Exchange and Transport Systems

Question 1

Define digestion

Answer 1

The hydrolysis of large, insoluble molecules into smaller, smaller molecules that can be absorbed across cell membranes.

Question 2

What is hydrolysis?

Answer 2

Breaking the chemical bonds of a molecule by adding a molecule of water

Question 3

What are carbohydrates broken down into?

Answer 3

Disaccharides-> monosaccharides

Question 4

What are lipids broken down into?

Answer 4

Fatty acids and monoglycerides (has one fatty acid attached)

Question 5

What are proteins broken down into?

Answer 5

Amino acids

Question 6

Describe the process of starch digestion.
(s -> m)

Answer 6

Salivary glands secrete saliva = contains amylase = catalyses hydrolysis of starch into maltose = glycosidic bonds broken
In pancreas = starch digestion continues in duodenum = pancreatic amylase secreted from pancreas = catalyses hydrolysis of any undigested starch into maltose = glycosidic bonds broken = substrate is complementary to the shape of the active site

Question 7

Why can’t maltose be absorbed?

Answer 7

It is a large molecule that is too big to fit through.

Question 8

Describe the small intestine brush border.

Answer 8

Maltase is an enzyme found in the cell membranes of epithelial cells = catalyses the hydrolysis of maltose into glucose = breaks the glycosidic bonds = substrate is complementary to the shape of the active site

Question 9

Where is amylase produced?

Answer 9

Pancreas and salivary glands

Question 10

Describe the digestion of lipids

Answer 10

Bile salts produced by liver = emulsify lipids = increases surface area for lipase to work on
Monoglycerides and fatty acids attach onto bile salts to form micelles

Question 11

What are micelles?

Answer 11

Monoglycerides and fatty acids attached onto bile salts

Question 12

Why are fats emulsified?

Answer 12

Provides a larger surface area for faster hydrolysis action by lipase

Question 13

What do micelles do?

Answer 13

They deliver the monoglycerides, glycerol and fatty acids to the epithelial cells lining the ileum by diffusion

Question 14

How is the small intestine adapted for absorption?

Answer 14

Contains villi which are surrounded by a network of capillaries- maintain concentration gradient
Epithelial cells are covered with microvilli- large surface area
The epithelial cells are thin- short diffusion pathway

Question 15

Where is lipase produced?

Answer 15

Pancreas

Question 16

How are large polypeptides digested?

Answer 16

Endopeptidases
Hydrolyse peptide bonds
Between the amino acids in the central region
Smaller peptide molecules

Question 17

Where are endopeptidases produced?

Answer 17

Stomach and small intestine

Question 18

How are smaller polypeptides digested?

Answer 18

Exopeptidases
Hydrolyse peptide bonds
Between terminal amino acids
Dipeptides + amino acids

Question 19

Where are exopeptidases produced?

Answer 19

Pancreas

Question 20

Why is it beneficial to digest polypeptides in the middle to produce smaller peptides?

Answer 20

To increase the surface area and provide more “ends” for exopeptidases

Question 21

How are lipids digested?

Answer 21

Emulsified by bile salts
Lipase hydrolyses the ester bonds
Glycerol and fatty acids (monoglycerides)

Question 22

What is the role of bile?

Answer 22

Emulsifies fats to provide lipase with a larger surface area to work on

Question 23

What happens during co-transport?

Answer 23

Sodium is actively transported out of the epithelial cell into the bloodstream
Low con of sodium
Sodium moves into the cell via facilitated diffusion along with glucose due to specific shape of binding site on the co-transport protein
Glucose is transported out of the cell and into the blood via facilitated diffusion

Question 24

How are lipids absorbed?

Answer 24

Micelles come into contact with epithelial cells
They break down and release fatty acids and glycerol
Fatty acids and glycerol are non-polar so they can easily diffuse into the epithelial cells
Reform to form triglycerides
Transported into the bloodstream via exocytosis