Exchange- Digestion and Absorption

Question 1

Why do large biological molecules need to be broken down?

Answer 1

They are too big to cross cell membranes so can’t be absorbed from the gut into the blood

Question 2

What happens during digestion?

Answer 2

Large molecules are broken down into smaller molecules which can move across cell membranes so they can be easily absorbed from the gut to the blood to be transported around the body for use by the body cells

Question 3

How are large biological molecules (polymers) broken down into smaller molecules (monomers)?

Answer 3

Hydrolysis reactions that use water

Question 4

What are carbohydrates hydrolysed into?

Answer 4

Disaccharides and monosaccharides

Question 5

What are fats hydrolysed into?

Answer 5

Fatty acids and monoglycerides

Question 6

What are proteins hydrolysed into?

Answer 6

Amino acids

Question 7

How are digestive enzymes produced?

Answer 7

By specialised cells in the digestive system of mammals which are the released into the gut to mix with food

Question 8

Why are different enzymes needed?

Answer 8

Because they only work with specific substrates so different enzymes are needed to catalyse the breakdown of different food molecules

Question 9

What is amylase?

Answer 9

A digestive enzyme that catalyses the conversion of starch into the smaller sugar maltose which involves hydrolysis of the glycosidic bonds

Question 10

How is amylase produced?

Answer 10

By the salivary glands (releases amylase into mouth) and by the pancreas (releases amylase into the small intestine)

Question 11

What are membrane-bound disaccharides?

Answer 11

Attached to cell membranes of epithelial cells lining the ileum that help break down disaccharides into monosaccharides which involves hydrolysis of glycosidic bonds

Question 12

How can monosaccharides be transported across cell membranes of the ileum epithelial cells?

Answer 12

Via specific transporter proteins

Question 13

What is lipase?

Answer 13

A digestive enzyme that catalyses the breakdown of lipids into monoglycerides and fatty acids which involves the hydrolysis of ester bonds in lipids

Question 14

Where are lipases made?

Answer 14

In the pancreas

Question 15

Where do lipases work?

Answer 15

In the small intestine

Question 16

Why are bile salts produced by the liver?

Answer 16

They emulsify lipids- cause lipids to form small droplets

Question 17

Why are bile salts important in the process of lipid digestion?

Answer 17

Several small lipid droplets have a bigger surface area than a single large droplet so the formation of small droplets greatly increases the surface area of lipid that’s available for lipases to work on

Question 18

What happens once a lipid has been broken down?

Answer 18

Monoglycerides and fatty acids stick with the bile salts to form micelles

Question 19

How are proteins broken down?

Answer 19

By a combination of different peptidases that catalyse the conversion of proteins into amino acids by hydrolysing peptide bonds between amino acids

Question 20

What do endopeptidases do?

Answer 20

Hydrolyse peptide bonds within a protein

Question 21

What are examples of endopeptidases?

Answer 21

Trypsin, chymotrypsin and pepsin

Question 22

Where are endopeptidases synthesised?

Answer 22

The pancreas

Question 23

Where are endopeptidases secreted to?

Answer 23

The small intestine

Question 24

How is pepsin released?

Answer 24

Into the stomach by cells in the stomach lining

Question 25

When does pepsin work?

Answer 25

Only in acidic conditions that are provided by hydrochloric acid in the stomach

Question 26

What do exopeptidases do?

Answer 26

Hydrolyse peptide bonds at the ends of protein molecules and remove single amino acids from proteins

Question 27

What are dipeptidases?

Answer 27

Exopeptidases that work specifically on dipeptides and act to separate the two amino acids that make up a dipeptide by hydrolysing the peptide bond between them

Question 28

Where are dipeptidases often located?

Answer 28

In the cell-surface membrane of epithelial cells in the small intestine

Question 29

How is glucose absorbed?

Answer 29

By active transport with sodium ions via a co-transporter protein

Question 30

How is fructose absorbed?

Answer 30

Via facilitated diffusion through a different transporter protein

Question 31

Why can monoglycerides and fatty acids diffuse directly across the epithelial cell membrane?

Answer 31

They are lipid soluble