MediumBiologyHigh School (9–10)GeneralPlant Biology › Plant Hormones and MovementsHuman Body › Hormones and the Endocrine SystemConceptual
In a school garden, Rohan sees two plant movements.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In a school garden, Rohan sees two plant movements. A touch-me-not folds its leaflets a second after he touches them. A pea tendril takes two days to curl around a stick. Explain how each movement is made, and why one is so much faster.
Need a reminder? The key ideaShow
A tropism is a growth movement towards (positive) or away from (negative) a stimulus. Shoots grow towards light and away from gravity. Roots grow towards gravity and towards water. A pollen tube grows towards a chemical made by the ovule. A part bends when one side grows faster than the other.
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. The touch-me-not. The touch is passed from cell to cell. Cells at the base of the leaflets lose water and go limp, so the leaflets fold. No growth is needed.
Step 2. The tendril. The side away from the stick grows faster than the side touching it, so the tendril curls. This is a growth movement.
Step 3. Why the speeds differ. Water can leave a cell in a moment. Growth needs new material, which takes hours or days.
Answer: the touch-me-not moves by a quick change of water in its cells; the tendril moves by uneven growth, which is slow.
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