Photosynthesis is a metabolic pathway consisting of light-dependent and light-independent reactions. Overall, water and carbon dioxide are used to produce carbohydrates, with oxygen as a waste product.
• Photosynthesis is anendergonic process of carbon reduction• Cell respiration is anexergonicprocess of carbon oxidation.• Photosynthesis can be considered anabolic, while respiration is catabolic.
An Overview• Light-dependent reactions- – Occurs in the thylakoids and grana of chloroplasts – Solar energy is converted to chemical energy – Chlorophyll drives the transfer of electrons and hydrogen from water to the electron acceptor NADP+ – Oxygen is released when water splits (photolysis) – ATP is formed during the light reactions through chemiosmosis by photophosphorylation – Products include: NADPH and ATP
An Overview• Light-independent reactions – Involves the Calvin Cycle – Occurs in the stroma – Carbon dioxide is incorporated into existing organic compounds by carbon fixation – These compounds are then reduced to form carbohydrates – Reducing power and chemical energy comes from NADPH and ATP, products of the light-dependent reactions – Products include: organic molecules
Factors that affect photosynthesisThere are many steps in the reactions of photosynthesis, each requiring optimal conditions for maximum activity. Whichever factor is closest to the minimum is known as the limiting factor. It will therefore slow the whole process down.
Factors that affect photosynthesisFactor EffectLight Intensity Needed for photoactivation of electrons and photolysis of water. Low light results in low production of protons, low activity of proton pumps and low recycling of hydrogen ionsCarbon dioxide Needed for carboxylation of RuBP in the Calvin Cycle.concentration Low CO2 results in low production of glycerate-3-phospate (G3P) and therefore low yield of triose phosphate (TP).Temperature As an enzyme-controlled series of reactions, photosynthesis has an optimum temperature. Low temperature gives slower reactions due to lower energy, high temperatures lead to denaturation of enzymes.
Action Spectrum• The action spectrum of photosynthesis is the range of wavelengths of light over which photosynthesis is most active.• The effectiveness of different wavelengths in fuelling photosynthesis shows that red and blue/violet influence the rate more than the other colors.
Absorption Spectrum• Shows the amount of light that is absorbed by the different pigments• Green light is poorly absorbed whereas red and blue/violet is absorbed well.