DP Biology (first assessment 2025)

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Question SPM.2.SL.TZ0.8

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Date May Specimen-2023 Marks available [Maximum mark: 15] Reference code SPM.2.SL.TZ0.8
Level SL Paper 2 Time zone TZ0
Command term Distinguish, Explain Question number 8 Adapted from N/A
8.
[Maximum mark: 15]
SPM.2.SL.TZ0.8

Biological systems are sensitive to temperature changes, so they have mechanisms to resist temperature changes.

(a)

Explain the mechanisms involved in thermoregulation in humans.

[7]

Markscheme
  1.  normal body temperature is 37 ºC;
  2.  peripheral thermoreceptors detect environmental temperature;
  3.  supporting conscious behaviour to avoid temperature extremes, e.g. wearing more clothing;
  4.  sends messages to hypothalamus/temperature control centre of the brain;
  5.  the hypothalamus sends messages to pituitary gland;
  6.  (pituitary) releases TSH;
  7.  stimulating thyroxin release from thyroid;
  8.  thyroxin controls metabolic rate / production of heat;
  9.  muscle random contraction/shivering to generate heat;
  10.  (brown) adipose tissue burns fat to generate waste heat;
  11.  vasoconstriction to conserve heat / vasodilation to exchange heat with the environment;
(b)

Explain the relationship between temperature and the activity of enzymes.

[4]

Markscheme
  1.  as temperature increases, the rate of molecular motion increases;
  2.  increasing the frequency of collision between enzyme and substrate;
  3.  increasing the rate of reaction;
  4.  until an optimum temperature is reached;
  5.  with further increase in temperature, enzymes denature;
(c)

Distinguish between the thermal properties of air and water as they relate to the habitat of animals.

[4]

Markscheme
  1.  water has a (much) higher specific heat capacity (than air);
  2.  water requires more energy gain/loss to change temperature;
  3.  (water) provides more stable thermal habitats than air / temperature of water bodies remains more constant than air temperature;
  4.  water has a higher thermal conductivity than air;
  5.  more heat is transferred from organisms to water than to air;
  6.  water is a good evaporative coolant and air is not;
  7.  aquatic mammals have (proportionally) more body fat as insulation;

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