practical skills

Question 1

Use of Benedict’s test

Answer 1

To test for presence of reducing sugars

Question 2

Steps of Benedict’s test

Answer 2

1. Prepare a boiling water bath
2. Add 2 cm cube of the food solution to a clean test tube
3. Add equal volume of Benedict’s solution to the test tube
4. Shake the mixture
5. Place the test tube in the boiling water bath for a maximum of 5 minutes
6. Observe precipitate formation and color changes, if any

Question 3

Results of Benedict’s test

Answer 3

No reducing sugar is present- solution remained blue
Little concentration of reducing sugar is present- green/yellow precipitate is formed
Moderate concentration of reducing sugar is present- orange precipitate is formed
Large concentration of reducing sugar is present - brick-red precipitate is formed

Question 4

Use of Biuret’s test

Answer 4

To test for the presence of protein

Question 5

Steps of Biuret’s test

Answer 5

1. Add 2cm cube of food solution to a clean test tube
2. Add 1cm cube of sodium hydroxide solution to the test tube
3. Shake thoroughly
4. Add 1% copper (II) sulfate solution, drop by drop, shaking after each drop
5. Record observations

Question 6

Results of Biuret’s test

Answer 6

Protein is present - violet coloration was observed
Protein is absent - solution remained blue

Question 7

Use of iodine test

Answer 7

To test for the presence of starch

Question 8

Steps of iodine test

Answer 8

1. place 2-3 drops of food solution on a white tile
2. Add 2-3 drops of dilute iodine solution to the substance to be tested
3. Observe color changes, if any

Question 9

Results of iodine test

Answer 9

Starch is present - blue black coloration was observed
Starch is absent- solution remained brown

Question 10

Use of ethanol emulsion test

Answer 10

To test for presence of fats

Question 11

Steps of ethanol emulsion test

Answer 11

1. Add 2 cm cube of food solution to a clean test tube
2. Add 2cm cube of ethanol to the test tube
3. Shake thoroughly
4. Pour the ethanol mixture into another test tube containing 2cm cube of water
5. Record observations

Question 12

Results of ethanol emulsion test

Answer 12

Fat is present- a white emulsion was formed
Fat is absent - solution remained colorless

Question 13

Precautions of ethanol emulsion test

Answer 13

Ethanol is flammable. Keep it away from any flames.

Question 14

Magnification

Answer 14

Size of drawing / size of specimen

Question 15

Title of biological drawings

Answer 15

T.S. of (specimen name)

Question 16

Reliability

Answer 16

A reliable experiment has results which can be obtained consistently. To ensure that results are reliable: the experiments must be repeated and consistent results obtained.

Note: repetition will only determine reliability

Question 17

Accuracy

Answer 17

Accuracy depends on the design of the experiment and the sensitivity of the instruments used. Results are accurate of they are close to the value of the quantity being measured.

Question 18

Why is a food solution used instead of a food sample

Answer 18

To prevent the color of the food sample from affecting the accuracy of the results

Question 19

Using mortar and pestle to crush food samples

Answer 19

Crushing will damage the cell wall and membranes to release nutrients