Chapter Four - Digestion and Enzymes

Question 1

What is absorption?

Answer 1

When food is digested, the products must be transported around the body to the places they are needed. First they need to be absorbed in the ileum (lower part of small intestine) to get into the blood supply. For this the ileum has these adaptions;

• large surface area because of long length, numerous folds and lots of villi (finger like projections sticking out into lumen of gut)
• thin and permeable membranes
• good blood supply ensures concentration gradient is maintained

Question 2

What are villi?

Answer 2

finger like projections sticking out into lumen of gut

Question 3

Label diagram of structure and function of a villus

Answer 3

• lacteal - absorbs breakdown products of fat (glycerol&fatty acids) and returns them to blood later
• Capillary network in the villus - absorbs breakdown products of protein (amino acids and starch (glucose)
• lumen of gut

Note
- villus extends into lumen of gut, increases surface area in contact with digested food

• short distance between lumen, capillary and lacteal speeds up rate of absorption

Question 4

What are enzymes

Answer 4

Special proteins or biological catalysts that help speed up chemical reactions. Particularly important in digestive system where they help break down food.

Question 5

Label diagram of how enzymes work

Answer 5

1. • substrate
   • active site
   • enzyme
2. Substrate and enzyme fit tightly together in active site
3. Substrate has been broken down into two product molecules (some enzymes build smaller molecules up into larger ones)

Question 6

Explain how enzymes work

Answer 6

An enzymes active site is complementary in shape to the substrate. Like a ‘lock and key’. This explains enzyme specificity. Each enzyme fits only one substrate and therefore there is a different enzyme for each reaction.

Question 7

Explain effect of temperature on enzyme activity

Answer 7

• at lower temps enzymes and substrates move very slowly (low kinetic energy) so there are few collisions and therefore enzyme activity is low.
• maximum enzyme activity occurs at optimum temp of 35-40*C
• at higher temps (around 60*C) enzymes are denatured - the heat changes their shape and the active site no longer fits the substrate

Question 8

Effect of pH on enzyme activity

Answer 8

• each enzyme works best at their optimum pH - at either side of this pH they work less well because incorrect pH changes shape of active site
• as with high temps the further from optimum the greater the degree of irreversible change caused to active site (denaturation)
• pepsin acts in acidic conditions in stomach
• amylase acts in neutral / slightly alkaline conditions in mouth

Question 9

Effect of enzyme concentration on enzyme activity

Answer 9

• rate levels off as enzyme concentration increases because their are not enough substrate molecules left to react with the enzyme

Question 10

Why are enzymes important in digestion?

Answer 10

To break down large insoluble food molecules into smaller, more soluble ones that can enter the blood stream. These soluble molecules can be absorbed by all cells in the body for use.

Question 11

Explain enzyme for starch protein and fat, include products of digestion, where they are and sources

Answer 11

1. Starch 
Enzyme - Amylase
Product - glucose 
Where - mouth, duodenum/small intestine
Source - saliva from salivary glands, pancreatic juice and intestinal juice from wall of small intestine 

2. Protein
   Enzyme - protease
   Product - amino acids
   Where - stomach, duodenum/small intestine
   Source - gastric, pancreatic and intestinal juices

3. Fat (lipid) 
Enzyme - lipase 
Products - glycerol and fatty acids 
Where - duodenum 
Source - pancreatic and intestinal juice

Question 12

What are enzymes in the human body’s optimum temps and pH?

Answer 12

• 37*C

- pH varies some are around 7 however in the stomach closer to 3 due to acidic conditions

Question 13

Other uses for enzymes?

Answer 13

• cleaning products

- biological washing powders to break down stains on clothing

Question 14

Label diagram of the alimentary canal and its functions from top to bottom

Answer 14

1. Buccal cavity (mouth) - ingestion & start of starch digestion (salivary amylase).
2. Oesophagus - peristalsis moves food into stomach
3. Stomach - produces gastric juice containing acid and protease enzymes that begin protein digestion
4. Liver - produced bile which neutralises stomach acid & emulsifies fats, increasing surface area for action of lipase enzymes
5. Gall bladder - stores bile
6. Pancreas - releases pancreatic juice - contains enzymes that act on food in the duodenum
7. Small intestine - site of starch, protein and fat digestion&absorption
   - duodenum - site of digestion
   - ileum - site of absorption
8. Colon (large intestine) - absorption of water
9. rectum - waste food is stored prior to removal
10. Anus - site of egestion