R3101 Feb ‘19
a) Describe the process of anaerobic respiration. [6 marks]
b) Describe how ONE NAMED plant is able to survive anaerobic conditions. [4 marks]
This question relates to the following part of the syllabus:
Understand photosynthesis, respiration, water/solute relations in the plant and their relevance to horticulture.
3.3 Describe the processes of respiration.
Describe anaerobic respiration: Glycolysis (sugar (glucose) split to form pyruvate, production of ATP); pyruvate converted to ethanol (toxic) and CO2 in the cytoplasm.
Energy output 2 ATP for EACH glucose molecule. Describe examples of horticultural situations leading to anaerobic respiration.
3.6 Explain how plants are adapted to different habitats.
Explain how plants are adapted for: low light levels (shade plants – to include differences in leaf surface area, chlorophyll density, palisade layer); anaerobic conditions (bog plants – to include aerenchyma, pneumatophores); reduced water supply (xerophytes - to include xeromorphic adaptations in Pinus).
To include ONE NAMED plant example for EACH adaptation.
The first part of the question is very straightforward, and the examiners’ comments point out that high scores were gained by describing the process in detail and in a logical manner. This highlights the importance of taking a little time to think about your answer before you start writing. It can help just to jot down the main points you want to write about at the top of the answer as a checklist. This is also a good idea if you are ever running short on time for any questions. Then you will at least gain some marks for the basic points.
The examiners’ comments state the following – ‘Glucose is split into two pyruvate molecules in the process of glycolysis, which are further broken down to release carbon dioxide and ethanol. Two molecules of ATP are generated. The process takes place in the cytoplasm’.
It is important to just include what is required for the question and not waste time giving extra information. The examiners’ comments state that marks were not awarded for mentioning the toxicity of ethanol and comparisons with aerobic respiration as these were not asked for.
For part b) the full botanical name for a suitable plant was required.
Before starting this type of question have a think about the amount of detail you can include for your chosen example. Choose a different one if you can’t think of much to write about it.
Suitable examples were suggested as:
Typha minima and Juncus effusa, both with ‘aerenchyma tissue in their stems and roots, with large interconnecting air spaces that channel air and therefore oxygen down to the submerged roots from above the water’.
Nymphaea alba, with ‘floating leaves whose stomata are on the upper surface with aerenchyma tissue connecting leaves with roots’.
It was pointed out that marks were lost when a plant wasn’t named and only general descriptions used, and when the general term of ‘mangrove’ was used rather than a specific plant.
A plant with pneumatophores could have been described for this.
The examiners’ comments state that Gunnera manicata was given as an example, but does not actually have pneumatophores. A suitable plant for this could be Taxodium distichum.