Photosynthesis
- CBSE · NCERT Class 10, Ch 5 Life Processes
- ICSE Class 10, Unit 2 Plant Physiology
Photosynthesis is the process in which green plants use light energy, trapped by chlorophyll, to make glucose from carbon dioxide and water, giving out oxygen.
It happens in the chloroplasts of green leaves. Carbon dioxide enters through stomata, tiny pores in the leaf. Water comes up from the soil. The work runs in two phases:
- Light phase, which ICSE calls photochemical: chlorophyll takes in light. Water splits and gives off oxygen. The cell makes ATP, a step called photophosphorylation.
- Dark phase, which ICSE calls biosynthetic: hydrogen joins carbon dioxide to form glucose. So carbon dioxide is reduced.
NCERT lists the same work as three events: light absorbed, water split, carbon dioxide reduced. Spare food is stored as starch.
A small example
The balanced equation is 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂, with sunlight and chlorophyll written on the arrow. Why 12 water molecules on the left but 6 on the right? The oxygen comes from splitting water. New water forms in the dark phase.
Where marks go
In CBSE, Question 1 of the 2026-27 Science sample paper asks what happens to carbon dioxide and water as glucose forms. The board's Science marking scheme for 2026-27 gives the 1 mark to one option: carbon dioxide gains hydrogen, while water loses electrons. It tests the events, not just the word equation.
In ICSE, the 2025 Biology paper gave 1 mark for the equation. CISCE's report on the 2025 ICSE Biology paper names what went wrong: water left out, the equation not balanced, or a condition missing. It wants sunlight above the arrow, chlorophyll below it, and water on both sides. The 2027 specimen paper asks for the same equation in its draft marking scheme. The 2024 paper wanted "photophosphorylation", and its report names "photolysis" as a wrong answer given.
Sources
Facts last checked against these sources on 30 September 2026.
- Science, Class X (2026-27), Chapter 5: Life Processes · NCERT
- Science (086) Marking Scheme, Class X 2026-27 - Question 1 · CBSE Academic Unit
- Science (086) Sample Question Paper, Class X 2026-27 - Question 1 · CBSE Academic Unit
- ICSE Biology syllabus, Examination Year 2028 edition (January 2026), Class X unit 2 · CISCE
- Analysis of Pupil Performance, ICSE Biology 2025 (October 2025) - Question 3(i) · CISCE
- Analysis of Pupil Performance, ICSE Biology 2024 (November 2024) - Question 1(ii) · CISCE
- ICSE 2027 Biology specimen question paper and draft marking scheme - Question 7(ii) · CISCE
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