26 Parts of Photosystem 1) Rxn center/e- acceptor 2) Pigment Chlorophyll uses light energy to move e- to next energy level2) PigmentLight absorption, photon acceptor3) Light-harvesting complexProteins, contain pigment
34 Dark Reactions How plants actually make food (carbohydrates) Don't require light directly to runAlso known as the Calvin cycle or C3 Ps
35 Calvin cycle/Dark reaction Anabolic – builds sugars from smaller moleculesFunction - use ATP and NADPH to build food from CO2Location - stroma of the chloroplastCalvin Cycle movie
36 Rubisco Ribulose BisPhosphate Carboxylase Enzyme that adds CO2 to an acceptor moleculeMost important enzyme on earthCatalyzes first step of dark rxn
37 C3 Ps C3 plants are plants that DO use Rubisco enzyme “normally” Keep stomata open during dayMOST plants are C3 plantsWhen you “think of Ps”, you think of a C3 plant performing PsAdaptive value: Require lessLess enzyme activity, no specialized organs/anatomy
38 PhotorespirationWhen Rubisco accepts O2 instead of CO2 as the substrateGenerates no ATPActually uses ATPDecreases Ps output by as much as 50%
39 PhotorespirationMay reflect a time when O2 was less plentiful and CO2 was more commonImportant to evolution of autotrophsPhoto=occurs in lightRespiration=consumes oxygen while producing CO2
41 Intro to C4 and CAMRemember: MOST plants are C3 plants that performs Ps “normally”Both are adaptations to arid conditionsCAM plants “idle” and save energy while C4 plants go through Ps faster
42 C4 Ps Uses a different enzyme to initially capture CO2 Separates CO2 capture from carbon fixation into sugarStill uses C3 Ps to make sugar, but only does so in the bundle sheath cells
43 C4 Ps Found in 19 plant families Characteristic of hot regions with intense sunlightExamples - sugarcane, Bermuda grass, crab grass
44 C3 Ps vs C4 Ps Can use photorespiration Shade to full sun High water useCool temperaturesSlow to moderate growth ratesCool season cropsNo PhotorespirationFull sun onlyModerate water useWarm temperaturesVery fast growth ratesWarm season crops
45 CAM plantsFound in plants from arid conditions (where water stress is a problem)Avoid H2O stress by keeping stomates closed during the dayGenerally have slow growthEx: pineapple, cacti, orchids
46 CAM Plants, cont. Store CO2 as C4 acid During the day, the acid is broken down and CO2 is made into sugar.
48 Ps:Rs Ratios Reflect a plant’s balance in making food and using food 1. Ps > Rs, energy available for growth and reproduction2. Ps = Rs, no growth, but don’t die either3. Ps < Rs, death by starvation
49 Comments - Ps:Rs Rs happens 24 hours a day Ps only in light Plants overwinter on stored food when Ps > RsIf Ps < Rs, best solution is to increase the amount of light
50 Factors Affecting Ps 1. Light - quantity and quality 2. Temperature - too hot or too cold3. CO2 - often limits C3 plants4. Minerals - especially NPK and Mg
51 Importances of Ps1. Food - either directly or indirectly comes from plants2. Oxygen in the air3. CO2 balance4. Plant products5. Life on Earth
52 Summary Identify the basic equation of photosynthesis. Identify the main reactions of photosynthesis.Recognize the function, location, requirements and products of the photosynthesis reactions.Recognize the role of light and pigments in the photosynthesis process.Recognize the effects and importance of photorespiration.Recognize various types of photosynthesis and their importance.Identify the biological and economic importance of photosynthesis.
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