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Photosynthesis and Cellular Respiration Matter is recycled; energy is not. Energy from the sun arrives on earth in the form of visible light, a type of electromagnetic radiation How objects appear different colors White light is a mixture of all wavelengths (and colors) of light White light Green light Is reflected and transmitted Red and blue light Is absorbed We see the Plant as green Figure 10.6 Why leaves are green: interaction of light with chloroplasts The wavelength of light a compound absorbs can be determined by a spectrophotometer Energy Pathway: The Big Picture cellular Chemical photosynthesis respiration energy for Chemical Light energy stored in energy from use in the glucose, fats, or the sun form of ATP carbohydrates Anabolism Catabolism Overview of Cellular Respiration C6 H12 O6 + 6 O2 Glucose oxygen 6 CO2 carbon dioxide + 6H 2 O + energy water ADP + Pi + energy In mitochondria, the energy released from the catabolism of glucose is used to make ATP from ADP and Pi . The process is called phosphoryllation. ATP Overview of Photosynthesis 6 CO2 + 1 2H2 O Carbon water dioxide + Solar energy C6 H12 O6 Glucose + 6 O2 + oxygen In photosynthesis, energy from the sun (in packets called photons) is absorbed by pigment molecules (primarily chlorophyll) and used to produce glucose from CO2 6H 2 O Photoautotrophs: Use sunlight to produce food molecules; includes plants and cyanobacteria Photosynthesis takes place in the chloroplasts of plant cells Leaf cross-section Leaves contain millions of chloroplasts Cells containing chloroplasts ` DAY TWO www.ftexploring.com Photosynthesis Review • Occurs in the chlorplast • Chlorophyll and accessory pigments capture electromagnetic energy by absorbing photons of light. • The energy from light is captured and converted to chemical energy which is stored in the bonds of a biomolecule. • Chemical energy is harvested to make ATP during cellular respiration. Different plant pigments absorb different wavelengths of light. Amount of light absorbed Chlorophyll a Chlorophyll b Carotenoids 400 500 600 Wavelength of light (nm) 700 Pigments include chlorophyll (a and b), carotenoids, xanthophylls and anthocyanins. Figure 10.9 Location and structure of chlorophyll molecules in plants Pigments are found in chloroplasts. Outer membrane Inner membrane Thylakoids Granum Stroma Inner membrane Outer membrane Stroma Granum Thylakoid Factors affecting the rate of photosynthesis *LIGHT INTENSITY *TEMPERATURE *CO2 LEVEL Photosynthesis: The Big Picture • Light Dependent Reactions – Occur in thylakoid membranes of grana – Energy from the high energy electron of chlorophyll is used to make ATP and NADPH • Light Independent Reactions (Calvin Cycle) – Occur in enzyme-rich stroma – ATP and NADPH are used to make glucose from CO2 (carbon fixation) Photosynthesis Equation 6CO2 + 12 H2O + Light energy C6H12O6 + 6O2 + 6 H2O Two components: Light-dependent reactions Light energy H2O O2 Chemical energy (ATP, NADPH) Energy Harvest Light-independent reactions Chemical energy (ATP, NADPH) CO2 Synthesis Chemical energy (C6 H12O6) When a photon of light strikes chlorophyll, an electron can be promoted to a higher energy state Electrons can be promoted to discrete highenergy states: e– Blue photons excite electrons to a higher energy state e– Red photons excite electrons to a high-energy state Photons 0 1 Energy state of electrons in chlorophyll 2 Light excites e- in chl.a in PSII e- move to electron acceptor E- from PSI enter second e.t.c. which ends by making NADPH e- transferred along electron transport chain; as they lose energy, H+ protons move into thylakoid Light excites e- in chl a of PSI. Moving Electrons • LEO = lose electrons “oxidized” • GER = gain electrons “reduced” OR OIL RIG Oxidized is lost ……….Reduced is gained Replacing electrons • Water molecules inside the thylakoid membranes are split by an enzyme • Process is called photolysis • Results: • 2H2O 4H+ + 4e- + O2 Chemiosmosis The movement of protons (H+) into the stroma releases energy which is used to phosphoryllate ADP + Pi to form ATP. SUMMARY Alternative Carbon Pathways • C3 plants = Fix carbon exclusively through the Calvin cycle (see previous slide) • C4 plants = used when CO2 levels are low (hottest part of the day, stomates closed) – Includes corn, sugar cane, grasses – Can produce same amount of carbs with half the water loss • CAM plants = “crussulacean acid metabolism” – CO2 incorporated into organic acids at night and released for fixation during the day – Includes cacti, pineapples Cellular Respiration Overview Glycolysis • Occurs in the cytoplasm • Use 2 ATP to break 6-carbon sugar into two 3-carbon pyruvate; produces 4 ATP (net gain of 2) and 2 NADH • If oxygen present, pyruvates continue to Krebs cycle • If no oxygen present, pyruvates continue to fermentation (lactic acid or alcohol) Alcohol fermentation: no oxygen present • Pyruvate is converted to ethanol and CO2 is released. • Glycolysis is believed to have been what ancient prokaryotes used for energy production long before oxygen levels were high enough to support electron transport chain. Lactic Acid fermentation • Pyruvate is directly reduced by NADH to form lactate. (NADH becomes NAD+) • Used in human muscle cells when there is not enough oxygen getting to the muscles such as during strenuous exercise. A chemical pathway removes lactic acid as oxygen becomes available. The Krebs cycle is the first part of cellular respiration. • Pyruvate is oxidized to form acetyl CoA – carbon dioxide released – NADH produced – coenzyme A (CoA) bonds to two-carbon molecule The Krebs cycle • Produces energy-carrying molecules including ATP NADH and FADH2 • Citric acid is formed and CO2 is released Electron Transport Chain • The second part of cellular respiration when protein carriers are used to make NADH and FADH2 and ATP. – high-energy electrons enter electron transport chain – energy is used to transport hydrogen ions across the inner membrane – hydrogen ions flow through a channel in the membrane – One glucose nets up to 36 ATP – Water is released as a waste product.