Understand the nature of an ecosystem.

• Identify biotic and abiotic environmental factors.
• Explain how energy is related to ecosystems.

Recognize the types of relationships that organisms have to each other.

• Explain why plants are called producers.
• Identify the trophic levels occupied by herbivores and carnivores and why they are called consumers.
• Describe the role of decomposers.

Understand energy flow through an ecosystem.

• Explain why predators are rarer than herbivores.
• Describe why useful energy is lost as energy flows from one trophic level to the next.
• Describe the benefits and shortcomings of using each of the following: pyramid of numbers, pyramid of biomass, and pyramid of energy.

Understand that materials are cycled through organisms and the abiotic parts of ecosystems.

• Describe the flow of atoms through the carbon, nitrogen, phosphorus, and hydrologic cycles.
• Explain why animals must eat.
• Describe the importance of bacteria in nutrient cycles.
• Explain why carbon and nitrogen must be recycled in ecosystems.

Understand that humans have altered natural ecosystems.

• Describe the kinds of ecosystems that have been converted to agriculture.
• Explain why people in poor countries eat mostly plant material.