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Energy and Matter | Principles of Biology from Nature Education contents Principles of Biology 2 Energy and Matter Organisms interact with their environment, exchanging energy and matter. The Sun. Most ecosystems receive their energy from the Sun's radiation. NASA/European Space Agency. Topics Covered in this Module Matter and Energy in the Earth System Major Objectives of this Module Define energy and matter. Describe the components of an ecosystem. Explain the difference between exergonic and endergonic reactions. page 10 of 989 3 pages left in this module contents Principles of Biology 2 Energy and Matter Our universe is composed of matter and energy. Matter is defined as anything that occupies space and has mass. All tangible substances, including living organisms, are made from matter. Energy is defined as the capacity to do work. Energy takes many forms, such as light, chemical or kinetic (the energy of motion). One form of energy may be converted to another. Organisms require energy for essential life functions such as growth and reproduction. Where do matter and energy come from, and how do organisms acquire the matter and energy they need to survive? Matter and Energy in the Earth System Some types of matter were produced in the Big Bang that formed the universe. Other types of matter were produced in nuclear reactions that occurred in the cores of stars. Earth and other planets formed from the accumulation of heavier forms of matter drifting in space following the explosive deaths of stars. Earth went through its period of matter accumulation during the origin of our solar system, about 4.5 billion years ago. The Earth system — including its living and nonliving components — generally contains a finite amount of matter (except for small amounts that enter or leave the Earth's atmosphere). How do countless generations of living organisms survive on a finite amount of matter? The answer lies in the continual recycling of matter. The matter that makes up our bodies has cycled through other organisms, including bacteria, dinosaurs, and plants, since life began about 3.8 billion years ago. Most of the Earth's living organisms acquire their energy directly or indirectly from the Sun. Like all stars, the Sun emits electromagnetic energy, which includes light in the visible, ultraviolet, and infrared spectra as well as X-rays, microwaves, radio waves, and gamma radiation. Organic molecules are compounds that contain carbon and hydrogen atoms and may include other types of atoms. Organic molecules are an important component of all living organisms. Carbon dioxide, which does not contain hydrogen, is considered inorganic. Organisms that are able to convert carbon dioxide into organic molecules are called producers. The bonds that hold organic molecules together contain more energy than the bonds in carbon dioxide. Therefore, energy is required to make organic molecules from carbon dioxide. Many producers, including plants, algae, some protists, and many prokaryotes, acquire the energy needed for making organic molecules from sunlight (Figure 1). The process of using sunlight to make organic molecules from carbon dioxide, or "fixing carbon" is called photosynthesis. The photosynthesis chemical reaction is written as follows. Carbon dioxide + water + energy → organic molecules + oxygen In this reaction, carbon dioxide and water are reactants (substances that undergo a reactions). Organic molecules and oxygen are products. Energy is required and is also considered a reactant. Other types of producers are able to acquire energy through inorganic chemicals reactions, a process called chemosynthesis. However, photosynthesis is the main source of organic molecules on Earth. Figure 1: Common bracken fern (Pteridium aquilinum) capturing sunlight. Photosynthesizers, including plants like ferns, transform the energy in sunlight into chemical energy. Rachel Warne/Science Source. Many organisms, such as animals and some protists and bacteria, cannot fix carbon dioxide into organic molecules, nor can they acquire energy from sunlight. Instead, these organisms, called consumers, acquire organic matter by eating food derived from producers or other consumers. Organic molecules have a relatively high energy content, and these organisms extract energy from organic molecules through a process called cellular respiration. Carbon dioxide, water and heat are waste products of cellular respiration. Producers also can use cellular respiration to extract energy stored in organic molecules. The reactions for cellular respiration is the reverse of the reaction for photosynthesis: organic molecules + oxygen → Carbon dioxide + water + energy Decomposers, which include bacteria and fungi, consume organic matter from waste products and once-living organisms, thereby salvaging some of the stored energy and recycling organic matter in the ecosystem. The process of decomposition refers to the breakdown of organic matter. Interacting producers, consumers, and decomposers and the nonliving components of their environment form an ecosystem. In an ecosystem, energy flows from producers to consumers to decomposers. However, at each step only a small amount of energy is transferred; the rest is lost as heat. Matter cycles through the ecosystem in a manner that is mutually beneficial to all its members. For example, oxygen, which is a waste product of photosynthesis, is used for cellular respiration in most organisms. Carbon dioxide, which is a waste product of cellular respiration, is used for photosynthesis. Figure 2: Matter cycling within an ecosystem. Photosynthetic producers use energy from sunlight to convert carbon dioxide and water into organic molecules. Consumers and decomposers use cellular respiration to extract energy from organic molecules, which produces carbon dioxide and water. © 2014 Nature Education All rights reserved. Test Yourself What is an organic molecule? Why is carbon dioxide not considered organic? Submit Chemical reactions. Chemical energy is stored in bonds that join atoms together into molecules. Molecular bonds are made and broken through chemical reactions that convert reactants into products. Some chemical reactions, called exergonic reactions, release energy so that the products have less energy than the reactants (Figure 3, top). Cellular respiration is an exergonic reaction. Other chemical reactions, called endergonic reactions, consume energy so that the products have more energy than the reactants (Figure 3, bottom). Photosynthesis is an endergonic reaction. Notice that if a forward reaction is exergonic, the reverse reaction is exergonic. A specific amount of energy is required to initiate a reaction. This energy, called the activation energy, is released as the reaction progresses. Many endergonic and exergonic reactions occur in a living organism. An organism's metabolism is the sum of all the chemical reactions occurring in every cell. Figure 3: Chemical energy. Exergonic reactions release energy so that the products have less energy than the reactants (top). Endergonic reactions consume energy so the products have more energy than the reactants (bottom). © 2014 Nature Education All rights reserved. Figure Detail Test Yourself What is the difference between an exergonic reaction and an endergonic reaction? Submit Matter cycles between living and nonliving elements of the Earth system. Biogeochemical cycles involve the transfer matter through living and non-living parts of the ecosystem. The biogeochemical cycle includes cycles of various elements and molecules. For example, the carbon cycle involves movement of carbon from carbon dioxide gas to organic matter and back to carbon dioxide gas. Biogeochemical cycles also involve non-biological processes — for example, water evaporates from the ocean and falls again as rain. Biogeochemical cycles can be perturbed by human activity, as is currently happening with the carbon cycle (Figure 4). Coal, oil and natural gas, known as fossil fuels, come from deposits of once-living organisms that were buried beneath the Earth's crust. When these fuels are burned, the carbon that was fixed in them is released as carbon dioxide gas. While much of this carbon dioxide is taken up by plants and converted into back into living matter, some remains in the atmosphere. As a result, atmospheric carbon dioxide levels are increasing. Before the industrial revolution, the atmosphere contained about 600 gigatons of carbon, mostly in the form of carbon dioxide. Organisms contained similar amounts. The vast majority of the Earth's carbon, 6.6 x 106 gigatons, was bound in soils, sediments and rocks, and the deep ocean (Figure 4). Today, because the burning of fossil fuels has released large quantities of the carbon that was fixed and buried below the Earth's crust, the amount of carbon the atmosphere is closer to 750 gigatons. Carbon dioxide acts as a greenhouse gas that influences global climate. Figure 4: Carbon reservoirs on Earth. Approximate carbon levels in various reservoirs, measured in gigatons (Gt; 1 Gt = 1015 grams), are shown. © 2014 Nature Education All rights reserved. Test Yourself Describe the carbon cycle. How is the burning of fossil fuels perturbing the carbon cycle? Submit Organic molecules. Life on Earth is carbon-based. The carbon atom has four electrons in its outer shell that can each form a bond with another atom. Because carbon is able to form four bonds, carbon atoms can form chains and rings. In organic molecules, carbon is associated with at least one hydrogen. Organic molecules found in living organisms often contain other types
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