Food tests and enzyme basics

Question 1

Test for Glucose/ reducing sugars

Answer 1

1. Place food sample in a test tube.
2. Add enough Benedict’s solution for sample to turn blue.
3. Heat test tube in a boiling water bath for 5 minutes.
4. Take the test tube out and observe the colour.
   Positive result is from blue to orange/ brick red.

Question 2

Safety precautions for reducing sugars test

Answer 2

Handle test tube with tongs.
Wear safety goggles and heatproof gloves.
Tie hair, wear a lab coat. Goggles.

Question 3

Test for Starch

Answer 3

1. Place food sample in test tube.
2. Add a few drops of iodine to the food sample.
3. Observe the colour.
   Positive result is from orange/brown to blue/black

Question 4

Test for Protein

Answer 4

1. Place food sample in test tube.
2. Add drops of Biuret solution to the food sample.
3. Observe colour.
   A positive result is from blue to violet/purple

Question 5

Test for fat

Answer 5

Place food sample into test tube. Add ethanol to the sample and shake. Add water and also shake.
Positive result is colourless to milky white emulsion.

Question 6

Enzyme for starch

Answer 6

amylase

Question 7

Enzyme for proteins

Answer 7

protease

Question 8

Enzyme for lipids

Answer 8

lipase

Question 9

Starch is broken down into

Answer 9

simple sugars/glucose

Question 10

Proteins are broken down into

Answer 10

amino acids

Question 11

Lipids are broken down into

Answer 11

fatty acids and glycerol

Question 12

Relationship between rate of reaction and temperature with enzymes

Answer 12

Rate of reaction increases with temperature at 40oC. After 40oC collisions are too violent and the active site is denatured.

Question 13

Relationship between rate of reaction and pH.

Answer 13

All enzymes have an optimum pH. At extremes of pH the active site can change shape causing the enzyme to become denatured. Reaction cannot take place and the change can be irreversible.

Question 14

Describe the structure of DNA.

Answer 14

Double helix shape. Sugar-Phosphate backbones. Phosphate and a nitrogenous base. ATCG.

Question 15

What are enzymes?

Answer 15

Biological catalysts in metabolic reactions

Question 16

Describe enzyme activity at low temperatures

Answer 16

Enzymes have little kinetic energy.
Few collisions between enzymes and substrates. Few enzyme-substrate complexes formed.

Question 17

Describe enzyme activity at optimum temperatures (40oc)

Answer 17

Optimum temperatures. Enzymes have lots of kinetic energy. Lots of collisions between enzymes and substrates. Lots of enzyme-substrate complexes formed. High rate of reaction.

Question 18

Describe enzyme activity above optimum temperatures

Answer 18

Enzymes have too much kinetic energy. Collisions between enzymes and substrates are too violent. Active site of enzyme changes shape. Enzyme is denatured. Rate of reaction decreases.