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Science 11th grade LEARNING OBJECT LEARNING UNIT Why does the sun release so much energy? How do world components change? S/K Skill 1: Explain atomic models developed through history based on experimental evidence. Skill 2: Explain radioactive decay phenomena α and β based on the current atomic model. Skill 3: Explain how nuclear energy is obtained from atom structure alteration, and contrast its risks and benefits. Skill 4: Explain the principles, which have led to use of radioisotopes in medicine. Skill 5: Argument why carbon 14 measure allows us to determine the age in fossils. Skill 6: Talk to a partner about why the discovery of atomic models was important for humanity. Language English Socio cultural context of the LO Colombia Curricular axis Physical Environment Standard competencies Establish relations between gravitational and electrostatic fields, as well as, electric and magnetic fields. Background Knowledge Gravitational force, electrical force, mass-energy relation, periodic table. English Review topic Past Simple Vocabulary box • • Leaf: (n) something thin like a leaf, especially the page of a book. Bounce: (V) to hit a surface and then move quickly away, or to make something do this. • • • • Crust: (n) a hard surface especially the outer layer of the earth. Feasible: (adj.) possible to do. Mold: (n) a green or black substance that grows in wet places or on old food. Beam: (n) a line of light that shines from something. NAME: _________________________________________________ GRADE: ________________________________________________ Introduction They discovered an important and unique paleontological piece in Colombia: A seven-meter long Kronosaurus. This is kept at the fossil museum in Villa de Leyva as part of an invaluable fossil collection. This marine reptile, which lived a little more than 100 million years ago, is the most complete found so far. Have you asked yourself what archeologists have done to determine the age of this and other fossils found? You will be able to answer that question as you progress in this learning unit. In addition, you will find key information, which will help you better understand radioactive processes existing in nature, and how human beings have been able to use those for our benefit. Objectives 1. To explain some nuclear reactions and interpret its disintegration kinetics. 2 To argue about radioactivity advantages and disadvantages. 3. To assume a critical position in relation to electrical power generation through nuclear processes. Activity 1 Skill 1: Explain atomic models developed through history based on experimental evidence. Skill 2: Explain radioactive decay phenomena α and β based on the current atomic model. Atomic Models Dalton’s atomic model. He raised the following postulates: • • • Atoms are indivisible and indestructible. Atoms belonging to one same element are all equal but different to the ones belonging to another element. Atoms in one element can combine with atoms belonging to another element, forming new atoms. Thomson’s atomic model: He discovered the electron in an experiment with gases trapped in a vacuum tube. When he applied several thousand volts to them, they emitted colored light beams called cathode rays, which are deviated by electric and magnetic fields. After carefully studying the deviation presented by cathodic rays, Thomson proved the existence of negatively-charged particles he called electrons and he stated: • Atoms are spherical and have a positive charge distributed evenly around its entire volume. On the other hand, electrons are negative charge particles embedded all over the sphere. (Fig.1). Figure 1. Thomson’s Atomic Model Negative charge particles embedded in a positive sphere. Retrieved from: http://4.bp.blogspot.com/_EoFgsPmlS1g/TOcm3hrbt_I/AAAAA AAAAAs/JcESHUG-Zok/s1600/image_gallery.jpg Very important… Electrons are assumed as electrical or elemental charge units, since a lower charged particle has not been discovered. Its value is -1.6·1019 Coulombs. Rutherford’s Atomic Model: He stated an atom made of a central nucleus and a crust (Fig. 2). Figure 2. Rutherford’s Atomic Model Nucleus and crust structured Retrieved from: https://edbar01.files.wordpress.com/2014/05/atom.gif Rutherford was able to prove the existence of a nucleus, due to an experiment in which he managed to make an alpha beam influence a gold leaf projected on a fluorescent screen. There they observed how the majority of the particles followed the same direction, but some of them were deviated and others, in less quantity, bounced towards the sender (Fig. 3). Figure 3. Rutherford’s experiment. Alpha particles influencing a gold leaf. Retrieved from: http://concurso.cnice.mec.es/cnice2005/93_iniciacion_interacti va_materia/curso/materiales/atomo/bombardeo.htm With this experiment, Rutherford was able to state that: • • The nucleus had a very small size compared to the total atom size. This is where the positive charge and approximately the entire atom mass concentrated. The entire negative charge was at the crust; such charge was represented by electrons. Bohr’s Atomic Model: He proposed the atom crust was structured at different energy levels where the electrons were located. If an electron absorbs energy from the outside, it could move up from a level E1 to a higher energy level E2 and there it would last a very short time, to finally return to its original level E1 emitting light (Fig. 4). Figure 4. Bohr’s atomic model. An electron can move up from one energy level to another one. Retrieved from: http://www.emdialogo.uff.br/sites/default/files/images/saltoq uantico.jpg In such a way, electrons turn around the nucleus in orbits featuring concrete energy values, therefore, not every orbit is allowed but a finite number. Did you know that…? Visible White light coming from the sun can decompose in different colors using a prism, obtaining a continuous spectrum. Atom Current Model In the same way as Einstein proposed wave-particle duality regarding light behavior, De Broglie raised the possibility that electrons and other particles can also have wave properties. According to this possibility, and after proving electron diffraction, Schrödinger proposes a new Atom Model stating that: • • • Every moving electron is associated with a wave. The concept of probability is introduced to describe position, speed and electron energy at a specific time frame. Electron energy is quantized, it means, it can only have certain values. Schrödinger’s wave equation establishes the region of space where it is more feasible to find an electron. This region is called orbital and has a shape and size determined by the energy of the electron. (Fig. 5). Figure 5. Current Atomic Model. Regions where it is more feasible to find the electron. Retrieved from: http://clasedelaquimica.weebly.com/uploads/1/9/2/6/192625 71/105713766.jpg Very important… Heisenberg’s uncertainty principle states that it is not possible to know the position and speed of an electron simultaneously and with absolute accuracy. Atomic Nucleus The nucleus in atoms is composed of protons and neutrons, which remain linked by a strong nuclear force. (Fig. 6). Figure 6. Atomic nucleus. Positive protons and neutrons with no electrical charge. Retrieved from http://www.nodo50.org/cerraralmaraz/Image9.jpg • • Protons have positive charge with same value as the charge of electrons, but their mass is 1,840 times higher. Neutrons do not have charge and their mass is a bit higher than the mass of protons. Some atomic nuclei have a proton and neutron combination, which does not respond to a stable configuration, those unstable nuclei are radioactive. Radioactivity It is the phenomenon originated because of the spontaneous disintegration of some heavy atomic nuclei, and high-energy electromagnetic radiations or emission particles are emitted. The particles which can be released in a radioactive disintegration are: (see figure 7): • • • Alpha (α): It is made of a helium atomic nucleus, which has two protons and two neutrons. They are scarcely penetrating particles and a piece of paper can stop them. Beta (β): They are electrons emitted to high speeds close to the speed of light. They are more penetrating particles than the alpha ones and can be stopped by a metal sheet. Gamma (γ): They are highly energetic particles with no mass. They are highly penetrating particles and are stopped by a lead or concrete (cement) wall. Figure 7. Nuclear Radiations. Alpha (α), beta (β) and gamma (γ) penetrating particles. Retrieved from: http://www.100ciaquimica.net/images/temas/tema3/ima/radi acionb.gif Did you know that…? Protons and Neutrons are not fundamental particles, but they are made of smaller particles called quarks. Alpha disintegration. When the nucleus releases an alpha particle, it transforms into a new element. The uranium most common isotope is U238, which contains 92 protons and 146 neutrons. When uranium disintegrates, it releases an alpha particle, having Thorium Th-234 as a result, which contains 90 protons and 144 neutrons. Another example is americium Am-241 disintegration, which results in Neptunium Np-237 when releasing an alpha particle. (Fig. 8). Figure 8. Alpha disintegration. Americium-241 disintegration into Neptunium-237, releasing an alpha particle. Beta disintegration. When the nucleus releases a beta particle, it transforms into a new element. Thorium Th-234 is also radioactive and at the moment of disintegrating, it releases a beta particle from its nucleus. This is possible since an electron becomes a proton and a neutron, but the proton remains in the nucleus, so the number of protons at the nucleus increases by one, having Protactinium as a new element Pa-234 with 91 protons and 143 neutrons. Another example is Hydrogen H-3 (Tritium), which becomes Helium He3 since it emits a beta particle from its nucleus. (Fig. 9). Figure 9. Beta disintegration. Retrieved from: http://web.educastur.princast.es/proyectos/jimena/pj_francisc ga/leydesin.htm Radioactivity Kinetics. The number of atoms, which disintegrate at a given time, is directly proportional to the number of atoms present in the sample. Constant proportionality is known as disintegration constant. Radioactive Disintegration Simulator. Remember that… An isotope is an atom belonging to the same chemical element; it has the same proton quantity, but a different number of neutrons. Learning Activity 1 The following activity will help you strengthen concepts about the Atomic Models, which have been developed through history. Match the following experimental evidences to its corresponding Atomic Model: Evidence Model 1. When applying a high voltage to the atoms of an element in gaseous state, these emit particles with negative charge. A. Dalton’s atomic theory. 2. Electron leaps from higher to lower energy levels or vice versa involve either emission or absorption of electromagnetic energy. (Light photons). B. Thomson’ s atomic theory. 3. The crust is practically an empty immense space compared to the dimensions in the nucleus. C. Rutherfor d’s atomic theory. 4. Electrons occupy a region of space according to a probability distribution. D. Bohr’s atomic theory. 5. In chemical reactions, atoms exchange themselves from one substance to another, but no atom belonging to an element disappears or transforms into the atom of another element. E. Current Atomic Model. Activity 2 Skill 3: Explain how nuclear energy is obtained from atom structure alteration, and contrast its risks and benefits. Skill 4: Explain the principles, which have led to use of radioisotopes in medicine. Nuclear Fusion Nuclear strength is responsible for keeping protons and neutrons together in the center of the atom. In uranium and other heavy elements, nuclear force is not so strong. Consequently, electric repulsion forces between protons can defeat nuclear force and divide the nucleus into two; this phenomenon is called Nuclear Fusion. Figure 10. Fission Reaction. Uranium-235 fission chain reaction, divided into Barium-141 and Krypton-92. Retrieved from: https://quimica-iti-1213.wikispaces.com/file/view/17_2.jpg/385552358/17_2.jpg In figure 10, we can see a neutron impacting a nucleus of Uranium U-235 neutron, which is divided into two lighter atoms (Barium Ba-141 and Krypton Kr-92), releasing energy and three neutrons, which will affect the other Uranium nuclei generating a chain reaction eventually. In Colombia, the “Servicio Geológico Nacional” started to carry out geological studies in 2010 to explore Uranium, Thorium and Potassium in potential areas located in Boyacá, Cundinamarca and the southern region of the province called Santander. They found Uranium in all the studies. Did you know that…? Only 0.7% of Uranium found in a natural way corresponds to isotope U235 used in nuclear reactors. Nuclear Fusion Another way to generate nuclear energy is by means of a union of two light atomic nucleuses to form a heavier one. This process is called Nuclear Fusion and can generate more energy by fusion than by fission; this kind of energy is evidenced in the speed reached by the released neutrons. Therefore, a great amount of heat quantity would be obtained when those neutrons stop; this could be transformed into electrical power. . Figure 11. Fusion Reaction. Deuterium and Tritium fusion to form Helium atoms by releasing a neutron and an amount of energy. https://sputnik87.files.wordpress.com/2011/01/fusionnuclear-infografc3ada1.png In figure 11, we can see the Nuclear Fusion of two hydrogen isotopes, Deuterium H-2 and Tritium H-3, forming a helium nucleus and releasing a neutron and a considerable amount of energy. This nuclear reaction is the one occurring in our sun. In Colombia, through Universidad Nacional, they want to be part of the TEIR (Thermonuclear Experimental International Reactor) project, which seeks to produce electrical power in order to use it commercially through Nuclear Fusion. Universidad Nacional contributes to this project by encouraging research groups, making students participate, collaborate and work in professor and student exchanges. Did you know that…? The quantity of Deuterium H-2, which is found in a liter of water, is able to release an amount of energy equivalent to the one found in 88 gas gallon. Nuclear Plant A nuclear plant is a facility, which takes advantage of the heat obtained from the Nuclear Fission of radioactive elements such as Uranium or Plutonium to generate electrical power. In the following animation, you can see the steps to obtain electrical power in a nuclear plant. Figure 12. Nuclear Plant. Transformation process of nuclear energy into electrical power in a nuclear plant. Retrieved from: https://www.youtube.com/watch?v=nMZJ7ABkvRw 1. Double security retaining Wall (concrete and steel walls). 2. Reactor nucleus: Here you can find the fuel (Uranium or Plutonium), which releases heat by fission. 3. Steam Generator: water tank, which evaporates because of the heat, delivered by the reactor. 4. Turbines and generator: Turbines are moved by water steam and generate electrical power. 5. Transformer: it transforms voltage into a suitable value for its distribution. 6. Electricity grids: they transport electrical power. 7. Cooling tower: Water steam, which moves the turbines, goes to a condenser, which cools it down and makes it liquid so that it can be thrown back into lakes or rivers. Colombian Nuclear Reactor. In Colombia, there is a small 30 kilowatt Nuclear Reactor IAN R-1, which is used for research. It was donated by the United States Government in 1965 and was renewed in 2009 in a new treaty between the International Physics Center and the Servicio Geológico Nacional, which is the institution in charge of the “Programa Estratégico de Energía Nuclear” in Colombia as the reactor administrator and operator. Fifty years with the nuclear reactor in Colombia. Radiation: uses and damages In figure 13, you can see some of the most relevant radioactive processes; and figure 14 shows the damages caused to human beings. Uses Medicine and research: X rays produce bone images from the inside of our organisms. Also the radioisotope techique is used for diagnosing diseases. Industry: Radioisotopes are employed to determine the speed of a fluid, detect leaks in pipelines, non-destructive analysis of machinery pieces, among others. Agronomy : to detect the path followed by sinthetized carbohydrates in vegetables. Science: C-14 to determine the age of antiques, verify the authenticity of art pieces, nuclear plants, definition of underground water flows, etc. Food preservation: It destroys and disables bactera and mold spores found in food. Figure 13. Radiation Uses. We can see different fields where radioactivity is exploited. By the Author. Figure 14. Info graphic image on radiation effects. We can see some negative effects of radiation on the human body. Retrieved from http://4.bp.blogspot.com/-bUDAw2QiIc/Tarb4zKAiyI/AAAAAAAALys/pr2g61BdDms/s1600/EFECTOSDE-LA-RADIACION-EN-EL-ORGANISMO-HUMANO.jpg Radioisotope in medicine Radioactive isotopes are highly used in medicine to diagnose heart, lung, renal, and brain diseases, among others. There are natural and human-made isotopes, but for medical use, they only use the ones produced by nuclear reactors, since they have the necessary characteristics for its function. Figure 15. Medical Scanner. It is used to detect osseous diseases. Retrieved from: http://www.cancer.gov/images/cdr/live/CDR742469-750.jpg Some radioisotopes emit alpha or beta radiation, which is used to treat diseases like cancer. Others emit gamma or positron radiation, which are used along with powerful medical scanners to take pictures of processes and structures inside the body. (Fig.15). The most used radioisotopes in medicine are: • • • • • • • Technetium Tc-99: to study the brain, lungs, liver, arm and bones. Chromium Cr-51: for taking images of the arm and locate internal bleeding. Sodium Na-24: to detect vascular injuries. Strontium Sr-85: to make pictures of bones and check cracks or osteoporosis. Samarium Sm-153: used in bone cancer treatment, it acts as a painkiller for the pain caused by metastasis. Thallium Tl-201: Used to detect the obstruction in coronary arteries. Iodine I-131: used to detect the cause of thyroid dysfunction. Very Important… Radioisotopes administered to patients during diagnosis or treatment, falter or are totally eliminated becoming stable (non-radioactive) elements, within some minutes or hours. Learning Activity 2 The following activity will help you to strengthen concepts related to radioisotopes used in medicine. Complete the table with the information about the most common radioisotopes used in the field of medicine. Use the periodic table offered to you in the following link: http://www.ptable.com/?lang=es Radioisotope Symbol # Protons # Neutrons Samarium-153 Sm 62 91 Technetium99 Chromium-51 Sodium-24 Estrontium-85 Iodine-131 Activity 3 Skill 5: Argument why carbon 14 measure allows us to determine the age in fossils. Carbon C-14 A stable carbon atom has six protons and six neutrons. In Carbon 14, its unstable (radioactive) isotope has six protons and eight neutrons (Fig. 16) and it is present in considerable amounts in the earth atmosphere. Figure 16. Carbon Isotope. We can see the three atoms feature the same number of protons and neutrons, but a different neutron number. Retrieved from http://2.bp.blogspot.com/AdgroiL0B1E/TsoDfBLNaeI/AAAAAAAAAZQ/HyfKDkbWpkI/s160 0/is%C3%B3topos+de+carbono.jpg Cosmic radiation produces neutrons, which come into the atmosphere and react to Nitrogen producing a heavy carbon isotope C-14. This mixes with common carbon C-12, in atmospheric oxygen; it goes into all living beings through Carbon dioxide. Plants absorb it during photosynthesis, which are then eaten by herbivores, which are carnivore’s food. When a living being dies, the carbon atom absorption stops and its concentration by radioactive disintegration starts to decrease. Remember that… An average lifetime is the time that needs to pass for half of the atoms in a radioactive atom sample to disintegrate into atoms of lighter elements Carbon -14 Dating The average life period of C-14 is 5,730 years, this means that after 5.730 years half of the original quantity of the isotope has faltered; after a similar period, what was left is reduced to a half, which reduces it to a quarter of the total initial and so on. Measuring the quantity of Carbon 14 in a fossil, we can determine its approximate age. The mass in Carbon-14 belonging to any fossil decreases at an exponential rate, which is known, as we can observe in figure 17. Figure 17. Average C-14 life We can see the relation between the number of particles of C-14 and time in years. Retrieved from: http://bibliotecadigital.ilce.edu.mx/sites/ciencia/volumen1/cie ncia2/08/htm/sec_8.html Example. A man’s prehistoric human remains were found in the Nemocón valley (Fig.18). They were analyzed by using the Carbon 14 technique. The amount of Carbon-14 was determined by means of a radioactive particle counter, and it was compared to the quantity of Carbon-14 in the atmosphere at different eras. The result was that this fossil was approximately eight thousand years old. Figure 18. Checua man. This was an archeological finding in Nemocón. Retrieved from: http://lapaleontologiaencolombia.blogspot.com.co/2014/05/elmastodonte-de-nemocon-cundinamarca.html Did you know that…? Carbon 14 method is only useful for determining fossil ages from 45,000 to 50,000 years. Learning Activity 3 The following activity will help you better understand why Carbon 14 measurement allows us to know the age of fossils. Answer True (T) or False (F), as appropriate. Answer True (T) or False (F) as it corresponds: 1. Carbon 14 can determine the earth’s age. ( ) 2. When 70,000 years have passed, the Carbon 14 percentage found in a fossil is null. ( ) 3. Carbon-14 is absorbed in carnivores after consuming herbivores ( ) Complete according to the graphic in figure 17. 4. An 18,190-year-old fossil has a C-14 percentage corresponding to __________%. 5. For finding the 25% of C14 in a fossil, ___________years must have passed. Abstract Homework The following activity allows you to go deep into knowledge regarding radioactivity applications in determining fossils age, to do this, it is necessary for you to review and understand the concepts presented in activity 3. 1. Check different bibliographic references to answer the following questions: a. What are C-14 limitations in determining fossil ages? b. What other radioactive elements can be used to date antique events? c. What is the decay chain in the elements researched on the preceding point? Record in your notebook. 2. Once you finish checking the information, get together with two classmates and share the information. 3. In your group, fill the following table out comparing, at least five radioactive elements checked. Use the following table as a model: Number Radioactive Element Average life Nuclear watch uses Limitations 1 2 3 4 5 4. On a poster, draw the decay chain of one of the five elements in the table. 5. Do a presentation to your classmates using the poster you made. Briefly explain the importance of the element you chose concerning the dating of antique events. Evaluation The purpose of this evaluation is to review the concepts studied in this LO; to do so it is necessary for you to go over each activity, understand the proposed resources and develop the learning activities proposed. I. Solve the following puzzle: Clues 1. Radioactive decay where a helium nucleus is released. 2. Radioactive element used to determine the age of fossil. 3. Nuclear process consisting of the division of a heavy nucleus. 4. Scientist who stated the atom was made of nucleus and crust. 5. Heisenberg formulated this principle based on the Current Atom Model. Complete the statement: Hydrogen isotopes are _______________ along with a proton and a _______________ and __________________ along with ________ proton and ____________neutrons. II. III. Choose the radioactive elements among the following: • Carbon-12 • Iodine-131 • Uranium-235 • Oxygen-16 • Hydrogen-3 Bibliography • Romero, O., & Rincón, L. (2008). Nueva Física 11. Bogotá: Santillana. • Castañeda, H. (1991). Hola Física Grado 11. Medellín: Susaeta ediciones. Endesa educa. (2014). Centrales nucleares. Retrieved from http://www.endesaeduca.com/Endesa_educa/recursosinteractivos/produccion-de-electricidad/x.-las-centrales-nucleares E-ducativa. Modelo atómico de Rutherford. Retrieved from http://educativa.catedu.es/44700165/aula/archivos/repositorio/1000/116 2/html/2_modelo_atmico_de_rutherford.html Biblioteca digital del ILCE. (2013). Los relojes nucleares. Retrieved from http://bibliotecadigital.ilce.edu.mx/sites/ciencia/volumen1/ciencia 2/08/htm/sec_8.html Gobierno de Canarias. Modelo atómico actual. Retrieved from http://www3.gobiernodecanarias.org/medusa/lentiscal/1CDQuimica-TIC/applets/Actual/teoriamodeloactual.htm • • • • • • • • • • • • • • • • • • Educastur. (2010). Radioactividad. Retrieved from http://web.educastur.princast.es/proyectos/jimena/pj_franciscga/l eydesin.htm CNICE. (2006). Datación absoluta. Retrieved from http://concurso.cnice.mec.es/cnice2006/material082/actividades/ paleo_c14/actividad.htm#mh2 The dinosaur picture database. Kronosaururs picture. Retrieved from http://images.dinosaurpictures.org/Kronosaurus_5054.jpg Modelosatomicospalacios. El átomo de Thomson. Retrieved from https://sites.google.com/site/modelosatomicospalacios/Home/eldescubrimiento-del-electron/el-atomo-de-thomson Wordpress.com. Física cuántica. Retrieved from https://edbar01.files.wordpress.com/2014/05/atom.gif Emdialogo. Saltoquantico. Retrieved from http://www.emdialogo.uff.br/sites/default/files/images/saltoquanti co.jpg Clase de la química. El átomo a través del tiempo. Retrieved from http://clasedelaquimica.weebly.com/uploads/1/9/2/6/19262571/1 05713766.jpg Innecesaria. Energéticamente ineficiente. Retrieved from http://www.nodo50.org/cerrar-almaraz/Image9.jpg Ciencia Química. Penetración de las radiaciones nucleares. Retrieved from http://www.100ciaquimica.net/images/temas/tema3/ima/radiacio nb.gif Quimica ITI-12-13. (2016). Reactores de Fisión Nuclear. Retrieved from https://quimica-iti-1213.wikispaces.com/REACTORES+DE+FISI%C3%93N+NUCLEAR FS 210 Biofísica, Universidad Nacional Autónoma de Honduras. Efectos de la radiación sobre el cuerpo humano. Retrieved from https://fs210secc1002.wordpress.com/el-atomo/efectos-de-laradiacion-sobre-el-cuerpo-humano/ National Cancer Institute. (2006). Retrieved from http://www.cancer.gov/images/cdr/live/CDR742469-750.jpg Ciencia NXT. (2015). Datación mediante el carbono 14. Retrieved from http://www.cancer.gov/images/cdr/live/CDR742469-750.jpg El Espectador. (2012). Colombia cuenta con un reactor nuclear renovado. Retrieved from http://www.elespectador.com/noticias/nacional/colombia-cuentaun-reactor-nuclear-renovado-articulo-376262 • La Paleontología en Colombia. (2014). El Mastodonte de Nemocón, Cundinamarca. Retrieved from http://lapaleontologiaencolombia.blogspot.com.co/2014/05/elmastodonte-de-nemocon-cundinamarca.html#uds-search-results Glossary • • • • • • • Light beam: Set of electromagnetic rays, which head only one direction. Fluorescence: property of some bodies that emit a light when radiation is received. Prism: Transparent crystal piece which decomposes light Spectrum: Set of radiations with different frequency. Concrete: stone mixture, concrete and sand used in constructions. Fossil: remains of an organic death being found petrified. Photosynthesis: process of some vegetal cells in which they transform inorganic substances thanks to light energy.