Exam Questions

Question 1

What is a homologus pair of chromosomes? (1)

Answer 1

Two chromosomes that carry the same genes

Question 2

What is meant by species richness? (1)

Answer 2

A measure of the number of different species in a community

Question 3

Formation of an enzyme substrate complex increases the rate of reaction. Explain how. (2)

Answer 3

Reduces activation energy

Due to bending of bonds

Question 4

Heat stress decreases the light-dependent reaction of photosynthesis. Explain why this leads to a decrease in the light-dependent reaction. (2)

Answer 4

Less/no ATP

Less/no reduced NADP

Question 5

A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis. Explain why. (2)

Answer 5

Less/no CO2 reacts with RuBP

Less/no GP

Question 6

Describe how alterations to tumour suppressor genes can lead to the development of tumours (3)

Answer 6

Increased methylation of tumour suppressor genes
Mutation in tumour suppressor genes
Tumour suppressor genes are not transcribed/expressed
Results in rapid/uncontrollable cell division

Question 7

Describe how you would determine the mean percentage cover for beach grass on a sand dune (3)

Answer 7

Method of randomly determining position of quadrats
Large sample of quadrats
Divide total percentage by number of quadrats/samples/readings

Question 8

In genetic crosses, the observed phenotypic ratio obtained is often not the same as the expected ratios. Give two reasons why. (2)

Answer 8

Small sample size
Fusion/fertilisation of gametes is random
Linked Genes
Epistasis

Question 9

Dopamine is similar to acetylcholine and stimulates the production of nerve impulses in postsynaptic neurones. Describe how. (3)

Answer 9

Dopamine diffuses across synapse
Attaches to receptors on postsynaptic membrane
Stimulates entry of sodium ions and depolarisation/action potential

Question 10

GABA is a neurotransmitter, and causes negatively charged Cl- to enter postsynaptic neurones. Explain how this inhibits postsynaptic neurones. (3)

Answer 10

Inside of postsynaptic neurone becomes more negative/hyperpolarisation
More sodium ions required to reach threshold
For depolarisation/action potential

Question 11

Explain why the antibody binds to the transcription factor. (2)

Answer 11

Transcription factor has specific tertiary structure

Complementary shape

Question 12

Describe the roles of two enzymes used to insert DNA fragments into plasmids (2)

Answer 12

Restriction endonuclease to cut plasmid/vector

Ligase joins DNA to plasmid/vector

Question 13

People with achromatopsia have only rods and no functioning cone cells, and have difficulty seeing in detail. Explain why. (3)

Answer 13

No functional cones/only rods
Cones are connected to a single neurone, multiple rods connected to single neurone
Cones send separate impulses to the brain, rods send a single set

Question 14

Red-green colour blindness affects more women than men. Explain why. (2)

Answer 14

Gene/allele is on X chromosome

Females require two alleles, and males only require one

Question 15

People with red-green colour blindness are unable to distinguish between red and green, but also other colours. Explain why. (3)

Answer 15

Green sensitive pigment/ cones non-functional
Three different types of pigment/cone
Other/different colours seen due to stimulation of more than one cone/pigment

Question 16

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. (4 marks)

Answer 16

Trachea and bronchi and bronchioles
Down pressure gradient
Down diffusion gradient
Across alveolar epithelium
Across capillary epithelium

Question 17

Species richness and an index of diversity can be used to measure biodiversity. What is the difference between these two? (1)

Answer 17

Species richness measures only number of different species, does not measure number of individuals

Question 18

Explain the difference in the structure of the starch molecule and the cellulose molecule. (2)

Answer 18

Starch formed from a-glucose but cellulose from b-glucose

Position on hydrogen and hydroxyl groups on carbon atom 1 inverted

Question 19

Explain one way in which starch molecules are adapted for their function in plant cells (2)

Answer 19

Insoluble - doesn’t affect water potential
Helical - compact
Large molecule - cannot leave

Question 20

Explain how cellulose molecules are adapted for their function in plant cells (3)

Answer 20

Long and straight chains
Become linked together by many hydrogen bonds to form fibrils
Provide strength to cell wall

Question 21

Contrast the processes of facilitated diffusion and active transport (3)

Answer 21

FD involves channel or carrier proteins whereas AT only involves carrier proteins
FD does not use ATP, AT does
FD takes place down a concentration gradient whereas AT can occur against a concentration gradient

Question 22

What is meant by genetic diversity? (1)

Answer 22

Number of different alleles of each gene

Question 23

Explain why new nucleotides can only be added in a 5’ to 3’ direction (4)

Answer 23

Reference to DNA polymerase
Which is specific
Only complementary to 5’ end of strand
Only complementary with phosphate end of the developing strand

Question 24

Describe the mass flow hypothesis of translocation in plants (4)

Answer 24

In source, sugars actively transported into phloem
By companion cells
Lowers water potential of sieve tube and water enters by osmosis
Increase in pressure causes mass movement towards sink
Sugars used in root for respiration for storage

Question 25

mRNA is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell (6)

Answer 25

Helicase
Breaks hydrogen bonds
Only one DNA strand acts as template
RNA nucleotides attracted to exposed bases
According to base pairing rule
RNA polymerase joins RNA nucleotides together
Pre-mRNA spliced

Question 26

Describe the structure of proteins (5)

Answer 26

Polymer of amino acids
Joined by peptide bonds
Formed by condensation
Primary structure is order of amino acids
Secondary structure is folding of chain due to hydrogen bonding
Tertiary structure is 3D folding due to H+, Ionic, Disulfide
Quaternary structure is two or more polypeptide chains

Question 27

Describe how proteins are digested in the human gut (4)

Answer 27

Hydrolysis of peptide bonds
Endopeptidases break polypeptides into smaller peptide chains
Exopeptidases remove terminal amino acids
Dipeptidases hydrolyse dipeptides into amino acids