Digestion and absorption exam questions

Question 1

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. 6 m

Answer 1

Micelles contain bile salts and fatty acids/monoglycerides;
Make fatty acids/monoglycerides (more) soluble (in water)
Bring/release/carry fatty acids/monoglycerides to cell/lining (of the iluem)
Maintain high(er) concentration of fatty acids/monoglycerides to
cell/lining (of the ileum);
Fatty acids/monoglycerides absorbed by diffusion;
Triglycerides (re)formed (in cells
Vesicles move to cell membrane;
Accept exocytosis for ‘vesicles move’

Question 2

Explain the function of this ATP hydrolase 2 marks

Answer 2

(ATP to ADP + Pi ) Releases energy;
energy allows ions to be moved against a concentration gradient/ energy allows active transport of ions

Question 3

The movement of Na+ out of the cell allows the absorption of glucose into
the cell lining the ileum.
Explain how. 2 marks

Answer 3

Maintains/generates) a concentration/diffusion gradient
for Na+ (from ileum into cell);
Na+ moving (in) by facilitated diffusion, brings glucose with it

Question 4

Use your knowledge of lipid digestion to explain the differences in the
results for samples A and B shown in the table above.
You should assume that no absorption had occurred. 3 marks

Answer 4

Triglycerides decrease because of the action of lipase /Fatty acids increase because of the action of lipase;
Triglycerides decrease because of hydrolysis (of triglycerides)/
Fatty acids increase because of hydrolysis (of triglycerides);
Triglycerides decrease because of digestion of ester bonds (between fatty acid and glycerol)/
Fatty acids increase because of digestion of ester bonds (between fatty acid and glycerol);

Question 5

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

Answer 5

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

Question 6

Describe the role of micelles in the absorption of fats into the cells lining
the ileum. 3 m

Answer 6

Micelles include bile salts and fatty acids;
Ignore other correct components of micelles.
Make the fatty acids (more) soluble in water
Bring/release/carry fatty acids to cell/lining (of the ileum);
Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
Fatty acids (absorbed) by diffusion;

Question 7

Describe the role of enzymes in the digestion of proteins in a mammal 4 m

Answer 7

(Reference to) hydrolysis of peptide bonds;
Endopeptidase act in the middle of protein/polypeptide
Endopeptidase produces short(er) polypeptides/ increase number of ends
Exopeptidases act at end of protein/polypeptides
Exopeptidase produces dipeptides/amino acids;
Dipeptidase acts on dipeptide/between two amino acids
Dipeptidase produces (single) amino acids;

Question 8

What can you conclude about the absorption of the products of protein digestion as the percentage of protein increased in the rabbits’ food? 3 marksThe food eaten by a rabbit is digested mainly by microorganisms in its
caecum. The caecum is a section of intestine attached between the ileum
and the large intestine. The resulting semi-digested material leaves the
anus of a rabbit as soft, caecal droppings. The rabbit then eats these
caecal droppings.
Use this information and Figure 2 to suggest how eating its own caecal
droppings helps a rabbit’s digestion and absorption of dietary protein.

Answer 8

No significant difference (in protein absorption);
(because ± 2) SDs overlap;
Accept error bar for SD
(So mean) percentage absorbed not affected by percentage in diet;
Amount of protein (in diet) is not a limiting fact
Something else is limiting factor eg amount of protease;
(But) small range of protein in diet
(Should) Investigate wider range;

Question 9

The food eaten by a rabbit is digested mainly by microorganisms in its
caecum. The caecum is a section of intestine attached between the ileum
and the large intestine. The resulting semi-digested material leaves the
anus of a rabbit as soft, caecal droppings. The rabbit then eats these
caecal droppings.
Use this information and Figure 2 to suggest how eating its own caecal
droppings helps a rabbit’s digestion and absorption of dietary protein.

Answer 9

More/remaining/undigested (protein) broken down;
Accept all (protein) broken down
2. (So more) amino acids absorbed;
3. (Because) protein/food passes again through stomach/ileum;

Question 10

Explain the advantages of lipid droplet and micelle formation 3 marks

Answer 10

Droplets increase surface areas (for lipase /
enzyme action);
2. (So) faster hydrolysis / digestion (of triglycerides / lipids);
3. Micelles carry fatty acids and glycerol / monoglycerides to / through membrane / to
(intestinal epithelial) cell;

Question 11

Name structure Q in the diagram above and suggest how it is involved in
the absorption of lipids.

Answer 11

Golgi (apparatus);
Modifies / processes triglycerides;
Combines triglycerides with proteins;
Packaged for release / exocytosis
Forms vesicles;

Question 12

Cells lining the ileum of mammals absorb the monosaccharide glucose by
co-transport with sodium ions. Explain how. 3 m

Answer 12

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