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A student grows four pieces of tobacco tissue on a jelly…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student grows four pieces of tobacco tissue on a jelly. Each dish holds auxin and cytokinin in the amounts below, in mg/L.
| Dish | Auxin | Cytokinin |
|---|---|---|
| P | 4 | 1 |
| Q | 1 | 4 |
| R | 2 | 2 |
| S | 0 | 0 |
- Which dish forms roots, and which forms shoots?
- What does dish R form?
- What is the likely outcome in S, and why?
Need a reminder? The key ideaShow
Gibberellins (GA3, from the fungus Gibberella) are terpenes that lengthen the stem, promote bolting, delay senescence and speed malting. Cytokinins are adenine derivatives (kinetin, zeatin) that promote cell division and lateral shoots, overcome apical dominance and delay senescence. A high auxin to cytokinin ratio gives roots and a low ratio gives shoots.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Ratios. P: . Q: . R: . S: no hormones.
Step 2. (a) A high ratio gives roots, so P forms roots. A low ratio gives shoots, so Q forms shoots.
Step 3. (b) A middle ratio gives callus, a mass of undifferentiated cells.
Step 4. (c) In S there is little or no cell division. The tissue does not grow much, because cell division needs both regulators.
Answer: (a) P roots, Q shoots; (b) callus; (c) little growth, as there is no auxin or cytokinin.
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