Digestion and Absorption A1

Question 1

Define digestion.
(3)

Answer 1

1. the hydrolysation ( by enzymes)
2. of large insoluble molecules into smaller soluble molecules
3. which can be absorbed by the small intestine

Question 2

What order does the human digestive track go in?
(7)

Answer 2

1. salivary glands
2. oesophagus
3. stomach
4. pancreas
5. small intestine
6. large intestine
7. rectum

Question 3

Name the three different glands and the enzyme they produce.
(3)

Answer 3

1. salivary glands - salivary amylase
2. pancreas - pancreatic amylase, lipases and proteases
3. stomach - protease (pepsin)

Question 4

What are the following hydrolysed into and by what enzyme?…
-proteins
-carbohydrates
-fats

Answer 4

1. amino acids by protease
2. simple sugars by carbohydrase
3. glycerol, fatty acids and monoglycerides by lipase (+ bile salts)

Question 5

What role does the salivary glands carry out?

Answer 5

secretes saliva containing amylase (the enzyme which hydrolyses starch to maltose)

Question 6

What role does the stomach carry out?

Answer 6

food is mixed with gastric juice which is acidic - kills microorganisms, contains proteases which breaks down protein to amino acid

Question 7

what role does the pancreas carry out?

Answer 7

secretes pancreatic juice containing amylase (and other carbohydrase), protease and lipases

Question 8

What role does the small intestine carry out?

Answer 8

adapted to provide a large surface area for absorption of the products of digestion - maltase enzymes are embedded within the epithelium cell membrane of the small intestine. This enzyme breaks down maltose to glucose, so its available for rapid absorption.

Question 9

Name the two enzymes involved in the digestion of starch and what they do.

Answer 9

1. amylase - produced by salivary glands and pancreas, convert starch to maltose
2. maltase - produced in epithelial cell membrane of small intestine (embedded in microvilli of SI), converts maltose to glucose

Question 10

Describe the steps in carbohydrate digestion.
(5)

Answer 10

1. food enters the mouth and broken up by teeth (mechanical digestion), then mixed with saliva
2. salivary amylase starts to hydrolyse starch to maltose (chemical digestion)
3. in stomach salivary amylase is denatured due to acidic PH
4. in small intestine pancreatic amylase continues to hydrolyse starch to maltose
5. maltose then hydrolysed to glucose by maltase enzyme in membrane of epithelial cells. The glucose can then be absorbed.

Question 11

Describe the process of starch digestion.
(6)

Answer 11

1. salivary/pancreatic amylase
2. maltose hydrolysed by maltase (enzyme in epithelial cell membrane)
3. maltose to glucose
4. hydrolysis
5. break glycosidic bonds

Question 12

Describe how proteins are digested in the human gut.
(4)

Answer 12

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 so they can then be absorbed by facilitated diffusion and active transport.

Question 13

How is glucose absorbed into the blood?
(4)

Answer 13

1. sodium ions are actively transported out of epithelial cell into blood (by sodium potassium pump)
2. this created concentration gradient of sodium ions
3. sodium ions and glucose enter the cell by facilitated diffusion (through co-transport protein)
4. glucose diffuses into blood by facilitated diffusion

Question 14

Explain how amino acids are absorbed across the epithelium into the blood.
(5)

Answer 14

1. absorbed by facilitated diffusion and active transport using SPECIFIC carrier proteins (co-transport)
2. sodium ions are actively transported out of epithelial cell into blood (by sodium potassium pump)
3. this created concentration gradient for sodium ions
4. sodium ions and amino acids enter the cell by facilitated diffusion (through co-transport protein)
5. amino acids diffuse into blood via facilitated diffusion

Question 15

Describe the process of emulsification.
(4)

Answer 15

1. bile (created in liver, stored in gallbladder)
2. increases surface area of fats
3. by grouping them into smaller clusters (emulsification droplets) in small intestine
4. bile salts stop fats binding together again

Question 16

What is lipase enzymes role?
(4)

Answer 16

1. hydrolyses lipid into glycerol, fatty acids and monoglycerides
2. this increases SA
3. for faster hydrolysis
4. micelles carry fatty acids and glycerol through membrane (for golgi function)

Question 17

Describe the process of lipid absorption.
(6)

Answer 17

1. monoglycerides and fatty acids associate with bile salts and phospholipids to form micelles.
2. micelles transport monoglycerides and fatty acids to surface of epithelial cell, here they cross the membrane via simple diffusion and they are non-polar.
3. triglycerides, cholesterol and phospholipids are packaged into lipoproteins called chylomicrons
4. chylomicrons are water soluble so can be carried in blood
5. these are transported to a lymph vessel by exocytosis
6. they then enter the blood

Question 18

What makes up a carbohydrate?

Answer 18

1. carbon, hydrogen, oxygen
2. in the ration 1:2:1

Question 19

Explain why glucose and maltose both taste sweet but starch does not?

Answer 19

1. glucose and maltose are insoluble
2. so bind to tongue
3. starch is a salt so dissolves instead

Question 20

Explain why milk would have to be passed through a reactor used to produce lactose-reduced milk several times?
(4)

Answer 20

1. enzymes may have been all used up after first time passing through
2. so not all lactose in milk reacted
3. by passing through again, enzyme substrate (lactase) are free again
4. to bind with the leftover lactose

Question 21

The formula of galactose is C6-H12-O6.
What is the formula of lactose?

Answer 21

C12-H22-O11

Question 22

People who are unable to produce lactase are lactose intolerant. Explain why they get diarrhoea when they drink milk?
(4)

Answer 22

1. high concentration of lactose in small intestine
2. cannot be absorbed as too large
3. water osmoses from high to low water potential
4. into small intestine causing diarrhoea