Students know that food provides molecules that serve as fuel and building material for all organisms. Plants, algae (including phytoplankton), and many microorganisms use the energy in light to make sugars (food) from carbon dioxide and from the atmosphere and water through the process of photosynthesis, which also releases oxygen. This food can be used immediately for fuel or materials or it may be stored for later use. Animals obtain food from eating plants or eating other animals. Within individual organisms, food moves through a series of chemical reactions in which it is broken down and rearranged to form new molecules, to support growth, or to release energy;. In most animals and plants, oxygen reacts with carbon-containing molecules (sugars) to provide energy and produce waste carbon dioxide; anaerobic bacteria achieve their energy needs in other chemical processes that do not require oxygen. Organisms that eat plants break down the plant structures to produce the materials and energy they need to survive. Then they are consumed by other organisms.

Students know that over a long time, matter is transferred from one organism to another repeatedly and between organisms and their physical environment. As in all material systems, the total amount of matter remains constant, even though its form and location change.

Students know that the flow of energy through ecosystems can be described and illustrated in food chains, food webs, and pyramids (energy, number, and biomass). These are all models that demonstrate how matter and energy is transferred between producers (generally plants and other organisms that engage in photosynthesis), consumers, and decomposers as the three groups interact- primarily for food- within an ecosystem. Transfers of matter into and out of the physical environment occur at every level, for example when molecules from food react with oxygen captured from the environment, the carbon dioxide and water thus produced are transferred back to the environment, and ultimately so are waste products, such as fecal material. Decomposers recycle nutrients from dead plant or animal matter back to the soil in terrestrial environments or to the water in aquatic environments. The atoms that make up the organisms in an ecosystem are cycled repeatedly between the living and nonliving parts of the ecosystem.

Students know how the flow of energy is interconnected with the cycling of matter.

· A food chain is the simplest path that energy takes through an ecosystem. Energy enters an ecosystem from the Sun. Each level in the transfer of energy through an ecosystem is called a trophic level. The organisms in each trophic level use some of the energy in the process of cellular respiration, lose energy due to heat loss, and store the rest.

o The first trophic level consists of producers (green plants or other autotrophs).

§ Primary producers capture the Sun’s energy during photosynthesis, and it is converted to chemical energy in the form of simple sugars.

§ The autotroph uses some of the simple sugars for energy and some of the simple sugars are converted to organic compounds (carbohydrates, proteins, and fats) as needed for the structure and functions of the organism.

§ Examples of primary producers include land plants and phytoplankton in aquatic environments.

o The second trophic level consists of primary consumers (heterotrophs).

§ Primary consumers that eat green plants are called herbivores.

§ The herbivore uses some of the organic compounds for energy and some of the organic compounds are converted into the proteins, carbohydrates and fats that are necessary for the structure and functions of the herbivore. Much of the consumed energy is lost as heat.

§ Examples of primary consumers include grasshoppers, rabbits and zooplankton.

o The third trophic level, or any higher trophic level, consists of consumers.

§ Consumers that eat primary consumers are called carnivores; consumers that eat both producers and primary consumers are called omnivores.

§ The carnivores or omnivores use some of the organic compounds for energy and some of the organic compounds are converted into the proteins, carbohydrates and fats that are necessary for their body structures and functions. Much of the consumed energy is lost as heat.

§ Examples of consumers include humans, wolves, frogs, and minnows.

o A heterotroph that breaks down organic material and returns the nutrients to soil, water, and air making the nutrients available to other organisms is called a decomposer.

o The energy available for each trophic level in an ecosystem can be illustrated with a food chain diagram.

· A food web represents many interconnected food chains describing the various paths that energy takes through an ecosystem. The energy available in an ecosystem can be illustrated with a food web diagram.

· Ecological pyramids are models that show how energy flows through ecosystems. Pyramids can show the relative amounts of energy, biomass, or numbers of organisms at each trophic level in an ecosystem. The base of the pyramid represents producers. Each step up represents a different level of consumer. The number of trophic levels in the pyramid is determined by the number of organisms in the food chain or food web.

o An energy pyramid represents the energy available for each trophic level in an ecosystem.

§ The energy needs of organisms are greater from level to level in an ecosystem.

§ Therefore, the total amount of energy available at each level decreases in an ecosystem.

§ Each successive level in an ecosystem can support fewer numbers of organisms than the one below. With each level of the pyramid, only 10% of the energy available is used by organisms while there is an energy loss of about 90% to the environment.

o A number pyramid represents the number of individual organisms available for energy at each trophic level in an ecosystem. It can be used to examine how the population of a certain species affects another.

§ The autotrophic level is represented at the base of the pyramid. This represents the total number of producers available to support the energy needs of the ecosystem.

§ The total numbers of individual organisms tend to decline as one goes up trophic levels.

o A biomass pyramid represents the total mass of living organic matter (biomass) at each trophic level in an ecosystem.

§ Since the number of organisms is reduced in each successive trophic level, the biomass at each trophic level is reduced as well.

§ Even though a biomass pyramid shows the total mass of organisms available at each level, it does not necessarily represent the amount of energy available at each level. For example, the skeleton and beak of a bird will contribute to the total biomass but are not available for energy.