MCQ Detailed View

Plants, like all living organisms, respire continuously to survive. During the day, they perform photosynthesis, a process where they take in carbon dioxide (CO₂) from the air and release oxygen (O₂) as a byproduct, using sunlight to produce energy-rich food molecules. However, at night, in the absence of sunlight, photosynthesis cannot occur because it depends on light energy to make glucose and oxygen.

Instead, plants switch entirely to cellular respiration, a process similar to that in animals. During respiration, plants intake oxygen from the air and use it to break down the glucose stored during the day. This process releases energy for cellular activities and produces carbon dioxide and water as waste products. The carbon dioxide is then released back into the atmosphere.

This means that at night:

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  Oxygen intake: Plants absorb oxygen through tiny openings on their leaves called stomata. Oxygen is essential for breaking down glucose to release usable energy in the form of ATP (adenosine triphosphate).

  
  


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  Carbon dioxide release: As a result of respiration, carbon dioxide is produced as a waste gas and expelled into the air.

  
  

It is important to note that while plants release oxygen during the day due to photosynthesis, at night the process reverses because there is no sunlight for photosynthesis to occur. However, the amount of carbon dioxide released by plants at night is relatively small compared to the oxygen they produce during the daytime. This is why plants are still considered net producers of oxygen.

In conclusion, at night, plants take in oxygen and release carbon dioxide, which is why option A (Oxygen – Carbon dioxide) is correct. This natural process demonstrates that plants, like animals, require oxygen for respiration to sustain life functions when photosynthesis is not active.