high importancemedium difficulty4 min

Stomata and gaseous exchange in leaves

Stomata are tiny pores on leaves that allow gas exchange and transpiration.

In one line: Stomata are the leaf's tiny doors.

Practice This Concept

Understand it

Stomata open and close with the help of guard cells.
When open, carbon dioxide enters for photosynthesis and oxygen can leave.
Water vapour also escapes.
This balance helps the leaf manage gas exchange and water loss.

Example

A plant in sunlight often has open stomata for active photosynthesis.

Rule to remember

Rule: Open stomata support gas exchange and transpiration; closed stomata reduce water loss.

See it worked out

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

Worked example

If a plant is kept in bright light, guard cells usually become more turgid, stomata open, and gas exchange increases for photosynthesis.

Method you can reuse

1Identify the pore.
2State the role of guard cells.
3Mention carbon dioxide entry.
4Mention oxygen and water vapour exit.
5Link it to photosynthesis and transpiration.

Sketch it in your answer

Label the two guard cells, stomatal pore, and surrounding epidermal cells; show open and closed positions.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

What happens to stomata when guard cells become turgid?

Think first, then show answer

When guard cells become turgid, the stomatal pore opens, allowing carbon dioxide to enter and oxygen and water vapour to move out.

Common wrong answer

Stomata only release oxygen.

Why it loses marks: They also let carbon dioxide enter and water vapour escape.

Don't mix this up

Students confuse stomata with veins or think only oxygen enters through them.

Exam tip

Mention guard cells, the stomatal pore, and the direction of gas movement in your answer.

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

Draw and label stomata, explain opening and closing, or state how gas exchange occurs in leaves.

1
Enough for 1 mark
Stomata are tiny pores on leaves that allow gas exchange and transpiration.
2
Add for 2 marks
Example: A plant in sunlight often has open stomata for active photosynthesis.
3
Add for 3 marks
Stomata open and close with the help of guard cells.

MCQ Quiz

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