Tests

Question 1

What test do you do for proteins and what results do you expect?

Answer 1

Biuret test and if positive goes from blue to lilac

Question 2

What test do you do for reducing sugars and what results do you expect?

Answer 2

Benedict’s test and if positive goes from blue to brick red

Question 3

What test do you do for non reducing sugars and what results do you expect?

Answer 3

Boil with HCl, neutralise it then do Benedict’s test

If positive then goes from blue to brick red

Question 4

What test do you do for lipids and what results do you expect?

Answer 4

Emulsion test

If positive a white emulsion will appear

Question 5

What test do you do for starch and what results do you expect?

Answer 5

Iodine test

If positive goes from orange to blue/black

Question 6

How do you carry out an emulsion test?

Answer 6

2cm sample+2cm ethanol
Shake
Let it settle
Add to 4cm of water

Question 7

Explain the procedure for testing for reducing sugars

Answer 7

Add Benedict’s solution

Place in water bath (80 degrees celsius)

Question 8

Explain the procedure for testing for non reducing sugars

Answer 8

Boiled with dilute hydrochloric acid
Cooled and neutralised
Then add Benedict’s solution
Place in a water bath

Question 9

How would you determine the concentration of glucose using a colorimeter?

Answer 9

Prepare a set of serial dilutions of glucose
Take a set volume of each of the serial dilutions and do the Benedict’s test
Pour out the precipitate into a cuvette and measure the absorbance at each at each concentration.
Plot absorbance against glucose concentration and draw a line of best fit
Now do Benedict’s test with unknown substance and measure the absorbance
Read off the concentration of glucose at this value from your graph.

Question 10

How do biosensors work?

Answer 10

Convert a biological response into an electrical signal

Question 11

What uses are there for biosensors?

Answer 11

Measuring blood glucose levels
Measuring levels of contaminants in water
Measuring levels of pathogens/toxins

Question 12

What is chromatography?

Answer 12

A technique used to separate the components in a mixture

Question 13

What can chromatography be used for?

Answer 13

Work out the levels of any contaminants in drugs/food

Test for drugs in athletes urine

Question 14

What are the 2 phases of chromatography?

Answer 14

Stationary phase - paper/thin layer chromatography plate

Mobile phase - solvent that carries the biological molecules (water/ethanol)

Question 15

How do you work out the Rf value in chromatography?

Answer 15

Distance travelled by pigment

Distance travelled by solvent front

Question 16

How are Rf values used?

Answer 16

If Rf value of a molecule is known then you can work out which molecule is in the mixture.

Question 17

Describe how you could separate a mixture of amino acids using thin layer chromatography

Answer 17

Wear eye protection and gloves.
Draw a pencil line 2cm from the bottom of the plate and put a dot where the mixture will be added.
Spot the mixture of amino acids on the dot, allow to dry, repeat a few times.
Lower TLC plate into solvent, stop before solvent reaches pencil line.
Take PLC plate out of solvent when nearly at the top.
Allow to dry, spray with ninhydrin.
Circle amino acids and work out Rf values.

Question 18

What is a photosystem?

Answer 18

A collection of different pigments

Question 19

What are the 5 steps of DNA extraction from plant cells by precipitation?

Answer 19

Sample is ground to break cell wall
Mixed with detergent to break down cell membrane
Salt is added to break hydrogen bonds within DNA
Protease breaks down associated proteins
Ethanol is added which causes the DNA to precipitate out