Chapter 28 BSC 1005 TidwellHow Do Ecosystems Work?- Two basic laws underline ecosystem function:o Nutrients constantly cycle and recycleo Energy moves in a continuous one-way flow- Nutrients are atoms and molecules that organisms obtain from their living and nonlivingenvironment and that are required for survival- The energy to drive life’s activities come from the suno The sun converts hydrogen to helium, transforming a relatively small amount of matter into enormous quantities of energy.o Since only a tiny fraction of solar energy is captured by plants, life on Earth is supported by less than 0.03% of the energy reaching Earth from the sun.- Each category of organisms is called a trophic levelo Producers (autotrophs) make their own food using inorganic nutrients and solar energy from the environment.o Organisms that cannot photosynthesize are called consumers (heterotrophs). They require energy and nutrients from molecules in the bodies of other organisms.o Primary consumers feed directly and exclusively on producers These herbivores include animals such as grasshoppers, mice, and zebras,and form the second trophic level.o Carnivores act as secondary consumers that prey on herbivores. Carnivores such as spiders, hawks, cheetahs, and salmon are higher-level consumers Some carnivores eat other carnivores are called tertiary consumers.o The energy that photosynthetic organisms store and make available to other members of the community over a given period is called net primary production.o Tropical rain forests and estuaries (coastal areas where rivers meet the ocean) have an abundance of resources and have high productivities.- A food chain is a linear feeding relationship with just one representative at each trophic level.o Aquatic food chains have phytoplankton as their dominant producers.o Phytoplankton are consumed by zooplankton, which consist of protists and small, shrimp-like crustaceans.o Zooplankton are consumed by fish, which are eventually eaten by larger fish.- A food web shows the actual feeding relationships in a community, including its many interconnecting food chains.Page 1 of 4Chapter 28 BSC 1005 Tidwell- Omnivores act as primary, secondary, and tertiary consumers because they consume both plants and animals.- Detritus feeder and decomposers release nutrients for reuse.o Detritus feeders live on dead organic matter, including the bodies of other organisms, fallen leaves and fruit, and wastes.o Decomposers digest food outside of their bodies by secreting digestive enzymes. They primarily consist of fungi and bacteria, which liberate nutrients from the environment.o Detritus feeders and decomposers convert the bodies of dead organisms into simple molecules, such as carbon dioxide, water, and minerals.- The net energy transfer between trophic levels is roughly 10% efficient and is known as the “10% law”o An energy pyramid illustrates the general energy relationships between trophic levels.- Biomass is the weight of living material at each trophic levelo Because the dry weight of an organism’s body at each trophic level is roughly proportional to the amount of energy stored at that level, a biomass pyramid for a given community has the same shape as its energy pyramid.o This pattern of energy transfer has some important ramifications: Plants dominate most communities because they have the most energy available to them, followed by herbivores and carnivores. We can feed more people directly of grain that on meat from animals fed on grain.- Certain persistent toxic chemicals become increasingly concentrated in the bodies of animals that occupy higher trophic levels by a process called biological magnification.- Macronutrients are required by organisms in large amounts and include water, carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, and calcium.- Micronutrients including zinc, molybdenum, iron, selenium, and iodine are required in trace amounts.- Nutrient cycles (biogeochemical cycles) describe the pathways nutrients follow betweencommunities and the nonliving portions of ecosystems.o Reservoirs are sources and storage sites of nutrients.o Major reservoirs are usually in the abiotic environment.Page 2 of 4Chapter 28 BSC 1005 Tidwell- The water cycle (hydrologic cycle) describes the pathway that water takes as it travels from its major reservoir through the atmosphere, to reservoirs in freshwater lakes, rivers, and groundwater, and then back again o the oceans.o The oceans contain more than 97% of Earth’s water.- A small amount enters underground reservoirs called aquifers.o Aquifers are tapped to supply water for irrigating crops.- Plants absorb water through roots, but most is evaporated back to the atmosphere fromleaves, through a process called transpiration.- The carbon cycle has major reservoirs in the atmosphere, oceans, and fossil fuel.o Chains of carbon atoms form the framework of all organic molecules, the building blocks of life.o The carbon cycle describes the movement of carbon from its major short-term reservoirs in the atmosphere and oceans, through producers and into the bodies of consumers and detritus feeders, and then back to its reservoirs.o Carbon enters communities through capture of CO2 during photosynthesis.o Much of Earth’s carbon is bound up in limestone rock.o Fossil fuels are formed when the remains of prehistoric organisms are buried andsubjected to high temperatures and pressures for millions of years. Burning fossil fuels releases stored energy in hydrocarbons and releases carbon into the atmosphere as CO2.- The nitrogen cycle is the process by which nitrogen moves from nitrogen gas in the atmosphere to reservoirs of ammonia and nitrate in the soil and water.o While nitrogen gas (N2) makes up 78% of the atmosphere. Plants utilize nitrate (NO3-) or ammonia (NH3).o Nitrogen is a crucial component of proteins, many vitamins, nucleotides (ATP), and nucleic acids.o N2 is converted to ammonia by specific bacteria during a process called nitrogen fixation. Some of these bacteria live in water and soil and convert the ammonia into nitrate that plants can directly use. Others live in symbiotic associations with plants called legumes, which include alfalfa, soybeans, clover, and peas.o Denitrifying bacteria break down nitrate and release N2.- The phosphorus cycle describes the process by which phosphorus moves from phosphate-rich rocks to reservoirs