Tennessee Biology I EOC LS2 (Ecology and Interdependence): a complete overview of energy flow, the cycling of matter, populations, ecosystem stability, and human impact

What the LS2 ecosystems core idea demands

Ecosystems: Interactions, Energy, and Dynamics (LS2) is the ecology core idea of the Tennessee Biology I course. This guide runs from how energy moves through an ecosystem, through how matter is recycled, to what controls population sizes, what keeps ecosystems stable, and how humans affect them. The recurring crosscutting concept is energy and matter in systems: tracing the one-way flow of energy and the cyclic movement of matter.

This guide ties together the matching topic pages, each with its own practice questions: energy flow and food webs, the cycling of matter, population dynamics and carrying capacity, ecosystem stability and resilience, and human impact on ecosystems.

Energy flow

Energy enters as sunlight, captured by producers (photosynthesis), and flows to consumers and decomposers. Each feeding level is a trophic level, shown in an energy pyramid. Only about 10 percent of energy passes to the next level (the rest is lost, mostly as heat from respiration), so pyramids narrow upward and food chains are short. Energy flows one way and is not recycled.

The cycling of matter

Unlike energy, matter is recycled. In the carbon cycle, photosynthesis removes carbon dioxide and respiration returns it. In the nitrogen cycle, nitrogen-fixing bacteria make nitrogen usable, and decomposers recycle it. The water cycle moves water by evaporation, condensation, precipitation, and transpiration. Decomposers are essential to every cycle, returning nutrients to producers.

Populations

With unlimited resources a population grows exponentially (J-shaped); in reality it follows a logistic (S-shaped) curve, leveling off at the carrying capacity. Density-dependent limiting factors (competition, predation, disease) intensify as the population gets denser; density-independent factors (weather, drought, fire) act regardless of density.

Ecosystem stability

A diverse ecosystem is more stable and resilient because many species provide redundancy. Species interact through symbiosis (mutualism, commensalism, parasitism), competition, and predation. After a disturbance, an ecosystem changes through succession: primary (from bare rock, no soil, slow) or secondary (where soil remains, faster).

Human impact

Habitat destruction is the leading cause of species loss; pollution, climate change (from greenhouse gases like carbon dioxide), invasive species, and overharvesting also reduce biodiversity and stability. Conservation (protecting habitats, reducing pollution and fossil-fuel use, recycling, restoring ecosystems, sustainable management) reduces the harm.

Check your knowledge

A mix of recall and reasoning questions covering the LS2 ecosystems core idea. Attempt them under timed conditions, then check against the solutions.

1. Name the three roles organisms play in energy flow and give an example of each. (3 marks)
2. About what percentage of energy passes from one trophic level to the next? (1 mark)
3. State the difference between how energy and matter move through an ecosystem. (2 marks)
4. Name the two processes that cycle carbon between living things and the air. (2 marks)
5. Explain the role of nitrogen-fixing bacteria. (2 marks)
6. Define carrying capacity. (1 mark)
7. Classify each as density-dependent or density-independent: disease, a flood. (2 marks)
8. State the difference between primary and secondary succession. (2 marks)
9. Name the leading cause of species loss and give one conservation strategy. (2 marks)