LESSON 03 · LIFE
How do plants make food?
The short answer
Plants make their own food through photosynthesis. Leaves capture sunlight and use its energy to turn water and carbon dioxide into sugar. Oxygen is released into the air as a by-product.
Leaves are food factories
Plants do not eat the way animals do. Instead, their leaves make sugar, which gives the plant energy and the material it needs to grow. The green color comes from chlorophyll, a pigment inside tiny structures called chloroplasts.
The ingredients
Photosynthesis needs three things: light energy from the Sun, water drawn up from the soil through the roots and stem, and carbon dioxide from the air, which enters through tiny openings in the leaves called stomata.
The recipe
Inside the chloroplasts, light energy is used to combine water and carbon dioxide into glucose, a kind of sugar. As a word equation: carbon dioxide + water → glucose + oxygen, powered by light and made possible by chlorophyll.
Why leaves are green
Chlorophyll absorbs mostly red and blue light and uses that energy. It reflects much of the green light, and that reflected green light is what reaches our eyes.
Why it matters
Photosynthesis releases the oxygen we breathe and makes the food at the start of almost every food chain. Plants also use some of the sugar they make for respiration, which releases the energy they need to live and grow.
Try it at home
Watch a leaf make bubbles
You will need
- Two clear glasses of water
- Two fresh leaves of the same kind, such as spinach
- A sunny windowsill and a dark cupboard
- A magnifying glass (optional)
What to do
- Put one leaf in each glass so that it is fully under water.
- Place one glass in bright sunlight and the other in a dark cupboard.
- After one to two hours, look closely at the surface of each leaf.
- Compare how many tiny bubbles you see on each leaf.
SafetyAsk an adult before picking leaves, and wash your hands after handling plants.
What's happening?
In sunlight, the leaf keeps photosynthesizing and releases oxygen, which can collect as small bubbles. Some bubbles are simply air that was already dissolved in the water, which is why the leaf in the dark cupboard is an important comparison. More bubbles on the leaf in the light suggest that light makes a difference.
Key words
- Photosynthesis
- The process plants use to make sugar from light, water, and carbon dioxide.
- Chlorophyll
- The green pigment that absorbs light energy.
- Stomata
- Tiny openings in leaves that let gases in and out.
- Glucose
- A simple sugar that stores energy.
Check your understanding
Which gas do plants take in for photosynthesis?
Carbon dioxide, which enters through the stomata in their leaves.
Why do we keep one leaf in the dark?
It is the comparison, or control. Comparing the two leaves shows whether light makes a difference.
What does chlorophyll do?
It absorbs light energy, mostly red and blue light, which the plant uses to make sugar.