Biomolecules- Food Tests

Question 1

What solution do you use to test for sugars?

Answer 1

Benedict solution.

Question 2

What is the process for testing for sugars?

Answer 2

You need to add equal volumes of Benedict’s reagent and solution being tested, it is then boiled.

Question 3

What would a positive test look like for sugars?

Answer 3

If a reducing sugar is present then the solution will turn from blue through green, yellow and orange to a brick red precipitate.

Question 4

What would a non-reducing sugar result, be for testing reducing sugars?

Answer 4

It would give a negative test so will remain blue.

Question 5

What is the process for testing non-reducing sugars?

Answer 5

You need to heat with hydrochloric acid. Benedict’s reagent needs alkaline conditions to work so alkali is added Benedict reagent and is added again and boiled if the solution now turns a brick red precipitate then a non-reducing sugar was present.

Question 6

What sort of measurement is the concentration of sugar described as?

Answer 6

It is a quantitive measurement when using a colorimeter or biosensor. However it is classed as a semiquantitative asked if you were to compare the tests with each other.

Question 7

What equipment can be used to detect the concentration of the sugars?

Answer 7

A colorimeter or biosensor gives an accurate measurement of the concentration.

Question 8

Give me an example of a biosensor being used in every day life?

Answer 8

A biosensor is important in monitoring medical conditions like diabetes when accurate measurement of concentration of blood glucose is required.

Question 9

What do used to test for the presence of starch?

Answer 9

An iodine solution, this is when iodine is dissolved in a aqueous solution of potassium iodide.

Question 10

What result would the iodine give if starch was present?

Answer 10

It would turn from orange/brown to blue/black.

Question 11

What sort of test is the test for the presence of starch?

Answer 11

It is a qualitative test and an accurate concentration can’t be determined.

Question 12

What do you use to test for lipids?

Answer 12

Absolute ethanol

Question 13

What is the process of testing for lipids?

Answer 13

A sample which is tested is mixed with absolute ethanol which dissolves any lipids present. It is then shaking with an equal volume of water. The dissolved lipids come out of solution as they are insoluble in water this then forms a white emulsion.

Question 14

What will give a positive result for testing lipids?

Answer 14

It will form a white emulsion

Question 15

What is used to test for protein?

Answer 15

Biuret reagent is used (sodium hydroxide and copper sulphate).

Question 16

What causes the biuret solution to change colour?

Answer 16

The copper hydroxide interacts with a peptide bonds present in the protein which turns the biuret reagent purple.

Question 17

What colour would a positive test be for protein?

Answer 17

It would turn from blue to purple.

Question 18

What sort of test is the biuret test?

Answer 18

At low concentrations the colour change is difficult to detect by eye. The more concentrated the protein the darker the colour purple is so the test is qualitative. It can however be used as a semi qualitative test by comparing the intensity of the colour purple into identically treated experiments.

Question 19

What could you use to measure the concentration of a protein?

Answer 19

You could measure the absorbance of the purple in a colorimeter using a yellow filter 580nm and in which case gives an estimate of relative concentrations of protein present within a sample. But in order to detect the concentration of the specific protein a biosensor would be required