biomolecule tests

Question 1

what is the test for starch?

Answer 1

iodine test

Question 2

test for starch

Answer 2

• add a few drops of iodine to the sample
• iodide ions react with the centre of starch molecules
• turns blue black in presence of starch

Question 3

what is the test for reducing sugars?

Answer 3

benedicts test

Question 4

test for reducing sugars

Answer 4

• benedicts test
• add blue benedicts reagent to a sample solution
• heat in water bath
• brick red precipitate forms if reducing sugar is present

Question 5

test for non-reducing sugars

Answer 5

• after negative result for reducing sugar (stays blue)
• add acid and boil
• wait to cool and add alkali to neutralise
• add benedict’s solution
• positive test : colour change from blue to green/yellow/orange/red

Question 6

what is the test for proteins?

Answer 6

biuret test

Question 7

test for proteins

Answer 7

• add biuret solution at 45 degree angle to form a layer.
• observe colour change, gently mix and observe again.
• if turns violet indicates presence of protein

Question 8

what is the test for lipids?

Answer 8

emulsion test

Question 9

test for lipids

Answer 9

• emulsion test
• dissolve the sample in ethanol by adding ethanol and shaking
• add distilled water
• positive test : white emulsion forms

Question 10

explain the reason for the colour change in the benedicts test

Answer 10

copper sulphate being reduced by copper oxide

Question 11

explain the colour change in the iodine test

Answer 11

due to the starch being digested by enzymes

Question 12

explain the precipitation formation in the emulsion test

Answer 12

lipids dissolve in non polar substances but not polar substances like water

Question 13

risk assessment of biomolecule tests

Answer 13

biuret reagent - dont dispose down sink
ethanol - dont use near naked flame

Question 14

colorimeter method

Answer 14

• to get quantitative answers
• set filter
• calibrate
• insert samples
• create calibration curve

Question 15

biosensors

Answer 15

• strand of DNA or protein is immobilised
• sample will bind to immobilised DNA/protein
• binding causes change in a transducer
• current determines concentration of sample

Question 16

serial dillution

Answer 16

• 5 test tubes
• each contain a known concentration
• each test tube is of equal volume
• each tube has a concentration decrease of the same amount each time
• e.g. tube 1 = 10cm3 solution
  tube 2 = 8cm3 solution, 2cm3 water
  tube 3 = 6cm3 solution, 4cm3 water

Question 17

what is the purpose of a control test tube? (2)

Answer 17

it acts as a blank. this is to show the impact of the manipulation of the IV in comparison to without.

Question 18

how can reliability of experiments be improved (2)

Answer 18

• repeat
• sample each test tube twice

Question 19

describe how a student could carry out a chemical test for reducing sugar and suggest how they can estimate the amount of reducing sugar in a sample (5)

Answer 19

• add benedicts reagent and observe any colour change
• colour change will be blue to brick red
• compare the colour with that of a known solution
• mass of precipitate formed reflects concentration

Question 20

chromatography of a protein

Answer 20

• separate mixtures
• mobile phase flows through the stationary phase
• carries the components of the mixture with it

Question 21

how to measure Rf value

Answer 21

distance travelled by compound ÷ distance travelled by solvent = Rf

Question 22

risk assessment/evaluation of chromatography of protein

Answer 22

• plates from compromised powder, dont chip with pencil
• waft the plate to dry, don’t blow as spit has proteins
• no fingers on plate