WAEC 2017 Biology · Question 44

Which of the following processes are associated with photosynthesis? I. Energy from sunlight is absorbed II…

Question

Which of the following processes are associated with photosynthesis? I. Energy from sunlight is absorbed II. Carbon dioxide is evolved III. Oxygen is given off IV. Glucose is synthesized

A.I and II only
B.I, II and IV only
C.I, III and IV only
D.I, II, III and IV

Answer: C. I, III and IV only

Explanation written with AI and checked against the answer key

Analyze the question: You are asked to pick the statements that correctly describe photosynthesis.

Concept: Photosynthesis is the process by which green plants use light energy, carbon dioxide and water to make glucose, releasing oxygen as a by-product.

Equation: 6CO₂ + 6H₂O → (light energy, chlorophyll) → C₆H₁₂O₆ + 6O₂

Check each statement:

I. Energy from sunlight is absorbed. TRUE. Chlorophyll traps light energy, which drives the light reaction.
II. Carbon dioxide is evolved. FALSE. Carbon dioxide is absorbed (used up) in photosynthesis. It is evolved (given off) in respiration. This is the trap in the question.
III. Oxygen is given off. TRUE. Oxygen is released when water is split (photolysis) in the light stage.
IV. Glucose is synthesized. TRUE. Carbon dioxide is reduced to glucose in the dark stage (Calvin cycle).

Correct statements: I, III and IV only.

Matching to the options: This is option C. Options A, B and D all include II, which is wrong.

Tip: Remember the direction of gases. In photosynthesis, CO₂ goes in and O₂ comes out. In respiration, O₂ goes in and CO₂ comes out. When you see "carbon dioxide is evolved", think respiration, not photosynthesis.

AI can make mistakes. Report anything that looks wrong.