Question

Radioactive isotopes can be added to reactants to identify reaction pathways and the presence of radioisotope in products can be checked. In which of the following radioactively labelled isotope of oxygen in water is found in photosynthetic reaction?

• A. In glucose molecules
• B. In water
• C. In oxygen gas
• D. In ATP
• E. In carbon dioxide

Answer 1

The correct option is C In oxygen gas

During photosynthesis, water molecules serve as electron donor and splitting of water molecules in presence of Sunlight leads to the release of oxygen gas. Therefore, radioactive oxygen atoms of water molecule will be expressed as radioactive oxygen gas. Caron dioxide is fixed into glucose molecules using the energy of ATP formed during photophosphorylation. Water molecules do not serve as a source of oxygen atoms of the glucose molecule. Thus, the correct answer is C.