DP Biology (first assessment 2025)

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Question 22M.2.SL.TZ2.3

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Date May 2022 Marks available [Maximum mark: 7] Reference code 22M.2.SL.TZ2.3
Level SL Paper 2 Time zone TZ2
Command term Describe, Distinguish, Explain Question number 3 Adapted from N/A
3.
[Maximum mark: 7]
22M.2.SL.TZ2.3

Methane can be the product of anaerobic respiration in some organisms.

(a)

Describe anaerobic respiration in humans and in yeast.

[3]

Markscheme
  1. (in both) anaerobic respiration gives a small amount of ATP/2 ATP/energy from glucose;
  2. anaerobic respiration occurs when there is no oxygen;
  3. anaerobic respiration in yeast produces ethanol and carbon dioxide/alcoholic fermentation;
  4. anaerobic respiration in humans (in muscle) produces lactate/lactic acid/lactic acid fermentation;
  5. both undergo glycolysis;

Do not accept mpd if CO2 also included.

Examiners report

In 3a. the top candidates scored all three marks with ease, but many, especially in Spanish scored zero. A common mistake was to say that humans produce lactic acid and CO2. In bi, many were confused by the term ‘thermal properties’, but most were able to gain at least one point for comparing their boiling/freezing temperatures, specific heat capacities and latent heat of fusion. The best candidates also explained the differences in terms of hydrogen bonds between the water molecules. In bii, few got past stating that methane is a greenhouse gas/causes an increase in temperature of the atmosphere. The better candidates stated that it was a powerful greenhouse gas, but it had a relatively short life span compared to CO2. A surprising number thought that methane’s main danger was that it destroyed the ozone layer.

(b.i)

Distinguish between the thermal properties of water and methane.

[2]

Markscheme
  1. water has higher boiling/melting point;
  2. water has a higher specific heat capacity;
  3. water has a higher latent heat of vaporization;
  4. differences due to water having many H-bonds/polarity between the molecules while methane has no H-bonds/polarity;
(b.ii)

Explain the role of methane in climate change.

[2]

Markscheme
  1. methane is a greenhouse gas
    OR
    methane causes an increase in temperature of the atmosphere;
  2. methane is one of the most powerful greenhouse gases / more powerful than CO2;
  3. methane has a relatively short lifespan compared to CO2/decomposes to CO2;

Other verifiable sources.

Syllabus sections