Matter and Energy Flow WCPSS/NC 8 th Science

Key Vocabulary Autotrophs: producers; organisms that produce complex organic compounds from simple inorganic molecules using a source of energy such as sunlight Food chain: a description of the path by which energy moves from the sun to plants and animals Food web: a diagram that shows how food chains in a community are related and interlinked Heterotrophs: consumers; organisms that obtain carbon from outside sources Nitrogen cycle: model describing how nitrogen moves from the atmosphere to the soil, to living organisms, and then back to the atmosphere Photosynthesis: a process in which plants use sunlight, water, and carbon dioxide to produce sugar and release oxygen Cellular respiration: the process of consuming oxygen and releasing carbon dioxide Water cycle: model describing how water moves from Earth’s surface to the atmosphere and back to the surface again through evaporation, condensation, and precipitation

Everything is connected! Organisms interact constantly with other organisms, most often when one feeds on another. Food contains nutrients and energy need for survival. When one organism is food for another, some of the energy in the first organism (the food) is transferred to the second organism (the consumer). The transfer of energy does not stop here! When organisms die, other organisms, decomposers, take in energy as they break down the remains of the organisms. This constant movement of energy through a community can be diagrammed as a food chain or a food web.

Food Chains A food chain is a simple way of showing how energy, in the form of food, passes from one organism to another. For example, a pond food chain may look like this: Aquatic plants → insects → bluegill (fish) → bass (fish) → humans Food chains usually have only 3-4 links because the available energy decreases from one link to the next. At each energy transfer, some energy is lost as heat because of the activities of the organisms. In the final link there is only a small amount of energy left from the first link in the chain.

This image shows where the energy starts for a plant. Only a small amount of that plant’s energy is left for the lion at the end of the chain. Another example of the energy flow from plant to owl. Again, not much energy is left from the flower by the time the owl eats the snake.

Food webs Food chains are too simple to describe the many interactions among organisms in an ecosystem. A food web is a series of overlapping food chains that exist in an ecosystem. A food web provides a more complete model of the way energy moves through an ecosystem and are more accurate because it shows how many organisms are part of more than one food chain in an ecosystem.

Example of Food Web

Aquatic Food Web Example Image:

Ecological Pyramids Most of all the energy in the biosphere comes from the sun. Producers take in and transform only a small part of the energy that reaches Earth’s surface. When an herbivore eats a plant, some of the energy in the plant passes to the herbivore. The majority of the energy from the plant is given off into the atmosphere as heat. This continues to happen as other animals eat. An ecological pyramid is a model of the number of organisms at each level. The bottom is always the producers of an ecosystem.

An Ecological/Energy Pyramid

Energy Pyramid An energy pyramid compares the energy available at each level of the food chain in an ecosystem. A pyramid of energy usually has 3-4 levels (like a food chain). Only about 10% of the energy at each level of the pyramid is available to the next level. By the time the top level is reached, the amount of energy available is greatly reduced.

Energy Pyramid

The Cycles of Matter Water Cycle: the constant recycling of water throughout the Earth through evaporation, condensation, and precipitation. Nitrogen Cycle: the transfer of nitrogen from the atmosphere to producers then to consumers; the nitrogen then moves back to the atmosphere or directly into producers again

Resources Images: cited beneath Information: Chapter 9, Section 3: Matter and Energy Glencoe Science, North Carolina Science Grade 8 Guidance from 8Science_RevisedSeptember2012.docx.pdf 8Science_RevisedSeptember2012.docx.pdf