Which description best defines an ecosystem?

A community of organisms interacting with one another and with the nonliving environment — B is correct because an ecosystem includes both interactions among organisms and interactions with nonliving surroundings. A describes a population, while C incorrectly excludes abiotic factors. D is incomplete because biomes and ecosystems are not identified by precipitation alone.

A forest floor has low light but high moisture, while the canopy has intense light and drying winds. Which conclusion is best supported by this pattern?

Abiotic conditions and resource distribution can create different opportunities and limits for species — B is correct because light and moisture vary across space, creating different conditions for organisms. A and D ignore spatial differences in resources. C is incorrect because species in different forest layers may still interact indirectly through shared resources and ecological relationships.

Two plant species live in the same forest. One uses dim understory light, while the other grows rapidly in bright canopy openings. What ecological process is illustrated when they use different light environments?

Resource partitioning — A is correct because the plants use different portions of the light resource, reducing direct competition. B is not the process described, C contradicts the variation in light availability, and D reverses the energy transformation explained in the article.

Which climate and vegetation combination most strongly identifies a savanna rather than a temperate seasonal forest?

Warm temperatures, a distinct rainy season, a distinct dry season, and grasses with scattered trees — B is correct because savannas are warm and have distinct rainy and dry seasons, with grasses and scattered trees. A, C, and D describe the year-round precipitation and four-season pattern associated with a temperate seasonal forest rather than a savanna.

A climate record shows four seasons, moderate temperatures, and precipitation in every month. Which biome is the best interpretation?

Temperate seasonal forest — B is correct because four distinct seasons combined with precipitation throughout the year are characteristic of a temperate seasonal forest. A would have warm conditions with a pronounced rainy season and dry season. The article does not provide the defining climate patterns for deserts or chaparral in this comparison.

Why should a biome not be identified from temperature alone?

Biome identification requires matching temperature, precipitation amount, precipitation timing, and characteristic vegetation and organisms — B is correct because temperature, precipitation amount, precipitation timing, and ecosystem structure must be considered together. A is false because temperature strongly affects which organisms can survive. C is false because precipitation patterns differ among biomes. D is incorrect because elevation, seasonal patterns, and local conditions also matter.

From the free course AP Environmental Science on Lykke

8.3 Endocrine Disruptors · 8.4 Human Impacts on Wetlands and Mangroves

Key concepts: Endocrine disruptors · Interference with the endocrine system in animals · Birth defects and developmental disorders caused by endocrine disruptors · Gender imbalances in fish and other species · Wetlands as providers of regulating ecosystem services · Human impacts of urbanization and development on wetlands · Mangrove and wetland environmental problems · Nutrient and sediment pollution in estuaries · Environmental solutions for aquatic pollution · Water-quality improvement through filtration

A chemical does not need to kill an animal immediately to damage an ecosystem: if it interferes with hormones during development, it can alter reproduction, growth, or sexual development across an entire population.

8.3 Endocrine Disruptors · 8.4 Human Impacts on Wetlands and Mangroves

Endocrine disruptors: chemical interference with hormones

The endocrine system is the network of glands and hormones that regulates processes such as growth, development, reproduction, and metabolism. An endocrine disruptor is a chemical that interferes with this system in an animal. It may imitate a natural hormone, block a hormone’s action, or change how much hormone an animal produces or breaks down.

STB-3.C — Describe endocrine disruptors.
STB-3.C.1 — Endocrine disruptors are chemicals that can interfere with the endocrine system of animals.

The ecological danger is often indirect. A contaminant may not cause immediate mortality, yet still reduce the number of healthy offspring produced or alter the proportion of males and females. Because reproduction and development determine future population size, a subtle chemical effect can become a population-level problem over time.

Effects on animals and ecosystems

Endocrine disruptors can lead to birth defects, developmental disorders, and gender imbalances in fish and other species. For example, if a chemical causes unusually high production of female fish in a population, the population may eventually contain too few males for successful reproduction. The result is not merely an individual abnormality; it can reduce recruitment, meaning the addition of new individuals to the population.

STB-3.D — Describe the effects of endocrine disruptors on ecosystems.
STB-3.D.1 — Endocrine disruptors can lead to birth defects, developmental disorders, and gender imbalances in fish and other species.

Worked example: A wastewater discharge enters a stream below a city. Fish downstream show abnormal development and a strongly uneven sex ratio, while fish upstream do not. A defensible explanation is that a chemical in the discharge interferes with the fish endocrine system, producing developmental effects and fewer reproductively successful pairings. Over several generations, the downstream population could decline even if adult fish do not die immediately.

Misconception check — “Only poisonous chemicals are harmful.” Acute toxicity and endocrine disruption are different mechanisms. A chemical can be harmful at relatively low concentrations if it alters hormonal signaling, especially during sensitive stages such as embryonic or juvenile development.

For AP reasoning, Science Practice 1: Concept Explanation, especially 1.A Describe environmental concepts and processes, is central here. A strong response names the chemical interference, identifies the endocrine system as the affected biological system, and connects the effect to development or reproduction; simply stating that “pollution harms fish” is too vague.

Wetlands and mangroves as regulating systems

A wetland is an area where water covers the soil either all or part of the time. Marshes, swamps, tidal flats, and mangrove forests are examples. Mangroves are coastal wetlands whose salt-tolerant vegetation slows water movement and traps material carried by runoff and tides.

STB-3.E.1 — Wetlands are areas where water covers the soil, either part or all of the time.

Wetlands provide regulating ecosystem services: benefits produced when ecosystems control or moderate environmental conditions. Their vegetation, saturated soils, and sediments can filter water and reduce flooding.

Wetland feature	Regulating service	Mechanism
Dense roots and stems	Water purification	Slow water and trap sediment and some pollutants
Saturated soil and shallow basins	Flood reduction	Store water and release it more gradually
Mangrove roots along coasts	Shoreline protection	Reduce wave energy and hold sediment in place

Water purification is a form of filtration. As nutrient- and sediment-rich runoff moves through wetland vegetation and soils, suspended particles can settle and plant uptake can remove some nutrients from the water. This does not make wetlands limitless pollution sinks: excessive inputs can overwhelm their capacity.

Urbanization and a defensible environmental response

Urbanization replaces permeable soil and vegetation with roads, buildings, and drainage systems. Development can therefore increase the delivery of nutrient- and sediment-rich runoff to an estuary, while filling, draining, or fragmenting wetlands removes the very areas that would have slowed and filtered that water.

STB-3.E.2 — Wetlands provide a variety of ecological services, including water purification and flood protection.

Worked contextual example: An estuary surrounded by expanding neighborhoods has declining water quality and stressed manatees. A strong response is to reduce nutrient and sediment pollution before it reaches the estuary—for example, by protecting or restoring vegetated wetland buffers, improving stormwater filtration, and reducing polluted runoff from developed land.

The reasoning chain is:

$$ \text{urban development} \rightarrow \text{more nutrient and sediment runoff} \rightarrow \text{poorer estuary water quality} $$

$$ \text{wetland protection and filtration} \rightarrow \text{less nutrient and sediment delivery} \rightarrow \text{improved water quality} $$

The advantages extend beyond effects on manatees. Cleaner water can support fish and invertebrates, improve habitat for wading birds, reduce sediment accumulation, preserve wetland functions, and lower flood risk. A response earns stronger environmental-solutions reasoning when it identifies both the action and the environmental mechanism.

This applies Science Practice 7: Environmental Solutions, particularly 7.B Describe potential solutions to environmental problems. It also uses Science Practice 1: Concept Explanation, 1.B Explain environmental concepts and processes, when the response links filtration or nutrient reduction to improved water quality rather than merely naming a solution.

Misconception check — “Wetlands are wastelands that should be drained.” Wetlands provide valuable regulating services. Removing them can increase flooding and pollution because development eliminates natural water storage and filtration.

Retrieval and interpretation check

What makes a chemical an endocrine disruptor?
Name two ecosystem-level effects of endocrine disruption.
Why can wetland filtration improve an urban estuary?
Why does reducing nutrient and sediment pollution benefit more than one species?

Answers: An endocrine disruptor interferes with an animal’s endocrine system. Effects include birth defects, developmental disorders, and gender imbalances. Wetland filtration slows runoff, traps sediment, and removes or retains some nutrients, improving water quality. Cleaner water supports multiple organisms and preserves wetland and estuary functions, not only manatees.