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Energy and Metabolism How living things use energy Energy Takes Many Forms Energy is the ability to make matter change or move. Forms of energy include chemical, mechanical, light, sound, thermal (heat), and electrical. Energy can also exist as kinetic(causing movement right now), or potential (stored for use at a later time). Energy can change from one form to another. Thermodynamics is the study of energy transformations. The first law of thermodynamics says that energy is neither created nor destroyed, it just changes form. The second law of thermodynamics says that disorder (entropy) in the universe constantly increases. Things tend to become disorganized. All living things need a constant supply of energy. Almost all energy for living systems comes from the sun. Energy Flow Through Living Systems Energy from the sun enters most living systems by the process of photosynthesis. Some bacteria get energy by the process of chemosynthesis. Organisms that harvest energy either by photosynthesis or chemosynthesis are called autotrophs. Living things that cannot harvest energy directly must eat food to get energy. These organisms are called heterotrophs. Energy stored in food is released by the process of cellular respiration. The energy in food is stored in the electrons of C—H bonds. When these electrons are transferred to new bonds, so is the energy! Chemical reactions that transfer electrons are called oxidation-reduction reactions. Oxidation is the loss of electrons, and reduction is the gaining of electrons. Energy and Chemical Reactions Chemical reactions absorb or release energy. If the reactants contain more energy than the products, energy is released. If the products contain more energy than the reactants, then energy is absorbed. Energy from chemical reactions that drives cell activities is called free energy. Reactions that release free energy are called exergonic. Reactions that absorb free energy are called endergonic. Activation energy is the energy needed to start a chemical reaction. Exergonic Reaction Reactants Activation Energy Free Energy Released Endergonic Reaction Activation Energy Products Free Energy Absorbed Speed of Chemical Reactions I. II. III. IV. In order for living things to stay alive, their chemical reactions must take place very quickly. There are four ways to increase the speed of a chemical reaction: Increase the temperature. Increase reactant concentration. Increase the surface area of the reactants. Use a catalyst. Cells cannot increase temperature to speed up their reactions more than a few degrees, because high temperatures destroy cell structure. Cells cannot increase reactant concentration significantly without destroying cell structure. Cells cannot increase the surface area of their reactants because the reactants are dissolved in water and are already individual molecules. The most efficient way for cells to make reactions happen fast enough to maintain life is to use a catalyst. Enzymes Are Catalysts in Cells Any substance that lowers the activation energy of a reaction is called a catalyst. In living systems, enzymes do this. Like other catalysts, enzymes are not permanently changed by the chemical reactions they catalyze. The reactant molecule that the enzyme binds to is called a substrate. Because of their shapes, enzymes only bind to certain substrates. The part of the enzyme that binds to the substrate is called the enzyme’s active site. Without enzymes, the chemical reactions of living things would happen too slowly to sustain life. Enzymes work best at certain temperatures and certain pH ranges. Substrates Active Site Enzyme Energy Flow Through Ecosystems - Producers Autotrophs, which include all plants, some protists, and some bacteria, make their own food from small inorganic molecules. Most producers are photosynthetic, which means that they use energy from the sun to power food production. Some bacteria are chemosynthetic. This means that they use the energy from chemical bonds in inorganic molecules to power their food production. These bacteria are found at the openings of undersea volcanoes and form the basis for deep-sea ecosystems. In terrestrial ecosystems, plants are the major producers. In most aquatic ecosystems protists and cyanobacteria are the major producers. Gross primary productivity measures how fast producers in an ecosystem capture energy. Photosynthetic producers use this energy for tissue repair, or to make new organic material by growth or reproduction. This new organic material is called biomass. The biomass available to other organisms is called net primary productivity and measures the health of an ecosystem. Comparative Productivity of Ecosystems Net primary productivity varies from one kind of ecosystem to another. Although rainforests take up only 5% of the Earth’s surface area, they account for nearly 30% of the Earth’s net primary productivity from terrestrial ecosystems. Changes in light, precipitation, and temperature are responsible for most of the differences in productivity among terrestrial ecosystems. Changes in light and available nutrients cause productivity differences in aquatic systems. Comparative Productivity of Ecosystems Average net primary productivity (g/m2/yr) 2000 1500 1000 500 0 Desert Open Ocean Temperate Grassland Lake Savanna Estuary Tropical Rainforest Energy Flow Through Ecosystems - Consumers All animals, most protists, all fungi, and many bacteria are heterotrophs (consumers). They cannot make their own food, and so must eat (consume) other organisms or organic waste. Consumers are grouped according to their main type of food. Herbivores eat producers. Cattle, deer, grasshoppers, and some zooplankton in the oceans are herbivores. Carnivores eat other consumers. Wolves, lions, spiders are carnivores. Omnivores eat both producers and consumers. Bears and humans are omnivores. Detrivores are consumers that eat dead organisms or parts of organisms, or animal wastes. Many fungi, vultures, and bacteria are detrivores. Decomposers are consumers that cause decay by breaking down the large molecules in organic wastes or dead organisms into small molecules that can be recycled. Some bacteria, fungi, and protists are decomposers. Decomposers recycle molecules so new life can grow using those molecules. Energy Flow Through Ecosystems – Energy Flow When one organism eats another Roughly 10 percent of the total organism, molecules and the energy consumed in a trophic level is energy within them are transferred. available to be passed on to an This is how energy flows through organism at the next level of the the living world. pyramid. One way to study energy flow is to The other 90 percent of the energy group organisms into a pyramid produced or consumed is used to according to how they get their carry out life functions or is released energy. back to the environment in the form of heat, and is thus unusable. Trophic Level Large Because so little energy is available 4 carnivores for transfer to the next trophic level, energy pyramids rarely have more 3 Small carnivores than four levels. Organisms at lower trophic levels are 2 Herbivores more abundant than those at higher levels. Higher trophic levels have Producers 1 less available energy and so can support fewer organisms.
