Enzymes and Digestion

Question 1

Enzyme

Answer 1

a biological catalyst.

Question 2

Catalyst

Answer 2

it is a substance which increases the speed of a reaction, without being changed or used up in a reaction.

Question 3

How does an enzyme work?

Answer 3

.Every enzyme has an active site with a unique shape that fits onto the substance involved in the reaction.
.For the enzyme to work, the substrate has to fit into the active site of the enzyme.
. The chemical reaction then takes place.
. The products are then released

Question 4

Optimum conditions for enzymes: Temperature

Answer 4

.A higher temperature increases the rate at first.
.But if it gets too hot, some of the bonds holding the enzyme together break.
.This changes the shape of the active site, so the substrate won’t fit anymore.
.The enzyme is said to be denatured

Question 5

What is the optimum temperature in a human body?

Answer 5

37 degrees Celsius

Question 6

Optimum conditions for enzymes:
pH

Answer 6

.If the pH is too high or too low, it interferes with the bonds holding enzyme together.
.This changes the shape of the active site, so the substrate can no longer fit.
. The enzyme is now denatured

Question 7

What is the optimum pH in many enzymes?

Answer 7

pH 7, but not for all enzymes

Question 8

REQUIRED PRACTICAL:
Investigating the effect of pH on amylase

Answer 8

1. Put a drop of iodine solution into every well of a spotting tile
2. Place a Bunsen burner on a heat-proof mat, and a tripod and gauze over it.
3. Put a beaker on top of the tripod and heat the water until it is 35°C
4. Use a syringe to add 1cm^3 of amylase solution and 1cm^3 of buffer solution with a pH of 5 to a boiling tube.
5. Using test tube holders, put the boiling tube into he beaker of water and wait for 5 minutes.
   6.Next, use a different syringe to dd 5cm^3 of a starch solution to the boiling tube
6. Immediately, mix the contents of the boiling tube and start a stop clock.
7. Continuously sample to record how long it takes for the amylase to break down all the starch. Use a dropping pipette to take a fresh sample from the boiling tube every 30 seconds and put a drop into a well.
8. Repeat the whole experiment with buffer solutions of different pH values.
9. When the iodine solution remains browny-orange, starch s no longer present.

Question 9

Control variables for pH practical

Answer 9

. Concentration of amylase solution
. Volume of amylase solution

Question 10

Rate of reaction

Answer 10

Rate = 1000/time

Question 11

Rate of reaction change over time

Answer 11

change/time

Question 12

Mechanical digestion

Answer 12

teeth grinding down food and stomach churning up food

Question 13

Chemical digestion

Answer 13

Where enzymes help to break down food

Question 14

What do carbohydrases break down into?

Answer 14

convert starch into maltose

Question 15

Amylase

Answer 15

Where it is produced:
salivary glands, pancreas and small intestine
Where it works:
mouth and small intestine

Question 16

What do proteases break down into?

Answer 16

convert proteins into amino acids

Question 17

Protease

Answer 17

Where it is produced:
stomach, pancreas, small intestine
Where it works:
stomach and small intestine

Question 18

What do lipases break down into?

Answer 18

convert lipids into fatty acids and glycerol

Question 19

Lipase

Answer 19

Where it is produced:
pancreas and small intestine
Where it works:
small intestine

Question 20

Bile

Answer 20

.produced in the liver
.stored in the gall bladder
.The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly.
.Bile is alkaline - it neutralises the acid and makes conditions alkaline.
. It also emulsifies fats which means it breaks the fat into tiny droplets.
.This gives a much bigger surface area of fat for the enzyme lipase to work on - which makes digestion faster.

Question 21

REQUIRED PRACTICAL: Testing for sugars

Answer 21

1. Prepare a food sample and transfer 5cm^3 to a test tube.
2. Prepare a water bath so that it’s set to 75°C.
3. Add some Benedict’ solution to the test tube ( about 10 drops ) using a pipette.
4. Place the test tube in the water bath for 5 minutes.

Question 22

Results for Benedict’s solution

Answer 22

blue to brick red

Question 23

REQUIRED PRACTICAL: Testing for starch

Answer 23

1. Add a few drops of iodine solution into a test tube along with 5cm^3 of your food sample.
2. Mix the contents

Question 24

Results for Iodine solution

Answer 24

orange/brown to blue/black

Question 25

REQUIRED PRACTICAL: Testing for proteins

Answer 25

1. Add 2cm^3 of biuret solution to 2cm^3 of your food sample
2. Mix the contents by gently shaking it.

Question 26

Results for Biuret test

Answer 26

blue to purple

Question 27

REQUIRED PRACTICAL: Testing for lipids

Answer 27

1. Use a pipette to add 3 drops of ethanol to the test tube with 5cm3 of food sample.
2. Gently shake the tube

Question 28

Results for ethanol

Answer 28

colourless to milky white emulsion