ICSE Class 10 Biology: Photosynthesis — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: Define photosynthesis. Write the balanced equation.
  Ans: Photosynthesis is the process by which green plants synthesise carbohydrates (glucose) from carbon dioxide and water using sunlight energy, with oxygen released as a byproduct. Equation: 6CO₂ + 6H₂O → (sunlight, chlorophyll) → C₆H₁₂O₆ + 6O₂. It occurs in chloroplasts.
• Q: What are the conditions necessary for photosynthesis?
  Ans: Conditions: (1) Sunlight — provides energy for the reaction. (2) Chlorophyll — green pigment that absorbs light energy. (3) Carbon dioxide — obtained from atmosphere through stomata. (4) Water — absorbed by roots from soil. Optimum temperature: 25-35°C. Light intensity and CO₂ concentration are limiting factors.
• Q: Describe the light reaction and dark reaction of photosynthesis.
  Ans: Light reaction (in thylakoids/grana): Chlorophyll absorbs light energy → water is split (photolysis): 2H₂O → 4H⁺ + 4e⁻ + O₂. ATP and NADPH are produced. O₂ is released. Dark reaction / Calvin cycle (in stroma): CO₂ is fixed using ATP and NADPH from light reaction. CO₂ + RuBP → (RuBisCO) → PGA → G3P → glucose. Does not require direct light but needs products of light reaction.

Long Answer / Application Questions (4-6 Marks)

• Q: Draw a neat labelled diagram of a chloroplast.
  Ans: A chloroplast has: Outer membrane, Inner membrane, Stroma (fluid matrix where dark reactions occur), Thylakoids (flattened membrane sacs where light reactions occur), Grana (stacks of thylakoids), Lamellae/Stroma lamellae (connecting thylakoids between grana), DNA and ribosomes (in stroma).
• Q: What are stomata? How do they help in photosynthesis?
  Ans: Stomata are tiny pores on the lower epidermis of leaves, each surrounded by two kidney-shaped guard cells. Role in photosynthesis: (1) Allow CO₂ to enter the leaf for photosynthesis. (2) Allow O₂ (byproduct) to exit. (3) Regulate water loss (transpiration). Guard cells control opening/closing: turgid → stomata open, flaccid → stomata close.

Exam Tips for This Chapter

• Revise all definitions and laws from Photosynthesis — they are commonly asked as 1-2 mark questions
• Practice diagrams related to Photosynthesis — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Photosynthesis carries 8-12 marks in the board exam