Section 3- Digestion

Question 1

What part of the digestive system stores and digests food?

Answer 1

Stomach

Question 2

What it special about the ileum to increase product absorption?

Answer 2

Inner walls folded into villi- gives larger surface area.

Villi has microvilli again increasing surface area.

Question 3

Where is food further digested by enzymes?

Answer 3

Illeum

Question 4

What does the large intestine do?

Answer 4

Absorb water

Question 5

What is digestion?

Answer 5

The breaking down of large insoluble molecules into small soluble ones that can be assimilated into cells.

Question 6

What are some of the adaptions of the small intestine?

Answer 6

Lots of villi for larger surface area

Long and tightly packed for larger surface area

Small diffusion distance

Rich blood supply

Question 7

What does chemical digestion do?

Answer 7

Hydrolyses large, insoluble molecules into smaller, soluble ones.

Question 8

What are the 3 main digestive enzymes?

Answer 8

• Carbohydrases
• Peptidases
• Lipases

Question 9

What enzymes are involved in carbohydrate digestion?

Answer 9

Amylase
Maltase
Sucrase/ lactase

Question 10

Where is amylase produced and what does it do?

Answer 10

Produced in saliva and by the pancreas

Hydrolyses glyosidic bonds of starch to form maltose

Question 11

Where is maltase found and what does it do?

Answer 11

Found on the lining of the ileum

Hydrolyses maltose to a-glucose

Question 12

Where is sucrase/ lactase found?

Answer 12

Found on the lining of the ileum

Question 13

What does lipase do?

Answer 13

Hydrolyses the ester bond of triglyceride to form a monoglyceride and fatty acid.

Question 14

What is lipid digestion sped up by?

Answer 14

Bile

Neutralises acid from the stomach which ensure correct conditions for enzymes released into small intestine.

Question 15

What needs to happen before the lipids can be digested?

Answer 15

Must be emulsified by bile salts produced by the liver.

This breaks down large fat molecules into smaller, soluble molecules (micelles), increasing surface area.

Question 16

What enzymes are involved in protein digestion are what are their roles?

Answer 16

Endopeptidases- hydrolyse peptide bonds within polypeptide chain.

Exopeptidases- hydrolyse the peptide bonds between terminal amino acids.

Dipeptidases- break dipeptides into amino acids.

Question 17

What are 2 structures that produce amylase?

Answer 17

Salivary glands

Pancreas

Question 18

Why does the stomach not have villi or microvilli?

Answer 18

Food in the stomach has not been hydrolysed into soluble molecules.

Cannot be absorbed so are unnecessary.

Question 19

What are 3 enzymes produced by the epithelium of the ileum?

Answer 19

Maltase
Sucrase
Lactase

Question 20

How is the ileum adapted for absorbing the products of digestion?

Answer 20

• Wall of ileum is folded (villi)
• Thin walls lined with epithelial cells
• Large network of blood capillaries

Question 21

How are the villi specialised for the absorption of the products of digestion?

Answer 21

Increase surface area for diffusion

Very thin walls –> reduces diffusion distance

Well supplied with blood vessels –> maintain diffusion distance- can carry away absorbed molecules

Epithelial cells lining the villi have microvilli

Question 22

How are triglycerides absorbed?

Answer 22

Non-polar monoglycerides and fatty acids diffuse across epithelial cell membrane.

Triglycerides are re-synthesised in SER and Golgi
Combined with proteins and cholesterol forming CHYLOMICRONS

Chylomicrons move into lacteals by exocytosis

Chylomicrons carried through lymphatic system enter bloodstream at vena cava

Question 23

What are 3 organelles that you would expect to be well-developed in epithelial cell of ileum?

Answer 23

Endoplasmic reticulum- re-synthesis triglyceride from monoglyceride and fatty acid

Golgi apparatus- form chylomicrons from triglycerides, cholesterol and lipoproteins

Mitochondria- provide ATP required for co-transport of glucose and amino acid molecules

Question 24

In addition to microvilli, what is another feature of the epithelial cells that would increase the rate of absorption of amino acids?

Answer 24

Increase in number of protein channels and carrier proteins

Question 25

Why would endocellulases and exocellulases act at different places on a cellulose molecule?

Answer 25

Active sites are different shapes

So different enzyme-substrate complexes are formed.

Question 26

How do chylomicrons leave the epithelial cell?

Answer 26

Exocytosis

Too large

Question 27

What type of enzyme would you find bound to the membrane of cells lining the small intestine?

Answer 27

Dipeptidases

Question 28

How could a mutation of a gene cause someone to be unable to digest lactose?

Answer 28

Changes primary structure

No complementary active site to glucose

Question 29

Describe the role of micelles in the absorption of fata into the cells lining the ileum?

Answer 29

Micelles composed of monoglyceride, fatty acids, bile salts

Make fatty acids more soluble in water

Bring fatty acid to cell lining

Maintain higher concentration of fatty acid to cell

Fatty acid absorbed by diffusion