Food Tests & Factors Affecting Enzymes

Question 1

What is the reagent used to test for the presence of glucose?

Answer 1

Benedict’s Solution

Question 2

List the steps to test for the presence of glucose: (3)

Answer 2

1. Add a small amount of the food into a test tube
2. Add 1cm 3(cubed) of Benedict’s solution
3. Heat in the 80*C water bath, until it boils

Question 3

What is the colour change is observed if glucose is present?

Answer 3

Blue —> Green —> Orange —> Brick Red

Question 4

What is the reagent used to test for the presence of starch?

Answer 4

Iodine

Question 5

List the steps to test if starch is present: (3)

Answer 5

1. Place the food on a spotting tile
2. Add a couple of drops of iodine
3. Colour change form orange to blue/black if starch is present

Question 6

What colour change is observed if starch is present?

Answer 6

Orange —> Blue/black

Question 7

What is the reagent used to test for the presence of protein?

Answer 7

Biuret solution

Question 8

List the steps that test for the presence of protein: (3)

Answer 8

1. Add a small amount of the food to a test tube
2. Add 4-5 drops of fresh biuret solution
3. If protein is present then it’s a lilac colour change

Question 9

What colour change is observed if protein is present?

Answer 9

Orange —> Lilac

Question 10

What is the reagent used to test for the presence of fat?

Answer 10

Ethanol

Question 11

List the steps used to test if fat is present: (4)

Answer 11

1. Dissolve a little of the food in 3cm 3(cubed) of ethanol
2. Pour the liquid into another test tube leaving any food residue behind
3. Add 3cm 3(cubed) of water and shake
4. Cloudy liquid - an emulsion indicated the presence of fat droplets

Question 12

What colour change indicates that fat is present? (Trick Question..)

Answer 12

Cloudy Emulsion

Question 13

Name 3 factors that can affect enzymes:

Answer 13

1. pH
2. Temperature
3. Concentration

Question 14

What is the optimum temperature for enzymes?

Answer 14

37.5*C
—> same as the average body temperature

Question 15

What happens after the enzymes had reaches the optimum temperature?

Answer 15

It eventually denatures

Question 16

What is pH?

Answer 16

A measure of how acidic or alkali something is. This ranges from pH 0-14

Question 17

What is the optimum pH in the mouth?

Answer 17

pH 7

Question 18

What is the optimum pH in the stomach?

Answer 18

pH 2
—> due to hydrochloride acid, enzymes have to be able to deal with strong acidic conditions

Question 19

What is the optimum pH in the small intestine?

Answer 19

pH 7-8

Question 20

What happens when enzymes are not exposed to the optimum pH?

Answer 20

They denature

(This means that the active site changes shape so the substrate cannot fit)

Question 21

Explain how the rate of enzyme activity changes with the rate of substrate concentration:

Answer 21

As the substrate concentration increases, so does the rate of enzyme activity.
—> The optimum temperature is reached
—> Any continued increase in substrate concentration results in the same activity won’t change as there are not enough enzymes molecules to break down the excess substrate molecules
—> You have saturated the enzymes