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Unit 6 Chapter 8 Photosynthesis Learning Target #1 •Describe the role of ATP in cellular activity. Energy currency – ATP (adenosine triphosphate) 1. cell’s energy storage molecule=ATP 2. used for activation energy 3. Why is ATP useful? •it can easily release and store energy •Energy source for all cells Structure of ATP • adenosine •ribose sugar and an adenine base • 3 phosphates • enzymes easily break bond between 2nd and 3rd phosphate to release energy • phosphate transferred to another molecule ATP-ADP cycle -P ATP Releases energy For cell to do work ADP +P Comes from Energy in food Formed during cellular respiration Stores Energy for a little time Where does ATP come from? • autotroph - manufacture own food from inorganic substance and energy •photosynthesis - capture light energy to be stored in organic compounds •plants, algae, some bacteria • heterotroph - cannot make own food •eat autotrophs •heterotrophs that feed on autotrophs • For humans•ATP comes from the food we eat • all life ultimately depends on SUN ENERGY and autotrophs Learning Target (8.2) •Explain how cellular structures and molecules are involved in photosynthesis. Leaf Anatomy and Terms • See attached sheet given to you! Structure of a chloroplast • Chloroplast is the site of photosynthesis • thylakoids - system of interconnected membranes, flattened sacs • contain chlorophyll • contain electron transport chain • grana - stacks of thylakoids • stroma - liquid surrounding thylakoids Light • Light appears white : •actually a variety of colors •visible spectrum • Light can be: • reflected •Transmitted •Absorbed Chloroplast pigments • pigment - compound that absorbs light • chlorophyll a (green) - absorbs less blue but more red • directly involved in light reactions • chlorophyll b (green) - absorbs more blue and less red • assists chlorophyll a in light absorption • accessory pigment • accessory pigments • carotenoids - yellow, orange, brown • xanthophylls - yellow • in leaves, chlorophyll masks others • others show in fruits, flower Learning Target (8.3). •Describe how a photosynthetic organism converts the sun’s energy into chemical energy An Overview of Photosynthesis • Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen. • In symbols: • 6 CO2 + 6 H2O C6H12O6 + 6 O2 • In words: • Carbon dioxide + Water Sugars + Oxygen Light Dependent Reaction (A.K.A. Light Reaction) • photosystem • cluster of pigment molecules • two photosystems: 1 and 2 1. light is absorbed by chlorophyll a in photosystem 2 • 2 electrons are energized (excited) to higher energy level 2. electrons leave chlorophyll a (oxidized) (LEO) • goes to primary electron acceptor in thylakoid membrane (reduced)(GER) 3. electrons donated to electron transport chain - lose energy • used to move protons into thylakoid High-Energy Electrons • The high-energy electrons produced by chlorophyll are highly reactive and require a special “carrier.” • Think of a high-energy electron as being similar to a hot potato. If you wanted to move the potato from one place to another, you would use an oven mitt—a carrier—to transport it. • Plants use electron carriers to transport high-energy electrons from chlorophyll to other molecules. Light Dependent Reaction (A.K.A. Light Reaction) 4. at same time photosystem 2 absorbs light, so does photosystem 1 • 2 electrons leave chlorophyll a to another primary electron acceptor • photosystem 1 electron replaced by electron from photosystem 2 5. primary electron acceptor of photosystem 1 sends 2 electrons toward stroma and they combine with 2 protons (H+) and NADP+ (coenzyme) (reduced to NADPH) 6. electron of photosystem 2 replaced by splitting of water: 2H + 2e- + 1/2O2 • H2 O • Products of the Light Rxn: O2 + NADPH + ATP • H+ produced remain in thylakoid, • O2 produced diffuses out of plant • http://www.fw.vt.edu/dendro/forestbiology/photosynthesis.swf High-Energy Electrons • NADP+ (nicotinamide adenine dinucleotide phosphate) is a carrier molecule. • NADP+ accepts and holds two high-energy electrons, along with a hydrogen ion (H+). In this way, it is converted into NADPH. • The NADPH can then carry the high-energy electrons to chemical reactions elsewhere in the cell. Light Reaction Chemiosmosis 1. Process to synthesize ATP •protons from splitting of water are pumped from stroma into the thylakoid (ACTIVE TRANSPORT) •concentration gradient of protons higher inside thylakoid than in stroma (represents potential energy) • ATP synthase in thylakoid makes ATP by adding phosphate to ADP • movement of protons to stroma provides energy 2. NADPH and ATP needed to run dark reactions Light Independent Reaction A.K.A.-Calvin Cycle (do not need light) (in stroma) Light Independent Reaction A.K.A.-Calvin Cycle (do not need light) (in stroma) Carbon fixation- inclusion of CO2 into organic compounds 1. CO2 diffuses through stomates (stoma) from atmosphere into cells • stomata- small pores on the leaf that allow CO2 and O2 through 2. CO2 diffuses into stroma from cytoplasm • starting compound is RuBP (ribulose biphosphate) • CO2 combines with RuBP(5C) • 6C unknown formed • splits immediately into two PGA (3C) (phosphoglycerate) Light Independent Reaction A.K.A.-Calvin Cycle (do not need light) (in stroma) Light Independent Reaction 3. PGA converted to PGAL (3C) (steps of how) (phosphoglyceraldehyde) •phosphate from ATP •PGA + ATP DPGA (PGA-P) + ADP • H added from NADPH and phosphate released producing PGAL •ADP, P, and NADP+ cycled back to light reactions 4. most PGAL converted back to RuBP Light Independent Reaction A.K.A.-Calvin Cycle (do not need light) (in stroma) Light Independent Reaction: Synthesis of Glucose 1. 2 PGAL join to form glucose, fructose, or galactose • glucose used for cell respiration by plant •excess glucose: sucrose can be made starch and cellulose can be formed amino acids and lipids can be formed • http://www.youtube.com/watch?v=OYSD1jOD1dQ&fe ature=relate • http://fdmcbiology12.weebly.com/calvin-cycle.html Over all photosynthesis reaction: C6H12O6 + 6O2 + 6H2O 6CO2+ 12H2O + light Learning Target 8.3 c •Identify the factors that affect the rate of photosynthesis (8.3) Rate of Photosynthesis 1. light intensity (when reaches certain intensity, rate levels off) 2. level of CO2 3. temperature (too high inhibits enzyme action)