Question

What is photosynthesis? Name the organelle and the organs in which photosynthesis takes place. Where does the oxygen liberated come from during this process? What happens to the carbohydrates which are not immediately used by the plant?

Hint:

Chloroplasts are the sites of photosynthesis; oxygen is released from water splitting.

Answer 1

Photosynthesis is the process by which green plants prepare their own food (glucose) using sunlight, carbon dioxide and water. It is an anabolic, endothermic process.
- Organelle: Photosynthesis takes place inside the chloroplasts which contain the green pigment chlorophyll.
- Organs: The main organs where photosynthesis occurs are the green leaves of the plant.
During photosynthesis, oxygen is produced from the photolysis of water molecules. The water molecules are split by sunlight into hydrogen and oxygen:
\[ 6CO_2 + 6H_2O \xrightarrow{\text{Sunlight, Chlorophyll}} C_6H_{12}O_6 + 6O_2 \] The oxygen released comes from water, not from carbon dioxide.
Carbohydrates that are not immediately used by the plant are stored as starch in leaves, stems, roots or fruits for later use.