Digestive System and Enzymes

Question 1

What is ingestion?

Answer 1

Taking food in through the mouth and swallowing

Question 2

What is digestion?

Answer 2

Breaking down large insoluble molecules in food into smaller pieces and smaller soluble molecules.

Question 3

What is absorption?

Answer 3

Movement of small soluble molecules out of the gut and into the blood by diffusion and active transport.

Question 4

What is egestion?

Answer 4

Passing out undigested food through the anus.

Question 5

What is assimilation?

Answer 5

Building larger biological molecules from the smaller soluble molecules in all cells

Question 6

What are the two types of digestion?

Answer 6

Mechanical
Chemical

Question 7

What is mechanical digestion?

Answer 7

Food is broken up into smaller pieces in the mouth by chewing. This increases the surface area for enzymes and also prevents discomfort when swallowing.

Question 8

What is chemical digestion?

Answer 8

Saliva is released into the mouth by salivary glands. It makes the food easier to swallow and also contains the enzyme amylase.
Amylase works best at a neutral pH so is denatured when it reaches the stomach and stops working.

Question 9

What does amylase do?

Answer 9

Breaks down starch into maltose

Question 10

What is peristalsis?

Answer 10

There is muscular tissue all the way down the alimentary canal. The circular muscles contract behind the bolus pushing it along.

Question 11

What does maltase do?

Answer 11

Converts maltose into glucose

Question 12

What does protease do?

Answer 12

Converts proteins into amino acids

Question 13

What does lipase do?

Answer 13

Converts lipids into glycerol and 3 fatty acids

Question 14

What does pepsin/trypsin do?

Answer 14

Converts protein into peptide

Question 15

What happens in the stomach?

Answer 15

The gastric glands in the stomach wall secrete the enzyme pepsin which begins the process of digesting proteins into peptides.
Contractions of the stomach wall causes mixing of the contents of the stomach, maximising contact between enzymes and food.

Question 16

What are pepsin’s optimum conditions?

Answer 16

An acidic pH, the conditions of the stomach are acidic due to the release of hydrochloric acid by the gastric glands.

Question 17

What does the hydrochloric acid in the stomach do?

Answer 17

Kills many bacteria and fungi which may be present in the food we eat

Question 18

The duodenum is the final site of chemical digestion. The pancreas makes several enzymes:

Answer 18

Trypsin
Amylase
Lipase

Question 19

The duodenum wall also contains glands which make enzymes and secretes them into the duodenum:

Answer 19

Maltase
Peptidase

Question 20

What does peptidase do?

Answer 20

Converts peptide into amino acids

Question 21

What are the two functions of bile?

Answer 21

1. Neutralises the stomach acid, enzymes in the duodenum work best at pH 7-8.
2. Emulsifies lipids - breaks large droplets into smaller droplets, increasing the surface area for lipase to digest the fats

Question 22

What happens in the ileum?

Answer 22

Digestion is over and absorption begins
The ileum has many folds and is covered in finger projections called villi

Question 23

What do the villi do?

Answer 23

It is through these that the small soluble molecules are absorbed .
Some are absorbed by diffusion however some such as glucose are also absorbed via active transport which moves particles against a concentration gradient using ATP

Question 24

How is the rate of diffusion increased in the ileum?

Answer 24

Large SA - folding of ileum, villi, microvilli
Short diffusion distance - villi walls are one cell thick
High concentration gradient - capillary network

Question 25

What are the two sections of the large intestine?

Answer 25

Colon
Rectum

Question 26

What is the colon?

Answer 26

The site for all reabsorption of water

Question 27

What is the rectum?

Answer 27

Where the faeces are stored and then egested from the anus

Question 28

What is an experiment to discover the effect of pH on enzymes?

Answer 28

Potato contains the enzyme catalase which breaks down hydrogen peroxide forming water and oxygen.
Add 10 potato disks to 20cm3 catalase and hydrogen peroxide and measure the volume of gas produced in 5 minutes.
The pH can be altered by adding different volumes of a weak alkali or a weak acid.
Use universal indicator paper to determine the pH of the solution each time.

Question 29

What is the effect of temperature on enzymes using amylase?

Answer 29

Amylase digests starch.
Mix 10cm3 of 10% starch suspension and 5cm3 of 5% amylase in a boiling tube and heat in a water bath
Every minute take one drop of this mixture and add it to one drop of iodine solution in the spotting tile.
When digestion is complete and starch is present, iodine solution will stay orange
Repeat using enzymes of water baths that are different temperatures.

Question 30

What is a catalyst?

Answer 30

A chemical which increases the rate of reaction without being used up itself in the reaction.

Question 31

Explain the lock and key theory.

Answer 31

The substrate and enzyme collide
The substrate binds to the active site of the enzyme
Binding to the enzyme site strains the chemical bonds in the substrate molecules and so the reaction occurs by an alternative pathway with a lower activation energy.
Once the reaction has occurred the products do not fit the active site’s shape as well as the substrate did so they are released.

Question 32

What are the 3 roles of the stomach?

Answer 32

1. Contract it’s muscular walls to mix the food
2. Produces pepsin which breaks down proteins into amino acids
3. Produces hydrochloric acid which provides the right pH for pepsin to function and kills microorganisms

Question 33

What are the 2 roles of bile?

Answer 33

Emulsify lipids
Neutralise stomach acid