medium importancemedium difficulty5 min

Phototropism

Phototropism is the growth movement of a plant part in response to light.

In one line: Photo means light, so phototropism means light-guided growth.

Practice This Concept

Understand it

Phototropism is seen when plant parts grow towards or away from light.
Shoots usually show positive phototropism and grow towards light to get more energy for photosynthesis.
Roots generally do not show strong positive phototropism.
The key idea is that light acts as the stimulus and the growth direction changes because of it.

Example

A sunflower shoot bending towards sunlight is a common example of phototropism.

Rule to remember

Rule: photo means light, so phototropism is directional growth caused by light.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1A plant kept in a dark room with light from one side grows towards the window.
2The shoot bends because the cells on the shaded side grow more, producing positive phototropism.

Method you can reuse

1Identify light as the stimulus.
2Check which plant part is growing.
3State the direction of growth.
4Name it phototropism.
5If needed, add positive or negative depending on direction.

Visual tip

A clean diagram can show a shoot bending towards a light source from one side.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why does a shoot bend towards light in phototropism?

Think first, then show answer

A shoot bends towards light because light is the stimulus and the shoot grows in that direction to receive more light for photosynthesis. This is called positive phototropism.

Common wrong answer

A common wrong answer is to call every bending of a plant phototropism without checking the stimulus. The stimulus must be light.

Don't mix this up

Students often think roots and shoots always react the same way to light. They do not. Shoots usually grow towards light, while roots generally do not.

Exam tip

If the stimulus is light, use the term phototropism and state whether the growth is towards or away from the light.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Board questions may ask for the meaning of phototropism, examples of positive phototropism, or why shoots bend towards light.

1
Enough for 1 mark
Phototropism is the growth movement of a plant part in response to light.
2
Add for 2 marks
Example: A sunflower shoot bending towards sunlight is a common example of phototropism.
3
Add for 3 marks
Phototropism is seen when plant parts grow towards or away from light.

MCQ Quiz

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