3.3 Digestion and Absorption

Question 1

Explain what happens in digestion

Answer 1

Large insoluble biological molecules hydrolysed to smaller soluble molecules
That are small enough to be absorbed across cell membranes

Question 2

Describe the digestion of starch in mammals

Answer 2

Amylase (produced by salivary glands/pancreas) hydrolysed starch to maltose
Membrane bound maltose (attached to cells lining ileum) hydrolyses maltose to glucose
Hydrolysis of glycosidic bond

Question 3

Describe the digestion of disaccharides in mammals

Answer 3

Membrane bound disaccharides hydrolyse disaccharides to 2 monosaccharides
Maltase-Maltose—>glucose + glucose
Sucrase-Sucrose—>glucose + glucose
Lactase-Lactose —>Galactose + glucose

Question 4

Describe the digestion of lipids in mammals,including action of bile salts

Answer 4

Bole salts produced by liver emulsify lipids causing them to form smaller lipid droplets
This increases surface area of lipids for increased/faster lipase activity
Lipase( made in pancreas) hydrolysed lipids (e.g. triglycerides)—> monoglycerides + fatty acids
Hydrolysis of ester bind

Question 5

Describe the digestion of proteins by a mammal

Answer 5

Endopeptidases—> hydrolyse internal (peptide) bonds within a polypeptide —> smaller peptides
So more ends/surface area for exopeptidases
Exopeptidases- hydrolyse terminal peptide bonds at ends of polypeptide—>single amino acids

Question 6

Suggest why membrane bound enzymes are important in digestion

Answer 6

Membrane bound enzymes are located on cell membranes of epithelial cells lining ileum
By hydrolysing molecules at the site of absorption they maintain a conch gradient for absorption

Question 7

Describe the pathway for absorption of products of digestion in mammals

Answer 7

Lumen of ileum —>cells lining ileum —> blood

Question 8

Describe the absorption or amino acids and monosaccharides in mammals

Answer 8

Co transport:

Question 9

Describe the absorption of lipids by a mammal including the roles of micelles

Answer 9

Micelles contain bile salts,monoglycerides and fatty acids
Make monoglycerides and fatty acids more soluble in water
Carry/release fatty acids and monoglycerides to cell/lining of ileum
Maintains high concentration of fatty acids to cell/lining
Monoglycerides fatty acids absorbed by diffusion
Triglycerides reformed in epithelial cells and aggregate into globules
Globules coated with proteins forming chylomicrons which are then packaged inti vesicles
Vesicles move to cell membrane and leave by exocytosis
Enter lymphatic vessels and eventually return to blood circulation