During photosynthesis, the oxygen in glucose is from?
(a) Water
(b) Carbon dioxide
(c) Both from ${{CO}_{2}}$ and water
(d) Oxygen in air

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Hint: This compound is very much essential for the process of photosynthesis because in its absence plants won’t be able to prepare their food and it also provides for the requirement of carbon and oxygen during photosynthesis.

Complete step by step answer:

When plants make the glucose molecule, they obtain the carbon and oxygen atoms needed from the carbon dioxide molecule, which is taken by the air through the stomata.

By the process of carbon fixation, the carbon dioxide is converted into sugars. This process involves two steps: light reaction, and dark reaction. The light reaction involves the absorption of light energy by the chlorophyll, conversion of light energy into chemical energy and finally splitting of a water molecule into hydrogen and oxygen. In dark reactions, light is not required for the reduction of carbon dioxide into glucose (carbohydrates).

                    Photosynthetic processes

Additional Information:
- ATP and NADPH2​ are produced in the light reaction which is utilized for carbon fixation during the dark reaction.
-Carbon fixation is an endothermic redox reaction
-Carbon dioxide doesn't have any hydrogen atom in it. So, plants use water as a source for hydrogen.
-Plants release oxygen into the air as a by-product of the photosynthetic reaction.

So, the correct answer is, ‘carbon dioxide’.


-Cornelis Bernardus van Niel (1897-1985) was a Dutch-American microbiologist.his study was based on purple sulfur bacteria and green sulfur bacteria. In 1931, he was the first scientist to demonstrate that photosynthesis is a light-dependent redox reaction.
-Organisms that photosynthesize are called photoautotrophs. Some of them, other than green plants are Rhodobacter capsulatus( a species of purple bacteria), Chromatium, Chlorobium, and several cyanobacteria.
-Chromatium is a genus of Gram-negative bacteria that are found in water. The cells are straight rod-shaped or slightly curved. They belong to the purple sulfur bacteria.
-Chlorobium is a genus of green sulfur bacteria also known as Chlorochromatium.