Digestion

Question 1

Digestion – Proteins (4)

Answer 1

1. Hydrolysis of peptide bonds;
2. Endopeptidases break polypeptides into smaller
   peptide chains;
3. Exopeptidases remove terminal amino acids;
4. Dipeptidases hydrolyse/break down dipeptides into amino acids;

Question 2

Digestion – Compare endopeptidase and exopeptidase (3)

Answer 2

1. Endopeptidases hydrolyse internal (peptide bonds);
2. Exopeptidases remove amino acids/hydrolyse
   (bonds) at end(s);
3. More ends or increase in surface area (for
   exopeptidases);

Question 3

Digestion - Describe the action of membrane-bound
dipeptidases and explain their importance (2)

Answer 3

1. Hydrolyse (peptide bonds) to release amino acids;
2. Amino acids can cross (cell) membrane by facilitated diffusion;
   OR
   Maintain concentration gradient of amino acids for
   absorption;

Question 4

Digestion – Describe the complete
digestion of starch by a mammal (6)

Answer 4

1. Hydrolysis;
2. (Of) glycosidic bonds;
3. (Starch) to maltose by amylase;
4. (Maltose) to glucose by disaccharidase/maltase;
5. Disaccharidase/maltase membrane-bound;

Question 5

Digestion - Function of bile salts and micelles (3)

Answer 5

1. (Bile salts emulsify lipids forming) droplets which
   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 6

Digestion – describe the process of lipid digestion (3)

Answer 6

1. lipase hydrolyses triglycerides
2. ester bonds
3. Form monoglycerides and fatty acids

Question 7

Digestion – Explain the advantages of emmulsification and micelle formation (2)

Answer 7

1. 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 8

Absorption - Describe and explain the features you would expect to find in a cell specialised for absorption (4)

Answer 8

1. Folded membrane/microvilli so large surface area
   (for absorption);
2. Large number of co-transport/carrier/channel
   proteins so fast rate (of absorption)
   OR
   Large number of co-transport/carrier proteins for active transport
   OR
   Large number of co-transport/carrier/channel
   proteins for facilitated diffusion;
3. Large number of mitochondria so make (more)
   ATP (by respiration)
   OR
   Large number of mitochondria for aerobic respiration
   OR
   Large number of mitochondria to release energy for
   active transport;
4. Membrane-bound (digestive) enzymes so maintains concentration gradient (for fast absorption);

Question 9

Absorption - Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels (4)

Answer 9

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 simple diffusion;
4. Triglycerides (re)formed (in cells);
   Accept chylomicrons form
5. Vesicles move to cell membrane;

Question 10

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

Answer 10

1. Micelles include bile salts and fatty acids;
   Ignore other correct components of micelles.
2. Make the fatty acids (more) soluble in water;
   For ‘fatty acids’ accept fats / lipids.
3. Bring/release/carry fatty acids to cell/lining (of the
   ileum);
   For ‘fatty acids’ accept fats/lipids.
4. Maintain high(er) concentration of fatty acids to
   cell/lining (of the ileum);
5. Fatty acids (absorbed) by diffusion;

Question 11

Absorption - Describe how the golgi apparatus is involved in the absorption of lipids.(3)

Answer 11

1. Modifies / processes triglycerides;
2. Combines triglycerides with proteins;
3. Packaged for release / exocytosis
   OR
   Forms vesicles;

Question 12

Absorption – Explain how monosaccharides and amino acids are absorbed into the
blood (5)

Answer 12

1. Some by facilitated diffusion (when higher concentration in lumen)
2. Sodium ions actively transported from ileum cell to blood;
3. Maintains / forms diffusion / concentration gradient for sodium to enter cells from gut (and with it, glucose);
4. sodium ions enter cell by facilitated diffusion and bring with it a molecule of glucose by co-transport;
5. Facilitated diffusion of glucose into blood/capillary;