Digestion & Absorption

Question 1

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. [5]

Answer 1

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 diffusion; REJECT Micelle enters cell
4. Triglycerides (re)formed (in cells); (Smooth Endoplasmic Reticulum)
5. (Golgi) Vesicles move to cell membrane;

Question 2

Describe the role of micelles in the absorption of fats into the cells of the ileum. [5]

Answer 2

1. Micelles include bile salts and fatty acids;
2. Make the fatty acids (more) soluble in water;
3. Bring/release/carry fatty acids to cell/lining (of the ileum);
4. Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
5. Fatty acids (absorbed) by diffusion;
   REJECT MICELLES enter cell

Question 3

Describe the role of enzymes in the digestion of proteins in a mammal. [4]

Answer 3

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 4

The action of endopeptidases and exopeptidases can increase the rate of protein digestion. Describe how. [2]

Answer 4

1. Exopeptidases hydrolyse peptide bonds at the ends of a polypeptide/protein AND endopeptidases hydrolyse internal peptide bonds within a polypeptide/protein;
2. More ‘ends’ OR More surface area;

Question 5

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

Answer 5

1. Folded membrane/microvilli so large surface area (for absorption);
   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 6

Describe the mechanism for the absorption of amino acids in the ileum. [5]

Answer 6

1. Facilitated diffusion of amino acid (into cell when higher concentration in lumen);
2. Co-transport;
3. Sodium ions actively transported from cell to blood/capillary/tissue fluid;
4. Creating sodium ion concentration/diffusion gradient;
5. Facilitated diffusion of amino acid into blood/capillary;

Question 7

Describe the process of starch digestion [5]

Answer 7

(salivary/pancreatic) Amylase;
Starch to Maltose;
Maltase;
Maltose to glucose;
Hydrolysis;
Glycosidic bonds

Question 8

Describe the absorption of glucose (Cotransport) [4]

Answer 8

1. Sodium ions actively transported from ileum cell in to blood;
2. Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose);
3. GLucose enters cell down the sodium ion gradient
4. Glucose enters by facilitated diffusion with sodium ions;