An evidence of the occurrence of photosynthesis in an experiment is the?

Analyze the question: The question asks which observable sign shows that photosynthesis has taken place in an experiment.

Concept: Photosynthesis is the process by which green plants use light energy, carbon (IV) oxide and water to make glucose (food), releasing oxygen:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of light and chlorophyll)

Evaluate each option:

• A. Release of carbon (IV) oxide: Wrong. CO₂ is taken in during photosynthesis. Its release is a sign of respiration.
• B. Release of oxygen: Correct. Oxygen is a by-product that can be observed directly. In an aquatic plant experiment (e.g., Hydrilla or Elodea under a funnel in water), bubbles of gas collect in the test tube. The gas relights a glowing splint, which confirms it is oxygen.
• C. Formation of water molecules: Wrong. Water is a raw material that is used up. (Water is actually produced in respiration, not as the evidence of photosynthesis.)
• D. Formation and release of fructose: Wrong. The main product is glucose, which is converted to starch for storage. It is not released from the plant as fructose.

Answer: The release of oxygen is the easily observable evidence, so the answer is B.

Exam tip: Remember "Photosynthesis gives off O₂, respiration gives off CO₂." In experiments, the evidence for photosynthesis is usually one of two things:

1. Oxygen bubbles (aquatic plants), or
2. Starch present in a leaf (iodine turns blue-black).