What it shows
A leaf has an epidermis, palisade cells full of chloroplasts, loose spongy cells with air spaces, veins and stomata. The layers are built to catch light and let gases move.
The science
The upper epidermis is covered by a waxy cuticle that reduces water loss. Beneath it are tightly packed palisade cells with many chloroplasts, where most photosynthesis happens. The spongy layer has air spaces so carbon dioxide can spread. Stomata, each controlled by two guard cells, open to let gases in and out and close to save water. Veins carry water up (xylem) and sugars away (phloem).
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Coloured foam sheets or thin thermocol layers
- Green and yellow clay
- Straws cut for vein tubes
- A cardboard base
- Glue and a pen
- Pins and labels
Safety
For this project: An adult must cut the foam and straws. Keep pins away from small children.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Cut a thick base strip of foam about 20 cm by 10 cm as the leaf block.
Stack five layers: cuticle and upper epidermis, palisade, spongy mesophyll, lower epidermis.
Add rows of tall green oval clay for the palisade cells.
Make irregular green shapes with gaps for the spongy cells.
Place a vein tube through the middle with straws, two colours for xylem and phloem.
Cut small gaps in the lower epidermis with a pair of bean-shaped guard cells.
Label each part and its job.
Add arrows for carbon dioxide in, oxygen out and water vapour out.
What you should see
A labelled cross-section showing six parts and the flow of gases through the stomata.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Where does most photosynthesis happen?
In the palisade layer.
2What controls the stomata?
The guard cells.
3Why are there air spaces in the spongy layer?
To let gases move through the leaf.
4What do xylem and phloem carry?
Water and minerals up, and food away.
Take it further
Peel a thin layer from a leaf and look for stomata under a microscope.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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