Paper 1 2023

Question 1

Answer 1

• DNA (from bones) is cut into fragments (1)
• { radioactive tracers / fluorescent tags} attached to
DNA (1)
• (fragments of) DNA loaded onto (agarose) gel /
samples placed in wells (1)
• electric current passed through (the gel) / potential
difference set up (through buffer/ across gel) (1)

Question 2

Given that the biodiversity index for pond B is 2.65

Answer 2

• {species richness is lower/fewer species present } (1)
• because {most species cannot survive /fewer species
can survive} (in the polluted conditions) (1)
• adaptations required for polluted conditions (1)
• lack of competition in pond B therefore large numbers
of those species present (1)

Question 3

Answer 3

• tissue treated with hydrochloric acid (1)
• tissue heated (1)
• stained with {toluidine blue / (acetic) orcein} (1)
ALLOW HCl
IGNORE concentration of acid
• tissue {macerated / squashed } (1)

Question 4

Answer 4

• (seeds from different plants of the same species)
ensures {genetic diversity / a large gene pool /
genetic variation} (1)
• therefore greater chance of {survival/adaptation} (1)
• (if the plants are reintroduced) {conditions may have
changed / may be a different habitat} (1)

Question 5

Answer 5

• acidic conditions in the stomach (1)
• (because acidic conditions) denature the enzymes of
microorganisms (1)
OR
• gut flora {outcompete / compete with} other
microorganisms (1)
• therefore inhibiting {growth / reproduction} of
pathogens (1)

Question 6

Answer 6

• (many) alveoli provide large surface area for {gas exchange / diffusion } (1)
• thin walls of alveoli / alveoli have walls that are one cell thick (1)
• therefore short diffusion {distance /pathway} (for gas exchange) (1)
• network of capillaries (surrounding alveoli) maintains the concentration gradient (1)
• network of capillaries increases surface area for
{diffusion / gas exchange } (1)

Question 7

Answer 7

• (a change in the base sequence of DNA) causes a
change to the triplet code (1)
• therefore there will be a change in the amino acids (in
the myoglobin) (1)
• changing the bonding and therefore the (tertiary)
structure (of the protein) (1)

Question 8

Answer 8

• histamine is released (1)
• (histamine) causes {vasodilation / dilation of
arterioles } (1)
• (vasodilation) increases the blood flow (1)
• capillaries become more permeable (1)
• (therefore) {white blood cells / phagocytes} reach the
{infected area / bacteria / pathogen} (1)

Question 9

Discuss the mechanisms bacteria have developed to become resistant to antibiotics and the code of practice used to overcome this resistance. (6)

Answer 9

Question 10

Answer 10

• introns are removed (1)
• exons can then be arranged in several different ways /
exons can be removed (1)
• this produces different mRNA (from the same gene)
(1)
• translation (of the mRNA) gives different {amino acid
sequences / different polypeptides / different
proteins} (1)

Question 11

Answer 11

• (life cycle) depends on metabolic reactions (1)
• (increase in temperature) increases the kinetic energy
of enzymes (1)
• (therefore) there will be {more frequent collisions
between enzyme and substrate / faster rate of formation
of enzyme-substrate complexes} (1)