10.3.18 — Photosynthesis: Core
Cambridge IGCSE Chemistry (0620) · Papers 2, 3 & 4 Style · 15 Questions · 32 Marks
Score
0 / 32
Section A
Word Equation
Q1–5
Section B
Conditions
Q6–10
Section C
Environment
Q11–15
Section A: The Word Equation
Questions 1–5
State the word equation for photosynthesis.
💡 This is a guaranteed 2-mark question in Paper 2. Both sides must be complete.
In the word equation for photosynthesis, identify the two reactants and state where each enters the plant.
💡 A common 'application' twist — connects the word equation to plant biology.
In the word equation for photosynthesis, identify the two products and state what happens to each one.
💡 Tests understanding of product fate — where does glucose go? Where does oxygen go?
A student writes the following word equation for photosynthesis: 'glucose + oxygen → carbon dioxide + water' Is the student correct? Explain your answer.
💡 Classic error-spotting question. Tests conceptual understanding, not just recall.
Carbon dioxide and water are the reactants in photosynthesis. Name the form of energy that drives this reaction and state where in the plant it is captured.
💡 Bridges the word equation to the conditions — perfect link question.
Section B: The Conditions
Questions 6–10
State two conditions required for photosynthesis to occur.
💡 A classic 2-mark recall question. Two distinct conditions needed.
Explain the role of chlorophyll in a leaf.
💡 A 'purpose/function' question. Two marks = two distinct points.
A variegated leaf (partly green, partly white) is used in a starch test. Predict and explain the result.
💡 A classic Paper 6 / Paper 3 practical prediction question.
A plant is kept in complete darkness for 48 hours before a starch test. Predict the result and explain why.
💡 Tests the 'light energy' condition directly.
Describe the experimental steps a student would take to test a leaf for the presence of starch.
💡 A classic Paper 3/6 practical method question. 3 marks = 3 key steps minimum.
Section C: Environmental Impact
Questions 11–15
Explain how photosynthesis helps to reduce the greenhouse effect.
💡 Directly links biology to environmental chemistry. A high-frequency exam question.
Deforestation (cutting down large areas of forest) is linked to an increase in atmospheric carbon dioxide levels. Explain why, using your knowledge of photosynthesis.
💡 An application question linking photosynthesis to real-world environmental concerns.
The graph below shows CO₂ concentration over 12 months in a forest. It dips in summer and rises in winter. Explain this pattern using your knowledge of photosynthesis.
💡 A data interpretation question — very common in Paper 4.
Suggest why planting new forests (reforestation) is recommended as a strategy to combat climate change.
💡 An evaluation question — students must connect photosynthesis to a real solution.
A scientist claims: 'Photosynthesis is the most important chemical process on Earth.' Evaluate this claim by considering: (a) the role of photosynthesis in the carbon cycle, and (b) how it supports all food chains.
💡 An extended writing / evaluation question. Paper 4 style. Look for balance and scientific justification.
📊 Exam Performance Summary
Section A
0/9
0%
Section B
0/11
0%
Section C
0/12
0%
Grade Boundary Guide
🌿 Key Examiner Reminders
- • The word equation: carbon dioxide + water → glucose + oxygen
- • Conditions: light energy + chlorophyll (not CO₂ / water)
- • Photosynthesis removes CO₂ → reduces the greenhouse effect
- • Iodine test: blue-black = starch present; orange-brown = absent
- • Ethanol must be heated in a water bath — never over a naked flame
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