3.3 Digestion and Absorption Questions

Question 1

Figure 1 shows a cell from the lining of the ileum specialised for absorption of products of digestion.
SGLT1 is a carrier protein found in the cell-surface membrane of this cell, it transports glucose and sodium ions (Na+ ) into the cell.
(a) The action of the carrier protein X in Figure 1 is linked to a membrane-bound ATP hydrolase enzyme.
Explain the function of this ATP hydrolase

Answer 1

1. (ATP to ADP + Pi ) Releases energy;
   Reject ‘produces/makes/creates energy’.
2. (energy) allows ions to be moved against a concentration gradient
   OR
   (energy) allows active transport of ions;

Question 2

The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum.
Explain how.

Answer 2

1. (Maintains/generates) a concentration/diffusion gradient
   for Na+ (from ileum into cell);
   Accept ‘(Maintains/generates) a lower concentration
   of Na+ inside the cell compared with outside the
   cell’.
2. Na+ moving (in) by facilitated diffusion, brings glucose with it
   OR
   Na+ moving (in) by co-transport, brings glucose with it;
   Accept ‘co-transporter’ for ‘co-transport’.

Question 3

After collecting the samples, the scientist immediately heated them to 70 °C for 10 minutes.
Explain why. (enzymes 2m)

Answer 3

1. To denature the enzymes/lipase;
   Accept description of denaturation in terms of
   change in tertiary structure.
2. So no further digestion/hydrolysis/catalysis occurred;

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

Cells lining the ileum of mammals absorb the monosaccharide glucose by
co-transport with sodium ions. Explain how.

Answer 5

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;