Q.A tree is believed to be releasing oxygen during night time. Do you believe the truthfulness of this statement? Justify your answer by giving reasons.
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Start your 14-day free trial to unlock the full solution →The claim is not scientifically justified for ordinary trees: oxygen evolution needs light (it comes from the photolysis of water in the light reactions), so in the dark, a tree only respires, taking in O2 and releasing CO2, not the other way round.
Oxygen is released by a plant specifically as a by-product of the light reactions of photosynthesis, where light energy is used to split (photolyse) water molecules at Photosystem II: 2H2O → 4H+ + 4e- + O2. This process is strictly light-dependent — without light there is no photolysis of water, and therefore no O2 evolution — regardless of whether the plant uses the C3, C4, or CAM pathway of carbon fixation. (Even CAM plants, which do open their stomata and take up CO2 at night as an adaptation for arid conditions, only FIX carbon at night; their light reactions, and hence O2 release, still happen only during the day when light is available.)
At night, in the absence of light, photosynthesis (and thus O2 release) stops entirely in the plant, while cellular respiration continues around the clock in all living cells of the plant. Respiration consumes O2 and releases CO2 as it breaks down stored sugars to generate ATP. So during the night, a tree is a net consumer of oxygen and a net releaser of carbon dioxide, not the reverse.
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