Photosynthesis Site of photosynthesis chloroplast thylakoid lumen inside the thylakoid stroma the matrix between the thylakoid and chloroplast membrane Summary of Photosynthesis When a photon strikes an electron energy is imparted to electron Electron is boosted in energy to another energy level or electron shell However the 2nd law of thermodynamics stipulates that the electron will lose energy and fall back In photosynthesis the high energy electron is boosted out of the atom and captured by another molecule electron acceptor 1 endergonic uphill reaction sunlight energizes electron to a high energy state 2 energized electron falls back downhill energy is harvested as ATP and NADPH 3 harvested energy drives the uphill reaction that makes glucose from CO2 and water 1 Light Dependent Reaction Photo antenna complex light absorbed by an array of pigments photosystems special chlorophyll molecules that carry out reactions of photosynthesis two phases of electron boosting occur in photosynthesis this reaction occurs in something referred to as a photosystem photosystem II occurs first before photosystem I Each time the electron is boosted it falls back And each time it falls back it s energy is harvested the sun s energy boosts an electron out of the chlorophyll molecule the electron is captured in an electron transport chain where its energy is harvested ATP is stored as a result of reactions of photosystem II NADPH is stored as a result of reactions in photosystem I Chlorophyll which lost an electron when struck by solar energy now wants its electron back it gets this electron back by breaking down water photolysis and taking its electron Takes it from the hydrogen and oxygen is left behind why it is a waste product Summary of Light Dependent Reaction 1 energy from the sun twice boosts electrons to higher energy states 2 twice they flow downhill solar energy is harvested as ATP NADPH Solar energy is captured in chemical bonds 3 This harvested energy will drive the endergonic uphill reaction that makes glucose from CO2 and water Light Independent Reaction Synthesis occurs in stroma where the Calvin Cycle is assembly of glucose occurs in Calvin cycle stomata tiny pores on a leaf where CO2 enters leaf regulate passage of water let oxygen out Steps of Calvin Cycle 1 CO2 enters and binds with RuBP a 5 carbon sugar This is a process known as carbon fixation it is where carbon dioxide gas is fixed into a solid 3 carbon sugar molecule The enzyme that facilitates this reaction is called Rubisco Where Carbon Dioxide is fixed 2 3 PGA is formed 3 ATP and NADPH react with 3 PGA to form G3P Two G3P molecules exit the cycle and combine to form glucose and other compounds 4 these molecules exit cycle to form glucose 5 remainder of G3P continues on to re generate RuBP Three types of photosynthesis C3 C4 CAM C3 photosynthesis referred to as such because all the Calvin cycle intermediates are 3 carbon molecules Glitch in photosynthesis rubisco the enzyme that binds CO2 at the beginning of the Calvin cycle often binds with oxygen instead of CO2 C4 photosynthesis an intervening cycle that has 4 carbon molecules C4 plants have a carbon fixing enzyme that does not bind oxygen this process delivers pure CO2 to Calvin cycle Adaptation for plants in warm climates Two disadvantages to C4 requires an expenditure of ATP to shuttle the CO2 to the Calvin cycle is an adaptation to warm climates C4 plants would not do well in cooler climates Climate Change Green house effect when energy from the sun and usually bounces back off into space doesn t instead stays in the Earth s atmosphere Good thing Carbon dioxide and water vapor are what make up the green house gases mid 1800s was when scientists first understood that carbon dioxide was a greenhouse gas 90 million tons of carbon dioxide every day Equilvant to 3 000 years of photosynthesis Svante Arrhenius 1859 1927 1896 Arrhenius made a calculation that if we keep putting carbon dioxide we will probably see the world heat up first to state that humans had to do with the earth s climate change Carbon tracking goes back 800 000 years from 800 00 to 100 000 only went up 280 parts per million Now it went up to 400 parts per million goes up 2 parts per million a year Himalayan Glaciers 40 of the world s population depends on the Himalayan watershed for water Sea level rise is caused mostly 1 by expanding water in warmer oceans Hurricane s get their strength from warm water Methane is 20x more powerful than carbon dioxide 70 reduction in population of Adelie penguins at Palmer Station
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