Air for food
Carbon dioxide and starch.
What about air?
We know a leaf needs sunlight, water and chlorophyll. Air is also all around the leaf. One gas in air is carbon dioxide.
If part of a leaf has no carbon dioxide around it, what will happen to that part?
What this lesson covers
The idea
Carbon dioxide present in the air is essential for plants to prepare starch.
What about air?
We know a leaf needs sunlight, water and chlorophyll. Air is also all around the leaf. One gas in air is carbon dioxide.
If part of a leaf has no carbon dioxide around it, what will happen to that part?
- It makes starch as usual
- It does not make starch
- Air makes no difference to a leaf
The bottle experiment
Run the three stages in order. A teacher does this experiment.
Carbon dioxide is essential
The caustic soda solution absorbed the carbon dioxide inside the bottle. The part of the leaf inside made no starch. The part outside, in ordinary air, did.
Carbon dioxide present in the air is essential for plants to prepare starch.
- Part of the leaf | Carbon dioxide | After iodine
- Outside the bottle | From the air | Blue-black: starch
- Inside the bottle | Absorbed by caustic soda | Not blue-black: no starch
Notes
Carbon dioxide present in the air is essential for plants to prepare starch.
Check yourself
Why did the part of the leaf inside the bottle not turn blue-black?
What does the caustic soda solution do in the bottle?
Which gas of the air is essential for plants to prepare starch?
The part of the leaf outside the bottle turned blue-black. What does that show?
- That part had too much water. The difference was carbon dioxide, not water.
- The caustic soda solution absorbed the carbon dioxide, so no starch was made — correct. Yes! Without carbon dioxide no starch was made.
- That part of the leaf had no chlorophyll. It was part of the same leaf. The difference was carbon dioxide.
- It gives the leaf water. It absorbs carbon dioxide from the air in the bottle. It does not give water.
- It makes starch. It does not make starch. It absorbs carbon dioxide.
- It absorbs carbon dioxide — correct. Yes! That is why it is used.
- Carbon dioxide — correct. Yes! It is essential for preparing starch.
- Oxygen. Plants release oxygen when they make food. They need carbon dioxide to prepare starch.
- Nitrogen. The leaf needs carbon dioxide to prepare starch.
- It had no starch. Blue-black shows that starch is present.
- It had starch, made with carbon dioxide from the air — correct. Yes! It got carbon dioxide.
- It had no chlorophyll. The blue-black colour shows starch, which is made where chlorophyll is.