Photosynthesis and the Environment 6 CO 2 (g) + 6 H 2 O (l)  [CH 2 O] + 6 O 2(g) Net CO 2 uptake= photosynthetic CO 2 uptake – photorespiratory CO 2 evolution – respiratory CO 2 evolution Net O 2 evolution = photosynthetic O 2 evolution – photorespiratory O 2 uptake – respiratory O 2 uptake

Light Intensity and the Rate of Photosynthesis Irradiance – light intensity per unit area of leaf Light response curve shows the effect of increasing irradiance on the rate of photosynthesis Light-compensation point - CO 2 uptake equals CO 2 evolution Light-saturation point – occurs at the irradiance level at which the carbon fixation reactions reach a maximum overall rate

Temperature and the Rate of Photosynthesis The light reactions are not affected by temperature Calvin cycle is affected because of enzymes Optimal temperature is between 10 O C – 30 O C Above 40 O C enzymes may become denatured Influence of some factors on the rate of photosynthesis

Oxygen Concentration and the Rate of Photosynthesis High oxygen levels have an inhibitory effect on photosynthesis Competition between O 2 and CO 2 for the active sites on rubisco

Photosynthetic Efficiency Quantum yield: net CO 2 uptake per unit of light energy (photons) absorbed C 3 plants are more efficient at lower temperatures and C 4 plants are more efficient at higher temperatures

Sun Plants vs. Shade Plants Shade plants have thinner, broader and greener leaves Shade plants more efficient at harvesting light at low intensities Sun plants have a higher light-compensation point Sun plants have a higher light-saturation point

Cheaper New More Effective Solar Cells Imitate Photosynthesis - They employ synthetic pigments imitating the natural ones - Softpedia