MCQ Detailed View

Photosynthesis is a vital biological process in which green plants, algae, and certain bacteria convert carbon dioxide (CO₂) and water (H₂O) into glucose (C₆H₁₂O₆) and release oxygen (O₂) using the energy from sunlight. The source of oxygen released during photosynthesis is water, not carbon dioxide, salts, or glucose.

Process of Oxygen Production:

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   Light-Dependent Reactions:

   
   
   
   
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     Occur in the thylakoid membranes of chloroplasts.

     
     
   
   
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     Photolysis of water takes place, where light energy splits water molecules (H₂O) into:

     
     
     
     
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       Hydrogen ions (H⁺)

       
       
     
     
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       Electrons (e⁻)

       
       
     
     
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       Oxygen gas (O₂)

       
       
     
     
     
     
   
   
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     The electrons and hydrogen ions are used in later stages to produce energy-rich molecules (ATP and NADPH).

     
     
   
   
   
   


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   Release of Oxygen:

   
   
   
   
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     The oxygen atoms from water molecules combine to form O₂, which diffuses out of the plant into the atmosphere.

     
     
   
   
   
   

Importance of Water as the Oxygen Source:

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  Water acts as an electron donor in the light reactions of photosynthesis.

  
  


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  Without water, plants cannot produce oxygen or drive the formation of sugars efficiently.

  
  


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  This process is fundamental to maintaining Earth’s oxygen balance, supporting life forms that depend on aerobic respiration.

  
  

Why Other Options Are Incorrect:

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  Salts and Minerals: Essential for plant nutrition but do not directly release oxygen.

  
  


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  Glucose: A product of photosynthesis, not a reactant that produces oxygen.

  
  


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  Carbon dioxide: Provides the carbon for glucose, but oxygen atoms from CO₂ remain bound in sugar molecules.

  
  

Thus, the correct answer is Option A: Water, as it is the true source of the oxygen released during photosynthesis in plants and algae.