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Quiz: Ecosystems and Biomes

Test your understanding of Earth's major terrestrial and aquatic biomes, ecosystem structure, and energy flow with these review questions.

1. What two climate factors are primarily used to classify terrestrial biomes?

  1. Wind speed and elevation
  2. Temperature and precipitation
  3. Soil type and sunlight hours
  4. Latitude and ocean currents
Show Answer

The correct answer is B. Terrestrial biomes are classified primarily by average temperature and average precipitation. These two variables determine what kinds of plants can grow in a region, and the plant communities in turn determine which animals can live there. The combination of temperature and precipitation acts as the defining "address" for each biome.

Concept Tested: Terrestrial Biomes

2. Which biome is defined primarily by its dryness rather than its temperature?

  1. Tundra biome
  2. Chaparral biome
  3. Desert biome
  4. Taiga biome
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The correct answer is C. The desert biome is defined by receiving less than 25 cm of precipitation per year, regardless of temperature. While many people associate deserts with extreme heat, cold deserts also exist -- Antarctica is technically a desert. The defining characteristic is aridity, not temperature.

Concept Tested: Desert Biome

3. Why are wetlands sometimes called "nature's kidneys"?

  1. They produce hormones that regulate the water cycle in surrounding ecosystems
  2. They filter pollutants, absorb floodwaters, and trap sediments
  3. They are shaped like kidneys when viewed from aerial photographs
  4. They remove excess oxygen from water before it enters the ocean
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The correct answer is B. Wetlands earn the nickname "nature's kidneys" because they perform critical filtering functions similar to kidneys in the human body. They remove pollutants from water, absorb excess floodwaters during storms, and trap sediments before they reach downstream ecosystems. Despite this ecological value, over 50% of the world's wetlands have been drained or filled.

Concept Tested: Wetlands

4. What role do decomposers play in an ecosystem?

  1. They capture sunlight energy and convert it into glucose through photosynthesis
  2. They hunt primary consumers to regulate herbivore populations
  3. They break down dead organisms and waste, recycling nutrients back into the environment
  4. They transport seeds and pollen between different plant species
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The correct answer is C. Decomposers, primarily fungi and bacteria, break down dead organisms and waste products, recycling nutrients back into the soil or water where producers can use them again. Without decomposers, nutrients would remain locked in dead tissue and ecosystems would eventually grind to a halt. A single teaspoon of healthy soil contains more microorganisms than there are people on Earth.

Concept Tested: Decomposers

5. According to the ten percent rule, if producers capture 20,000 kcal of energy, how much energy is available to secondary consumers?

  1. 2,000 kcal
  2. 200 kcal
  3. 20 kcal
  4. 2 kcal
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The correct answer is B. Using the ten percent rule: producers capture 20,000 kcal, primary consumers receive 10% of that (2,000 kcal), and secondary consumers receive 10% of the primary consumers' energy (200 kcal). This dramatic loss of energy at each trophic level explains why most ecosystems can only support four or five trophic levels.

Concept Tested: Ten Percent Rule

6. What is coral bleaching and what causes it?

  1. A natural color change that occurs when corals reproduce during seasonal cycles
  2. The process of corals expelling symbiotic algae when water temperatures rise above normal
  3. A disease caused by bacterial infection that turns coral skeletons white
  4. The natural erosion of coral reefs by wave action and ocean currents
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The correct answer is B. Coral bleaching occurs when water temperatures rise just 1-2 degrees Celsius above normal, causing corals to expel their symbiotic zooxanthellae algae. These photosynthetic algae normally provide corals with food and their vibrant colors. Without their algal partners, corals turn white and can die if conditions do not improve quickly.

Concept Tested: Coral Reefs

7. What distinguishes a food web from a food chain?

  1. A food web only includes producers and primary consumers while a food chain includes all trophic levels
  2. A food web shows energy transfer in aquatic ecosystems while a food chain applies to terrestrial ecosystems
  3. A food web is a network of interconnected food chains showing complex feeding relationships
  4. A food web measures energy in kilocalories while a food chain measures energy in joules
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The correct answer is C. A food chain is a single linear sequence showing who eats whom (e.g., grass to grasshopper to frog to snake to hawk). A food web is a network of interconnected food chains in an ecosystem, showing the complex feeding relationships that actually exist in nature. Food webs are more realistic because most organisms eat and are eaten by multiple species.

Concept Tested: Food Webs

8. Which feature defines the tundra biome and prevents trees from growing there?

  1. Extremely high levels of annual precipitation that flood root systems
  2. Permafrost beneath the surface and a growing season of only 6-10 weeks
  3. Acidic soil caused by decomposing conifer needles that inhibits tree growth
  4. Constant high winds that erode topsoil and prevent seed establishment
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The correct answer is B. The tundra biome is defined by permafrost -- a layer of permanently frozen soil beneath the surface -- and an extremely short growing season of only 6-10 weeks. These conditions prevent trees from establishing deep root systems, resulting in vegetation limited to low-growing shrubs, mosses, lichens, and grasses. The tundra also stores approximately twice as much carbon as the entire atmosphere.

Concept Tested: Tundra Biome

9. Why is the taiga considered the world's largest terrestrial biome?

  1. It has the highest biodiversity of any land biome on Earth
  2. It receives more precipitation than any other terrestrial biome
  3. It stretches in a massive band across northern Russia, Canada, and Scandinavia
  4. It contains the tallest trees and thickest canopy cover of any forest biome
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The correct answer is C. The taiga, also called boreal forest, is the world's largest terrestrial biome by area, stretching in a massive band across northern Russia, Canada, and Scandinavia. It is dominated by coniferous trees such as spruce, pine, and fir. Despite its vast size, the taiga has relatively low biodiversity compared to tropical biomes due to its harsh climate with long, cold winters.

Concept Tested: Taiga Biome

10. What powers the deep-ocean communities that live around hydrothermal vents?

  1. Sunlight that penetrates to the ocean floor through clear water columns
  2. Organic matter that sinks from the surface ocean in a process called marine snow
  3. Chemosynthesis by bacteria that convert chemical energy from hydrogen sulfide
  4. Geothermal heat that warms the water enough for photosynthetic algae to grow
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The correct answer is C. Deep-ocean hydrothermal vent communities are powered by chemosynthesis rather than photosynthesis. Bacteria at these vents convert chemical energy from hydrogen sulfide and other minerals in the superheated water into organic molecules. These chemosynthetic bacteria serve as the producers for an entire ecosystem of giant tube worms, crabs, and shrimp, demonstrating that life can thrive without sunlight.

Concept Tested: Deep Ocean