June 2017 P1

Question 1

The enzymes DNA helicase and DNA polymerase are involved in DNA replication.

Describe the function of each of these enzymes (4)

Answer 1

DNA helicase - to catalyse the hydrolysis of hydrogen bonds between DNA strands, unwind the DNA helix

DNA polymerase - to join adjacent nucleotides

Question 2

Explain the role of the heart in the formation of tissue fluid (2)

Answer 2

Contraction of ventricles produces high hydrostatic pressure

This forces water and some dissolved substances out of blood capillaries

Question 3

Lymphoedema is a swelling in the legs which may be caused by a blockage in the lymphatic system.

Suggest how a blockage in the lymphatic system could cause lymphoedema (1)

Answer 3

Excess tissue fluid cannot be reabsorbed

Question 4

Explain how the chromosome number is halved during meiosis (2)

Answer 4

Homologous chromosomes

One of each goes to each cell

Question 5

Describe the process of crossing over and explain how it increases genetic diversity (4)

Answer 5

Homologous pairs of chromosomes form a bivalent

Chiasmata form

Equal lengths of non sister chromatids are exchanged

Production of new combinations of alleles

Question 6

Describe how you would use cell fractionation techniques to obtain a sample of chloroplasts from leaf tissue. Do not include in your answer information about any solutions (3)

Answer 6

Homogenise cells in solution

Centrifuge

At different speeds until chloroplast fraction obtained

Question 7

Give three properties of water that are important in biology (3)

Answer 7

Is a metabolite

Is a solvent

Has a relatively high heat capacity

Question 8

Define species and species richness (2)

Answer 8

Species - a group of organisms that are able to produce fertile offspring

Species richness - the number of different species in a community