Describe anaerobic respiration in humans and in yeast.

Distinguish between the thermal properties of water and methane.

Explain the role of methane in climate change.

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.

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;

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.

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.