13 4 Food Chains And Food Webs KEY
13. 4 Food Chains And Food Webs KEY CONCEPT Food chains and food webs model the flow of energy in an ecosystem.
13. 4 Food Chains And Food Webs A food chain is a model that shows a sequence of feeding relationships. • A food chain links species by their feeding relationships. • A food chain follows the connection between one producer and a single chain of consumers within an ecosystem. GRAMA GRASS DESERT COTTONTAIL HARRIS’S HAWK
13. 4 Food Chains And Food Webs • Consumers are not all alike. – Herbivores eat only plants. – Carnivores eat only animals. – Omnivores eat both plants and animals. – Detritivores eat dead organic matter. – Decomposers are detritivores that break down organic matter into simpler compounds. carnivore decomposer
13. 4 Food Chains And Food Webs • Specialists are consumers that primarily eat one specific organism or a very small number of organisms. • Generalists are consumers that have a varying diet.
13. 4 Food Chains And Food Webs • Trophic levels are the nourishment levels in a food chain. – Primary consumers are herbivores that eat producers. – Secondary consumers are carnivores that eat herbivores. – Tertiary consumers are carnivores that eat secondary consumers. – Omnivores, such as humans that eat both plants and animals, may be listed at different trophic levels in different food chains.
13. 4 Food Chains And Food Webs A food web shows a complex network of feeding relationships. • An organism may have multiple feeding relationships in an ecosystem. • A food web emphasizes complicated feeding relationships and energy flow in an ecosystem.
13. 4 Food Chains And Food Webs Questions • Why are specialists more susceptible to extinction than generalists? • What happens to a food web's energy at each link?
13. 5 Cycling of Matter KEY CONCEPT Matter cycles in and out of an ecosystem.
13. 5 Cycling of Matter Water cycles through the environment. • The hydrologic, or water, cycle is the circular pathway of water on Earth. • Organisms all have bodies made mostly of water. precipitation condensation transpiration lake surface runoff evaporation water storage in ocean groundwater see pag e
13. 5 Cycling of Matter Elements essential for life also cycle through ecosystems. • A biogeochemical cycle is the movement of a particular chemical through the biological and geological parts of an ecosystem. • The main processes involved in the oxygen cycle are photosynthesis and respiration.
13. 5 Cycling of Matter • Oxygen cycles indirectly through an ecosystem by the cycling of other nutrients. oxygen photosynthesis respiration carbon dioxide
13. 5 Cycling of Matter • Carbon is the building block of life. – The carbon cycle moves carbon from the atmosphere, through the food web, and returns to the atmosphere. – Carbon is emitted by the burning of fossil fuels. – Some carbon is stored for long periods of time in areas called carbon sinks. carbon dioxide in air combustion respiration photosynthesis respiration decomposition of organisms fossil fuels photosynthesis carbon dioxide dissolved in water
13. 5 Cycling of Matter • The nitrogen cycle mostly takes place underground. – Some bacteria convert gaseous nitrogen into ammonia through a process called nitrogen fixation. – Some nitrogen-fixing bacteria live in nodules on the nitrogen in atmosphere roots of plants; animals others live freely in the soil. plant nitrogen-fixing bacteria in decomposers roots ammonification nitrogen-fixing ammonium bacteria in soil nitrifying bacteria nitrates nitrifying bacteria nitrites denitrifying bacteria
13. 5 Cycling of Matter – Ammonia released into the soil is transformed into ammonium. – Nitrifying bacteria change the ammonium into nitrate. – Nitrogen moves through the food web and returns nitrogen in atmosphere to the soil during animals decomposition. plant nitrogen-fixing bacteria in decomposers roots ammonification nitrogen-fixing ammonium bacteria in soil nitrifying bacteria nitrates nitrifying bacteria nitrites denitrifying bacteria
13. 5 Cycling of Matter • The phosphorus cycle takes place at and below ground level. – Phosphate is released by the weathering of rocks. – Phosphorus moves through the food web and returns to the soil during decomposition. rain geologic uplifting – Phosphorus leaches into groundwater weathering of phosphate from rocks from the soil and runoff plants is locked in sediments. animalsphosphate in solution in soil – Both mining and leaching agriculture add sedimentation phosphorus into decomposers forms new rocks the environment.
13. 5 Cycling of Matter Questions • What occurs during the process of nitrogen fixation? • What cycles through the environment in the hydrologic cycle? • Why do all living things depend on the cycling of matter? • How does oxygen enter the atmosphere in the oxygen cycle? • Which of the following does not return carbon to the atmosphere?
13. 6 Pyramid Models KEY CONCEPT Pyramids model the distribution of energy and matter in an ecosystem.
13. 6 Pyramid Models An energy pyramid shows the distribution of energy among trophic levels. • Energy pyramids compare energy used by producers and other organisms on trophic levels. • Between each tier of an energy pyramid, up to 90 percent of the energy is lost into the atmosphere as heat. • Only 10 percent of the energy at each tier is transferred from one trophic level to the next. energy lost energy transferred
13. 6 Pyramid Models Other pyramid models illustrate an ecosystem’s biomass and distribution of organisms. • Biomass is a measure of the total dry mass of organisms in a given area. tertiary consumers 75 g/m 2 150 g/m 2 secondary consumers primary consumers producers 675 g/m 2 2000 g/m 2
13. 6 Pyramid Models • A pyramid of numbers shows the numbers of individual organisms at each trophic level in an ecosystem. tertiary consumers 5 secondary consumers 5000 primary consumers 500, 000 producers 5, 000 • A vast number of producers are required to support even a few top level consumers.
13. 6 Pyramid Models • Why do energy pyramids and biomass pyramids usually have a similar shape? • Why is so much energy lost from one trophic level to another? • If producers in a food chain take in 1000 kcal of energy, how much energy will likely be passed on to the second trophic level? • What type of pyramid would show many grass plants can support a population of grasshoppers?
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