| Date | May 2016 | Marks available | 3 | Reference code | 16M.3.HL.TZ0.3 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Explain | Question number | 3 | Adapted from | N/A |
Question
Achieving successful rooting of cuttings is difficult in some shrub species. An experiment was undertaken to determine whether juvenile shoots (J) of shrubs root more successfully than mature shoots (M).
Distinguish between the rooting success of the juvenile shoots and the mature shoots.
Suggest one reason for the difference in the rooting success in the juvenile shoots and the mature shoots.
Outline one variable that would need to be controlled in this experiment.
Auxin is a hormone that can be applied to improve the percentage success of rooting in those study plants with poor rooting success. Explain the effects of auxin on plant cells.
Markscheme
«all» juvenile shoots root more successfully/significantly/show higher percentage rooting success
Need comparative wording for the mark
Juvenile shoots have more undifferentiated/meristem/dividing tissues
Juvenile shoots have faster response to auxin
The starting leaf area/size/mass/length of cutting would need to be kept similar in all treatment groups (Accept other reasonable answers)
Light/temperature/nutrients/rooting mixture/moisture would need to be the same for all plants and both treatment groups
Cutting taken from same relative point of the shrub/branch
A brief description is required rather than a simple naming of the variable.
Increases cell elongation/growth/enlargement
OR
has effect on rate of mitosis
Changes the pattern of gene expression
OR
promotes transcription of some genes
Changes the pH of the extracellular environment/cell wall
OR
increases activity of proton pumps
Breaks cross links/connections between cellulose fibres in cell wall
Increases cell wall plasticity
«varying» auxin concentrations have different effects in different parts of the plant
Examiners report
Almost all were able to use the data and see that juvenile shots rooted more successfully than mature shoots.
Only the better candidates were able to give a correct reason for this. Many candidates incorrectly simply said that juvenile shoots were more adaptable to change or better able to grow without suggesting why. Few remembered meristem tissue.
This question asked candidates to ‘outline’ which is to give a brief account or summary, not ‘state’. Thus more than simply naming a variable was required for the mark.
This was a very discriminating question with a range of marks from 0 to 3. Many received zero or were only able to score one out of the 3 marks available for noting that auxin played a role in cell elongation. Candidates overlooked the fact that the question asked for ‘the effects of auxin on plant cells’, often describing phototropism in plants shoots instead which was not awarded any marks. How auxin works on plant cells walls was a new addition to the syllabus and does not seem to have been covered by all.
