Georgia Milestones Biology EOC, Ecology (SB5): a complete overview of energy flow, the cycling of matter, populations, biodiversity, succession, and human impact

What the Ecology domain demands

Ecology (SB5) is the interdependence of organisms and their environment, and it is the largest domain on the Georgia Milestones Biology EOC at about 27 percent. It covers how energy flows, how matter cycles, what controls populations, why biodiversity matters, how ecosystems change and recover, and how humans affect them. Because it carries the most points, ecology deserves the most study time, and many items are data and graph interpretation (food webs, energy pyramids, growth curves).

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, biodiversity and ecosystem stability, environmental change and succession, and human impact and conservation.

Energy flow

Energy enters from the sun, is captured by producers, and flows to consumers, with decomposers recycling matter. A food chain is one path; a food web is many linked paths. At each trophic level, only about 10 percent of energy passes to the next (the ten percent rule), the rest lost as heat. This is why an energy pyramid narrows toward the top and food chains are short. Energy flows one way and is not recycled.

Cycling of matter

Unlike energy, matter cycles and is reused. The carbon cycle runs on photosynthesis (removes carbon dioxide) and respiration (returns it). The nitrogen cycle depends on nitrogen-fixing bacteria that make atmospheric nitrogen usable for plants, plus decomposers that recycle it. The water cycle moves water through evaporation, transpiration, condensation, and precipitation. Decomposers are central, returning nutrients from dead matter to producers.

Population dynamics

Populations show exponential (J-shaped) or logistic (S-shaped) growth. The level-off of logistic growth is the carrying capacity: the maximum the environment can support. Limiting factors hold populations near it: density-dependent factors (competition, predation, disease) intensify with crowding, while density-independent factors (drought, fire, temperature) act regardless of size. Reading these from a growth curve is a frequent item.

Biodiversity and stability

Biodiversity brings stability: many species and overlapping food-web links provide redundancy, so the loss of one species is less likely to collapse the system. A keystone species has an outsized effect; removing it cascades through the web. Species interact through symbiosis: mutualism (both benefit), commensalism (one benefits, one unaffected), and parasitism (one benefits, one harmed).

Succession

Ecological succession is the gradual change of a community over time. Primary succession starts on bare rock (no soil), with pioneer species (lichens, mosses) forming soil, so it is slow. Secondary succession starts where soil remains after a disturbance (fire, farm), so it is faster. Both head toward a climax community. A disturbance (natural or human) can reduce stability, and recovery depends on severity, surviving soil, and biodiversity.

Human impact and conservation

Human activities harm ecosystems through habitat destruction, pollution (including fertilizer runoff and algal blooms), invasive species (non-native, no predators, outcompete natives), and climate change (shifting habitats faster than species adapt). Each reduces biodiversity and stability. Conservation solutions include protecting habitats, reducing pollution and emissions, controlling invasives, and using resources sustainably. SB5.e asks you to design a solution matched to the specific problem.

Check your knowledge

A mix of recall and reasoning questions covering the Ecology domain. Attempt them under timed conditions, then check against the solutions.

1. About what percentage of energy passes from one trophic level to the next? (1 mark)
2. Explain why an energy pyramid narrows toward the top. (2 marks)
3. Name the two processes that cycle carbon between the air and living things. (2 marks)
4. State the role of nitrogen-fixing bacteria. (1 mark)
5. Define carrying capacity. (1 mark)
6. Classify "competition for food" as a density-dependent or density-independent factor. (1 mark)
7. Explain why high biodiversity makes an ecosystem more stable. (2 marks)
8. State the difference between primary and secondary succession. (2 marks)
9. Classify a relationship where both species benefit. (1 mark)
10. Name one human impact on ecosystems and one conservation solution. (2 marks)