absorption
3. Large number of mitochondria SO make ATP/ for aerobic respiration
4. Membrane bound enzymes SO maintains concentration gradient

Question 9

Describe how the structure of a protein depends on the amino acid it contains (5)

Answer 9

1. Structure is determined by position of amino acid
2. Primary structure is number and sequence of amino acids
3. Secondary structure formed by hydrogen bonding
4. Tertiary structure formed by hydrogen bonds, ionic bonds and disulphide bridges
5. Creates active site in enzymes
6. Quaternary structure contains more than one polypeptide chain