Photosynthesis and Rate  Aims:  Must be able to outline the factors that affect the rate of photosynthesis in plants.  Should be able to explain why these factors affect photosynthetic rate.  Could be able to outline the energy transfers involved in environments.

Factors Affecting Photosynthetic Rate  The rate at which plants can make food (the photosynthetic rate) is dependent on environmental factors.  These include:  the amount of light available.  the level of carbon dioxide (CO 2 ).  the temperature.

Factors Affecting Photosynthetic Rate  The effect of light intensity on photosynthetic rate is shown.  Experiment was carried out at a constant temperature and constant carbon dioxide level.  The rate of photosynthesis increases exponentially with light intensity until a maximum rate is achieved.  At this point increasing the light intensity has no effect on photosynthetic rate and the rate of photosynthesis reaches a plateau. Light intensity vs photosynthetic rate Rate of photosynthesis (mm 3 CO 2 cm -2 h -1 ) Units of light intensity (arbitrary scale)

Light intensity, CO 2, and temperature vs photosynthetic rate Rate of photosynthesis (mm 3 CO 2 cm -2 h -1 ) Units of light intensity (arbitrary scale) Increasing the temperature when CO 2 is limiting has little effect on photosynthetic rate. Factors Affecting Photosynthetic Rate  Photosynthetic rate increases as the CO 2 concentration increases.  At high concentrations, the rate of photosynthesis begins to slow as limiting factors other than CO 2 become important.  An increase in temperature increases photosynthetic rate because of its effect on enzyme activity.  Temperatures exceeding the optimum will decrease due to denaturation of enzyme High CO 2 at 30°C High CO 2 at 20°C Low CO 2 at 30°C Low CO 2 at 20°C

Action Spectrum  An action spectrum profiles the effectiveness of different wavelength light in fueling photosynthesis. It is obtained by plotting wavelength against some measure of photosynthetic rate (e.g. CO 2 production). The action spectrum closely matches the absorption spectrum for the photosynthetic pigments Action spectrum for photosynthesis (Effectiveness of different wavelengths in fueling photosynthesis) Rate of photosynthesis (as percent of rate at 670 nm) Wavelength (nm)

Limiting Factors  Light Intensity, Carbon dioxide concentration, Temperature or chlorophyll concentration (affected by the amount of Nitrogen present) are the main LIMITING FACTORS of photosynthesis.  The above factor that is furthest from it’s optimum level for photosynthesis will control the amount of photosynthesis that takes place.  E.g. if the temperature of the plant is furthest from it’s optimal level then the increasing the amount of carbon dioxide and light will not affect the rate of photosynthesis.

Questions  Biozone Book:Answer questions from p49 Complete p

Summary of Energy Transformations  Sunlight is primary source of energy in Autotrophs and Heterotrophs:  Sunlight energy – chemical energy in Glucose (PHOTOSYNTHESIS).  Chemical energy released to produce ATP (RESPIRATION) [more easily transported form].  Can be stored as GLYCOGEN in animals or as FAT in adipose cells when liver is full, STARCH in plants (mostly roots).  ATP releases energy as required for growth, repair, communication, movement, Active Transport, reproduction and biosynthesis.