digestion and absorption

Question 1

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels (5)

Answer 1

1. Micelles contain bile salts and fatty acids
2. Make fatty acids more soluble in water
3. Fatty acids absorbed by diffusion
4. Triglycerides reformed in cells
5. Vesicles move to cell membrane

Question 2

The action of carrier protein is linked to a membrane bound ATP hydrolyse enzyme, explain the function of this ATP hydrolyse (2)

Answer 2

1. ATP to ADP + Pi releases energy
2. Energy allows ions to be moved against a concentration gradient

Question 3

The movement of sodium out of the cell allows the absorption of glucose into the cell lining the ileum, explain how (2)

Answer 3

1. Maintains a concentration gradient for sodium from ileum into the cell
2. Sodium moves in by facilitated diffusion and brings glucose with it

Question 4

After collecting the samples the scientist immediately heated them to 70 degrees for 10 minutes, explain why (2)

Answer 4

• to denature the enzymes/ lipase
• so no further digestion occurs

Question 5

Describe the role of micelles in the absorption of fats into the cells lining the ileum (4)

Answer 5

• micelles include bile salts and fatty acids
• make the fatty acids more soluble in water
• bring fatty acids to lining of the ileum
• maintain higher concentration of fatty acids to lining of ileum
• fatty acids absorbed by diffusion

Question 6

Describe the role of enzymes in the digestion of proteins in a mammal (4)

Answer 6

1. Hydrolysis of peptide bonds
2. Endopeptidase act in middle of protein
3. Exopeptidase act at end of protein
4. Dipeptidase acts on dipeptide and produces two amino acids

Question 7

By which process do fatty acids and glycerol enter the intestinal epithelial cell (1)

Answer 7

Diffusion

Question 8

Explain the advantages of lipid droplet and micelle formation (3)

Answer 8

1. Droplets increase surface area for lipase action
2. Faster hydrolysis of triglycerides
3. Micelles carry fatty acids and glycerol to intestinal epithelial cell

Question 9

How is the Golgi apparatus involved in the absorption of lipids (3)

Answer 9

1. Modifies triglycerides
2. Combines triglycerides with proteins and cholesterol
3. Packaged for release/ or forms vesicles

Question 10

Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions, explain how (3)

Answer 10

1. Sodium ions actively transported from ileum cell to blood
2. Maintains diffusion gradient for sodium to enter cells from gut and with it glucose
3. Glucose enters by facilitated diffusion with sodium ions

Question 11

Endopeptidase and exopeptidases are involved in the hydrolysis of proteins, name the other type of enzyme required (1)

Answer 11

Dipeptidase

Question 12

why is maltase referred to as a membrane bound dissaccharidase (1)

Answer 12

it is part of the cell surface membranes of the epithelial cells lining the ileum

Question 13

define hydrolysis

Answer 13

breaking a chemical bond by adding water

Question 14

list 2 structures that produce amylase

Answer 14

salivary glands
pancreas

Question 15

suggest why the stomach does not have villi or microvilli

Answer 15

villi and microvilli increase SA so absorption of soluble molecules is faster

food in stomach not yet been hydrolysed into soluble molecules so they cant be absorbed

Question 16

name the final product of starch digestion in the gut

Answer 16

a-glucose

Question 17

list 3 enzymes produced by the epithelium of the ileum

Answer 17

maltase
lactase
sucrase

Question 18

suggest the process by which micro-organism produce a large volume of gas in lactose intolerant people
- suggest a reason why this gas is unlikely to be CO2

Answer 18

• respiration
• CO2 produced in aerobic respiration, but conditions in the colon are anaerobic

Question 19

suggest an explanation to why lactose intolerance is a problem for modern day humans but wasnt a problem for our ancestors

Answer 19

modern storage methods mean milk is readily available
ancestors barely consumed milk as adults

Question 20

explain how lowering water potential in the colon can cause diarrhoea

Answer 20

low water potential causes water to move into lumen of colon from epithelial cells
more water in faeces

Question 21

list 3 organelles you would expect to be numerous in an epithelial cell

Answer 21

• mitochondria- produce ATP for active transport

-endoplasmic reticulum- to reform triglycerides

-golgi apparatus- to modify triglycerides

Question 22

in addition to microvilli, state 1 feature of epithelial cells that would increase rate of absorption of amino acids

Answer 22

more carrier proteins

Question 23

describe carbohydrate digestion (4)

Answer 23

• amylase hydrolyses starch into maltose
• breaks the glycosidic bonds
• amylase produced by salivary glands and pancreas, released into mouth and ileum
• monosaccharides transported across cell membrane of ileum by transporters
• glucose absorbed by active transport with Na+ via co transporters

Question 24

describe lipid digestion (5)

Answer 24

• lipase catalyses breakdown of lipids into monoglycerides and fatty acids
• lipase made in the pancreas and works in ileum
• ester bonds are hydrolysed
• bile salts produced by liver emulsify lipids into small droplets
• these have a large SA so lipase hydrolyses them quicker

Question 25

describe the roles of enzymes in complete breakdown of starch (5)

Answer 25

• amylase
• starch to maltose
• maltase
• maltose to glucose
• hydrolysis
• of glycosidic bond

Question 26

describe the processes involved in absorption of products of starch digestion (5)

Answer 26

• glucose moves in with sodium
• via carrier protein
• sodium removed by active transport
• into blood
• maintains lows conc of sodium in epithelial cell
• glucose moves into blood
• by facilitated diffusion