12.8 Digestion and Absorption

Question 1

What is digestion?

Answer 1

• Process where large molecules are hydrolysed by enzymes into smaller molecules.
• To be absorbed across the cell membrane and into the blood to be assimilated into biological molecules.

Question 2

How are enzymes produced for digestion?

Answer 2

• Digestive juices are produced by the gland cells of the digestive system.
• Contain enzymes and other molecules to facilitate digestion.

Question 3

How are the enzymes used in digestion?

Answer 3

• Hydrolyse large insoluble food molecules (polymers) into smaller soluble molecules (monomers).
• Which can then be absorbed through the lining of the intestine.

Question 4

What are the proteins hydrolysed into and using what enzyme?

Answer 4

• Proteins hydrolysed into amino acids.
• Using the enzyme protease.
• Three types of proteases are endopeptidases, exopeptidases and membrane-bound dipeptidases.

Question 5

What are carbohydrates hydrolysed into and using what enzyme?

Answer 5

• Carbohydrates are hydrolysed into simple sugars.
• Using the enzyme carbohydrase.

Question 6

What are fats and lipids hydrolysed into and using what enzyme?

Answer 6

• Fats and lipids are hydrolysed into glycerol, fatty acids and monoglycerides.
• Using the enzyme lipase.
• Lipase is present in the small intestine.

Question 7

What enzyme do salivary glands secrete? What does this enzyme hydrolyse?

Answer 7

• Salivary glands secrete saliva containing amylase (salivary amylase).
• Amylase hydrolyses starch to maltose.

Question 8

Where is amylase produced?

Answer 8

In the salivary glands and pancreas.

Question 9

Where is maltase produced?

Answer 9

Within the membrane of epithelium cell membrane of ileum.
Hydrolyses maltose into glucose.

Question 10

In the stomach, food is mixed with acidic gastric juice. What does gastric juice contain? What does it kill?

Answer 10

• Contains endopeptidases and exopeptidases which break down proteins into dipeptides.
• Gastric juice kills microorganisms.

Question 11

What occurs in the pancreas during digestion?

Answer 11

• Pancreas secretes pancreatic juice into small intestine.
• Which contains amylase and other carbohydrase.

Question 12

What occurs in the pancreas during digestion?

Answer 12

• Pancreas secretes pancreatic juice into small intestine.
• Which contains amylase and other carbohydrase.

Question 13

What are some adaptations of the small intestine?

Answer 13

• Provide a large surface area for the absorption of products of digestion.
• Maltase enzymes are embedded in the epithelium cell membrane of the small intestine which hydrolyses maltose to glucose, so it is available for rapid absorption.
• There are also sucrase, lactase and dipeptidase enzymes (membrane bound disaccharides)

Question 14

Describe the role of enzymes in the digestion of starch.

Answer 14

• Food enters mouth and is broken up by teeth (mechanical digestion) and is mixed with saliva.
• Salivary amylase starts to hydrolyse glycosidic bonds in the starch producing maltose (chemical digestion)
• In the stomach, this salivary amylase is denatured due to the acidic pH.
• Pancreatic amylase continues to hydrolyse the starch to maltose.
• Maltose is then hydrolysed to glucose by maltase enzymes in the epithelial cell membrane. The glucose can then be absorbed.

Question 14

Describe the role of enzymes in the digestion of starch.

Answer 14

• Food enters mouth and is broken up by teeth (mechanical digestion) and is mixed with saliva.
• Salivary amylase starts to hydrolyse glycosidic bonds in the starch producing maltose (chemical digestion)
• In the stomach, this salivary amylase is denatured due to the acidic pH.
• In the small intestine, pancreatic amylase continues to hydrolyse the starch to maltose.
• Maltose is then hydrolysed to glucose by maltase enzymes in the epithelial cell membrane. The glucose can then be absorbed.

Question 15

Why are only monosaccharides transported across the epithelial cell membrane?

Answer 15

• Monosaccharides are small enough and are complementary to the binding sites of specific carrier proteins.
• These specific carrier proteins move specifically complementary monomers across the epithelial cell membrane.

Question 16

Describe how glucose is absorbed from the ileum into the blood.

Answer 16

• Na+ (sodium ions) are actively transported out of epithelial cell into the blood by sodium potassium pump.
• This creates a concentration gradient of Na+ (between lumen and ileum and the epithelial cell)
• Na+ and glucose enter by facilitated diffusion using complementary co-transporter proteins.
• Co-transporter proteins have 2 binding sites complementary to Na+ and glucose. Only when both molecules bind will the molecules be moved across the membrane.
• Na+ diffuse into the cell down its concentration gradient.
• Glucose moves into the cell against its concentration gradient.
• Glucose moves into the blood by facilitated diffusion.

Question 17

Describe the role of enzymes in the digestion of proteins in a mammal.

Answer 17

• Proteins/polypeptides are hydrolysed by enzymes called proteases; this begins in the stomach.
• (Reference to) hydrolysis of peptide bonds.
• Endopeptidase act in the middle of protein/polypeptide OR Endopeptidase produces shorter polypeptides/ increased number of ends.
• Exopeptidases act at end of protein/polypeptide and produce dipeptides/amino acids.
• Dipeptidase are embedded in cell surface membrane of epithelial cells. They hydrolyse dipeptides producing (single) amino acids.

Question 18

Describe how amino acids is absorbed from the ileum into the blood.

Answer 18

• Na+ (sodium ions) are actively transported out of epithelial cell into the blood by sodium potassium pump.
• This creates a concentration gradient of Na+ (between lumen and ileum and the epithelial cell)
• Na+ and amino acids enter by facilitated diffusion using complementary co-transporter proteins.
• Co-transporter proteins have 2 binding sites complementary to Na+ and amino acids. Only when both molecules bind will the molecules be moved across the membrane.
• Na+ diffuse into the cell down its concentration gradient.
• Amino acids move into the cell against its concentration gradient.
• Amino acids move into the blood by facilitated diffusion.

Question 19

How is the surface area of the lipids increased for lipase action?

Answer 19

• Lipids are only digested within the lumen of the ileum.
• In the stomach, lipids are churned into fat droplets.
• Bile contains bile salts, which emulsify fat droplet and form micelles.
• This makes digestion of lipids faster and more efficient.

Question 20

What is the role of lipases in lipid digestion?

Answer 20

Hydrolyse triglycerides into glycerol, fatty acids and monoglycerides.

Question 21

Explain lipid absorption.

Answer 21

• Micelles contain bile salts and fatty acids/monoglycerides;
• Micelles make fatty acids soluble in water and bring fatty acids to the surface of the epithelial cell membrane.
• Maintain higher concentration of fatty acids to cell membrane of the ileum.
• Fatty acids enter the epithelial cell by simple diffusion.
• At the SER, fatty acids and glycerol and recombined to form triglycerides.
• At the Golgi, triglycerides are modified, and proteins are added to form lipoproteins (called chylomicrons). These are packaged into vesicles.
• Chylomicrons are water soluble and so can be carried in the blood.
• Chylomicrons are transported into a cell membrane of lymph vessel/capillary via exocytosis. They then enter the blood.

Question 22

Describe the process of starch digestion

Answer 22

(salivary/pancreaticAmylase;
Maltose;
Maltase;
Maltose to glucose;
Hydrolysis;
Glycosidic bonds;

Question 23

Describe the role of micelles in the absorption of fats into the cells of the ileum.

Answer 23

1. Micelles include bile salts and fatty acids;
2. Make the fatty acids (more) soluble in water;
3. Bring/release/carry fatty acids to cell/lining (of the ileum);
4. Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
5. Fatty acids (absorbed) by diffusion;

Question 24

Describe the role of enzymes in the digestion of proteins in a mammal.

Answer 24

1. (Reference to) hydrolysis of peptide bonds;
2. Endopeptidase act in the middle of protein/polypeptide OR Endopeptidase produces short(er) polypeptides/ increase number of ends;
3. Exopeptidases act at end of protein/polypeptide OR Exopeptidase produces dipeptides/amino acids;
4. Dipeptidase acts on dipeptide/between two amino acids OR Dipeptidase produces (single) amino acids;