A farmer applied different concentrations off cytokinins to his pineapple plants and observed tne development of new shoots Over a period of time. The resul...
Question 1 Report
A farmer applied different concentrations off cytokinins to his pineapple plants and observed tne development of new shoots Over a period of time.
The result of his observation is shown below.
| S/No. | Conc. of Cytokinin(mg/litre) | No. of new shoots |
| 1 | 0 | 2 |
| 2 | 1 | 5 |
| 3 | 2 | 8 |
| 4 | 3.5 | 12 |
| 5 | 4 | 18 |
| 6 | 4.5 | 25 |
| 7 | 5 | 20 |
| 8 | 6 | 10 |
| 9 | 7.5 | 8 |
| 10 | 8 | 6 |
| 11 | 9 | 5 |
| 12 | 10 | 5 |
(a) Plot a graph to show the relationship between cytokinin concentration and shoot development.
(b) Use the graph to describe the effect of cytokinin concentration on shoot development.
(c) What advice should be given to the farmer based on the results from the graph?
(d) List (2) two substances in plants, (ii) two substances in animals which have similar effect as cytokinins.
Answer Details
The farmer's results are tabulated below and used to plot the graph in part (a).
| S/No. | Conc. of cytokinin (mg/litre) | No. of new shoots |
|---|---|---|
| 1 | 0 | 2 |
| 2 | 1 | 5 |
| 3 | 2 | 8 |
| 4 | 3.5 | 12 |
| 5 | 4 | 18 |
| 6 | 4.5 | 25 |
| 7 | 5 | 20 |
| 8 | 6 | 10 |
| 9 | 7.5 | 8 |
| 10 | 8 | 6 |
| 11 | 9 | 5 |
| 12 | 10 | 5 |
(a) Graph of cytokinin concentration against number of new shoots
Cytokinin concentration (the independent variable) is plotted on the horizontal (x) axis and the number of new shoots (the dependent variable) on the vertical (y) axis. Each of the twelve readings is plotted and the points joined with a smooth curve.
(b) Effect of cytokinin concentration on shoot development
Reading directly from the curve:
- As the concentration of cytokinin is increased from \(0\) to \(4.5\ \text{mg/litre}\), the number of new shoots produced increases steadily, rising from 2 shoots to a maximum of 25 shoots.
- Shoot development reaches its peak of 25 shoots at the optimum concentration of 4.5 mg/litre.
- Above this optimum concentration, shoot development declines progressively, falling to about 5 shoots and then levelling off (remaining roughly constant) at the highest concentrations.
Thus cytokinin promotes shoot development only up to an optimum concentration; beyond that optimum, higher concentrations become inhibitory.
(c) Advice to the farmer
The farmer should apply cytokinin at a concentration of about 4.5 mg/litre, because this gives the greatest number of new shoots (25). He should avoid concentrations higher than the optimum, since these reduce shoot production, waste the chemical and could harm the plants.
(d) Substances with a similar (growth-regulating) effect to cytokinins
(i) In plants:
- Auxins
- Gibberellins
(ii) In animals:
- Growth hormone (somatotrophin)
- Thyroxine
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