3.3.3 Digestion and Absorbtion

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

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

Describe the complete digestion of starch by a mammal.

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

Describe the 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

describe lipid digestion (3)

Answer 6

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

Question 7

Describe the Function of bile salts and micelles (3)

Answer 7

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 8

describe lipid digestion (3)

Answer 8

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

Question 9

Explain the advantages of emmulsification and
micelle formation. (2)

Answer 9

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 10

Describe and explain two features you would expect to find in a cell specialised for absorption. (4)

Answer 10

1. Folded membrane/microvilli so large surface area
   (for absorption);
   Reject references to ‘villi’.
   Accept ‘brush border’ for ‘microvilli’.
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 11

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

Answer 11

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 12

Describe
the role of micelles
in the absorption of
fats into the cells
lining the ileum (2)

Answer 12

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 13

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

Answer 13

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

Question 14

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

Answer 14

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;