Lesson 5 ·Class 10 · Chemical Coordination in Plants · Flow Lab
Chemotropism
Growth guided by a chemical.
The best example of chemotropism is one you already met in Class 9 — the pollen tube. Follow it again, this time as a tropism.
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🌾 Step 1 of 5 · Pollen lands on the stigma
A pollen grain reaches a receptive stigma and germinates.
Free play — step through the process at your own pace, and move the slider to see what changes. Switch to when you're ready to test yourself.
All five tropisms follow the same pattern: a directional stimulus produces a directional growth response. Only the stimulus changes — light, gravity, water, touch or a chemical.
What this lesson covers
Challenges to clear
- Advance to the step that makes this a tropism rather than a simple movement.
- Step through the whole example.
The task
The best example of chemotropism is one you already met in Class 9 — the pollen tube. Follow it again, this time as a tropism.
What this lesson covers
- Pollen lands on the stigma — A pollen grain reaches a receptive stigma and germinates.
- A chemical signal is released — The neck canal cells of the ovule secrete sugars and peptones, which diffuse up through the style.
- The tube grows toward the chemical — The pollen tube grows down the style in the direction of increasing concentration. The growth is directional, and the stimulus is chemical — that is chemotropism.
- It reaches the ovule — The tube enters the ovule through the micropyle, guided the whole way by the chemical gradient.
- Other examples — Fungal hyphae grow toward food-rich areas, and the tentacles of Drosera bend toward the nitrogenous chemicals of a trapped insect.
Hint
All five tropisms follow the same pattern: a directional stimulus produces a directional growth response. Only the stimulus changes — light, gravity, water, touch or a chemical.