practical skills Flashcards
Use of Benedict’s test
To test for presence of reducing sugars
Steps of Benedict’s test
- Prepare a boiling water bath
- Add 2 cm cube of the food solution to a clean test tube
- Add equal volume of Benedict’s solution to the test tube
- Shake the mixture
- Place the test tube in the boiling water bath for a maximum of 5 minutes
- Observe precipitate formation and color changes, if any
Results of Benedict’s test
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
Use of Biuret’s test
To test for the presence of protein
Steps of Biuret’s test
- Add 2cm cube of food solution to a clean test tube
- Add 1cm cube of sodium hydroxide solution to the test tube
- Shake thoroughly
- Add 1% copper (II) sulfate solution, drop by drop, shaking after each drop
- Record observations
Results of Biuret’s test
Protein is present - violet coloration was observed
Protein is absent - solution remained blue
Use of iodine test
To test for the presence of starch
Steps of iodine test
- place 2-3 drops of food solution on a white tile
- Add 2-3 drops of dilute iodine solution to the substance to be tested
- Observe color changes, if any
Results of iodine test
Starch is present - blue black coloration was observed
Starch is absent- solution remained brown
Use of ethanol emulsion test
To test for presence of fats
Steps of ethanol emulsion test
- Add 2 cm cube of food solution to a clean test tube
- Add 2cm cube of ethanol to the test tube
- Shake thoroughly
- Pour the ethanol mixture into another test tube containing 2cm cube of water
- Record observations
Results of ethanol emulsion test
Fat is present- a white emulsion was formed
Fat is absent - solution remained colorless
Precautions of ethanol emulsion test
Ethanol is flammable. Keep it away from any flames.
Magnification
Size of drawing / size of specimen
Title of biological drawings
T.S. of (specimen name)
Reliability
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
Accuracy
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.
Why is a food solution used instead of a food sample
To prevent the color of the food sample from affecting the accuracy of the results
Using mortar and pestle to crush food samples
Crushing will damage the cell wall and membranes to release nutrients
