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The Photosynthetic Process Photosynthesis Photo = light synthesis = to make Photosynthesis has been going on successfully for over 3 Billion years. Chlorophyll a (Primary photosynthetic pigment) has been around unchanged for about that long as well An amazing system that uses building blocks (Water and Carbon dioxide) that are abundant and cheap = requiring little energy to convert. Also many complicated molecules can be toxic or unstable in large quantities, however the starches made by photosynthesis are easily stored by the plant in large quantities without any problems to be used during leaner times. Light in the Wavelength Spectrum In the electromagnetic wavelength spectrum visible light is just a small sliver of the overall range. Plants operate using light from the infrared (IR) to the ultraviolet (UV) and the visible spectrum in-between. Photosynthesis Terms: • Chloroplast • Chlorophyll • Photosynthetic pigments • Accessory pigments • Antioxidants • Thylakoid • Thylakoid Membrane • Granna • Stroma • Lumen • Electron transport chain • ATP, (ADP) • NADPH (NADP+) • • • • • • • • • • Calvin Cycle Light reaction Protons Ions G3P Sucrose Photorespiration CAM plants C4 Photosynthesis Respiration It is Not Just Plants • Some photosynthetic protists, like euglena, contain chloroplasts as do plants. • Others, like the dinoflagellates, host endosymbiotic organisms or obtain chloroplasts from prey they consume. • Bacteria often contain bacteriochlorophyll. This compound resembles chlorophyll but absorbs light of slightly longer wavelengths. • Unlike plants, many bacteria do not require water for photosynthesis to occur. Because of this, they do not produce oxygen. Euglena Dinoflagellate Bacteria with bacteriochlorophyll Where in The Plant? - Chloroplast The chloroplast is a triple membraned organelle where photosynthesis takes place. The thylakoid is the poker chip like structure where the light reaction takes place. The granum is simply a stack of thylakoids. The thylakoid membrane is the center of activity for the light reaction. The lumen is the inside of the thylakoid (where hydrogen ions build up). The stroma is the fluid outside the thylakoids where the Calvin Cycle takes place Photosynthetic Pigments There are several photosynthetic pigments. chlorophyll b, beta carotene and xanthophylls are responsible for absorbing and channeling light energy to chlorophyll a where that pigment is excited into a higher energy potential. Absorption Spectrum Chromatography paper is used to separate out the various light absorbing pigments in different types of leaves or leaves at different times of the year. Leaves are typically ground up and the liquid applied to the paper which separates out the colors into bands across the paper. Accessory pigments like the carotenoids are thought to assist in absorption of different wavelengths of light but more importantly help to protect the plant from damage by too much light Carrot with chromoplasts Cells of the Bird of Paradise flower showing the bright chromoplasts Chromoplasts which hold pigments that absorb light are used in various parts of the plant like the fruit or flowers to make them more attractive to pollinators or their fruit more attractive to the animal world to help spread the seeds. Red bell pepper with chromoplasts Carotonoids Carotonoids are Red, Orange, and Yellow and are Considered Accessory pigments. Carotenoids are considered to perform two major functions in photosynthesis. They serve as accessory light harvesting pigments, extending the range of wavelengths over which light can drive photosynthesis, and they act to protect the chlorophyllous pigments from the harmful photodestructive reaction which occurs in the presence of oxygen Anthocyanins Anthocyanins are pigments that make up the Blues and reds found often in berries *Are not always produced in plants or in some plants are not produced consistently depending on things like weather conditions and how many stored sugars are present. *Most are water soluble and stored in the vacuoles of the plant. *Signal animals as to fruit ripening *Used in leaves to gather up stored sugars Xanthophylls Xanthophyll - These are the yellow pigments of the leaves and are classified as accessory pigments which absorb the wavelength of light that chlorophyll cannot absorb. They serve as protection to excessive amount of sunlight to prevent damage in the plant. Three kinds of xanthophyll are known: canthaxanthin, zeaxanthin and lutein. Health Importance of the Various Plant Pigments Many of the light absorbing and accessory pigments found in plants we have learned have significant health benefits. Mostly as a form of antioxidant preventing the onset of cancers Photosynthesis The most basic representation of the photosynthetic chemical reaction Light Reaction – Water and light energy (captured by the chlorophyll) are used to create two sources of energy – ATP and NADPH Calvin Cycle – Using the 2 energy sources, CO2 is introduced and used to build 3 carbon molecules used as building blocks for food and other products for the plant. In Simplest Terms The Light reaction uses water and light energy to formulate 2 forms of energy ATP and NADPH. The byproduct of that part of the process is oxygen. The Calvin Cycle uses CO2 and the energy sources built by the light reaction to convert a 5 carbon molecule into (2) 3 carbon molecules PGAL which are the building blocks for Sugar, cellulose and other carbon based molecules. Molecules and Ions In the Light Reaction Sunlight energy splits the water molecule H2O into an oxygen atom and 2 hydrogen ions releasing 2 electrons to the 2 H 2O system Water molecules This is now a molecule of Oxygen Gas Sunlight Energy = 4H+ + 4eSplits water molecule Hydrogen ions electrons 1. Using light energy the water 2. As the electron (e-) moves through the molecule is split releasing electrons into the system, hydrogen ions (H+) into the lumen, and O2 into the atmosphere electron transport chain, H+ ions are pulled into the system from outside in the stroma and deposited into the lumen 3. Finally the electron powered again by light energy causes a H+ Ion to connect with NADP+ and form a NADPH molecule to use as energy in the Calvin Cycle 4. As H+ Ions are being pumped into the inside of the thylakoid in the lumen the concentration builds up and the only exit is through a protein called ATP synthase. As it passes through the H+ combines with ADP Molecule and forms ATP to use in the Calvin Cycle Light Reaction • Photons of light are used to power the movement of electrons (From water molecule splitting) through an electron transport chain. (Pathway) • Water enters and splits into O2 molecule and hydrogen protons donating the electron to the system and pumping positively charged ions to the inside of the thylakoid membrane (lumen) • O2 becomes a by product but Hydrogen ions from the original water molecule congregate in the inside of the membrane creating a positive charge buildup • As the ions move to exit the only hole is a protein (called ATP synthase) . As the Hydrogen ions pass through that protein, it converts ADP into ATP which is an energy source needed in the Calvin cycle • As the electrons move through the system they create 2 forms of energy: NADPH and ATP. These now are in the Stroma outside the Thylakoid membrane and ready to fuel the Calvin Cycle which occurs there. ATP is used twice and NADPH once during one revolution of the Calvin Cycle to push the cycle along. 3. 1 of the G3P is used and combined with (2) CO2 molecules to regenerate the 5 carbon molecule (RuBP) to use at the beginning of the cycle again. 1. CO2 is brought in and added to 5 carbon molecule to make larger 6 carbon molecule (temporary). 2. The 6 Carbon molecule is split into (2) 3 Carbon molecules G3P that become building blocks for food or other products for the plant Calvin Cycle - Light Independent Reaction • ATP and NADPH from the light reaction are used as an energy source to convert Carbon From CO2 and a 5 carbon molecule 1st into a 6 carbon molecule and then into (2) 3 carbon molecules. • These 3 carbon molecules (G3P)are used by the plant as building blocks to make sucrose and other products like cellulose that the plant needs. • Some of the molecules are used to rebuild the 5 carbon molecule used at the beginning of the Calvin cycle so they return to the cycle. • ATP is now ADP and NADPH is now NADP+ and is returned to the light reaction Photosynthesis – In Simplest Terms What you have to know This Respiration PHOTOSYNTHESIS 6CO2 + 6H2O Energy C6H12O6 + 6O2 RESPIRATION C6H12O6 + 6O2 6CO2 + 6H2O + ENERGY Photorespiration • Photoresiration happens when there is a shortage of CO2 available to use in the Calvin Cycle of photosynthesis • Often O2 will fill in where CO2 entered before and another molecule instead of the normal 3 carbon building blocks is manufactured. • This new molecule has yet to prove to have any use to the plant and has to then be broken down again by the plant. • This is a part of C3 Photosynthesis which is the system of most plants and happens usually when stomata have to close on a hot day. Crassulacean Acid Metabolism (CAM) Plants CAM was first discovered in the Crassulaceae family of plants and are plants that have another way to carry out photosynthesis. Members of many other plant families are CAM plants: Euphorbiaceae Cactaceae Orchidaceae Liliaceae Bromiliadaceae Agavaceae Crassulacean Acid Metabolism Night - Stomata Open • CO2 brought into leaf cells used to make an acid – Malic acid • Malic acid is stored in the cells Day - Stomata Closed • Acid Broken down CO2 Photosynthesis • 6H2O + 6CO2 C6H12O6 + 6O2 By having stomata open at night water loss from the leaves is less than if stomata were open during the day giving the plant an advantage in hot dry areas Some Examples of CAM Plants Some Cactus Some Orchids Some bromeliads like pineapple Crassulaceae family “Jade Plants” C4 Photosynthesis • In C4 photosynthesis Stomata are open during the day • CO2 diffuses into the leaf • C4 plants are able to store CO2 in the leaf cells as an acid to use as a later source of CO2 • If water stress occurs during the afternoon, the stomata will close to protect the plant from water loss.s • C4 plant continues to photosynthesize using stored CO2 Warm season grasses are C4 plants. They use less water and even under water stress conditions, continue to photosynthesize and grow. Corn Examples of C4 Plants Bermudagrass C4 plants are typically able to endure challenging warm temperatures that might stress most (C3) plants. Sorghum The C4 Photosynthesis Advantage in Southern California For Warm Season Grasses Tall Fescue ‘Marathon II” - Cool Season Common Bermudagrass – Warm season We have no native turf grasses in California. We live in the middle of a transitional zone that doesn’t grow cool season grasses very easily. Our long dry Summers set the stage for competition between cool season grasses and warm season warm season grasses. Kikuyugrass – Warm season OCC Horticulture department lawn with Cool season Tall fescue being challenged by Common Bermudagrass - A weed Regional Grass Map of the United States showing the transitional area of Southern California being right on the edge of transitional and Warm Season grasses. What you need to know • • • • What part of the electromagnetic scale do plants use What are the parts of the chloroplast What happens in the light reaction - What powers it? - What is produced? What happens in the Calvin Cycle. What powers it. What molecule used as a building block is formed. • What is photorespiration? What causes it to happen? Why is it bad? • What is Crassulacean Acid Metabolism?(CAM) What types of plants are cam plants how does CAM photosynthesis method help these plants? • How does C4 photosynthesis work?