6.9 Enzymes and digestion

Question 1

What is the digestive system made up of (broadly)?

Answer 1

A long muscular tube and associated glands which produce enzymes to hydrolise large molecules for absorbtion.

Question 2

Describe the oesophagus.

Answer 2

A tube which carries food from the mouth to the stomach.

Question 3

Describe the stomach.

Answer 3

A muscular sack with an inner layer that produces enzymes.

Its role is to store and digest food, especially proteins, as it has glands which produce peptidases

Question 4

describe the Ileum.

Answer 4

A long, muscular tube which produces enzymes in its walls and glands to further digest food.

• Inner walls are folded into villi, increasing the SA.On the epithelium of each villus are micro villi.
• Large SA aids the surface to absorb products into the blood stream.

Question 5

Describe the rectum.

Answer 5

Where faeces is stored before egestion.

Question 6

Describe the salivary glands.

Answer 6

Release secretions into the mouth (amylase)

Question 7

Describe the pancreas.

Answer 7

Large gland below the stomach, produces pancreatic juice containing protease, lipase and amylase.

Question 8

What are the 2 stages of digestion?

Answer 8

• physical breakdown

- chemical digestion

Question 9

Describe physical breakdown.

Answer 9

• breaks food down into smaller parts to help with absorption and increase SA for chemical digestion.
• involves teeth and muscles (EG: stomach wall)

Question 10

Describe chemical breakdown.

Answer 10

Hydrolyses large, insoluble molecules into smaller ones by adding digestive enzymes.

Question 11

What is hydrolysis?

Answer 11

the breaking down of a molecule by the addition of water.

• digestive enzymes function by hydrolysis
• more than one enzyme is required to hydrolyze a molecule.

Question 12

What are the 3 most important digestive enzymes?

Answer 12

CARBOHYDRASES: hydrolyse carbohydrates into monosaccharides
LIPASES: hydrolyse lipids into glycerol and fatty acids
PROTEASES: Hydrolyse proteins into amino acids.

Question 13

Which enzymes are used for the digestion of starch?

Answer 13

AMYLASE: produced by the mouth and pancreas, hydrolyses alternate glycosidic bonds of the starch molecule to produce maltose (a disaccharide)
MALTASE: produced in the ileum lining (membrane-bound disaccharide). Breaks down maltase into alpha glucose monosaccharide by hydrolysis.

Question 14

Describe the process of the digestion of starch.

Answer 14

1) saliva enters mouth from salivary glands and mixes with food.
2) salivary amylase hydrolyses any starch into maltose.. salts maintain neutral PH.
3) Food enters stomach and acid denatures amylase and prevents further starch hydrolysis
4) Food passes through small intestine and mixes with pancreatic juice.
5) pancreatic amylase continues hydrolyzing starch. alkaline salts released by walls and pancreas maintain PH.
6) Muscles push food down ileum. epithelial lining produces maltase which hydrolises maltose.

Question 15

Describe the processes involved in the absorption of the products of starch digestion

Answer 15

1) Glucose moves with sodium into epithelial cell, via carrier/channel protein
2) Sodium removed from epithelial cell by active transport / sodium- potassium pump Into blood.
3) Maintaining low concentration of sodium in epithelial cell
4) Glucose moves into blood by (facilitated) diffusion.

Question 16

What are the other two disaccharides which are hydrolised and which enzymes do this?

Answer 16

SUCRASE hydrolyses single glycosidic bond inin SUCROSE, producing GLUCOSE and FRUCTOSE.

LACTASE hydrolyses single glycosidic bond in LACTOSE, producing GLUCOSE and GALACTOSE.

Question 17

Describe the process of lipid digestion.

Answer 17

1) bile salts produced by the liver break up lipid molecules into micelles by emulsification, increasing the surface area to increase lipase action.
2) Lipases from the pancreas hydrolyse lipids into fatty acids and monoglycerides.

Question 18

What are the 3 types of enzyme used in protein digestion?

Answer 18

Endopeptases
Exopeptases
Dipeptases

Question 19

Describe endopeptases.

Answer 19

Hydrolyse peptide bonds between amino acids in the centre of a protein forming a series of peptide molecules.

Question 20

describe exopeptases.

Answer 20

hydrolyse peptide bonds in terminal amino acids of peptide molecules forming endopeptidases. progressively release dipeptases and amino acids.

Question 21

describe dipeptases.

Answer 21

hydrolyse bond between two amino acids of a dipeptide. they are membrane-bound in the ileum