Enzymes

Question 1

What is an enzyme?

Answer 1

A biological catalyst

Question 2

What factors can effect the rate of reaction for enzymes?

Answer 2

• Temperature
• Concentration
• pH

Question 3

Why does temperature affect the rate of reaction?

Answer 3

As the temperature increases so does the rate of reaction, because the particles have more energy. This happens until the optimum temperature is reached and enzymes denature.

Question 4

How does concentration affect the rate of reaction for enzymes?

Answer 4

The higher the concentration of substrate, the faster the rate of reaction for enzymes. This happens until the optimum concentration is reached and there are not enough enzymes to break down all the substrates.

Question 5

How does pH affect the rate of reaction?

Answer 5

The higher the pH, the faster the rate of reaction for enzymes until the optimum pH is reached and the enzymes denature.

Question 6

What is the active site?

Answer 6

Where the enzyme and the substrate binds

Question 7

When a substrate bonds with a complementary active site, what is formed?

Answer 7

Substrate complex

Question 8

What does protease break down?

Answer 8

Proteins into amino acids

Question 9

What enzyme breaks down protein?

Answer 9

Protease

Question 10

What does amylase break down?

Answer 10

Starch into glucose

Question 11

What enzyme breaks down starch?

Answer 11

Amylase

Question 12

What does lipase break down?

Answer 12

Lipids into fatty acids and glycerol

Question 13

What is a catalyst?

Answer 13

Something that speeds up chemical reactions

Question 14

Why is an enzyme better than a regular catalyst?

Answer 14

It isn’t used up in a chemical reaction

Question 15

Why are there different enzymes for breaking down different molecules?

Answer 15

Because the active site needs to be completely to the substrate

Question 16

What do digestive enzymes do?

Answer 16

Catalyse the breakdown of large food molecules so they are small enough to cross cell membranes to get to cells for aerobic respiration

Question 17

How do you calculate rate of reaction?

Answer 17

Amount of products formed OR Amount of reactants used up
—————————————————————————————
Time taken

Question 18

What does it mean for an enzyme to denature?

Answer 18

The shape of the active site changes meaning it can no longer bind to its specific substrate

Question 19

What test would you use to identify starch?

Answer 19

Iodine test

Question 20

What would happen to iodine in the presence of starch?

Answer 20

It would change colour from orange to blue/black

Question 21

What test would you use to identify reducing sugars?

Answer 21

Benedict’s test

Question 22

What would happen to Benedict’s solution in the presence of reducing sugars?

Answer 22

It would change from blue to yellow, orange or red

Question 23

What do you do to the test tube after adding Benedict’s solution in a Benedict test?

Answer 23

Place it in a water bath at 75°C for a few mins

Question 24

What do you do to a food sample before testing it?

Answer 24

• Crush it
• Add water to it
• Stir it
• Filter it

Question 25

What test would you use to identify proteins?

Answer 25

Biuret test

Question 26

Describe the biuret test for proteins

Answer 26

• Add biuret solution to sample; stir
• If protein is present the colour would change from blue to purple

Question 27

What test would you use to identify lipids?

Answer 27

Emulsion test

Question 28

Describe the emulsion test for lipids

Answer 28

• Add ethanol to sample
• Add distilled water to sample
• Shake
• If solution is cloudy, lipids are present

Question 29

What is a calorimeter?

Answer 29

Machine that burns food and measures the energy given off

Question 30

Describe how you could investigate the effect of pH on enzyme activity

Answer 30

• Put two drops of iodine solution into each spot of a spotting tile
• Add 2cm³ of starch solution, 1cm³ of pH solution and 2cm³ of amylase to a test tube
• Start a stopwatch
• Every 20 secs add a few drops of solution into a section of the spotting tile using a pipette
• Repeat until solution stops turning black
• Repeat experiment with different pH solutions

Question 31

What is the purpose of stirring the water in calorimetry?

Answer 31

To evenly distribute the heat

Question 32

What is the purpose of the lid of a calorimeter?

Answer 32

To contain the heat

Question 33

Describe the method of calorimetry without a calorimeter

Answer 33

• Set up a raised boiling tube with a clamp stand filled with 25cm³ of water and a thermometer
• Record the starting temperature of the water and the mass of a food sample
• Burn the food sample bellow the boiling tube until there is no food left
• Record the final temperature of the water

Question 34

What is the calculation to find the energy in food?

Answer 34

Mass of water x Temperature change of water x 4.2

Question 35

What is the calculation to find the energy per gram of food?

Answer 35

Energy of food
————————
Mass of food

Question 36

What does carbohydrase break down?

Answer 36

Carboydrates into simple sugars