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CP Ch. 8 PHOTOSYNTHESIS Uses energy from sunlight Converts water and carbon dioxide from the environment into organic food molecules and oxygen gas Photosynthetic organisms – producers on land and in the water Two Sets of Reactions In chloroplasts 1. Light-Dependent (“light”) Reactions - Chlorophyll absorbs sunlight - Makes energy molecule ATP - Makes O2 gas 2. Light-independent reactions Calvin cycle (“dark” reactions) • Uses energy molecules from light reactions • Uses CO2 • Makes glucose 6 CO2 + 6 H2O C6H12O6 + O2 Cells use ATP for energy ATP - adenosine triphosphate High-energy bond between phosphate groups - breaks easily, bond energy is released - energy is used by cell to do work When a cell needs energy for work, 3rd phosphate comes off ATP and attaches to molecule doing work -Transfers ENERGY to new molecule -“phosphorylate” 8 ATP – ADP Cycle • ATP breakdown products (ADP + P) stay in cell • used again to make more ATP when needed ATP made in cell respiration ATP used for cellular work Very fast!! A cell can make 10 million ATP/second 9 <> Sunlight is white light, containing all colors Color of light Depends on wavelength (l) -Shorter wavelength higher energy - blue-violet end of spectrum -Longer wavelength lower energy -red-orange end of spectrum Visible light: small part of Electromagnetic spectrum travels as a wave ---- behaves as a particle (photon) Shorter wavelength Longer wavelength Higher energy Lower energy Colors of light absorbed by photosynthetic pigments Plants absorb blue and red light best Photosynthetic pigments •Plants have multiple pigments to absorb as much sun energy as possible •Chlorophyll a is the primary pigment – starts the chain of reactions •Chlorophyll b, carotenes, xanthophylls and others are accessory pigments. •They absorb wavelengths that chlorophyll a cannot absorb use more of sunlight Chromatography Separates a liquid mixture by solubility Colors of light absorbed by a chloroplast Colors NOT absorbed are reflected or transmitted -- the colors we SEE Absorbed light energy is transferred to electrons in pigment -- energized electrons Chlorophyll absorbs mostly from the red and blue ends of the spectrum - reflects green. Parts of a chloroplast Thylakoid membranes - have chlorophyll - absorb sunlight - site for 1st set of reactions Granum – stack of thylakoid sacs Stroma – fluid surrounding thylakoids - site for 2nd set of reactions Parts of a Leaf What are electron carriers? Electron carriers are coenzymes that take electrons (and H+ ions) from one molecule in a chain of reactions and transfer them to another molecule in a later reaction. a. transfer energy b. In photosynthesis, the carrier NADP accepts electrons and H+, becoming NADPH c. Helps change sunlight to chemical energy What is NADP? • NADP accepts electrons and H+ ions from water in “light” reactions NADP + H NADPH • Gives them to CO2 in Calvin cycle NADPH - H NADP • CO2 + H + e- glucose Coenzyme – helps in a reaction but is not the catalyst NADP is an electron and hydrogen “acceptor” It carries e- and H+ ions until a later reaction NADP + H NADPH NADPH – H NADP Light –dependent reactions TWO things happen 1.Photosystems absorb sunlight a.excited electrons from chlorophyll go to Electron Transport Chains b.Make ATP 2. Light Splits Water • H2O 2 H+ + 2 e- + O • Hydrogens (H+) reduce NADP NADPH • Oxygens O2 • Electrons - replace electrons lost from chlorophyll Light Reactions reactant products 1. Water Also need -Sunlight -chlorophyll 1. ATP 2. NADPH 3. Oxygen gas How does light make ATP? Light energizes electrons Electrons enter an Electron Transport Chain Series of membrane proteins transfer electrons Electrons power ATP synthesis Electrons pass from one membrane protein to the next Electron energy concentrates H+ ions Ions help make ATP Chemiosmosis How Cells make ATP H+ ions diffuse through ATP Synthase - (enzyme in thylakoid membrane) • Phosphorylates ADP (ADP + P) • Makes ATP chemiosmosis ADP + P ATP Summary of Light reactions 1. Capture light energy, make ATP 2. Split water (H2O) into 2 H+ + O + 2e1) Electrons replace those lost from chlorophyll 2) O makes oxygen gas 3. Add H+ and e- to NADP NADPH 1) Later they become part of glucose molecule Light Reactions make: ATP NADPH O2 2 1 3 Bubbles –oxygen gas made by an aquatic plant Calvin Cycle “Dark” reactions, or Light-Independent Reactions In stroma of chloroplast • Uses ATP made in light reactions • Fixes CO2 from air • Adds H+ ions from water • Adds electrons from ETC Makes GLUCOSE What is carbon fixing? CO2 from air becomes part of organic molecule Energy needed to make glucose comes from ATP made in the light reactions Calvin Cycle in stroma B) Carbon is “fixed” CO2 becomes part of a 3-carbon molecule A) Carbon compounds in stroma (RuBP) C) ATP and NADPH are used E) Stroma compounds returned D) (2) 3-C compounds make 1 glucose Overview of Photosynthesis LE 7-5 Photosynthesis uses light energy to make food molecules H2O Chloroplast CO2 Light “Fixes” carbon (CO2 becomes part of organic molecule) NADP ADP Absorbs light energy P LIGHT REACTIONS (in thylakoids) Makes energy molecules ATP, NADPH CALVIN CYCLE (in stroma) Uses energy molecules made in light ATP NADPH Makes glucose Light splits water -makes O2 Starch Lipids O2 Sugar proteins cellulose Factors Affecting Photosynthesis 1. Light – bright sun, more energy a. Long days (summer), more light absorbed b. Wavelength – cannot absorb green light 2. Temperature – warm, but not too hot a. Hot days – stomata close to save water 3. Water – soil must be moist a. Water comes up through xylem in veins b. Exits through open stomata c. Water low? – stomata close How CO2 concentration affects rate of photosynthesis plateau At high CO2 concentration, rate is constant because all coenzymes are being used At low CO2 concentration, rate increases as CO2 increases How amount of light affects rate of photosynthesis plateau At high light intensity, rate stays constant because all photosystems are being used At low light intensity, rate increases as light increases How temperature affects rate of photosynthesis Rate increases with increasing temp (energy) - To optimum Rate drops above optimum temp - stomata close to save water - enzymes denature Environmental Factors affecting Photosynthesis Ordinary plants in hot weather C-3 – carbon fixed into a 3-carbon compound In hot, dry weather, C-3 plants: • leaf openings close to save water • How can CO2 get inside? Leaf epidermis, stomata Guard cells open/close stomata Open Closed Close when [CO2] or water is low in plant C-4 Plants C-4 plants store CO2 while stomates are open - use stored carbon when stomates are closed Can still make sugar Corn Sugar Cane crabgrass CAM Plants Succulents cacti pineapples Fix CO2 during the night, when it is cool enough for open stomates - Do photosynthesis during the day, using the stored carbon Parasitic plants Supplement nutrition by taking from other organisms Dodder Plant Cannot make its own food Takes nutrients from host plant Mistletoe – supplements photosynthesis Carnivorous plants Eat insects to get nitrogen Venus Fly Trap Insect walking on leaves touches trigger hairs - Leaves close, insect digested Pitcher plant Insect climbs inside, can’t get out Walls of tube are slippery Sundew – eats insects Sugary “dew” attracts insects Insects get stuck, plant closes Carotenes in nature We can see carotenes, xanthophylls, and other pigments in places other than autumn leaves Is it a fruit or a vegetable? Botanically speaking, a fruit is a seed-bearing structure that develops from the ovary of a flowering plant, whereas vegetables are all other plant parts, such as roots, leaves and stems. By those standards, seedy outgrowths such as apples, squash and, yes, tomatoes are all fruits, while roots such as beets, potatoes and turnips, leaves such as spinach, kale and lettuce, and stems such as celery and broccoli are all vegetables.