Why is photosynthesis considered an endothermic reaction ?
Photosynthesis is an endothermic reaction because sunlight energy is absorbed during the process of photosynthesis by the plants.
And our definition says that when in a reaction heat is absorbed it is termed as endothermic reaction
In this process, plants use the energy from the sun to convert carbon dioxide and water into glucose and oxygen. This reaction requires 15MJ of energy (sunlight) for every kilogram of glucose that is produced:
Sunlight+6CO2(g)+6H2O(l)⟶C6H12O6(aq)+6O2(g)