Question

Oxygen gas is one of the products of photosynthesis. Which reactant is the source for oxygen gas and how is it released?

• A. Water, released when sunlight splits it into oxygen and hydrogen ions
• B. Glucose, released when glucose is broken down into carbon dioxide gas, oxygen gas and water
• C. Carbon dioxide, released when sunlight splits it into carbon and oxygen gas
• D. Electrons, released when they strike the chloroplasts
• E. NADPH, released when NADPH breaks down into is component elements

Answer 1

The correct option is A Water, released when sunlight splits it into oxygen and hydrogen ions

Green plants capture energy and convert it into chemical energy by the process known as photosynthesis. During photosynthesis, carbon dioxide and water are transformed into simple carbohydrates and oxygen is liberated into the atmosphere.

light

6CO₂ + 12H₂O ----------------> C₆H₁₂O₆ + 6O₂

chlorophyll

Water is also used as a source of hydrogen required for reduction of carbon dioxide to form carbohydrate.

Water is oxidised in presence of light and chlorophyll. Hydrogen is removed from water and oxygen is released as follows:

light

4‎H₂0 ---------------> 2‎H₂0 + 4H⁺ + 4e⁻ + O₂

chlorophyll

or,

2‎H₂O ----------------> 4H⁺ + 4e⁻ + O₂

Hence the source for oxygen gas is water and it is released when water splits in the presence of sunlight into oxygen and hydrogen ions.

So, the correct answer is 'Water, released when sunlight splits it into oxygen and hydrogen ions'.