Chemical Coordination in Plants — Part 2: Tropic movements: visual lesson, ICSE Class 10 Biology (Science Paper 3)

Lesson

Tropic Movements

Part 2 — how plant parts grow towards or away from a stimulus.

In this lesson you will

Identify the type of tropism from an example and say whether it is positive or negative
Explain phototropism of a shoot in terms of unequal auxin distribution
Describe simple experiments on phototropism, geotropism and hydrotropism

Concept

A tropism is the growth of a plant part towards (positive) or away from (negative) a stimulus coming from one direction.

Table of five tropisms with their stimulus and an example of each
Tropism	Stimulus	Example
Phototropism	Light	Shoot grows towards light (positive)
Geotropism	Gravity	Root grows down (positive); shoot grows up (negative)
Hydrotropism	Water	Root grows towards water (positive)
Thigmotropism	Touch	Tendril coils round a support
Chemotropism	Chemicals	Pollen tube grows to the ovule

Diagram

A shoot lit from one side bends towards the light: it is positively phototropic.