From R2101 PLANT CLASSIFICATION, STRUCTURE AND FUNCTION Level 2 Monday November 27th 2011.
Q.7. a. Name the site of aerobic respiration in the cell.
b. State the basic equation for aerobic respiration in words.
c. State how anaerobic conditions determine the efficiency of respiration.
Sample answers:
a. Name the site of aerobic respiration in the cell.
Aerobic respiration occurs in the mitochondrion, which is an organelle found within the plant cell.
b. State the basic equation for aerobic respiration in words.
Carbohydrate + Oxygen -> Water + Carbon Dioxide + Energy (ATP)
c. State how anaerobic conditions determine the efficiency of respiration.
Anaerobic respiration does not need oxygen. It happens when there is not enough oxygen for aerobic respiration, for instance, in a waterlogged or compacted soil. Here is the word equation for anaerobic respiration in plants:
glucose → ethanol+ energy
Anaerobic respiration is less efficient than aerobic respiration, and much less energy is released. This is because the glucose (or carbohydrate) is incompletely broken down. In addition, ethanol, the by-product of anaerobic respiration is toxic and builds up in the cytoplasm, eventually leading to the death of the cell.
Examiners comments on this question:
a) Most candidates were aware that the site of respiration is the mitochondrion. Some candidates stated ‘mitochondria cells’ incorrectly as mitochondria are organelles within living cells. A few candidates named various plant tissues. Long statements and descriptions were not required in this section of the question.
b) Candidates who provided the correct equation with all the inputs and outputs in the right order were awarded full marks. Glucose/starch/carbohydrate and oxygen are converted to carbon dioxide and water with the release of energy/ATP. Energy was commonly omitted from the word equation even though this is the key output.
c)Those candidates who stated that anaerobic respiration means ‘without oxygen’ and that the efficiency of respiration is reduced were awarded marks. Marks were also given where candidates provided some explanation of why this occurs i.e. carbohydrate is incompletely broken down so less energy is released; ethanol is a by-product which is toxic and that this will eventually lead to cell/plant death. Additional marks were awarded where candidates included a situation in which anaerobic conditions occur e.g. waterlogged/compacted soils.
