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Chapter 4 Photosynthesis and Respiration 4.1 • KEY CONCEPT All cells need chemical energy. Energy • All cells need energy • That energy is carried by ATP, adenosine triphosphate. • That energy is held in chemical bonds. • Example: the chemical bonds in wood are broken when wood burns and that bond energy is released. Glucose molecule and starch Starch molecule Glucose molecule ATP • ATP transfers energy from the breakdown of food molecules to cell functions. – Energy is released when a phosphate group is removed. – The third phosphate bond is called a high energy bond – ADP is changed into ATP when a phosphate group is added ATP phosphate removed ATP adenosine triphosphate tri=3 adenosine di=2 diphosphate Chemical Energy and ATP • Fats store the most energy – 80 percent of the energy in your body – About 146 ATP to form a triglyceride • Proteins are least likely to be broken down to make ATP. – Amino acids are usually not needed for energy – About the same amount of energy as a carbohydrate Energy Comparison Alternatives • A few types of organisms do not need sunlight and photosynthesis as a source of energy. • Photosynthesis: – Uses sunlight to build carbon based molecules. • Chemosynthesis – Chemical energy is used to build carbon-based molecules. – Similar to photosynthesis – Some organisms live in places that never get sunlight. For Example 4.2 • KEY CONCEPT The overall process of photosynthesis produces sugars that store chemical energy. Photosynthesis • Producers make their own source of chemical energy. • Plants use photosynthesis and are producers. • Photosynthesis captures energy from sunlight to make sugars Chlorophyll • Chlorophyll is a pigment molecule that absorbs light energy. • Found in chloroplasts in plants The chloroplast • Photosynthesis occurs two parts of the chloroplasts grana (thylakoids) chloroplast –Grana (thylakoids) –Stroma (fluid around the thylakoids) stroma Overview of Photosynthesis – The light-dependent reactions capture energy from sunlight take place in thylakoids – water and sunlight are needed – chlorophyll absorbs energy – energy is transferred along thylakoid membrane then to light-independent reactions – oxygen is released – P 104 Overview of Photosynthesis • The light independent reactions make sugars – Take place in stroma – Needs carbon dioxide from atmosphere – Use energy to build sugar in cycle of chemical reactions Overview of photosynthesis The equation for the overall process is: 6CO2 + 6H2O C6H12O6 + 6O2 granum (stack of thylakoids) 1 chloroplast 6H2 O 2 thylakoid 6CO2 3 6O2 energy Stroma 1 six-carbon sugar 4 C6H12O6 Summary of photosynthesis • Requires – Water: all life requires water – CO2: Uses the CO2 that we produce – Sunlight: the ultimate source of all food energy • Produces – Sugar: the food – Oxygen: for organisms to breathe 3.3 Photosynthesis in detail • KEY CONCEPT: Photosynthesis requires a series of chemical reactions. Light dependent reactions • Capture light energy • Splits water • Produces oxygen gas and hydrogen ions Photosystem II Captures and transfers energy – chlorophyll absorbs energy from sunlight – energized electrons enter electron transport chain – water molecules are split – oxygen is released as waste – hydrogen ions are transported across thylakoid membrane Photosystem I Captures energy and produces energycarrying molecules. – chlorophyll absorbs energy from sunlight – energized electrons are used to make NADPH – NADPH is transferred to light-independent reactions Light reactions overview • The Light dependent reactions produce ATP – hydrogen ions flow through a channel in the thylakoid membrane – ATP synthase attached to the channel makes ATP Light Independent reactions • The second stage of photosynthesis uses energy from the first stage to make sugars. • Light-independent reactions occur in the stroma and use CO2 molecules. • Enzyme RuBisCo fixes carbon dioxide carbon into the cycle. Light independent reactions Light independent Reactions • A molecule of glucose is formed as it stores some of the energy captured from sunlight. – carbon dioxide molecules enter the Calvin cycle – energy is added and carbon molecules are rearranged – a high-energy three-carbon molecule leaves the cycle – Two three carbon molecules bond to form a sugar – Remaining molecules stay in the cycle Light independent Reactions • A molecule of glucose is formed as it stores some of the energy captured from sunlight.