Photosynthesis Process

Study Notes

Photosynthesis is the process of converting energy-poor inorganic compounds (CO2 and water) into energy-rich carbohydrates (glucose) using light energy.
Chlorophyll and other photosynthetic pigments absorb light energy and convert it into chemical energy.
The reactants of photosynthesis are carbon dioxide, water, and light, while the products are glucose and oxygen.

Water appears on both sides of the equation because it is used as a reactant in some reactions and released as a product in others.
There is no net yield of H2O, allowing the summary equation of photosynthesis to be simplified.
Photosynthesis is the opposite of aerobic respiration, with photosynthesis using the products of respiration and respiration using the products of photosynthesis.

Photosynthesis occurs only during daytime, while respiration occurs day and night.
During darkness, leaves and other actively metabolizing cells respire and utilize oxygen, releasing carbon dioxide.
At dawn and dusk, the rate of photosynthesis and respiration may equal each other, resulting in no net gas exchange between the leaves and the atmosphere (compensation point).
As light intensity increases, the rate of photosynthesis increases, requiring more carbon dioxide, which respiration alone cannot supply.

Oxygen released during photosynthesis comes from water and is an important source of atmospheric oxygen.
Van Niel hypothesized in the 1930s that plants split water as a source of hydrogen, releasing oxygen as a by-product.
This hypothesis was later confirmed by scientists in the 1940s using isotopic tracers.

Water is one of the raw materials of photosynthesis, along with carbon dioxide.
Hydrogen produced by splitting water reduces NADP to NADPH2, which is used to reduce CO2 to form sugar during dark reactions.