3.2.2 Digestion and Absorption

Question 1

The duodenum is connect to the _____

Answer 1

stomach

Question 2

The ileum is connect to the _____

Answer 2

large intestine

Question 3

How is food physically broken down?

Answer 3

By teeth in the mouth and by muscular stomach

Question 4

How is food chemically broken down?

Answer 4

• Hydrolysis of large insoluble molecules into small soluble molecules
• Carried out by specific enzymes

Question 5

What are carbohydrates broken down into?

Answer 5

Disaccharides and then monosaccharides

Question 6

What are lipids broken down into?

Answer 6

Fatty acids and monoglycerides

Question 7

What are proteins broken down into?

Answer 7

Amino acids

Question 8

Name 2 enzymes that break down carbohydrates

Answer 8

• Amylase
• Membrane-bound disaccharidases

Question 9

What reaction does amylase catalyses?

Answer 9

Conversion of starch into maltose

Question 10

Where is amylase produced & where is it released to?

Answer 10

• Salivary glands - release amylase into mouth
• Pancreas - releases amylase into small intestine

Question 11

What are membrane-bound disaccharidases?

Answer 11

Enzymes that are attached to cell membranes of epithelial cells lining the ileum

Question 12

What reaction do membrane-bound disaccharidases catalyses?

Answer 12

Hydrolysis of disaccharides (e.g. maltose, sucrose, lactose) into monosaccharides (e.g. glucose, fructose and galactose)

Question 13

Fill in the blanks

Answer 13

Question 14

What reaction does lipase catalyse?

Answer 14

Hydrolysis of lipids into monoglycerides and fatty acids

Question 15

Where is lipase made and where does it work?

Answer 15

Pancreas - works in small intestine

Question 16

Where are bile salts produced?

Answer 16

Liver

Question 17

What do bile salts do?

Answer 17

• Emulsify lipids
  
  • Cause lipids to form small droplets

Question 18

What is the benefit of bile salts causing lipids to form small droplets?

Answer 18

• Several small lipid droplets have bigger SA than single large droplet
• Lipase can digest lipids faster

Question 19

What happens after the lipid has broken down?

Answer 19

Monoglycerides and fatty acids stick with bile salts to form tiny structures called micelles

Question 20

Name the different proteases (or peptidases) that break down proteins

Answer 20

• Endopeptidases
• Dipeptidases
• Exopeptidases

Question 21

What do endopeptidases do?

Answer 21

Break polypeptides into smaller peptide chains

Question 22

Where are trypsin and chymotrypsin (endopeptidases) synthesised and secreted into?

Answer 22

Synthesised in pancreas and secreted into small intestine

Question 23

Where is pepsin (endopeptidases) synthesised and secreted into?

Answer 23

Released into stomach by cells in stomach lining

Question 24

What do exopeptidases do?

Answer 24

• Act to hydrolyse peptide bonds at ends of protein molecules
• Remove terminal amino acids

Question 25

What are dipeptidases?

Answer 25

Exopeptidases that work specifically on dipeptides

Question 26

What do dipeptidases do?

Answer 26

• Hydrolses dipeptides into amino acids
• Breaks peptide bond between them

Question 27

Where are dipeptidases located?

Answer 27

In cell-surface membrane of epithelial cells in small intestine

Question 28

How is glucose and galactose absorbed?

Answer 28

By active transport with sodium ions via co-transporter protein

Question 29

How is fructose is absorbed?

Answer 29

Via facilitated diffusion through different transporter protein

Question 30

Describe how glucose is absorbed from lumen (middle) of ileum by co-transport

Answer 30

1. Na⁺ ions actively transported out of ileum epithelial cells into blood by sodium-potassium pump
   
   1. = creates concentration gradient
   2. Higher conc. of Na⁺ in lumen than inside cell
2. Causes Na⁺ to diffuse into epithelial cell by facilitated diffusion (down their concentration gradient)
   
   • Via sodium-glucose co-transporter proteins
3. Glucose absorbed with Na⁺ against their concentration gradient
   
   • = concentration of glucose inside cell increases
4. Glucose diffuses out of cell into blood, down its concentration gradient through protein channel by facilitated diffusion

Question 31

How are amino acids absorbed?

Answer 31

By co-transport (similar to glucose)

Question 32

Describe how amino acids are absorbed by co-transport

Answer 32

• Na⁺ ions actively transported out of ileum epithelial cells in blood
• Creates Na⁺ concentration gradient between lumen and cell
• Na⁺ can diffuse from lumen into epithelial cells through sodium-dependent transporter proteins, carrying amino acids with them

Question 33

Name two ways the concentration gradient between the inside of the ileum and blood is maintained

Answer 33

• Constant circulation of blood
• Ileum has muscles which uses peristalsis to keep food moving along the gut

Question 34

Describe how in detail how monoglycerides and fatty acids are absorbed and how they’re transported around the body

Answer 34

1. Micelles help to move monoglycerides and fatty acids towards epithelium
   
   • ∵ micelles constantly break up and reform they can ‘release’ monoglycerides and fatty acids = allows them to be absorbed
     
     • ∵ lipid-soluble = can diffuse directly across epithelial cell membrane
2. Monoglycerides and fatty acids transported to ER & combine to form triglycerides
3. Triglycerides associated with cholesterol and lipoproteins = form chylomicrons (lipid transport structures)
4. Chylomicrons enter lacteal (part of lymphatic system) by exocytosis
5. Only drain into bloodstream near heart

Question 35

The walls of the small intestine have lots of finger-like projections called ____

Answer 35

villi

Question 36

The epithelial cells on the surface of the villi have folds in their cell-surface membranes called ______

Answer 36

microvilli

Question 37

Explain the presence of bile in the colon (large intestine) (2)

Answer 37

• Secreted by the liver
• Bile passes unchanged from small intestine to colon

Question 38

Suggest why the peptides released when gluten is digested cannot by absorbed by facilitated diffusion (2)

Answer 38

• Too big/wrong shape
• Cannot pass through channel protein

Question 39

Describe the function of part X

Answer 39

Transports chylomicrons

Question 40

Suggest an advantage of having muscle cells in the villi (2)

Answer 40

• Enables villi to move
• Increased contact with food

Question 41

Suggest how chylomicrons leave the epithelial cells. Give an reason for your answer. (2)

Answer 41

• Exocytosis
• Too large to leave by other methods