Photosynthesis Questions & MCQ — Practice with Answers
Free photosynthesis MCQ questions with answers, based on analysis of past PSLE papers, MOE syllabus requirements, and common exam mistakes.
- Formally introduced in Primary 5 under the Energy theme
- Tested in both PSLE Booklet A (MCQ) and Booklet B (open-ended)
- 2024 PSLE trend: application questions combining photosynthesis with other topics
Key Concepts
What is photosynthesis?
Green plants make their own food using sunlight, water, and carbon dioxide. They produce glucose (the food) and release oxygen.
The word equation
Carbon dioxide + Water → Glucose + Oxygen (in the presence of light and chlorophyll)
PSLE tip: Always write "in the presence of chlorophyll" in open-ended answers — leaving it out loses marks.
Where does it happen?
In the leaves — specifically inside chloroplasts. The green pigment chlorophyll inside chloroplasts traps light energy. Gases move in and out through tiny pores called stomata on the underside of leaves.
Day vs. night
During the day: plants do both photosynthesis and respiration — but photosynthesis is faster, so they release more oxygen overall.
At night: no light means no photosynthesis. Only respiration happens, so plants take in oxygen and release carbon dioxide.
The starch test experiment
A classic PSLE experiment: cover part of a leaf with aluminium foil, leave the plant in sunlight, then test with iodine. The uncovered part turns blue-black (starch present). The covered part stays brown (no starch). This proves light is needed for photosynthesis.
Key Terms for PSLE
- Photosynthesis
- The process by which green plants make food (glucose) using sunlight, water, and carbon dioxide in the presence of chlorophyll.
- Chlorophyll
- The green pigment found in chloroplasts that traps light energy for photosynthesis.
- Chloroplasts
- Structures in plant cells where photosynthesis takes place. Found in the green parts of the plant, mainly in leaves.
- Stomata
- Tiny pores found on the underside of leaves. They allow gases (carbon dioxide and oxygen) and water vapour to move in and out.
- Glucose
- The food that plants produce during photosynthesis. Excess glucose is converted to starch for storage.
- Starch
- The stored form of food in plants. Tested using iodine solution — turns blue-black when starch is present.
Common Misconceptions
We reviewed PSLE marking schemes and student answer scripts to identify the mistakes that cost marks most often.
“Plants get food from the soil.” Plants absorb water and minerals from the soil — but they make their own food through photosynthesis. Glucose is the food. Water, carbon dioxide, and sunlight are just the ingredients.
“Plants don't respire — only animals do.” Plants carry out both photosynthesis and respiration. Respiration happens 24/7. Photosynthesis only happens with light. During the day, photosynthesis is faster — so the overall effect is oxygen out.
“Chlorophyll and chloroplast are the same thing.” Chloroplast is the structure (“factory”) where photosynthesis happens. Chlorophyll is the green pigment (“worker”) that traps light energy. PSLE expects students to tell them apart.
“Oxygen is the food that plants make.” Oxygen is a by-product, not the food. Glucose is the food — it gets stored as starch and broken down later for energy.
Practice Questions
Practice photosynthesis questions with answers below — great for revision. Each question is modelled on common PSLE patterns, with a detailed explanation covering why wrong answers are wrong — not just the right one.
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