What Are the Products of Photosynthesis? What Are the Products of Photosynthesis? What Are the Products of Photosynthesis? Result of Photosynthesis in Plants Chlorophyll in plant leaves converts carbon dioxide and water into the products glucose and oxygen. Connie Coleman, Getty Images Question: What are the products of photosynthesis? Short Answer: The products of photosynthesis are sugar (glucose) and oxygen. Photosynthesis is the name given to the set of chemical reactions performed by plants to convert energy from the sun into chemical energy in the form of sugar. Specifically, plants use energy from sunlight to react carbon dioxide and water to produce sugar ( glucose ) and oxygen . Many reactions occur, but the overall chemical reaction for photosynthesis is: 6 CO2 + 6 H2O + light → C6H12O6 + 6 O2 Carbon Dioxide + Water + Light yields Glucose + Oxygen In a plant, the carbon dioxide enters via leaf stomates by diffusion . Water is absorbed through the roots and is transported to leaves through the xylem. Solar energy is absorbed by chlorophyll in the leaves. The reactions of photosynthesis occur in the chloroplasts of plants.

In photosynthetic bacteria, the process takes place where chlorophyll or a related pigment is embedded in the plasma membrane. continue reading below our video Test Your General Science Knowledge The oxygen and water produced in photosynthesis exit through the stomata. Actually, plants reserve very little of the glucose for immediate use. Glucose molecules are combined by dehydration synthesis to form cellulose, which is used as a structural material. Dehydration synthesis is also used to convert glucose to starch, which plants use to store energy. Intermediate Products of Photosynthesis The overall chemical equation is a summary of a series of chemical reactions. These reactions occur in two stages. The light reactions require light (as you might imagine), while the dark reactions are controlled by enzymes. They don't require darkness to occur -- they simply don't depend on light. The light reactions absorb light and harness the energy to powder electron transfers. Most photosynthetic organisms capture visible light, although there are some that use infrared light. Products of these reactions are adenosine triphosphate (ATP) and reduced nicotinamde adenine dinucleotide phosphate (NADPH). In plant cells, the light-dependent reactions occur in the chloroplast thylakoid membrane.

The overall reaction for the light dependent reactions is: 2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O2 In the dark stage, ATP and NADPH ultimately reduce carbon dioxide and other molecules. Carbon dioxide from the air is "fixed" into a biologically usable form, glucose. In plants, algae, and cyanobacteria, the dark reactions are termed the Calvin cycle. Bacteria may use different reactions, including a reverse Krebs cycle . The overall reaction for the light independent reaction of a plant (Calvin cycle) is: 3 CO2 + 9 ATP + 6 NADPH + 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O During carbon fixation, the three-carbon product of the Calvin cycle is converted into the final carbohydrate product. Factors That Affect the Rate of Photosynthesis Like any chemical reaction, the availability of the reactants determines the amount of products that can be made. Limiting the availability of carbon dioxide or water slows the production of glucose and oxygen.

Also, the rate of the reactions is affected by temperature and the availability of minerals that may be needed in the intermediate reactions. The overall health of the plant (or other photosynthetic organism) also plays a role. The rate of metabolic reactions is determined in part by the maturity of the organism and whether it's flowering or bearing fruit. What are the two main products of photosynthesis? | Reference.com What are the two main products of photosynthesis? A: Quick Answer The two main output products of photosynthesis are oxygen and sugar. Plants use energy from the sun to produce these items from water and carbon dioxide. The oxygen produced is emitted as a waste product, while the sugar is used to produce energy through cellular respiration. Full Answer Photosynthesis takes six molecules of carbon dioxide and six of water and uses sunlight energy to convert them into six molecules of oxygen and a single sugar molecule with the structure C6H12O6. The oxygen produced in this chemical reaction provides the essential ingredient for respiration by humans and other animals; photosynthesis is thus necessary for both plants and animals to survive. Photosynthesis occurs inside plant cells in a material called chlorophyll. This substance is what gives plants their green color.

Chlorophyll absorbs energy from sunlight, particularly from the red and blue wavelengths; the green wavelengths are reflected away from the chlorophyll, giving a green appearance. This energy is required to make the chemical bonds that allow photosynthesis to take place. In order to achieve photosynthesis, a plant must have access to water, sunlight and carbon dioxide. However, different environments provide different access to these resources. For example, desert plants have very limited access to water. As a result, plants have evolved to maximize their local resources. Broad leaves provide massive surface area to volume ratios, ensuring maximum access to sunlight. Similarly, some plants have extensive root systems to provide greater access to water. PHOTOSYNTHESIS PHOTOSYNTHESIS What is Photosynthesis? | Back to Top Photosynthesis is the process by which plants, some bacteria, and some protistans use the energy from sunlight to produce sugar, which cellular respiration converts into ATP , the "fuel" used by all living things. The conversion of unusable sunlight energy into usable chemical energy, is associated with the actions of the green pigment chlorophyll . Most of the time, the photosynthetic process uses water and releases the oxygen that we absolutely must have to stay alive.

Oh yes, we need the food as well! We can write the overall reaction of this process as: 6H2O + 6CO2 ----------> C6H12O6+ 6O2 Most of us don't speak chemicalese, so the above chemical equation translates as: six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen Diagram of a typical plant, showing the inputs and outputs of the photosynthetic process. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Leaves and Leaf Structure | Back to Top Plants are the only photosynthetic organisms to have leaves (and not all plants have leaves). A leaf may be viewed as a solar collector crammed full of photosynthetic cells. The raw materials of photosynthesis, water and carbon dioxide, enter the cells of the leaf, and the products of photosynthesis, sugar and oxygen, leave the leaf. Cross section of a leaf, showing the anatomical features important to the study of photosynthesis: stoma, guard cell, mesophyll cells, and vein.

Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Water enters the root and is transported up to the leaves through specialized plant cells known as xylem (pronounces zigh-lem). Land plants must guard against drying out (desiccation) and so have evolved specialized structures known as stomata to allow gas to enter and leave the leaf. Carbon dioxide cannot pass through the protective waxy layer covering the leaf (cuticle), but it can enter the leaf through an opening (the stoma; plural = stomata; Greek for hole) flanked by two guard cells. Likewise, oxygen produced during photosynthesis can only pass out of the leaf through the opened stomata. Unfortunately for the plant, while these gases are moving between the inside and outside of the leaf, a great deal water is also lost. Cottonwood trees, for example, will lose 100 gallons of water per hour during hot desert days. Carbon dioxide enters single-celled and aquatic autotrophs through no specialized structures. Pea Leaf Stoma, Vicea sp. (SEM x3,520).

This image is copyright Dennis Kunkel at , used with permission. The Nature of Light | Back to Top White light is separated into the different colors (=wavelengths) of light by passing it through a prism. Wavelength is defined as the distance from peak to peak (or trough to trough). The energy of is inversely porportional to the wavelength: longer wavelengths have less energy than do shorter ones. Wavelength and other saspects of the wave nature of light. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The order of colors is determined by the wavelength of light. Visible light is one small part of the electromagnetic spectrum. The longer the wavelength of visible light, the more red the color. Likewise the shorter wavelengths are towards the violet side of the spectrum. Wavelengths longer than red are referred to as infrared, while those shorter than violet are ultraviolet. The electromagnetic spectrum. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Light behaves both as a wave and a particle.

Wave properties of light include the bending of the wave path when passing from one material (medium) into another (i.e. the prism, rainbows, pencil in a glass-of-water, etc.). The particle properties are demonstrated by the photoelectric effect. Zinc exposed to ultraviolet light becomes positively charged because light energy forces electrons from the zinc. These electrons can create an electrical current. Sodium, potassium and selenium have critical wavelengths in the visible light range. The critical wavelength is the maximum wavelength of light (visible or invisible) that creates a photoelectric effect. Chlorophyll and Accessory Pigments | Back to Top A pigment is any substance that absorbs light. The color of the pigment comes from the wavelengths of light reflected (in other words, those not absorbed). Chlorophyll , the green pigment common to all photosynthetic cells, absorbs all wavelengths of visible light except green, which it reflects to be detected by our eyes. Black pigments absorb all of the wavelengths that strike them. White pigments/lighter colors reflect all or almost all of the energy striking them. Pigments have their own characteristic absorption spectra, the absorption pattern of a given pigment. Absorption and transmission of different wavelengths of light by a hypothetical pigment.

Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Chlorophyll is a complex molecule. Several modifications of chlorophyll occur among plants and other photosynthetic organisms. All photosynthetic organisms (plants, certain protistans, prochlorobacteria, and cyanobacteria) have chlorophyll a . Accessory pigments absorb energy that chlorophyll a does not absorb. Accessory pigments include chlorophyll b (also c, d, and e in algae and protistans), xanthophylls, and carotenoids (such as beta-carotene). Chlorophyll a absorbs its energy from the Violet-Blue and Reddish orange-Red wavelengths, and little from the intermediate (Green-Yellow-Orange) wavelengths. Molecular model of chlorophyll. The above image is from . Molecular model of carotene. The above image is from . Carotenoids and chlorophyll b absorb some of the energy in the green wavelength. Why not so much in the orange and yellow wavelengths?

Both chlorophylls also absorb in the orange-red end of the spectrum (with longer wavelengths and lower energy). The origins of photosynthetic organisms in the sea may account for this. Shorter wavelengths (with more energy) do not penetrate much below 5 meters deep in sea water. The ability to absorb some energy from the longer (hence more penetrating) wavelengths might have been an advantage to early photosynthetic algae that were not able to be in the upper ( photic) zone of the sea all the time. The molecular structure of chlorophylls. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The action spectrum of photosynthesis is the relative effectiveness of different wavelengths of light at generating electrons. If a pigment absorbs light energy, one of three things will occur. Energy is dissipated as heat. The energy may be emitted immediately as a longer wavelength, a phenomenon known as fluorescence. Energy may trigger a chemical reaction, as in photosynthesis.

Chlorophyll only triggers a chemical reaction when it is associated with proteins embedded in a membrane (as in a chloroplast) or the membrane infoldings found in photosynthetic prokaryotes such as cyanobacteria and prochlorobacteria. Absorption spectrum of several plant pigments (left) and action spectrum of elodea (right), a common aquarium plant used in lab experiments about photosynthesis. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The structure of the chloroplast and photosynthetic membranes | Back to Top The thylakoid is the structural unit of photosynthesis. Both photosynthetic prokaryotes and eukaryotes have these flattened sacs/vesicles containing photosynthetic chemicals. Only eukaryotes have chloroplasts with a surrounding membrane. Thylakoids are stacked like pancakes in stacks known collectively as grana . The areas between grana are referred to as stroma . While the mitochondrion has two membrane systems, the chloroplast has three, forming three compartments. Structure of a chloroplast.

Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Stages of Photosynthesis | Back to Top Photosynthesis is a two stage process. The first process is the Light Dependent Process ( Light Reactions ), requires the direct energy of light to make energy carrier molecules that are used in the second process. The Light Independent Process (or Dark Reactions ) occurs when the products of the Light Reaction are used to form C-C covalent bonds of carbohydrates. The Dark Reactions can usually occur in the dark, if the energy carriers from the light process are present. Recent evidence suggests that a major enzyme of the Dark Reaction is indirectly stimulated by light, thus the term Dark Reaction is somewhat of a misnomer. The Light Reactions occur in the grana and the Dark Reactions take place in the stroma of the chloroplasts. Overview of the two steps in the photosynthesis process. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission.

Light Reactions | Back to Top In the Light Dependent Processes (Light Reactions) light strikes chlorophyll a in such a way as to excite electrons to a higher energy state. In a series of reactions the energy is converted (along an electron transport process) into ATP and NADPH . Water is split in the process, releasing oxygen as a by-product of the reaction. The ATP and NADPH are used to make C-C bonds in the Light Independent Process (Dark Reactions). In the Light Independent Process, carbon dioxide from the atmosphere (or water for aquatic/marine organisms) is captured and modified by the addition of Hydrogen to form carbohydrates (general formula of carbohydrates is [CH2O]n). The incorporation of carbon dioxide into organic compounds is known as carbon fixation. The energy for this comes from the first phase of the photosynthetic process. Living systems cannot directly utilize light energy, but can, through a complicated series of reactions, convert it into C-C bond energy that can be released by glycolysis and other metabolic processes. Photosystems are arrangements of chlorophyll and other pigments packed into thylakoids.

Many Prokaryotes have only one photosystem, Photosystem II (so numbered because, while it was most likely the first to evolve, it was the second one discovered). Eukaryotes have Photosystem II plus Photosystem I. Photosystem I uses chlorophyll a, in the form referred to as P700. Photosystem II uses a form of chlorophyll a known as P680. Both "active" forms of chlorophyll a function in photosynthesis due to their association with proteins in the thylakoid membrane. Action of a photosystem. This image is from the University of Minnesota page at . Photophosphorylation is the process of converting energy from a light-excited electron into the pyrophosphate bond of an ADP molecule. This occurs when the electrons from water are excited by the light in the presence of P680. The energy transfer is similar to the chemiosmotic electron transport occurring in the mitochondria. Light energy causes the removal of an electron from a molecule of P680 that is part of Photosystem II. The P680 requires an electron, which is taken from a water molecule, breaking the water into H+ ions and O-2 ions.

These O-2 ions combine to form the diatomic O2 that is released. The electron is "boosted" to a higher energy state and attached to a primary electron acceptor, which begins a series of redox reactions, passing the electron through a series of electron carriers, eventually attaching it to a molecule in Photosystem I. Light acts on a molecule of P700 in Photosystem I, causing an electron to be "boosted" to a still higher potential. The electron is attached to a different primary electron acceptor (that is a different molecule from the one associated with Photosystem II). The electron is passed again through a series of redox reactions, eventually being attached to NADP+ and H+ to form NADPH, an energy carrier needed in the Light Independent Reaction. The electron from Photosystem II replaces the excited electron in the P700 molecule. There is thus a continuous flow of electrons from water to NADPH. This energy is used in Carbon Fixation. Cyclic Electron Flow occurs in some eukaryotes and primitive photosynthetic bacteria. No NADPH is produced, only ATP.

This occurs when cells may require additional ATP, or when there is no NADP+ to reduce to NADPH. In Photosystem II, the pumping to H ions into the thylakoid and the conversion of ADP + P into ATP is driven by electron gradients established in the thylakoid membrane. Noncyclic photophosphorylation (top) and cyclic photophosphorylation (bottom). These processes are better known as the light reactions. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The above diagrams present the "old" view of photophosphorylation. We now know where the process occurs in the chloroplast, and can link that to chemiosmotic synthesis of ATP. Chemiosmosis as it operates in photophosphorylation within a chloroplast. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Halobacteria, which grow in extremely salty water, are facultative aerobes, they can grow when oxygen is absent.

Purple pigments, known as retinal (a pigment also found in the human eye) act similar to chlorophyll. The complex of retinal and membrane proteins is known as bacteriorhodopsin, which generates electrons which establish a proton gradient that powers an ADP-ATP pump, generating ATP from sunlight without chlorophyll. This supports the theory that chemiosmotic processes are universal in their ability to generate ATP. Dark Reaction | Back to Top Carbon-Fixing Reactions are also known as the Dark Reactions (or Light Independent Reactions). Carbon dioxide enters single-celled and aquatic autotrophs through no specialized structures, diffusing into the cells. Land plants must guard against drying out (desiccation) and so have evolved specialized structures known as stomata to allow gas to enter and leave the leaf. The Calvin Cycle occurs in the stroma of chloroplasts (where would it occur in a prokaryote?). Carbon dioxide is captured by the chemical ribulose biphosphate (RuBP ). RuBP is a 5-C chemical. Six molecules of carbon dioxide enter the Calvin Cycle, eventually producing one molecule of glucose. The reactions in this process were worked out by Melvin Calvin (shown below).

The above image is from , Ernest OrlandoLawrence Berkeley National Laboratory. " One of the new areas, cultivated both in Donner and the Old Radiation Laboratory, was the study of organic compounds labeled with carbon-14. Melvin Calvin took charge of this work at the end of the war in order to provide raw materials for John Lawrence's researches and for his own study of photosynthesis. Using carbon-14, available in plenty from Hanford reactors, and the new techniques of ion exchange, paper chromatography, and radioautography, Calvin and his many associates mapped the complete path of carbon in photosynthesis. The accomplishment brought him the Nobel prize in chemistry in 1961. (The preceding information was excerpted from the text of the Fall 1981 issue of LBL Newsmagazine.) Citation Caption: LBL News, Vol.6, No.3, Fall 1981 Melvin Calvin shown with some of the apparatus he used to study the role of carbon in photosynthesis." The first steps in the Calvin ccycle. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission.

The first stable product of the Calvin Cycle is phosphoglycerate (PGA) , a 3-C chemical. The energy from ATP and NADPH energy carriers generated by the photosystems is used to attach phosphates to ( phosphorylate ) the PGA. Eventually there are 12 molecules of glyceraldehyde phosphate (also known as phosphoglyceraldehyde or PGAL , a 3-C), two of which are removed from the cycle to make a glucose . The remaining PGAL molecules are converted by ATP energy to reform 6 RuBP molecules, and thus start the cycle again. Remember the complexity of life, each reaction in this process, as in Kreb's Cycle, is catalyzed by a different reaction-specific enzyme . C-4 Pathway | Back to Top Some plants have developed a preliminary step to the Calvin Cycle (which is also referred to as a C-3 pathway), this preamble step is known as C-4.

While most C-fixation begins with RuBP, C-4 begins with a new molecule, phosphoenolpyruvate (PEP), a 3-C chemical that is converted into oxaloacetic acid (OAA, a 4-C chemical) when carbon dioxide is combined with PEP. The OAA is converted to Malic Acid and then transported from the mesophyll cell into the bundle-sheath cell, where OAA is broken down into PEP plus carbon dioxide. The carbon dioxide then enters the Calvin Cycle, with PEP returning to the mesophyll cell. The resulting sugars are now adjacent to the leaf veins and can readily be transported throughout the plant. C-4 photosynthsis involves the separation of carbon fixation and carbohydrate systhesis in space and time. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission.

The capture of carbon dioxide by PEP is mediated by the enzyme PEP carboxylase, which has a stronger affinity for carbon dioxide than does RuBP carboxylase When carbon dioxide levels decline below the threshold for RuBP carboxylase, RuBP is catalyzed with oxygen instead of carbon dioxide. The product of that reaction forms glycolic acid, a chemical that can be broken down by photorespiration, producing neither NADH nor ATP, in effect dismantling the Calvin Cycle. C-4 plants, which often grow close together, have had to adjust to decreased levels of carbon dioxide by artificially raising the carbon dioxide concentration in certain cells to prevent photorespiration. C-4 plants evolved in the tropics and are adapted to higher temperatures than are the C-3 plants found at higher latitudes. Common C-4 plants include crabgrass, corn, and sugar cane. Note that OAA and Malic Acid also have functions in other processes, thus the chemicals would have been present in all plants, leading scientists to hypothesize that C-4 mechanisms evolved several times independently in response to a similar environmental condition, a type of evolution known as convergent evolution. Photorespiration.

Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. We can see anatomical differences between C3 and C4 leaves. Leaf anatomy of a C3 (top) and C4 (bottom) plant. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. The Carbon Cycle | Back to Top Plants may be viewed as carbon sinks , removing carbon dioxide from the atmosphere and oceans by fixing it into organic chemicals. Plants also produce some carbon dioxide by their respiration, but this is quickly used by photosynthesis. Plants also convert energy from light into chemical energy of C-C covalent bonds. Animals are carbon dioxide producers that derive their energy from carbohydrates and other chemicals produced by plants by the process of photosynthesis. The balance between the plant carbon dioxide removal and animal carbon dioxide generation is equalized also by the formation of carbonates in the oceans. This removes excess carbon dioxide from the air and water (both of which are in equilibrium with regard to carbon dioxide).

Fossil fuels, such as petroleum and coal, as well as more recent fuels such as peat and wood generate carbon dioxide when burned. Fossil fuels are formed ultimately by organic processes, and represent also a tremendous carbon sink. Human activity has greatly increased the concentration of carbon dioxide in air. This increase has led to global warming, an increase in temperatures around the world, the Greenhouse Effect. The increase in carbon dioxide and other pollutants in the air has also led to acid rain , where water falls through polluted air and chemically combines with carbon dioxide, nitrous oxides, and sulfur oxides, producing rainfall with pH as low as 4. This results in fish kills and changes in soil pH which can alter the natural vegetation and uses of the land. The Global Warming problem can lead to melting of the ice caps in Greenland and Antarctica, raising sea-level as much as 120 meters. Changes in sea-level and temperature would affect climate changes, altering belts of grain production and rainfall patterns. Learning Objectives | Back to Top After completing this chapter you should be able to: Study the general equation for photosynthesis and be able to indicate in which process each reactant is used and each product is produced.

List the two major processes of photosynthesis and state what occurs in those sets of reactions. Distinguish between organisms known as autotrophs and those known as heterotrophs as pertains to their modes of nutrition. Explain the significance of the ATP/ADP cycle. Describe the nature of light and how it is associated with the release of electrons from a photosystem. Describe how the pigments found on thylakoid membranes are organized into photosystems and how they relate to photon light energy. Describe the role that chlorophylls and the other pigments found in chloroplasts play to initiate the light-dependent reactions. Describe the function of electron transport systems in the thylakoid membrane. Explain the role of the two energy-carrying molecules produced in the light-dependent reactions (ATP and NADPH) in the light-independent reactions. Describe the Calvin-Benson cycle in terms of its reactants and products. Explain how C-4 photosynthesis provides an advantage for plants in certain environments. Describe the phenomenon of acid rain, and how photosynthesis relates to acid rain and the carbon cycle.. Review Questions | Back to Top 1.

The organic molecule produced directly by photosynthesis is: a) lipids; b) sugar; c) amino acids; d) DNA 2. The photosynthetic process removes ___ from the environment. a) water; b) sugar; c) oxygen; d) chlorophyll; e) carbon dioxide 3. The process of splitting water to release hydrogens and electrons occurs during the _____ process. a) light dependent; b) light independent; c) carbon fixation; d) carbon photophosphorylation; e) glycolysis 4. The process of fixing carbon dioxide into carbohydrates occurs in the ____ process. a) light dependent; b) light independent; c) ATP synthesis; d) carbon photophosphorylation; e) glycolysis 5. Carbon dioxide enters the leaf through ____. a) chloroplasts; b) stomata: c) cuticle; d) mesophyll cells; e) leaf veins 6. The cellular transport process by which carbon dioxide enters a leaf (and by which water vapor and oxygen exit) is ___. a) osmosis; b) active transport; c. co- transport; d) diffusion; e) bulk flow 7.

Which of the following creatures would not be an autotroph? a) cactus; b) cyanobacteria; c) fish; d) palm tree; e) phytoplankton 8. The process by which most of the world's autotrophs make their food is known as ____. a) glycolysis; b) photosynthesis; c) chemosynthesis; d) herbivory; e) C-4 cycle 9. The process of ___ is how ADP + P are converted into ATP during the Light dependent process. a) glycolysis; b) Calvin Cycle; c) chemiosmosis; d) substrate-level phosphorylation; e) Kreb's Cycle 10. Once ATP is converted into ADP + P, it must be ____. a) disassembled into components (sugar, base, phosphates) and then ressembled; b) recharged by chemiosmosis; c) converted into NADPH; d) processed by the glycolysis process; e) converted from matter into energy. 11. Generally speaking, the longer the wavelenght of light, the ___ the available energy of that light.

a) smaller; b) greater; c) same 12. The section of the electromagnetic spectrum used for photosynthesis is ___. a) infrared; b) ultraviolet; c) x-ray; d) visible light; e) none of the above 13. The colors of light in the visible range (from longest wavelength to shortest) is ___. a) ROYGBIV; b) VIBGYOR; c) GRBIYV; d) ROYROGERS; e) EBGDF 14. The photosynthetic pigment that is essential for the process to occur is ___. a) chlorophyll a; b) chlorophyll b; c) beta carotene; d) xanthocyanin; e) fucoxanthin 15. When a pigment reflects red light, _____. a) all colors of light are absorbed; b) all col;ors of light are reflected; c) green light is reflected, all others are absorbed; d) red light is reflected, all others are absorbed; e) red light is absorbed after it is reflected into the internal pigment molecules. 16. Chlorophyll a absorbs light energy in the ____color range.

a) yellow-green; b) red-organge; c) blue violet; d) a and b; e) b and c. 17. A photosystem is ___. a) a collection of hydrogen-pumping proteins; b) a collection of photosynthetic pigments arranged in a thylakjoid membrane; c) a series of electron-accepting proteins arranged in the thylakoid membrane; d. found only in prokaryotic organisms; e) multiple copies of chlorophyll a located in the stroma of the chloroplast. 18. The individual flattened stacks of membrane material inside the chloroplast are known as ___. a) grana; b) stroma; c) thylakoids; d) cristae; e) matrix 19. The fluid-filled area of the chloroplast is the ___. a) grana; b) stroma; c) thylakoids; d) cristae; e) matrix 20. The chloroplast contains all of these except ___. a) grana; b) stroma; c) DNA; d) membranes; e) endoplasmic reticulum 21.

The chloroplasts of plants are most close in size to __. a) unfertilized human eggs; b) human cheek cells; c) human nerve cells; d) bacteria in the human mouth; e) viruses 22. Which of these photosynthetic organisms does not have a chloroplast? a) plants; b) red algae; c) cyanobacteria; d) diatoms; e) dinoflagellates 23. The photoelectric effect refers to ____. a) emission of electrons from a metal when energy of a critical wavelength strikes the metal; b) absorbtion of electrons from the surrounding environment when energy of a critical wavelength is nearby; c) emission of electrons from a metal when struck by any wavelength of light; d) emission of electrons stored in the daytime when stomata are open at night; e) release of NADPH and ATP energy during the Calvin Cycvle when light iof a specific wavelength strikes the cell. 24. Light of the green wavelengths is commonly absorbed by which accessory pigment? a) chlorophyll a; b) chlorophyll b; c) phycocyanin; d) beta carotene 25.

The function of the electron transport proteins in the thyakoid membranes is ___. a) production of ADP by chemiosmosis; b) production of NADPH by substrate-level phosphorylation; c) pumping of hydrogens into the thylakoid space for later generation of ATP by chemiosmosis; d) pumping of hydrogens into the inner cristae space for later generation of ATP by chemiosmosis; e) preparation of water for eventual incorporation into glucose 26. ATP is known as the energy currency of the cell because ____. a) ATP is the most readily usable form of energy for cells; b) ATP passes energy along in an electron transport chain; c) ATP energy is passed to NADPH; d) ATP traps more energy than is produced in its formation; e) only eukaryotic cells use this energy currency. 27. Both cyclic and noncyclic photophosphorylation produce ATP. We can infer that the purpose of ATP in photosynthesis is to ____.

a) supply hydrogen to the carbohydrate; b) supply carbon to the carbohydrate; c) supply energy that can be used to form a carbohydrate; d) transfer oxygens from the third phosphate group to the carbohydrate molecule; e) convert RuBP into PGA 28. The role of NADPH in oxygen-producing photosynthesis is to ____. a) supply hydrogen to the carbohydrate; b) supply carbon to the carbohydrate; c) supply energy that can be used to form a carbohydrate; d) transfer oxygens from the third phosphate group to the carbohydrate molecule; e) convert RuBP into PGA. 29. The dark reactions require all of these chemicals to proceed except ___. a) ATP; b) NADPH; c) carbon dioxide; d) RUBP; e) oxygen 30. The first stable chemical formed by the Calvin Cycle is _____. a) RUBP; b) RU/18; c) PGA; d) PGAL; e) Rubisco 31.

The hydrogen in the carbohydrate produced by the Calvin Cycle comes from ___ a.) ATP; b) NADPH; c) the environment if the pH is very acidic; d) a and b; e) a and c 32. The carbon incorporated into the carbohydrate comes from ___. a) ATP; b) NADPH; c) carbon dioxide; d) glucose; e) organic molecules 33. C-4 photosynthesis is so named because _____. a) it produces a three carbon compound as the first stable product of photosynthesis; b) it produces a four carbon compound as the first stable produc of photosynthesis; c) it produces four ATP and four NADPH molecules for carbon fixation.; d) there are only four steps in this form of carbon fixation into carbohydrate. The important role of photosynthesis | MSU Extension The important role of photosynthesis Photosynthesis is not just about oxygen production it is also about energy production. Posted on April 9, 2013 by Bill Cook , Michigan State University Extension Pin It Most people would agree that photosynthesis is a great thing. I’ve never heard anyone argue against it. However, some folks have missed the purpose of photosynthesis. It’s not oxygen production.

The primary function of photosynthesis is to convert solar energy into chemical energy and then store that chemical energy for future use. For the most part, the planet’s living systems are powered by this process. It’s not particularly efficient by human engineering standards, but it does the job. Photosynthesis happens in regions of a cell called chloroplasts. The chemistry and physics are complex. It’s a bit humbling to consider that the energy in our bodies travels 93 million miles in a little more than eight minutes, and that life has tapped into that energy stream. For a short time that energy is tied up in biological systems before it continues on its merry way into the dark of space. In essence, green plants take carbon, hydrogen and oxygen from the molecules of carbon dioxide and water, and then recombine them into a new molecule called glucose. This happens in the presence of sunlight, of course. Energy is stored in the bonds of the glucose molecule. Glucose is a fairly simple sugar, easy to break down. Ever wonder why kids bounce off the walls and ceilings soon after a good dose of sugar? Chemically speaking, the inputs to photosynthesis are six carbon atoms, 12 hydrogen atoms and 18 oxygen atoms.

Glucose uses six carbon, 12 hydrogen, and six oxygen molecules. Simple math shows 12 leftover oxygen atoms, or six oxygen molecules. Oxygen atoms prefer mates. Interestingly, and not coincidentally, the process of respiration breaks apart the glucose molecule. Respiration occurs in the cells of nearly all living things. The released energy is then used for all sorts of metabolic activity, including the energy that you are using to read this article. Respiration happens in regions of a cell called mitochondria. The chemical reactions are the reverse of photosynthesis, using a glucose molecule and six oxygen molecules (12 atoms) as inputs. Energy is released along with some carbon dioxide and water. But this is enough chemistry. Trees and other green plants practice respiration, too, just like animals, but they also practice photosynthesis. This is why ecologists categorize green plants as “producers” and most every other life form as a “consumer.” It’s about the energy. OK, there are decomposers, too, but that’s another story and they’re still dependent upon the energy captured by the producers. Oxygen is a byproduct of photosynthesis and, correspondingly, carbon dioxide the byproduct of respiration.

Trees are often credited as the major oxygen generator for the planet, but that would be false. Most of the planet is covered with water and the collective photosynthesis of lowly algae is the true oxygen machine. Nevertheless, trees and forests are, indeed, significant oxygen producers. However, if oxygen was the only benefit of trees and forests, we could easily live without them. And some forests actually produce more carbon dioxide than oxygen. Fortunately, the benefits of both trees and forests extend far beyond something as narrow as oxygen production. Much of the basic structural material of plants and wood is cellulose, which is an especially complex sugar. The constituent molecules of carbon, hydrogen and oxygen can be recombined to form lots of useful chemicals such as ethanol, perfumes, bioplastics, clothing fabrics and a range of industrial ingredients. It’s generally agreed that sources from within renewable living ecosystems have distinct advantages over using the ancient materials that make up fossil fuels. Plants and photosynthesis are the basis of fossil fuels, too, but from millions and millions of years ago. Bringing huge volumes of those molecules back into living ecosystems has a few drawbacks that science has gotten pretty good at measuring and describing.

Trees, forests, forest soils and forest products are mighty important in the cycling of carbon and the relative size of various carbon pools. There are other elements that also cycle through forests. Science has a pretty good handle on these relationships, too. Michigan residents might do well to place a bit more weight on these service benefits of trees, forests, and forest management. As for photosynthesis itself, maybe it’s better if we think more about the energy capture and less about the oxygen production. This article was published by Michigan State University Extension . For more information, visit . To have a digest of information delivered straight to your email inbox, visit . To contact an expert in your area, visit , or call 888-MSUE4MI (888-678-3464). Related Events Photosynthesis Photosynthesis: Photosynthesis is the process by which green plants and certain other organisms transform light energy into chemical energy. Photosynthesis in green plants harnesses the energy of sunlight to convert carbon dioxide, water, and minerals into organic compounds and gaseous oxygen.

In addition to the green plants, photosynthetic organisms include certain protists (such as euglenoids and diatoms), cyanophytes (blue-green algae), and various bacteria. The process in photosynthetic protists and cyanophytes resembles that in green plants; it differs in the photosynthetic bacteria in that compounds other than water serve as a reactant and oxygen is not produced. All photosynthetic organisms--with the exception of a minor group of bacteria, the halobacteria--contain the light-absorbing pigment chlorophyll, which plays a key role in the transfer of energy from light to chemical compounds. Photosynthesis is the fundamental process that maintains life on Earth. Living cells convert food into energy and structural components. Almost all organisms derive this food, directly or indirectly, from the organic compounds formed within plants during photosynthesis. The stored energy in these compounds is essential for growth, repair, reproduction, movement, and other vital functions. Without photosynthesis, not only would replenishment of the fundamental food supply halt but the Earth would eventually become devoid of oxygen. Just as the organic molecules in the bodies of living organisms contain energy converted by photosynthesis from the energy of the Sun, so do the molecules of fossil fuels.

The energy provided by coal, oil, and gas comes from photosynthesis carried on by plants of earlier times and preserved down through the ages, to be released by combustion in modern industrial processes. Most of the energy released both by the burning of fossil fuels and by the metabolism of living cells is given off as heat and must be replaced by the continued input of radiant energy from the Sun. The principal organic products of plant photosynthesis are carbohydrates. Formation of the simple carbohydrate glucose is shown by the equation The molecules of glucose produced are usually linked with other molecules to form more complex carbohydrates. Other products of photosynthesis are formed by incorporating mineral elements into the process. The energy required to break the chemical bonds in the reactants and to create new bonds in the products is provided by light. The excess energy not used up in the chemical reactions is stored as chemical energy in the organic products formed. The rate of photosynthesis is dependent on the following environmental factors: light intensity, temperature, and the availability of carbon dioxide, water, and certain minerals. A shortage of any one of these factors can limit the rate of photosynthesis, and an increase in the particular rate-limiting factor will, up to a point, speed up the process.

The rate also varies with the plant species and its physiological state. Photosynthesis is not a single process but consists of a number of photochemical and enzymatic reactions. In green plants, the intricate apparatus required for such complex processes is located in the chloroplasts, the cell organelles that contain the chlorophyll. The chloroplasts are crowded with multiple layers of membranes, the lamellae, composed of proteins and lipids. The protein matter includes some of the enzymes and coenzymes used in the photosynthetic process; the lipid portion contains two types of chlorophyll, along with other pigments that assist in absorbing light energy. Excerpt from the Encyclopedia Britannica without permission. Main Structures and Summary of Photosynthesis About Watch and Favorite Watch Watching this resources will notify you when proposed changes or new versions are created so you can keep track of improvements that have been made. Favorite Favoriting this resource allows you to save it in the “My Resources” tab of your account. There, you can easily access this resource later when you’re ready to customize it or assign it to your students.

Main Structures and Summary of Photosynthesis In multicellular autotrophs, the main cellular structures that allow photosynthesis to take place include chloroplasts, thylakoids, and chlorophyll. Learning Objective Describe the main structures involved in photosynthesis and recall the chemical equation that summarizes the process of photosynthesis Key Points The chemical equation for photosynthesis is $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2.$ In plants, the process of photosynthesis takes place in the mesophyll of the leaves, inside the chloroplasts . Chloroplasts contain disc-shaped structures called thylakoids , which contain the pigment chlorophyll . Chlorophyll absorbs certain portions of the visible spectrum and captures energy from sunlight. Terms Full Text Overview of Photosynthesis Photosynthesis is a multi-step process that requires sunlight, carbon dioxide, and water as substrates . It produces oxygen and glyceraldehyde-3-phosphate (G3P or GA3P), simple carbohydrate molecules that are high in energy and can subsequently be converted into glucose , sucrose, or other sugar molecules. These sugar molecules contain covalent bonds that store energy.

Organisms break down these molecules to release energy for use in cellular work . Photosynthesis uses solar energy, carbon dioxide, and water to produce energy-storing carbohydrates. Oxygen is generated as a waste product of photosynthesis. The energy from sunlight drives the reaction of carbon dioxide and water molecules to produce sugar and oxygen, as seen in the chemical equation for photosynthesis. Though the equation looks simple, it is carried out through many complex steps. Before learning the details of how photoautotrophs convert light energy into chemical energy , it is important to become familiar with the structures involved. The basic equation for photosynthesis is deceptively simple. In reality, the process includes many steps involving intermediate reactants and products. Glucose, the primary energy source in cells, is made from two three-carbon GA3P molecules. Photosynthesis and the Leaf In plants, photosynthesis generally takes place in leaves, which consist of several layers of cells . The process of photosynthesis occurs in a middle layer called the mesophyll. The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata (singular: stoma ), which also play a role in the plant's regulation of water balance.

The stomata are typically located on the underside of the leaf, which minimizes water loss. Each stoma is flanked by guard cells that regulate the opening and closing of the stomata by swelling or shrinking in response to osmotic changes. Photosynthesis takes place in the mesophyll. The palisade layer contains most of the chloroplast and principal region in which photosynthesis is carried out. The airy spongy layer is the region of storage and gas exchange. The stomata regulate carbon dioxide and water balance. Photosynthesis within the Chloroplast In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast. For plants, chloroplast-containing cells exist in the mesophyll. Chloroplasts have a double membrane envelope composed of an outer membrane and an inner membrane. Within the double membrane are stacked, disc-shaped structures called thylakoids. Embedded in the thylakoid membrane is chlorophyll, a pigment that absorbs certain portions of the visible spectrum and captures energy from sunlight. Chlorophyll gives plants their green color and is responsible for the initial interaction between light and plant material, as well as numerous proteins that make up the electron transport chain.

The thylakoid membrane encloses an internal space called the thylakoid lumen . A stack of thylakoids is called a granum, and the liquid-filled space surrounding the granum is the stroma or "bed." photosynthesis | biology | Britannica.com Photosynthesis Elysia chlorotica Photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy . During photosynthesis in green plants, light energy is captured and used to convert water , carbon dioxide , and minerals into oxygen and energy-rich organic compounds . The location, importance, and mechanisms of photosynthesis. Encyclopædia Britannica, Inc. It would be impossible to overestimate the importance of photosynthesis in the maintenance of life on Earth . If photosynthesis ceased, there would soon be little food or other organic matter on Earth. Most organisms would disappear, and in time Earth’s atmosphere would become nearly devoid of gaseous oxygen. The only organisms able to exist under such conditions would be the chemosynthetic bacteria , which can utilize the chemical energy of certain inorganic compounds and thus are not dependent on the conversion of light energy.

Photosynthesis also is responsible for the “ fossil fuels ” (i.e., coal , oil , and gas ) that power industrial society. In past ages, green plants and small organisms that fed on plants increased faster than they were consumed, and their remains were deposited in Earth’s crust by sedimentation and other geological processes. There, protected from oxidation , these organic remains were slowly converted to fossil fuels. These fuels not only provide much of the energy used in factories, homes, and transportation but also serve as the raw material for plastics and other synthetic products. Unfortunately, modern civilization is using up in a few centuries the excess of photosynthetic production accumulated over millions of years. Consequently, the carbon dioxide that has been removed from the air to make carbohydrates in photosynthesis over millions of years is being returned at an incredibly rapid rate. The carbon dioxide concentration in Earth’s atmosphere is rising the fastest it ever has in Earth’s history, and this phenomenon is expected to have major implications on Earth’s climate . Similar Topics spermatophyte Requirements for food, materials, and energy in a world where human population is rapidly growing have created a need to increase both the amount of photosynthesis and the efficiency of converting photosynthetic output into products useful to people.

One response to those needs—the so-called Green Revolution —has achieved enormous improvements in agricultural yield through the use of chemical fertilizers , pest and plant- disease control, plant breeding, and mechanized tilling, harvesting, and crop processing. This effort has limited severe famines to a few areas of the world despite rapid population growth , but it has not eliminated widespread malnutrition . Despite the success of the Green Revolution, however, the rate at which yields of major crops have been increasing has declined since the early 1990s, especially for rice in Asia. In addition, for many countries, sustaining high rates of agricultural production requires ever-increasing inputs of fertilizers and pesticides, as well as the constant development of new plant varieties. A second agricultural revolution , based on plant genetic engineering , was forecast to lead to increases in plant productivity and thereby partially alleviate malnutrition. Achieving such increases, however, has turned out to be far more difficult than optimistic assessments predicted, and classical breeding techniques combined with improved farming practices have thus remained the most successful way to increase crop yields.

Since the 1970s, molecular biologists have possessed the means to manipulate a plant’s genetic material (deoxyribonucleic acid, or DNA ) with the hope of achieving improvements in disease and drought resistance, product yield and quality, frost hardiness, and other desirable properties. However, such traits are inherently complex, and the process of making changes to crop plants through genetic engineering has become far more complicated than some had hoped. In the future such genetic engineering may result in improvements in the process of photosynthesis, but by the first decades of the 21st century it had yet to demonstrate that it could dramatically increase crop yields. Plants: From Cute to Carnivorous Another intriguing area in the study of photosynthesis has been the discovery that certain animals are able to convert light energy into chemical energy. The emerald green sea slug ( Elysia chlorotica ), for example, acquires genes and chloroplasts from Vaucheria litorea, an alga it consumes, giving it a limited ability to produce chlorophyll. When enough chloroplasts are assimilated , the slug may forgo the ingestion of food.

The pea aphid (Acyrthosiphon pisum) can harness light to manufacture the energy-rich compound adenosine triphosphate (ATP); this ability has been linked to the aphid’s manufacture of carotenoid pigments. General characteristics Ringling Bros. Folds Its Tent Development of the idea The study of photosynthesis began in 1771 with observations made by the English clergyman and scientist Joseph Priestley . Priestley had burned a candle in a closed container until the air within the container could no longer support combustion . He then placed a sprig of mint plant in the container and discovered that after several days the mint had produced some substance (later recognized as oxygen) that enabled the confined air to again support combustion. In 1779 the Dutch physician Jan Ingenhousz expanded upon Priestley’s work, showing that the plant had to be exposed to light if the combustible substance (i.e., oxygen) was to be restored. He also demonstrated that this process required the presence of the green tissues of the plant.

In 1782 it was demonstrated that the combustion-supporting gas (oxygen) was formed at the expense of another gas, or “fixed air,” which had been identified the year before as carbon dioxide. Gas-exchange experiments in 1804 showed that the gain in weight of a plant grown in a carefully weighed pot resulted from the uptake of carbon, which came entirely from absorbed carbon dioxide, and water taken up by plant roots; the balance is oxygen, released back to the atmosphere. Almost half a century passed before the concept of chemical energy had developed sufficiently to permit the discovery (in 1845) that light energy from the sun is stored as chemical energy in products formed during photosynthesis. Overall reaction of photosynthesis In chemical terms, photosynthesis is a light-energized oxidation–reduction process . (Oxidation refers to the removal of electrons from a molecule; reduction refers to the gain of electrons by a molecule.) In plant photosynthesis, the energy of light is used to drive the oxidation of water (H2O), producing oxygen gas (O2), hydrogen ions (H+), and electrons .

Most of the removed electrons and hydrogen ions ultimately are transferred to carbon dioxide (CO2), which is reduced to organic products. Other electrons and hydrogen ions are used to reduce nitrate and sulfate to amino and sulfhydryl groups in amino acids , which are the building blocks of proteins . In most green cells , carbohydrates —especially starch and the sugar sucrose —are the major direct organic products of photosynthesis. The overall reaction in which carbohydrates—represented by the general formula (CH2O)—are formed during plant photosynthesis can be indicated by the following equation: Connect with Britannica Facebook Twitter YouTube Instagram Pinterest This equation is merely a summary statement, for the process of photosynthesis actually involves numerous reactions catalyzed by enzymes (organic catalysts ). These reactions occur in two stages: the “light” stage, consisting of photochemical (i.e., light-capturing) reactions; and the “dark” stage, comprising chemical reactions controlled by enzymes . During the first stage, the energy of light is absorbed and used to drive a series of electron transfers, resulting in the synthesis of ATP and the electron-donor-reduced nicotine adenine dinucleotide phosphate (NADPH).

During the dark stage, the ATP and NADPH formed in the light-capturing reactions are used to reduce carbon dioxide to organic carbon compounds. This assimilation of inorganic carbon into organic compounds is called carbon fixation. During the 20th century, comparisons between photosynthetic processes in green plants and in certain photosynthetic sulfur bacteria provided important information about the photosynthetic mechanism. Sulfur bacteria use hydrogen sulfide (H2S) as a source of hydrogen atoms and produce sulfur instead of oxygen during photosynthesis. The overall reaction is In the 1930s Dutch biologist Cornelis van Niel recognized that the utilization of carbon dioxide to form organic compounds was similar in the two types of photosynthetic organisms. Suggesting that differences existed in the light-dependent stage and in the nature of the compounds used as a source of hydrogen atoms, he proposed that hydrogen was transferred from hydrogen sulfide (in bacteria) or water (in green plants) to an unknown acceptor (called A), which was reduced to H2A.

During the dark reactions, which are similar in both bacteria and green plants, the reduced acceptor (H2A) reacted with carbon dioxide (CO2) to form carbohydrate (CH2O) and to oxidize the unknown acceptor to A. This putative reaction can be represented as: Britannica Lists & Quizzes Editor Picks: Exploring 10 Types of Basketball Movies Van Niel’s proposal was important because the popular (but incorrect) theory had been that oxygen was removed from carbon dioxide (rather than hydrogen from water, releasing oxygen) and that carbon then combined with water to form carbohydrate (rather than the hydrogen from water combining with CO2 to form CH2O). By 1940 chemists were using heavy isotopes to follow the reactions of photosynthesis. Water marked with an isotope of oxygen (18O) was used in early experiments. Plants that photosynthesized in the presence of water containing H218O produced oxygen gas containing 18O; those that photosynthesized in the presence of normal water produced normal oxygen gas. These results provided definitive support for van Niel’s theory that the oxygen gas produced during photosynthesis is derived from water.

Page 1 of 10 Photosynthesis in Plants Photosynthesis in Plants Home Photosynthesis in Plants Photosynthesis in Plants There are numerous species of plants all over the world. Some have adapted to desert conditions while other have adapted to cold climates. There are also plants that could only survive in cool, moist areas with adequate sunlight. These differences in climatic conditions and ecosystems have resulted in different types of photosynthesis in plants. The three types photosynthesis are C3, C4 and CAM photosynthesis. The definition of photosynthesis and the general equation can be found under Overview of Photosynthesis . Plants perform photosynthesis because it generates the food and energy they need for growth and cellular respiration. It is important to note that not all plants photosynthesize. Some are parasites and simply attach themselves to other plants and feed from them. For plants to perform photosynthesis they require light energy from the sun, water and carbon dioxide. Water is absorbed from the soil into the cells of root hairs. The water passes from the root system to the xylem vessels in the stem until it reaches the leaves. Carbon dioxide is absorbed from the atmosphere through pores in the leaves called stomata. The leaves also contain chloroplasts which hold chlorophyll.

The sun’s energy is captured by the chlorophyll. Leaves are essential for the well-being of plants. Most of the reactions involved in the process of photosynthesis take place in the leaves. The diagram below shows the cross section of a typical plant leaf. The typical plant leaf includes the following Upper and lower epidermis – the upper epidermis is the outer layer of the cells that controls the amount of water that is lost through transpiration. Stomata – these are pores (holes) in the leaves that are responsible for the exchange of gases between the plant leaves and the atmosphere. Carbon dioxide is absorbed from the atmosphere and oxygen is released. Mesophyll – these are photosynthetic (parenchyma) cells that are located between the upper and lower epidermis. These cells contain the chloroplasts. Vascular bundle – these are tissues that form part of the transport system of the plant. Vascular bundles consist of xylem and phloem vessels which transport water, dissolved minerals and food to and from the leaves. Process of Photosynthesis Photosynthesis in plants occurs in two stages. These stages are known as the light-dependent reactions and the Calvin Cycle.

Light-dependent Reactions The first stage of photosynthesis is the light dependent reactions. These reactions take place on the thylakoid membrane inside the chloroplast. During this stage light energy is converted to ATP (chemical energy) and NADPH (reducing power). Light-dependent Reactions Light is absorbed by two Photosystems called Photosystem I (PSI) and Photosystem II (PSII). These protein complexes contain light harvesting chlorophyll molecules and accessory pigments called antenna complexes. The photosystems are also equipped with reactions centers (RC). These are complexes of proteins and pigments which are responsible for energy conversion. The chlorophyll molecules of PSI absorb light with a peak wavelength of 700nm and are called P700 molecules. The chlorophyll molecules of PSII absorb light with a peak wavelength of 68Onm and are called P68O molecules. The light dependent reactions begin in PSII. A photon of light is absorbed by a P680 chlorophyll molecule in the light harvesting complex of PSII. The energy that is generated from the light is passed from one P680 chlorophyll molecule to another until it reaches the reaction center (RC) of PSII.

At the RC is a pair of P680 chlorophyll molecules. An electron in the chlorophyll molecules becomes excited as a result of a higher level of energy. The excited electron becomes unstable and is released. Another electron is released following the capture of another photon of light by the light harvesting complex and the transfer of energy to the reaction center. The electrons are transported in a chain of protein complexes and mobile carriers called an electron transport chain (ETC). Plastoquinone is the mobile carrier that transports the electrons from the reaction center of PSII to the Cytochrome b6f Complex as shown in the diagram above. The electrons lost from PSII are replaced by splitting water with light in a process called Photolysis. Water is used as the electron donor in oxygenic photosynthesis and is split into electrons (e-), hydrogen ions (H+, protons) and oxygen (O2). The hydrogen ions and oxygen are released into the thylakoid lumen. Oxygen is later released into the atmosphere as a by-product of photosynthesis. While the electrons pass through the ETC via Plastoquinone, hydrogen ions (protons) from the stroma are also tranferred and released into the thylakoid lumen.

This results in a higher concentration of hydrogen ions (proton gradient) in the lumen. As a result of the proton gradient in the lumen, hydrogen ions are transferred to ATP synthase and provide the energy needed for combining ADP and Pi to produce ATP. Cytochrome b6f transfers the electrons to Plastocyanin which then transports them to Photosystem I. The electrons have now arrived at PSI. They again receive energy, but this time from light absorbed by P700 chlorophyll molecules. The electrons are transferred to mobile carrier, ferredoxin. They are then transported to ferredixin NADP reductase (FNR), which is the final electron acceptor. At this point the electrons and a hydrogen ion are combined with NADP+ to produce NADPH. The lost electrons from PSI are replaced by electrons from PSII via the electron transport chain.

Summary of Light-dependent Reactions Photosystem II —–> b6-f complex —–> Photosystem I —-> NADP reductase Role of Photolysis Utilizes light to split water into the following: Electrons – donated to PSII to replace lost electrons Hydrogen ions – carried to ATP synthase to provide energy for the production of ATP Oxygen – released into the atmosphere as a by-product Products Light-dependent Reactions Animation The Calvin Cycle The second stage of photosynthesis is the Calvin Cycle. These reactions occur in the stroma of the chloroplast. Energy from ATP and electrons from NADPH are used to convert carbon dioxide into glucose and other products. “Overview of the Calvin Cycle pathway” Copyright 2010 Mike Jones, used under the Creative Commons Attribution-Share Alike 3.0 Unported license: One molecule of carbon dioxide is combined with one molecule of Ribulose Bisphosphate (RuBP). It is important to note that RuBP is a 5-carbon molecule. When it is combined with CO2 the reaction produces an unstable 6-carbon intermediate. The unstable 6-carbon intermediate quickly breaks down to form two 3-carbon molecules known as 3-phosphoglycerate (PGA).

The two 3-phosphoglycerate molecules receive energy from ATP and produce two molecules of 1,3-bisphosphoglycerate (BPGA). An electron from NADPH is combined with each 1,3-bisphosphoglycerate molecule to produce two molecules of Glyceraldehyde 3-phosphate (G3P). Two Glyceraldehyde 3-phosphate molecules are needed to make one molecule of glucose. The next important step in the cycle is to regenerate RuBP. The problem is there is not enough G3P. We only ran the cycle once with one molecule of CO2 and one molecule of RuBP. Only two molecules of G3P were produced. We still need an additional ten molecules of G3P for the cycle to continue. If you take another look at the photosynthesis equation you will notice that six molecules of carbon dioxide (6CO2) are needed for the process of photosynthesis. These six molecules of CO2 must be used to produce twelve G3Ps. This means that the steps above would have to be repeated five more times to produce ten additional molecules of G3P.

Two molecules of G3P will be used to produce glucose and the other ten will be used for the regeneration of RuBP.

Question: What is the main product of photosynthesis in plants?
Answer: Oxygen