Temperature, evolution and speciation: exam questions

Answer: B – Q₁₀ = 15 ÷ 6 = 2.5. A divides the lower rate by the higher rate; C is the difference in rate (15 − 6); D is the difference divided by the 10 °C interval.

• as temperature increases, molecules have more kinetic energy (1)
• so more frequent / more energetic collisions between enzyme and substrate, so more enzyme–substrate complexes (1)
• rate increases up to the optimum (1)
• above the optimum, bonds (hydrogen) break and the tertiary structure / active site changes shape (1)
• enzyme denatures, so substrate no longer fits and rate falls (1)
• Max 4

• Q₁₀ = rate at higher temperature ÷ rate at lower temperature (1)
• 10 to 20 °C: 50 ÷ 20 = 2.5 (1)
• 20 to 30 °C: 90 ÷ 50 = 1.8 (1)
• correct answers with no working gain full marks; Q₁₀ has no unit (ignore units given)

• Q₁₀ falls as temperature increases / rate does not double between 20 and 30 °C (1)
• the rate of increase is falling because enzymes are approaching their optimum / some enzymes begin to denature (1)
• beetle is an ectotherm, so its metabolic rate follows the environment temperature (1)
• warming may increase growth and development until the optimum, but above this enzymes denature and survival falls (1)
• Max 4

• set up water baths / incubators at several temperatures, for example 15 to 35 °C, checked with a thermometer (1)
• same volume and concentration of salt solution in each container (1)
• same number / mass of eggs from the same batch in each (1)
• same light, time and aeration in each (1)
• count the number hatched (or percentage hatching) after a fixed time (for example 24 h) (1)
• repeat at each temperature and calculate a mean (1)
• ethical: use minimum number of eggs / organisms (1)
• ethical: avoid extreme temperatures / treat humanely and dispose of the organisms humanely (1)
• Max 6

• 20 °C: 36 ÷ 120 × 100 = 30 % (1)
• 30 °C: 84 ÷ 120 × 100 = 70 % (1)
• 40 °C: 12 ÷ 120 × 100 = 10 % (1)
• enzymes (involved in development / hatching) denature at high temperatures / 40 °C is above the optimum, so development is disrupted (accept embryos killed / membranes damaged) (1)

• a mutation in a gene produced an allele giving resistance (1)
• mutation occurs at random / was present before the insecticide was used (1)
• insecticide is a selection pressure (1)
• resistant individuals survive and reproduce (1)
• they pass the allele to offspring (1)
• the frequency of the allele increases in the population (over generations) (1)
• Max 5

• geographical isolation prevents interbreeding / there is no gene flow between the populations (1)
• mutations occur independently in each population (1)
• different selection pressures on each island (1)
• allele frequencies diverge over generations (1)
• populations become unable to interbreed to produce fertile offspring (reproductive isolation) (1)
• this is allopatric speciation (1)
• Max 5

• sympatric occurs in the same area / allopatric requires a geographical barrier (1)
• in sympatric speciation, reproductive isolation arises without a physical barrier (1)
• valid example: different breeding seasons / different habitats within the same area / behavioural changes / polyploidy (1)