Chapter 7 Energy and Nutrient Relations Introduction Chapter 7 Energy and Nutrient Relations 1 Nutrients are the raw materials an organism must acquire from the environment to live The energy used by different organisms comes in the form of light organic molecules or inorganic molecules We generally group organisms on the basis of shared evolutionary histories creating taxa such as vertebrate animals insects coniferous trees and orchids We can also classify organisms by their trophic feeding biology Organisms that use inorganic sources of both carbon and energy are called autotrophs self feeders Photosynthetic autotrophs use carbon dioxide as a source of carbon and light as a source of energy to synthesize organic compounds molecules that contain carbon such as sugars amino acids and fats Chemosynthetic autotrophs synthesize organic molecules using carbon dioxide as a carbon source and inorganic chemicals such as hydrogen sulfide as their source of energy Heterotrophs other feeders are organisms that use organic molecules both as a source of carbon and as a Prokaryotes show more trophic diversity than do other groups of organisms Prokaryotes which have cells with no membrane bound nucleus or organelles include the bacteria The archaea are prokaryotes distinguished from bacteria on the basis of structural physiological and other biological features The protists are either photosynthetic or heterotrophic most plants are photosynthetic and all fungi and Prokaryotes include photosynthetic chemosynthetic and heterotrophic species Scientists discovered that energy production from light involving bacterial Rhodopsin is widely distributed in source of energy and the archaea animals are heterotrophic the oceans Bacterial rhodopsin from deep clear waters absorb light most strongly within the blue range of the visible spectrum while that from the shallow coastal waters absorbs most strongly in the green range 7 1 Photosynthetic Autotrophs Photosynthetic autotrophs synthesize organic molecules using CO2 as a source of carbon and light as an energy source The Solar Powered Biosphere the seasons wavelength Solar energy powers the winds and ocean currents and annual variation in sunlight intensity drives Light propagates through space as a wave with all the properties of waves such as frequency and When light interacts with matter it acts as particle Particles of light called photons bear a finite quantity of energy Longer wavelengths such as infrared light carry less energy than shorter wavelengths such as visible and ultraviolet light Chapter 7 Energy and Nutrient Relations 2 The main effect of infrared light on matter is to increase the motion of whole molecules which we measure as increased temperature Infrared light does not carry enough energy to drive photosynthesis Ultraviolet light carries so much energy that it breaks the covalent bonds of many organic molecules Ultraviolet light can destroy the complex biochemical machinery of photosynthesis Photosynthetically active radiation PAR is the light that we can see so called visible light with wavelengths between 400 700 nm carries sufficient energy to drive the light dependent reactions of photosynthesis but not so much as to destroy organic molecules Makes up 42 of the total energy content of the solar spectrum at sea level The energy actually available for photosynthesis amounts to about 26 of the total Infrared light accounts for about 46 and ultraviolet light for the remainder Measuring PAR surface each second with the time of day Ecologists quantify PAR as photon flux density the number of photons striking a square meter Light changes in quantity and quality with latitude with the seasons with the weather and Landscapes water and even organisms change with the amount and quality of the light Only the superficial euphotic zone receives enough light to support photosynthetic organisms Light changes in quality as well as quantity within the euphotic zone which ranges in depth from a few meters to about 100 m A mature temperate or tropical forest can reduce the total quantity of light reaching the forest floor to about 1 2 of the amount shining on the forest canopy Within the range of Photosynthetically active radiations leaves absorb mainly blue and red light and transmit mostly green light with a wavelength of about 550 nm Alternative Photosynthetic Pathways During photosynthesis the photosynthetic pigments of plants algae or bacteria absorb photons of light and transfer their energy to electrons Photosynthetic organisms convert the electromagnetic energy of sunlight into energy rich organic molecules the fuel that feeds most of the biosphere Three specific biochemical pathways carry out this energy conversion C3 Photosynthesis In the photosynthetic pathway used by most plants and all algae the CO2 combines with a five carbon compound called ribulose biphosphate RuBP The product of this reaction which is catalyzed by the enzyme RuBP carboxylase or rubisco is phosphoglyceric acid PGA a three ring carbon Therefore this photosynthetic pathway is usually called C3 Photosynthesis To fix carbon plants must open their stomata to let CO2 in to their leaves but as CO2 enters water exits Chapter 7 Energy and Nutrient Relations 3 In C3 plants there is another factor that contributes to a low rate of CO2 uptake RuBP carboxylase has a low affinity for CO2 High rates of water loss are not a problem for plants that live in moist conditions but in hot dry climates high rates of water loss can close the stomata and shut down photosynthesis Rubisco catalyzes another reaction that combines O2 with RuBP Photorespiration occurs in the light consumes energy and produces O2 Rubisco has a high affinity for O2 but a higher affinity for CO2 Photorespiration is most significant energetically when CO2 concentrations are reduced leading to increased O2 concentration C4 Photosynthesis into separate cells Separates carbon fixation and the light dependent reactions of photosynthesis C4 plants fixe CO2 in the mesophyll cells by combining it with phosphoenol pyruvate PEP to produced a four carbon acid C4 plants need to open fewer stomata to deliver sufficient CO2 to photosynthesizing cells Fewer stomata open conserves water The acids produced during carbon fixation diffused to specialized cells surrounding a structure called the bundle sheath C4 plants do better than C3 plants under conditions of high temperature high light intensity and limited water C4 plants are