Light falls on canary grass coleoptiles from the right only…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Light falls on canary grass coleoptiles from the right only. Say whether each coleoptile bends towards the light, and give the reason.
- The tip is cut off.
- The tip is covered with an opaque cap.
- The tip is covered with a transparent cap.
- Only the lower part is covered with an opaque sheath.
Need a reminder? The key ideaShow
Auxins are indole compounds made at growing tips. IAA and IBA are natural; NAA and 2,4-D are synthetic. They help cuttings to root, keep apical dominance, cause parthenocarpy, prevent early fruit and leaf drop, and 2,4-D kills dicot weeds. In Went's Avena test a coleoptile bends away from an agar block that holds auxin, and a bigger angle means more auxin.
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. (a) No bending. The part that senses the light is missing.
Step 2. (b) No bending. The tip cannot sense the light under an opaque cap.
Step 3. (c) It bends towards the light. A transparent cap lets the light reach the tip.
Step 4. (d) It bends towards the light. The tip is bare, and it sends the signal down to the growing region.
Answer: (a) no; (b) no; (c) yes; (d) yes. The tip senses the light, and the region below it bends.
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