AP Environmental Science Practice Test (2026)

Which of the following best describes the role of decomposers in an ecosystem?

A field-research team surveyed a remote biome site at 68 degrees N latitude across a single growing season. Mean annual temperature at the site was -9 degrees C, and total annual precipitation averaged 22 cm, most falling as snow. Soil cores extracted to a depth of 1.2 m showed a continuous frozen layer beginning 38 cm below the surface and extending downward throughout the core. Vegetation was dominated by ground-hugging mosses, lichens, and dwarf willow shrubs less than 25 cm tall; no trees were recorded on any of the 40 survey plots. The active growing season between the last and first freeze dates spanned 54 days.

Based on the field-study data, which biome did the research team survey?

In the open ocean, which zone is characterized by sufficient sunlight for photosynthesis and a wide variety of marine life?

Which of the following human activities directly contributes to an increase in atmospheric carbon dioxide levels?

Which process converts atmospheric nitrogen gas (N2) into ammonia (NH3), making it usable by plants?

Researchers studying phosphorus dynamics in the Cedar Fork Watershed estimated the total mass of phosphorus held in each major ecosystem compartment. Over a 10 square kilometer study area, estimated total phosphorus stocks were: atmospheric air column above the watershed, less than 0.5 kg; stream water sampled monthly at the outflow, about 40 kg; surface soil horizons to a depth of 1 m, about 12,000 kg; living biomass across forest plots, about 3,200 kg; and deep sedimentary bedrock underlying the watershed, about 870,000 kg. Over the five-year study, the team tracked only a small annual net transfer of phosphorus from bedrock to soil through weathering, and no measurable gaseous phosphorus exchange with the atmosphere.

Based on the watershed data, which reservoir holds the largest long-term pool of phosphorus in this system?

Which of the following processes in the hydrologic cycle involves water vapor returning to liquid form, forming clouds?

Net Primary Productivity (NPP) is a critical measure in ecology. Which of the following equations correctly represents NPP?

A fox that primarily eats rabbits, which in turn eat grass, would be classified as which of the following trophic levels?

According to the 10% rule of energy transfer, if primary producers in an ecosystem contain 10,000 kcal of energy, approximately how much energy would be available to the secondary consumers?

A keystone species is one that has a disproportionately large effect on its environment relative to its abundance. Which of the following scenarios best illustrates the impact of removing a keystone species from an ecosystem?

Which of the following best describes the climate and typical vegetation of a tropical rainforest?

A scientist is studying a forest ecosystem and collects data on the biomass of different trophic levels. They find that the producers (trees and plants) have a total biomass of 50,000 kg. The primary consumers (herbivores) have a biomass of 5,000 kg. The secondary consumers (carnivores that eat herbivores) have a biomass of 500 kg. The tertiary consumers (carnivores that eat other carnivores) have a biomass of 50 kg.

Based on the provided data, what is the approximate energy transfer efficiency from the primary consumers to the secondary consumers?

A diagram illustrates the carbon cycle, showing reservoirs like the atmosphere, oceans, fossil fuels, and living biomass. Arrows indicate processes such as photosynthesis, respiration, combustion, and dissolution. One arrow points from 'Atmosphere' to 'Oceans' labeled 'Dissolution', and another points from 'Fossil Fuels' to 'Atmosphere' labeled 'Combustion'.

Which of the following processes shown in the diagram represents a major human impact on the carbon cycle, leading to an increase in atmospheric carbon dioxide?

A graph shows the Net Primary Productivity (NPP) for various terrestrial biomes (e.g., Tropical Rainforest, Temperate Forest, Desert, Tundra). The Tropical Rainforest consistently shows the highest NPP, while the Desert and Tundra show the lowest NPP.

Based on the graph, which of the following factors is most likely a primary limiting factor for NPP in the desert and tundra biomes?

A food web diagram shows arrows representing energy flow. Grass is eaten by rabbits and deer. Rabbits are eaten by foxes and hawks. Deer are eaten by wolves. Foxes are also eaten by wolves. Decomposers are shown breaking down all dead organisms.

In this food web, if the population of wolves significantly declines due to hunting, which of the following is the most likely immediate consequence?

A diagram of the nitrogen cycle shows atmospheric N2 being converted to ammonia by nitrogen-fixing bacteria. Ammonia is then converted to nitrites and nitrates by nitrifying bacteria. Plants absorb nitrates. Animals consume plants. Decomposers convert organic nitrogen back to ammonia. Denitrifying bacteria convert nitrates back to N2 gas.

Based on the diagram, which group of organisms is responsible for returning nitrogen gas (N2) to the atmosphere?