What is photosynthesis?

In one line

The rule

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose, using sunlight, carbon dioxide, and water, and releasing oxygen. (NCERT)

The formula is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ Where:

• CO₂ = carbon dioxide (from air)
• H₂O = water (from soil)
• C₆H₁₂O₆ = glucose (food for the plant)
• O₂ = oxygen (released into air)

Let's understand it simply

Imagine a plant as a tiny kitchen. But instead of a gas stove, it uses sunlight to cook. The plant takes in water from the soil through its roots. It also breathes in carbon dioxide from the air through tiny holes in its leaves (called stomata). With the help of sunlight, the green part of the leaf (chlorophyll, like a solar panel) mixes these ingredients. The plant makes sugar (its food) and gives out oxygen as a waste.

Think of rolling a roti: you need flour, water, and heat. For the plant, the flour is carbon dioxide, the water is from the soil, and the heat is sunlight. The plant's leaf is like the tawa (pan) where everything comes together.

How it works

1. The plant absorbs water from the soil through its roots.
2. Leaves take in carbon dioxide from the air through stomata (tiny pores).
3. Sunlight falls on the leaves. The green pigment chlorophyll captures this light energy.
4. Inside the leaf, the plant uses sunlight energy to split water into hydrogen and oxygen.
5. The hydrogen joins with carbon dioxide to make glucose (sugar).
6. Oxygen is left over and goes out into the air through the stomata.

The story behind it

The word “photosynthesis” comes from Greek: "photo" means light, and "synthesis" means putting together. Scientists first noticed that plants could make food using sunlight in the late 1700s. Joseph Priestley, an English scientist, found that plants could "refresh" air for a candle to burn again. Later, Jan Ingenhousz showed that sunlight was needed for this process. The big formula was worked out over many years, with help from many scientists. One fun fact: the green colour in leaves, chlorophyll, is key for trapping sunlight.

Where you see it in real life

• A potted tulsi plant on your window: It grows well in sunlight, but looks weak in the shade. This is because it needs sunlight for photosynthesis.
• Crops in the field: Farmers wait for sunny days because crops grow faster with more photosynthesis.
• Aquarium plants: Bubbles of oxygen rise from underwater plants when sunlight hits them — that’s photosynthesis in action.
• A mango tree giving fruits: The tree uses photosynthesis to make the sugar in mangoes.
• Algae in a pond: Green scum on water is algae, making food by photosynthesis.
• Breathing fresh air under a tree: The oxygen you enjoy is made by photosynthesis.

Why it matters

• All food chains start here: Every living thing, from goats to humans, depends on plants making food by photosynthesis.
• Oxygen for breathing: The oxygen we breathe comes from this process.
• Controls carbon dioxide: Plants take in CO₂, helping keep the air clean.
• Basis for farming: Understanding photosynthesis helps farmers grow better crops.

Worked example

Let’s say a plant has these ingredients:

• 6 molecules of CO₂
• 6 molecules of H₂O
• Sunlight

What does it make?

Step 1: Write the formula    6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂
Step 2: Count the inputs     6 CO₂, 6 H₂O, sunlight
Step 3: Outputs              1 glucose (C₆H₁₂O₆), 6 oxygen (O₂)
Step 4: Meaning              Plant makes 1 unit of food and releases 6 units of oxygen

Common mistakes

• Thinking plants only need water: Plants also need sunlight and carbon dioxide.
• Forgetting about oxygen: Plants give out oxygen during photosynthesis, not just at night.
• Believing only leaves do it: Mostly leaves, but green stems and some algae also photosynthesise.
• Mixing up food and energy: Plants make food (glucose), not energy directly. They later use this food for energy.

Remember it

Plants use sunlight, water, and air to make food and oxygen — that’s photosynthesis!