Question

Although photosynthesis generates ATP, plants also generate ATP by respiration. Explain why this is necessary.

Answer 1

Because the ATP created by photosynthesis in the chloroplasts is only used to create sugars from water and carbon dioxide. It is only their source of 'food'.
Why?
This has to do with the evolutionary history of plants.The endo-symbiotic theory states that it is likely a primitive cell that used to feed itself by phagocytoses of bacteria (eating them, you might say) once tried to 'eat' a photosynthesis performing bacterium but failed to digest it. This bacterium continued to perform photosynthesis withing the cell, thus providing the cell with food.
Now, before the cell ate the photosynthetic bacteria, it needed a system to produce all the proteins etc that it needed build up it's cell organelles etc. You see, this part is still used to build the proteins the cell needs, and ATP is needed for that. It is generated by burning sugar. The sugar created by photosynthesis that is.

Its kind of hard to explain, but I hope I made it understandable.

Answer 2

ok thx