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BIO409H5 (3)
Chapter 9

Ch. 9 pt. 2

4 Pages

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Angela B Lange

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CH 9 pt 2 There is an optimal temperature for photosynthesisthe highest photosynthetic rates seen in response to increasing temperature represent the optimal temperature response when the optimal temperature for a given plant is exceeded photosynthetic rates decrease again it has been argued that this optimal temperature is the point at whichthe capacities of the various steps of photosynthesis are optimally balanced with some steps becoming limiting as the temperature decreases or increases what factors are associated with the decline in photosynthesis beyond the temp optimumrespiration rates increase as a function of temp not primary reasonmembranebound electron transport processes become unstable at high temps cutting off the supply of reducing power and leading to a sharp overall decrease in photosynthesis optimal temperatures have strong genetic adaptation and environmental acclimation componentsplants of different species growing in habitats with different temperatures have different optimal temps for photosynthesis and plants of the same species grown at different temps and then test for their photosynthetic responses show temperature optima that correlate with the temp at which they were grownplants grown at low temps maintain higher photosynthetic rates at low temps than plants grown at high temperatures These changes in photosynthetic rates in response to temp play an important role in plant adaptations to different environments plants are extremely plastic have been shown to live in Death valley and others at the other extreme of the Alpines In the C plant the quantum yield or light use efficiency remains constant with temp reflecting typical 4low rate of photorespiration In C plants the quantum yield decreases with temp reflecting a stimulation of photorespiration by 3temp and ensuring higher energy demand per net CO fixed 2C more common below 40 N like in terms of longitude and latitude and C species dominate about 4345 NPhotosynthetic Responses to Carbon Dioxide CO diffuses from the atmosphere into leaves first through stomata then through the intercellular air 2spaces and ultimately into cells and chloroplasts in the presence of adequate amounts of light higher CO concentrations support higher photosynthetic 2rates Low CO concentrations can limit the amount of photosynthesis in C plants 23Atmospheric CO concentrations keep rising 2 current atmospheric concentration of CO is almost twice the concentration that has prevailed during 2most of the last 420000 years Due to burning of fossil fuels such as coal oiland natural gas plants not used this higher level of atmospheric CO2 Greenhouse effectgreenhouse effect refers to the warming of Earths climate that is caused by the trapping of long wavelength radiation by the atmosphereconsequence of increase in atmospheric CO2The increased CO concentration and temperature associated with the greenhouse effect can influence 2photosynthesis at current CO concentrations photosynthesis in C plants is CO limited but this could change as 232atmospheric CO concentrations continue to rise 2
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