Biology AS Paper 2019

Question 1

Give three ways in which the DNA of a chloroplast is different from DNA in a nucleus
(3 marks)

Answer 1

nucleus-
linear
associated with histones
longer
chloroplast-
circular
no histones
shorter

Question 2

Give one difference between the structure of a DNA nucleotide and structure of a RNA nucleotide
(1 mark)

Answer 2

DNA- Deoxyribose sugar
RNA- Ribose sugar

Question 3

Not all mutations in nucleotide sequence of a gene causes a change in the structure of a polypeptide. Give two reasons why
(2 marks)

Answer 3

genetic code degenerate- multiple triplet codons for same amino acid sequence
occurs in introns

Question 4

What is a monoclonal antibody?
( 1 mark)

Answer 4

single type of antibody which is isolated and cloned from B-lymphocytes

Question 5

Give one example of using monoclonal antibodies in a medical treatment
(1 mark)

Answer 5

blocks receptors on cancer cells

Question 6

Describe role of antibodies in producing a positive result in an ELISA test
(4 marks)

Answer 6

add antibody specific to antigen- antibody binds to from antibody-antigen complex
excess antibodies washed away
second antibody with attached enzyme binds with first antibody
add colourless substrate
enzyme substrate complex- product is coloured

Question 7

A student carried out a Benedicts test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in solution
(2 marks)

Answer 7

filter and dry precipitate
measure mass of precipitate on balance

Question 8

Use of colorimeter would improve repeatability of the students results.
Give one reason why
(1 mark)

Answer 8

quantitative measure
standardises method

Question 9

Explain why it is more useful to calculate an index of diversity than to record species richness
(2 marks)

Answer 9

measures abundance of each species
reflects many of some species

Question 10

A biologist separated cell components to investigate organelle activity. She prepared a suspension of the organelles in a solution that prevented damage to the organelles
Describe three properties of this solution and explain how each property prevented damage to the organelles
(3 marks)

Answer 10

ice cold- reduces enzyme activity
buffered- prevents denaturing of enzymes by maintaining pH level
isotonic (same water potential)- prevents lysis during osmotic gain/loss

Question 11

Describe and explain the advantage of counter-current principle in gas exchange across a fish gill
(3 marks)

Answer 11

water and blood flow in opposite directions
maintains diffusion gradient of oxygen
diffusion occurs along entire length of lamellae

Question 12

Explain how the active site of an enzyme causes a high rate of reaction
(3 marks)

Answer 12

biological catalyst which increase rate by lowering activation energy
induced fit model: active site of enzyme changes shape to bind with substrate- enzyme substrate complex formed- bonds break- products released

Question 13

Describe a biochemical test to confirm the presence of protein in solution
(2 marks)

Answer 13

add biuret reagent
positive result purple

Question 14

Describe two ways in which all dipeptides are similar and one way in which they might differ
(3 marks)

Answer 14

similarities: amine and carboxyl groups
difference: variable R groups

Question 15

Suggest why preventing the formation of spindle fibres stops the cell cycle
(2 marks)

Answer 15

centromere cannot attach to spindle fibres
no metaphase

Question 16

Suggest how the scientist measured the rate of water flow in the river
(1 mark)

Answer 16

movement of object over known distance and given time

Question 17

Give one way in which sampling procedures can be standardised
(1 mark)

Answer 17

same size of area sampled