Biology 2201 Unit 1: Matter & Energy for Life Chapter 3 One of the basic characteristics of life is the need for energy. Organisms require energy to do work, and no matter what kind of organism, they all do work. There are two main classifications of organisms based upon their method of obtaining energy. 1. Autotrophs- able to make their own food. Plants use the process of photosynthesis to make their own food (sugars, starches) and carry out cellular respiration to burn the food they make for energy. 2. Heterotrophs not able to make their own food. Animals must get their food from their environment and carry out respiration. All energy ultimately comes from the sun. The energy of the sun can only be utilized by the chemical reaction called photosynthesis. Photosynthesis allows inorganic compounds, such as carbon dioxide and water, to be converted into organic, energy rich substances such as sugars which cells can then use as an energy source. Photosynthesis is the base of all food chains - it is the source of all life on earth. Photosynthesis is the process of converting carbon dioxide, CO 2 (g) and water, H 2 0 (l) into simple sugar by using the suns energy. Oxygen, O 2 (g) is given off as a waste product. CO 2 (g) + H 2 O (l) C 6 H 12 O 6 (s) + O 2 (g) Plants use carbon, in the form of CO 2 (g) during photosynthesis to make carbohydrates. This takes carbon from its inorganic state and transforms it into organic compounds. This carbon then gets passed up the food chain through consumers. Carbon is returned to its inorganic state when organisms break down carbohydrates to get energy. They use carbohydrates in a cell reaction process called cellular respiration. Cellular respiration requires oxygen. This reaction releases energy to the body and gives off inorganic carbon dioxide and water vapor to the air. Decomposer organisms also release carbon dioxide to the air. C 6 H 12 O 6 (s) + O 2 (g) CO 2 (g) + H 2 O (g) In fact, photosynthesis and cellular respiration are complementary reactions; they are the opposite of each other in terms of reactants and products: Photosynthesis is the base of all food chains. It also produces the oxygen necessary for the process of cellular respiration. Photosynthesis is the route by which inorganic molecules, carbon dioxide and water, are converted into organic molecules such as glucose which is useable in organisms for their metabolism. Cellular respiration recycles carbon back into inorganic form by releasing carbon dioxide. This allows the oxygen and carbon cycles to continue. There are two types of cellular respiration: Aerobic Respiration: a process that requires oxygen. (It will release 38 ATP molecules in bacterial cells and 36 ATP molecules in cells with mitochondria). See figure 3.14 pg. 82. Anaerobic Respiration: a process that will occur in the absence of oxygen. Some micro- organisms are capable of metabolizing without the presence of oxygen. (An example would be glycolysis which can occur in muscle cells. It will only release 2 ATP molecules from the breakdown of one glucose molecule). Test #2: Chapters 2 & 3 Thursday Nov. 4 th ! Study Hard