What is photosynthesis and how does it work?

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 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 you are making roti in the kitchen. You need flour, water, and heat from the stove. In the same way, a plant needs three things: sunlight (like the stove), water (from the soil), and carbon dioxide (from the air). The green part of the leaf, called chlorophyll (the green pigment), acts like your hands mixing everything together.

The plant takes in sunlight through its leaves, drinks water from its roots, and breathes in carbon dioxide from tiny holes (called stomata) on the leaves. With all these, it cooks up food (glucose) for itself and gives out oxygen, which we need to breathe.

How it works

1. Sunlight hits the leaves: The green pigment, chlorophyll, absorbs sunlight.
2. Water is taken up by roots: Water travels from the soil, up the stem, to the leaves.
3. Carbon dioxide enters the leaf: Tiny holes (stomata) on the leaf let in carbon dioxide from the air.
4. Making food: Inside the leaf, sunlight energy helps join water and carbon dioxide to make glucose (sugar) and oxygen.
5. Food is stored: The plant keeps the glucose for energy and growth.
6. Oxygen is released: The extra oxygen goes out through the stomata into the air.

The story behind it

The word 'photosynthesis' comes from Greek: 'photo' means light, 'synthesis' means putting together. Scientists like Jan Ingenhousz (in the 1770s) showed that plants use sunlight to make food and give out oxygen. Before this, people did not know how plants grew or why they were green. Ingenhousz used simple water plants and sunlight to prove his idea. One human detail: he used bubbles from water plants to show oxygen was being made!

Where you see it in real life

• A potted tulsi plant on your window: It grows well in sunlight, making its own food by photosynthesis.
• A banyan tree in the park: Its huge leaves soak up sunlight and make food for the whole tree.
• Algae in a village pond: The green layer on water is full of algae, which also photosynthesise.
• A wheat field in Punjab: Crops grow tall and healthy by making food from sunlight, water, and air.
• A money plant in your house: Even indoors, it needs some sunlight to photosynthesise and stay green.
• A bottle garden or terrarium: Plants inside a closed bottle survive because they keep photosynthesising and recycling air.

Why it matters

• Gives us oxygen: Every breath you take comes from plants doing photosynthesis.
• Food for all: All our food (rice, dal, fruits, vegetables) starts with plants making glucose by photosynthesis.
• Keeps the air clean: Plants remove carbon dioxide from the air and add oxygen.
• Basis of life: All animals, including us, depend on plants for food and oxygen.

Worked example

Let's say a plant uses 6 molecules of carbon dioxide and 6 molecules of water.

Given: 6CO₂ + 6H₂O + light energy
Step 1: Write the rule        6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
Step 2: Put in the numbers    6 carbon dioxide + 6 water + sunlight → 1 glucose + 6 oxygen
Step 3: Answer                The plant makes 1 molecule of glucose and 6 molecules of oxygen.

Common mistakes

• Thinking only leaves do photosynthesis: Mostly true, but some stems (like in cacti) can also photosynthesise.
• Forgetting sunlight is needed: No sunlight, no photosynthesis. Plants can't make food in the dark.
• Mixing up oxygen and carbon dioxide: Plants take in carbon dioxide and give out oxygen during photosynthesis.
• Believing all plants are green: Only green parts with chlorophyll can do photosynthesis. Non-green parts cannot.

Remember it

Plants use sunlight, water, and air to make food and give us oxygen — this is photosynthesis.