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Unit 6- Photosynthesis & Cellular Respiration 6a- Photosynthesis

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First Homework (New Semester) Bring a leaf to class tomorrow

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Life Requirements All organisms need a constant source of energy to survive. The ultimate source of energy for most life on Earth is the Sun.

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Trapping the Suns Energy Photosynthesis is the overall process by which solar energy is used to chemically convert water and carbon dioxide into chemical energy stored in simple sugars. Involves a complex series of chemical reactions in which the product of 1 reaction is a reactant in the next

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Photosynthesis The process of photosynthesis is generally represented using a balanced chemical equation. However, this equation does not represent all of the steps that occur. Sunlight 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2

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Steps of Photosynthesis Photosynthesis can be divided into two stages Light-dependent Reaction Solar energy is absorbed by chloroplasts and two energy-storing molecules (ATP & NADPH) are produced. Calvin Cycle (Light-independent reaction) Simple sugars (glucose) are formed using CO 2 & the energy stored in ATP & NADPH

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Structure of Chloroplasts Photosynthesis takes place in the chloroplasts Each chloroplast is surrounded by a pair of membranes. Inside the inner membrane is another system of membranes called thylakoids. Arranged as hollow disks Connected & layered to form stacks called grana Surrounding the grana is a solution called the stroma.

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Where does each step take place? Light-dependent reactions take place in the membranes of the thylakoid disks Calvin Cycle takes place in the stroma

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Review of Light Light from the sun- white light Can be separated into its component colors by passing the light through a prism Results in the visible spectrum (ROYGBIV) When white light strikes an object, its component colors can be reflected, transmitted, or absorbed. Pigments- compounds that absorb light Most absorb certain colors more strongly than others, so the light that is reflected no longer appears white.

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The Role of Chloroplasts and Pigments The thylakoid membranes contain the pigments that can absorb certain wavelengths of sunlight. The most important pigment is chlorophyll. Absorb most wavelengths of light except for green. Green is reflected making the plants appear green. In the fall, plants reabsorb chlorophyll leaving other pigments that reflect other wavelengths of light making the leaves appear red, yellow, or orange.

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Light-Dependent Reactions Sunlight strikes the chlorophyll molecules in the thylakoid membrane. Chlorophyll absorbs the light & the solar energy is used to split water molecules (photolysis) Results in the release of oxygen (O 2 ) as a waste product. Allows for the temporary transfer of the solar energy to electrons released by the broken bonds Electrons are passed down an Electron Transport Chain Photolysis

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Light Dependent Reactions The Electron Transport Chain is a series of proteins in the thylakoid membrane. As the electrons are transferred from one protein to another, some energy is released. This energy is used to make ATP & NADPH (electron carrier molecule)

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Light Dependent Reactions

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Light-dependent Reactions Solar Energy absorbed by chloroplasts NADPH released Oxygen released ATP Released Products of Light Reactions (ATP and NADPH) fuel the Calvin Cycle

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Video https://www.youtube.com/watch?v=joZ1EsA5 _NYhttps://www.youtube.com/watch?v=joZ1EsA5 _NY (3:30) https://www.youtube.com/watch?v=sQK3Yr4 Sc_khttps://www.youtube.com/watch?v=sQK3Yr4 Sc_k (7:35-8:20, end of light-dependent)

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Calvin Cycle A series of enzyme-assisted chemical reactions that produces 3-carbon sugars Occurs in the stroma of the chloroplast Uses the ATP & NADPH that was produced during the light reactions and CO 2 from the atmosphere

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Calvin Cycle 1.Carbon Fixation: An enzyme combines CO 2 with a 5-carbon molecule called ribulose biphosphate (RuBP). 6-carbon molecule is very unstable, so it immediately splits into two 3-carbon molecules called 3-phosphoglycerate (3-PGA or PGA) 2.Reduction Each 3-PGA is converted into another 3-carbon molecule, PGAL (aka G3P) in 2 steps. 1- receive a phosphate group from ATP; 2- receive a proton from NADPH ADP & NADP+ will be used again in light reaction 3.PGAL leaves & is used to build glucose (or other carbohydrates). 4.Regeneration Remaining PGAL molecules converted back to RuBP by the addition of a phosphate group from ATP. Enter Calvin Cycle again.

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The Calvin Cycle Uses Carbon Dioxide from the air Uses ATP and NADPH from light reactions to build PGAL- a 3- carbon sugar The 3-carbon sugars can be used to build a glucose molecule Uses another ATP to replenish RuBP Or the 3-carbon sugars can be recycled to keep the Calvin Cycle going.

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Photosynthesis Equation 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Carbon Dioxide from the air Used in the Calvin Cycle Water Split during Photolysis in the Light Reactions Glucose Made in the Calvin Cycle Oxygen Released during Photolysis in the Light Reactions Light Energy chlorophyll Plants can use this glucose molecule for energy during Cellular Respiration. Plants can also convert this glucose molecule into other organic compounds such as proteins and fats/lipids or other carbohydrates like starch and cellulose

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Cycle of Photosynthesis

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3 Factors that Affect Photosynthesis Carbon Dioxide (CO 2 ) Without CO 2, the plant would not have one of the raw materials needed for photosynthesis CO 2 is used in the first step of the Calvin Cycle Temperature The temperature must be in the appropriate range for the plant in order for photosynthesis to properly occur

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3 Factors that Affect Photosynthesis Intensity of Light If the intensity of light is lower, the available energy for photosynthesis is lower. In a greenhouse, if the light source is further away, intensity is lower and less photosynthesis can occur If light is not available at all, the light-dependent reactions cannot occur (nor can they provide the materials used in the Calvin Cycle)

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Video https://www.youtube.com/watch?v=joZ1EsA5 _NYhttps://www.youtube.com/watch?v=joZ1EsA5 _NY (3:30) https://www.youtube.com/watch?v=sQK3Yr4 Sc_khttps://www.youtube.com/watch?v=sQK3Yr4 Sc_k (8:20, end of light-dependent)