Photosynthesis — Class 10 Science Notes (Easy Explanation)
Key Points At A Glance
- Photosynthesis is how green plants make their own food (glucose) using sunlight.
- Equation: 6CO₂ + 6H₂O → (sunlight, chlorophyll) → C₆H₁₂O₆ + 6O₂.
- It takes place mainly in the chloroplasts of leaf cells, which contain chlorophyll.
- Raw materials are carbon dioxide, water and sunlight; products are glucose and oxygen.
- It has two phases: the light reaction and the dark reaction (Calvin cycle).
Have you ever wondered how a tiny seed grows into a huge tree without ever "eating" anything? The answer is photosynthesis — one of the most beautiful processes in nature, and a favourite topic in your Class 10 Science exam. Let's understand it step by step.
What Is Photosynthesis?
Photosynthesis is the process by which green plants prepare their own food using sunlight, carbon dioxide and water. The word itself explains it: photo means light and synthesis means to make. So photosynthesis literally means "making with light."
Because plants make their own food, they are called autotrophs. We humans cannot do this, which is why we depend on plants — directly or indirectly — for almost all our food.
The Photosynthesis Equation
You must remember this balanced equation for your exam:
- 6CO₂ + 6H₂O → (in the presence of sunlight and chlorophyll) → C₆H₁₂O₆ + 6O₂
In simple words:
- Carbon dioxide (from the air) + water (from the soil)
- in the presence of sunlight and chlorophyll
- produce glucose (the plant's food) + oxygen (released into the air).
Where Does It Happen?
Photosynthesis takes place mainly in the leaves, which is why leaves are sometimes called the "kitchen of the plant." Zooming in:
- Inside leaf cells are tiny structures called chloroplasts.
- Chloroplasts contain a green pigment called chlorophyll.
- Chlorophyll absorbs sunlight and starts the whole process.
This is also why most leaves are green — it's the colour of the chlorophyll inside them.
What Does a Plant Need? (Raw Materials)
For photosynthesis, a plant needs three things:
- Carbon dioxide — enters the leaf through tiny pores called stomata.
- Water — absorbed by the roots and carried up to the leaves.
- Sunlight — the energy source, captured by chlorophyll.
The Two Steps of Photosynthesis
Photosynthesis happens in two main phases.
1. The Light Reaction (Light-Dependent)
This step needs sunlight directly. Here:
- Chlorophyll absorbs light energy.
- Water splits into hydrogen and oxygen (this is where the oxygen we breathe comes from).
- Light energy is converted into chemical energy.
2. The Dark Reaction (Calvin Cycle)
Despite the name, this does not need darkness — it simply does not need light directly. Here the chemical energy made in step one is used to join carbon dioxide and hydrogen into glucose.
Why Photosynthesis Matters
Photosynthesis is not just an exam topic — it keeps the planet alive:
- It produces the oxygen almost all living things need.
- It removes carbon dioxide from the air, helping balance the atmosphere.
- It is the starting point of nearly every food chain on Earth.
Important Exam Questions
Practise writing these answers in your own words:
- Define photosynthesis and write its balanced equation.
- Why are green plants called autotrophs?
- Describe the role of chlorophyll and stomata.
- Differentiate between the light and dark reactions.
Quick Summary
- Photosynthesis = plants making food using sunlight, CO₂ and water.
- It happens in chloroplasts, using the green pigment chlorophyll.
- Products are glucose and oxygen.
Science topics like this one reward clear understanding plus repeated revision. To lock these points into memory, use the techniques in How to Study Smart for Exams. For a problem-solving subject that needs a very different approach, see our Quadratic Equations notes. You can explore every Science note and more study notes whenever you like.
Frequently Asked Questions
Photosynthesis is the process by which green plants use sunlight, carbon dioxide and water to make their own food (glucose) and release oxygen.
6CO₂ + 6H₂O, in the presence of sunlight and chlorophyll, gives C₆H₁₂O₆ (glucose) + 6O₂ (oxygen).
It takes place mainly in the chloroplasts inside the cells of green leaves. Chloroplasts contain the green pigment chlorophyll that traps sunlight.
Chlorophyll absorbs light energy from the sun and converts it into chemical energy. Without chlorophyll, the plant cannot capture sunlight to make food.
The raw materials are carbon dioxide, water and sunlight. The products are glucose (food) and oxygen, which is released into the air.
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