Photosynthesis in 5 Minutes — Free Quick Revision
Learn Photosynthesis in about 5 minutes — a free bite-sized module with a clear explanation, a worked example and a quick quiz for Indian students.
TL;DR: Learn Photosynthesis in about 5 minutes — a free bite-sized module with a clear explanation, a worked example and a quick quiz for Indian students.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
Plants use sunlight, water, and CO₂ to make glucose (food) and oxygen. The equation: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂.
Biology · Class 10 · about 8 minutes
The Idea
Photosynthesis is the process by which plants convert light energy into chemical energy stored in food (glucose).
The overall equation is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ (glucose) + 6O₂
Photosynthesis happens in two main stages:
1. Light-Dependent Reactions (in the thylakoid membranes) - Chlorophyll absorbs photons from sunlight. - Water molecules are split, releasing electrons, hydrogen ions, and oxygen. - Energy is captured in molecules like ATP and NADPH.
2. Light-Independent Reactions (Calvin Cycle, in the stroma) - Uses ATP and NADPH from stage 1 to fix CO₂. - CO₂ is reduced into glucose molecules.
The oxygen we breathe is a byproduct—plants release it to the atmosphere. The glucose feeds the plant (and eventually the food chain).
Worked Example: Why Do Plants Need Light?
Problem. Explain why plants cannot survive in a dark room, even with water and CO₂ available.
Solution.
Without light, the light-dependent reactions cannot occur. Chlorophyll cannot absorb photons, so no electrons are excited and no ATP/NADPH is produced.
Without these energy carriers, the Calvin Cycle cannot proceed—CO₂ cannot be fixed into glucose. The plant cannot make its own food and will eventually starve.
While CO₂ and water are necessary *inputs*, light energy is essential to *power the process*. No light = no photosynthesis = no food = plant death.
Quick Quiz
Answer each one before reading the explanation beneath it.
1. Where does the oxygen produced in photosynthesis come from?
- From CO₂ in the air
- From water (H₂O) molecules — correct
- From glucose
- From soil nutrients
From water (H₂O) molecules
2. Which stage of photosynthesis requires light?
- Only the Calvin Cycle
- Only the light-dependent reactions
- The light-dependent reactions; the Calvin Cycle uses ATP/NADPH produced by them — correct
- Neither stage requires light directly
The light-dependent reactions; the Calvin Cycle uses ATP/NADPH produced by them
3. What would happen if a plant is kept in a room with plenty of CO₂ and water but no light for a week?
- It would grow faster without light competing for resources
- It would survive indefinitely
- It would gradually weaken and eventually die — correct
- Nothing—light is not essential for plants
It would gradually weaken and eventually die
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