3.8 SL Photosynthesis Equation: Carbon Dioxide + water oxygen +

3.8 SL Photosynthesis Equation: Carbon Dioxide + water  oxygen + glucose 6 CO2 + 6 H2O  6O2 + C6H12O6 State that: 3.8.1 Photosynthesis involves the conversion of light energy into chemical energy 3.8.2 Light from the sun (white light) is composed of a range of wavelengths (colors) 3.8.3 Chlorophyll is the main photosynthetic pigment located in the chloroplast (have mitochondria) 3.8.5 Light energy is used to form ATP and to split water (hydrolysis) to form hydrogen and oxygen 3.8.6 ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules 3.8.4 Outline the differences in absorption between red, blue and green light by chlorophyll -absorbs most at the red and blue ends of spectrum -reflects most of green part of spectrum 3.8.6 Explain that the rate of photosynthesis can be measured directly by the production of oxygen or uptake of carbon dioxide, or indirectly by an increase in biomass -The rate of photosynthesis can be measured by changes in the amounts of inputs (CO2) or outputs (O2 or glucose) of the photosynthesis equation -Water cannot be measured as it is involved in a number of essential processes besides photosynthesis (e.g. condensation and hydrolysis reactions) Measuring CO2 Uptake -CO2 uptake can be measured by placing plant in an enclosed space with water containing hydrogen carbonate to provide CO2 -Carbon dioxide interacts with the water molecules, producing bicarbonate and hydrogen ions, which increases the acidity of the resulting solution -The change in pH can therefore provide a measure of CO2 uptake by a plant (increased CO2 uptake = more alkaline pH) -Layer of oil on surface can prevent CO2 in air from dissolving in the water Measuring O2 Production -O2 production can be measured by submerging a plant in an enclosed space with water attached to a sealed gas syringe -Any oxygen gas produced will bubble out of solution, thus O2 production can also be measured by a change in water level (via the position of the meniscus) Measuring Biomass (Indirect) -Glucose production can be indirectly measured by a change in a plant's biomass (weight) -This requires the plant to be completely dehydrated prior to weighing to ensure the change in biomass reflects a change in organic matter and not water content -An alternative method for measuring glucose production is to determine the change in starch levels in a plant (glucose is stored as starch) -Starch can be identified via iodine staining (resulting solution turns purple) and quantitated using a colorimeter