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Ch. 8 Photosynthesis • Autotroph – make their own food. Ex. Plants • Heterotroph – obtain energy from the foods they consume. Ex. Animals Adenosine Triphosphate • ATP Chemical Energy • Energy is stored within the chemical bonds in ATP. STORING ENERGY: • ADP: has two phosphate groups. • ATP: has three phosphate groups. • When a cell has energy available, it can store small amounts of it by adding a phosphate group to ADP molecules---making ATP. RELEASING ENERGY • Energy that is stored in ATP is released by breaking the chemical bonds between the second and third phosphates. Using Biochemical Energy • ATP powers pumps in cell membrane, protein synthesis, responses to chemical signals at the cell surface. Review Questions 1. What is the ultimate source of energy for plants? 2. What is ATP and what is its role in the cell? 3. Describe one cellular activity that uses the energy released by ATP. 4. How do autotrophs obtain energy? How do heterotrophs obtain energy? ACTIVITY - Photosynthesis article. - Mind Web from article. Mind Map • Read the article and create a mind map using the information from the article. 8-2 Photosynthesis: An Overview Van Helmont’s Experiment - To find out if plants grew by taking material out of the soil. - Determined the mass of a pot of dry soil and a small seedling. - He planted the seedling in the pot of soil. - He watered it regularly. - End of five years, the seedling, which by then had grown into a small tree, had gained about 75kg. - Mass of soil, however, was almost unchanged. - He thought that the mass had come from the water. - But where does the “carbon” come from in the plant? - He didn’t realize that carbon dioxide in the air made a major contribution to the mass of his tree. Priestley’s Experiment • Took a candle, placed a glass jar over it. • Watched as the flame gradually died out. • Something in the air was necessary to keep a candle flame burning. • When that substance was used up, the candle went out. • That substance was oxygen. • If he placed a live sprig of mint under the jar and allowed a few days to pass, the candle could be relighted and would remain lighted for a while. • The mint plant had produced the substance required for burning. • It released oxygen. • http://www.youtube.com/watch?v=fsa71gKvCaw Jan Ingenhousz • Showed that the effect observed by Priestley occurred only when the plant was exposed to light. • His and Priestley’s experiments showed that light is necessary for plants to produce oxygen. The Photosynthesis Equation 6CO2 + 6H2O ----- C6H12O6 + 6O2 Activity: What would happen if clouds formed and light wasn’t able to hit the earth. Think about what happens first and then eventually. At least one page in length. Light and Pigments Light and Pigments • Pigments – light absorbing molecules, plants use to gather sun’s energy. • Chlorophyll – plants’ principal pigment. • 2 types: • Chlorophyll a • Chlorophyll b Absorbs light very well in blue-violet and red regions. • Light energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons. • Electrons move down the electron transport chain. Review 1. What did van Helmont, Priestley, and Ingenhousz discover about plants? 2. Describe the process of photosynthesis, including the reactants and products. 3. Why are light and chlorophyll needed for photosynthesis? 4. Describe the relationship between chlorophyll and the color of plants. 8-3 The Reactions of Photosynthesis • Thylakoids – saclike photosynthetic membranes. • Grana – stacks of thylacoids. (granum) • Photosystems – clusters of chlorophyll and other pigments. Light-collecting units of the chloroplast. • Stroma – region outside the thylakoid membranes. Light rxn. Dark rxn. Reactants of Light rxn. From the Dark rxn. - light - NADP+ - water - ADP + P Reactants of Dark rxn. - CO2 From the Light rxn. - ATP - NADPH Light rxn. Dark rxn. Products of Light rxn. - ATP - NADPH - O2 Products of Dark rxn. - Sugars - NADP+ - ADP + P Electron Carriers • Sunlight excites electrons in chlorophyll. • E- gain a lot of energy. • Use carrier molecules to carry these e-. Ex. NADP+ (nicotinamide adenine dinucleotide phosphate) - Holds 2 high-energy electrons along with a hydrogen ion (H+). NADP+ ------NADPH Light-Dependent Reactions pg. 210 A: Light absorbed by photosystem II is used to break up water molecules into energized electrons, hydrogen ions (H+), and oxygen. B: High-energy electrons from photosystem II move through the electron transport chain to photosystem I. C: E- released by photosystem II are energized again in photosystem I. Enzymes in the membrane use the eto form NADPH. NADPH is used to make sugar in the Calvin Cycle. D: The inside of the thylakoid membrane fills up with positively charged hydrogen ions. This action makes the outside of the thylakoid membrane negatively charged and the inside positively charged. E: As hydrogen ions pass through ATP synthase, their energy is used to convert ADP into ATP. ATP Synthase • As it rotates it binds ADP and a phosphate group together to produce ATP. • Light-dependent rxn. Produces high-energy electrons (NADPH) and ATP. The Calvin Cycle The Calvin Cycle • Uses ATP and NADPH from the light-dependent rxns. to produce high-energy sugars. • Melvin Calvin, worked out the details of this cycle. • LIGHT-INDEPENDENT RXN. Or DARK REACTION Process of Calvin Cycle A: 6 Carbon dioxide molecules enter the cycle from the atmosphere. The carbon dioxide molecules combine with six 5-carbon molecules. The result is twelve 3carbon molecules. B: The twelve 3-carbon molecules are then converted into higher-energy forms. The energy for this conversion comes from ATP and high-energy electrons from NADPH. C: Two of the twelve 3-carbon molecules are removed from the cycle. The plant cell uses these molecules to produce sugars, lipids, amino acids, and other compounds needed for plant metabolism and growth. D: The remaining ten 3-carbon molecules are converted back into six 5-carbon molecules. These molecules combine with six new carbon dioxide molecules to begin the next cycle. • The Calvin cycle uses six molecules of carbon dioxide to produce a single 6-carbon sugar molecule.