Photosynthesis and the Environment

6 CO2 (g) + 6 H2O(l) [CH2O] + 6 O2(g)

Net CO2 uptake= photosynthetic CO2 uptake – photorespiratory CO2 evolution – respiratory CO2 evolution

Net O2 evolution = photosynthetic O2 evolution – photorespiratory O2 uptake – respiratory O2 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 - CO2 uptake equals CO2 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 10OC – 30OC• Above 40OC 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 O2 and CO2 for the active sites on rubisco

Photosynthetic Efficiency• Quantum yield: net CO2 uptake per unit of light energy

(photons) absorbed• C3 plants are more efficient at lower temperatures and

C4 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