More exchange and transport systems: Digestion and absorption

Question 1

What is digestion

Answer 1

The process by which large biological molecules such as carbohydrates, lipids and proteins get hydrolysed into their smaller molecules

Question 2

Why does digestion occur

Answer 2

It occurs so that large biological molecules can be broken down into nutrients, and absorbed into cell membranes - so it can be used for growth and repair

Question 3

What digestive enzymes catalyses the breakdown of carbohydrates (and state what they catalyse the hydrolysis of)

Answer 3

• Amylase
• Membrane-bound disaccharidases

Question 4

How many polysaccharides make up starch (and state the monomers of it)

Answer 4

• Its made of two polysaccharides chains
• Made of long chains of alpha glucose molecules

Question 5

How does amylase work (what bonds do they catalyse the hydrolysis of) (what does it produce)

Answer 5

Amylase works by catalysing the glycosidic bonds in starch to produce maltose (a disaccharide)

Question 6

Where is amylose produced

Answer 6

• The salivary glands - which releases it into the mouth
• The pancreas - which releases it into the small intestine

Question 7

What are membrane-bound disaccharidases

Answer 7

They are enzymes attached to the cell membranes of epithelial cells lining the ileum- breaking down disaccharides into monosaccharides

Question 8

How do membrane-bound disaccharidases work (what bonds do they catalyse the hydrolysis of) (what does it produce)

Answer 8

Membrane-bound disaccharidases works by catalysing the hydrolysis of glycosidic bonds in disaccharides (maltose) to produce alpha glucose (a monosaccharide)

Question 9

What digestive enzymes catalyses the breakdown of lipids

Answer 9

Lipase

Question 10

What does lipase catalyse the hydrolysis reactions of (and what does it produce)

Answer 10

It catalyses the hydrolysis reactions of ester bonds in lipids - breaking them down into some monoglycerides, glycerol and fatty acids

Question 11

What is emulsification

Answer 11

A process which large lipid globules are broken down into several small globules

Question 12

What substance emulsifies lipids

Answer 12

Bile salts

Question 13

Where are lipases mainly produced

Answer 13

The pancreas

Question 14

Where are bile salts produced

Answer 14

The liver

Question 15

Why is the emulsification of big lipid globules into micelles important

Answer 15

The formation of small droplets increases the surface area of lipids that available for the lipases to work on enabling faster hydrolysis

Question 16

Describe the process of lipid digestion in order

Answer 16

• Lipids are coated in bile salts to create an emulsion
• Lipase hydrolyses lipids into glycerol and fatty acids (sometimes monoglycerides)
• Micelles are formed of the fatty acids, glycerol, monoglycerides and bile salts
• Micelles release the monoglycerides, fatty acids and glycerol and due to their non-polar nature (lipid soluble), they diffuse across the cell membrane
• Once in the epithelial cell, they are modified back into triglycerides inside the ER and Golgi body

Question 17

How is the formation of micelles important (refer to the structure too)

Answer 17

They enable the lipid digestion products to be transported to the small intestinal surface for absorption

Question 18

What are micelles

Answer 18

Water soluble vesicles formed of the fatty acids, glycerol, monoglycerides and bile salts

Question 19

What are the two stages involved in the digestion of lipids

Answer 19

Physical digestion: emulsification & micelle formation

Chemical digestion: hydrolysis of ester bonds in lipids

Question 20

What three digestive enzymes break down proteins

Answer 20

• Endopeptidase
• Exopeptidase
• Membrane-bound dipeptidases

Question 21

How do membrane-bound dipeptidases work (what bonds do they catalyse the hydrolysis of) (what does it produce)

Answer 21

They catalyse the hydrolysis of peptide bonds between dipeptides (two amino acids)

Question 22

How do endopeptidases work (what bonds do they catalyse the hydrolysis of) (what does it produce)

Answer 22

They catalyse the hydrolysis of peptide bonds between the amino acids in the middle of a polypeptide chain

Question 23

How do exopeptidases work (what bonds do they catalyse the hydrolysis of) (what does it produce)

Answer 23

They catalyse the hydrolysis of peptide bonds between the amino acids at the end of a polypeptide chain

Question 24

State the path of protein digestion

Answer 24

It starts in the stomach and ends in the ileum (in the small intestines)

Question 25

Where are the products of digestion absorbed across

Answer 25

The ileum epithelium into the bloodstream

Question 26

How is glucose and galactose absorbed into the ileum epithelium then into the bloodstream

Answer 26

Active transport with sodium ions via co-transporter proteins

Question 27

How is fructose absorbed into ileum epithelium then into the bloodstream

Answer 27

They are absorbed by facilitated diffusion through another transporter protein than glucose + galactose

Question 28

How are monoglycerides and fatty acids absorbed into the ileum epithelium then into the bloodstream

Answer 28

• Micelles help move these products towards the epithelium where they release the products allowing the products to be absorbed
• Monoglycerides and fatty acids are lipid-soluble, so can diffuse differently across the epithelial membrane

Question 29

How are amino acids absorbed into the ileum epithelium then into the bloodstream

Answer 29

Active transport with sodium ions via co-transporter proteins

Question 30

Describe the process of how amino acids and some monosaccharides (glucose and galactose) are absorbed

Answer 30

• Sodium ions are transported out of the epithelial cells in the ileum unto the blood using ATP - creating a concentration gradient as Na+ ion concentration decreases in the cell
• Na+ ions then diffuse from the lumen of the ileum into the epithelial cell down the concentration gradient alongside the products of digestion through co-transporter protein
• The products of digestion then moves out of the cell through down its concentration gradient facilitated diffusion through a channel protein