DP Biology (last assessment 2024)

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Question 23M.2.SL.TZ2.6

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Date May 2023 Marks available [Maximum mark: 15] Reference code 23M.2.SL.TZ2.6
Level SL Paper 2 Time zone TZ2
Command term Describe, Explain, Outline Question number 6 Adapted from N/A
6.
[Maximum mark: 15]
23M.2.SL.TZ2.6

Between 1900 and 2020 the Earth’s average surface air temperature increased by about 1° C. Temperature affects many biological processes.

(a)

Explain how temperature affects enzymes.

[4]

Markscheme
  1. speed of reaction/catalysis increases as temperature rises;
  2. faster molecular motion so more collisions between substrate and active site;
  3. denaturation at higher temperatures;
  4. (denaturation causes) shape/conformation/structure of enzyme/active site altered/damaged;
  5. an enzyme works fastest at its optimum temperature;
  6. inactivation at lower temperatures (due to very few collisions);
  7. sketch graph to model the effect of temperature on enzyme activity;

Graphs would need to be well annotated.

Must not be bell shaped.

Examiners report

Most candidates gained some marks for explaining the effect of temperature on enzyme activity. One common error was to state that denaturation happens at too high and too low temperatures. Many candidates also explained the effect of changing pH which was outside the question and risked losing the quality mark for superfluous material.

(b)

Outline the role of the thyroid gland in helping to control body temperature in humans.

[4]

Markscheme
  1. secretes thyroxin;
  2. thyroxin causes the metabolic rate to rise;
  3. heat released by metabolism;
  4. thyroxin increases generation of body heat;
  5. thyroxin stimulates shivering/stimulates brown adipose tissue (to release heat);
  6. more thyroxin secreted if body temperature too low/converse;

 

Examiners report

Many candidates had not been taught about the thyroid gland. Those who had, gained some marks for relating thyroxine to metabolic rate.

(c)

Describe how human activities have caused average surface air temperatures on Earth to increase.

[7]

Markscheme
  1. release of carbon dioxide;
  2. combustion of fossil fuels produces carbon dioxide;
  3. forest fires (caused by humans) produce carbon dioxide;
  4. deforestation reduces carbon dioxide uptake by photosynthesis;
  5. release of methane;
  6. from cattle/sheep/ruminant digestive systems / other verified source of anthropogenic methane;
  7. greenhouse effect / carbon dioxide/methane is a greenhouse gas;
  8. carbon dioxide/methane allow short wave radiation in sunlight to pass through the atmosphere;
  9. longer wave/infra-red radiation emitted by the warmed Earth’s surface;
  10. carbon dioxide/methane absorbs/reflects back longer wave/infra-red radiation;

 

Examiners report

Common errors were confusing short and long wave radiation and trying to involve the ozone layer. Combustion of fossil fuels and the increase in methane from farming were well known.

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