Photosynthesis Process

Photosynthesis

• 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.

Photosynthetic Reactants and Products

• 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.

Comparison with Respiration

• 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

• 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.

Role of Water in Photosynthesis

• 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.