Inside a Leaf: The Food Factory
≈ 20 minGreen plants make their own food. The factory where that happens is the leaf, and every part of a leaf is shaped for the job.
| Feature | Why it helps |
|---|---|
| Broad, flat blade | Catches as much sunlight as possible |
| Very thin | Gases and light reach the inner cells quickly |
| Chlorophyll in tiny green packets called chloroplasts | Absorbs the light energy that drives food-making |
| Veins | Bring water up from the roots and carry the food away to the rest of the plant |
| Stomata — microscopic pores, mostly on the underside | Let carbon dioxide in and oxygen and water vapour out |
| Waxy cuticle on top | Waterproof layer that slows water loss |
The stomata are guarded by pairs of cells that swell to open the pore and shrink to close it. On a scorching Karoo afternoon a plant will close many of its stomata to save water — which also slows down its food-making. Every leaf lives with that trade-off.
Worked example. A learner notices that the leaves of a spekboom growing in full sun are thicker and smaller than the leaves of a fern growing in the shade of a stoep. Why?
- The fern gets little light, so a large, thin blade catches as much of it as possible.
- The spekboom gets plenty of light but little water, so a small, thick leaf loses less water through its stomata.
Both designs are answers to the same question — how do I catch enough light without drying out?
Which part of a leaf cell contains the green pigment that absorbs light energy?
What is the name of the microscopic pores, found mostly on the underside of a leaf, through which gases enter and leave?
A learner counts about 12 000 stomata on every square centimetre of the underside of a maize leaf. The underside has an area of 8 cm². About how many stomata does the leaf have altogether?
During a hot, dry afternoon in the Karoo, a plant closes many of its stomata. What is the trade-off it accepts by doing this?