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What is matter?Dr. Adrian Finzi in the
deciduous forest
All things — living and nonliving — are made of matter, and all matter is composed of tiny particles called atoms. Atoms combine together to form molecules. Atoms of different types are called elements. In the video for Session 8, Dr. Adrien Finzi walks us through a deciduous forest ecosystem and identifies some of the elements that compose living — or organic — matter. These elements include carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), sulfur (S), calcium (Ca) and iron (Fe). Nonliving — or inorganic — matter contains these elements too, but in very different proportions.How is matter connected to life?One of the five characteristics used to define life in Session 1 (What is Life?) was the need for a constant supply of matter. Why is this? In any organism, matter is constantly being used to both build and sustain the organism. Cell parts are continuously being replaced. In the thousands of chemical processes that go on inside a cell, atoms and molecules are both input and output. On a molecular level, almost all the matter that composes an organism at some point becomes part of the waste products that are expelled into the external environment. This matter must continuously be replaced.There are several properties of matter that characterize its connection to life.Matter can exist in different states: Scientists classify matter into four states: solid, liquid, gas, and plasma. Life is composed of, and interacts with, matter in the first three states — we are made of matter in solid, liquid, and gaseous forms. Plasma is a state of matter that composes the bulk of the universe. On Earth, plasma exists naturally only as lightning and the Aurora Borealis.Matter can change states: We are all familiar with the molecule H2O in its three states: solid (ice), liquid (water), and gas (vapor). Water and other molecules can change states, usually as a result of changes in temperature or pressure. As part of life’s chemical reactions, atoms can be moved around to molecules in different states. In photosynthesis, for example, the carbon in carbon dioxide gas and the hydrogen in liquid water become part of a sugar molecule, which is a solid.The basic units of matter cannot change forms: You may recall from Session 7 (Energy Flow in Communities) that energy can change forms. With a few exceptions that occur in extreme conditions, the basic units of matter — atoms — cannot change forms. As far as life is concerned, a carbon atom will remain a carbon atom no matter how it moves around from molecule to molecule. Your carbon atoms may have once been part of the first life form on Earth or even a Tyrannosaurus rex.Matter is conserved: A property that matter shares with energy is that it is conserved. What this means is that the total amount of matter that is part of a system stays the same, even if the matter changes state or the atoms and molecules are rearranged in chemical reactions many times. This translates to the level of atoms. If you start with a certain number of carbon atoms, for example, you’ll end with that same number even though they may be in different molecules.Matter stores energy: Atoms and molecules represent stored energy. The type of energy most important to sustaining life is the chemical energy stored in food. Matter and energy travel together in food along food chains. While the amount of useful energy decreases as energy changes form at each link in a food chain (i.e., it becomes heat energy), matter does not change form and ultimately remains available to the living world.
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