AP Environmental Science

Unit 1

The Living World: Ecosystems

8 practice questions · Free response

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Notes

Ecosystems and interactions

An ecosystem is all the living (biotic) and nonliving (abiotic) parts of an area. Species interact through predation, competition, mutualism, commensalism and parasitism.

  • Resource partitioning lets competing species share a resource by using it at different times, places or ways (warblers feeding in different parts of a tree).

Biomes

Biomes are defined by temperature and precipitation, which determine the plants that can grow.

  • Tropical rainforest: hot, wet, nutrient-poor soil. Desert: very dry. Tundra: cold, permafrost. Temperate forests and grasslands: moderate. Taiga (boreal forest): cold, conifers.
  • Aquatic biomes depend on salinity, depth, flow and temperature. Wetlands and estuaries are very productive and filter water; coral reefs have high biodiversity.

Biogeochemical cycles

  • Carbon: photosynthesis takes in $\mathrm{CO_2}$; respiration, decomposition and combustion release it. Big sinks: oceans, sediments, fossil fuels, forests.
  • Nitrogen: fixation (bacteria or lightning turn $\mathrm{N_2}$ into ammonia), nitrification (ammonia to nitrate), assimilation (plants take up nitrate), ammonification, and denitrification (back to $\mathrm{N_2}$).
  • Phosphorus: no gas phase; it cycles slowly through rock weathering. It's often a limiting nutrient, so runoff causes algal blooms.
  • Hydrologic cycle: evaporation, transpiration, condensation, precipitation, runoff and infiltration.

Energy flow

  • Primary productivity: GPP is the total energy captured by producers; NPP = GPP − respiration is what's left for consumers.
  • 10% rule: only about 10% of energy passes to the next trophic level. The rest is lost as heat (second law of thermodynamics). That's why food chains are short.
  • Food webs show many connected food chains; decomposers recycle nutrients.
Producers: 10,000 kcalPrimary consumers: 1,000 kcalSecondary consumers: 100 kcalTertiary consumers: 10 kcal
Only about 10% of energy reaches the next trophic level.

Practice

Which two factors mainly determine the type of biome in an area?
Which process removes $\mathrm{CO_2}$ from the atmosphere?
Which cycle has no significant atmospheric component?
Bacteria that convert $\mathrm{N_2}$ gas into ammonia carry out:
A forest has GPP of 2,500 kcal/m²/yr and producers use 1,000 kcal/m²/yr for respiration. What is NPP?
If producers have 50,000 kcal, about how much is available to tertiary consumers?
Two warbler species feed in different parts of the same tree. This is an example of:
Why is most energy lost between trophic levels?

Free response

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Free-response question

A farmer applies large amounts of nitrogen fertilizer, and much of it runs into a nearby pond.

(a) Describe how the nitrogen could lead to low dissolved oxygen in the pond.

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Excess nitrogen causes an algal bloom. When the algae die, decomposers break them down using lots of oxygen, lowering dissolved oxygen (eutrophication).

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(b) Identify one process in the nitrogen cycle that returns nitrogen to the atmosphere.

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Denitrification, in which bacteria convert nitrate back into $\mathrm{N_2}$ gas.

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(c) Propose one way the farmer could reduce fertilizer runoff.

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Plant a vegetative buffer strip along the pond, apply fertilizer in smaller amounts at the right time, or use cover crops to hold soil.

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