2 Vocabulary Review What is an autotroph? What is a heterotroph? Make their own energyWhat is a heterotroph?Aren’t able to make own energy– have to get it from another source
3 Photosynthetic Organisms Photosynthesis is one way to make your own energyWho does it?Plants, algae, some other protists, some prokaryotes (ex. cyanobacteria)
4 Location of Photosynthesis Photosynthesis occurs in the chloroplastsOrganelles that contain the pigment chlorophyll and other pigmentsOpenings in the leaf (stomata) allow CO2 (reactant) to enter and O2 (product) to leave
5 Equation for Photosynthesis 6 CO H2O + ENERGY C6H12O O2In terms of reactants and products, it is the reverse of cellular respiration, but process is different.
6 Stages of Photosynthesis Light ReactionsCaptures light energy to produce ATP and NADPHCalvin Cycle (“Dark” Reactions)Uses ATP and NADPH to “fix” carbon into a carbohydrate“fix” means to incorporate the carbon into a compound
7 Light ReactionsMain point = convert sunlight energy into chemical energy (ATP and NADPH)Sunlight can be divided into different wavelengths of light– only some are useful in photosynthesis
8 Light ReactionsPhotosynthetic pigments in the chloroplast absorb different wavelengthsChlorophyll aChlorophyll bCarotenoids
9 Question… Why are most plants green? The chlorophyll and carotenoid molecules absorb the blue-violet and red light and use it to perform photosynthesisThey reflect green light – colors we see are the reflected wavelengths.
10 Light Reactions: Photosystems Photosystems are the complex of pigments that receives the sunlight to begin the processPhotosystems absorb energy to excite an electron in chlorophyllThere are 2 different photosystems in chlorophyll – I and II.
11 Light Reactions: Noncyclic Flow Step 1: Light excites electrons in photosystems I and IIStep 2: Excited electrons are passed down an electron transport chain – generates ATP and NADPH
12 Noncyclic FlowExcited electron from Photosystem II fills the space left in Photosystem IWater is split (photolysis) to provide an electron to fill the space left in Photosystem II
13 Cyclic Electron FlowUnder certain circumstances, the excited electrons will only flow through Photosystem I (not II)
14 Cyclic Electron Flow Generates ATP Doesn’t generate NADPH Runs because the Calvin Cycle needs more ATP than NADPHMay shift from noncyclic to cyclic flow when NADPH levels are high
15 Electron Transport Chain very similar to cellular respirationAn H+ concentration gradient across the thylakoid membrane drives ATP synthesis
16 Calvin CycleAlso called the Dark Reactions, Non-light Dependent Reactions, or the Calvin Benson CycleUses the ATP and NADPH produced in the light reactions to produce glucose using CO2
17 Calvin Cycle: RubiscoRubisco is the enzyme that first “traps” CO2 into the cycleThrough a series of reactions, CO2 is used to eventually make glucose
18 Calvin CycleCO2 only contributes 1 carbon 6 “turns” of the calvin cycle are needed to produce one glucose.RuBP also has to be regenerated so that cycle can continue
19 The O2 released during photosynthesis comes from NADPHRuBP (RuDP)C6H12O615
20 Carbohydrate-synthesizing reactions of photosynthesis directly require LightProducts of the light reactionsDarknessO2 and H2OChlorophyll and CO215
21 The end products of the light-dependent reactions of photosynthesis are 15ADP, H2O, NADPHADP, PGAL, RuBP (RuDP)ATP, CO2, H2OATP, NADPH, O2CO2, H+, PGAL