3. Energy Flow Through Ecosystems Food contains nutrients and energy needed for survival. Matter and Energy 3 3 When one organism is food for another organism, some of the energy in the first organism (the food) is transferred to the second organism (the eater).

4. Energy Flow Through Ecosystems Producers are organisms that take in and use energy from the Sun or some other source to produce food. Consumers are organisms that take in energy when they feed on producers or other consumers. Matter and Energy 3 3 When organisms die, other organisms called decomposers take in energy as they break down the remains of organisms.

5. Food Chains A food chain is a model, a simple way of showing how energy, in the form of food, passes from one organism to another. When drawing a food chain, arrows between organisms indicate the direction of energy transfer. Matter and Energy 3 3

6. Food Chains Food chains usually have only three or four links. This is because the available energy decreases from one link to the next link. In a food chain, the amount of energy left for the last link is only a small portion of the energy in the first link. Matter and Energy 3 3

7. Food Webs 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. Matter and Energy 3 3

8. Food Webs Matter and Energy 3 3

9. Ecological Pyramids Most of 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. Matter and Energy 3 3

10. Ecological Pyramids An ecological pyramid models the number of organisms at each level of a food chain. The bottom of an ecological pyramid represents the producers of an ecosystem. Matter and Energy 3 3 The rest of the levels represent successive consumers.

11. 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 three or four levels. Matter and Energy 3 3 Only about ten percent of the energy at each level of the pyramid is available to the next level.

12. The Cycles of Matter The law of conservation of mass states that matter on Earth is never lost or gained. It is used over and over again. The carbon atoms in your body might have been on Earth since the planet formed billions of years ago. They have been recycled billions of times. Matter and Energy 3 3

13. Water Cycle The water cycle involves the process of evaporation, condensation, and precipitation. Heat from the Sun causes water on Earth’s surface to evaporate, or change from a liquid to a gas, and rise into the atmosphere as water vapor. Matter and Energy 3 3

14. Water Cycle Eventually, the water vapor changes back into tiny droplets of water. It condenses, or changes from a gas to a liquid. Matter and Energy 3 3 When the droplets become large and heavy enough, they fall back to Earth as rain or other precipitation.

15. Other Cycles in Nature Matter and Energy 3 3 The movement of carbon through Earth’s biosphere is called the carbon cycle.

16. Other Cycles in Nature The nitrogen cycle begins with the transfer of nitrogen from the atmosphere to producers then to consumers. Matter and Energy 3 3 The nitrogen then moves back to the atmosphere or directly into producers again. Phosphorus, sulfur, and other elements needed by living organisms also are used and returned to the environment.

17. 3 3 Section Check Question 1 Most of the energy in the biosphere comes from _______. A. Earth B. lava C. the Sun D. water

18. 3 3 Section Check Answer The correct answer is C. The Sun directly or indirectly provides the energy for all organisms.

19. 3 3 Section Check Question 2 Which describes grass? A. carnivore B. consumer C. decomposer D. producer

20. 3 3 Section Check Answer The answer is D. Grass takes in energy from the Sun for photosynthesis which produces carbohydrates that provide energy for the consumers that feed on the grass.

21. 3 3 Section Check Question 3 Which correctly correlates with the numbered illustration of the water cycle?

22. 3 3 Section Check A. Precipitation, Evaporation and Condensation B. Condensation, Evaporation and Precipitation

23. 3 3 Section Check C. Evaporation, Condensation and Precipitation D. Evaporation, Precipitation and Condensation

24. 3 3 Section Check Answer The answer is C. During the water cycle, water from Earth’s surface evaporates into the atmosphere, condenses to form clouds then falls back to Earth in the form of precipitation.

25. Chapter 18 Review 1 of 2 Water droplets form when water vapor cools off. In the carbon cycle, carbon follows various paths. Carnivores eat consumers. Nitrogen is used by both plants and animals. A food web is a more complete model of feeding relationships, as compared to a food chain.

26. Chapter 18 Review 2 of 2 As you move from level to level in an energy pyramid, energy decreases. Nitrogen cycle: begins with transfer of nitrogen from atmosphere to producers. Energy is recycled. Food web: overlapping food chains. Air: mixture of gases, such as oxygen, nitrogen, and carbon dioxide.