Ecosystems Practice Questions
20 free Ecosystems practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following terms describes the total dry weight of all living organic matter in a specific trophic level or ecosystem?
- A Productivity
- B Biomass
- C Net primary production
- D Ecological footprint
Correct answer: Biomass
Biomass refers to the mass of living biological organisms in a given area or ecosystem at a given time. It is a critical measure for understanding energy storage and flow within food webs.
In an energy pyramid, what percentage of energy is typically transferred from one trophic level to the next higher level?
- A 1%
- B 10%
- C 50%
- D 90%
Correct answer: 10%
The '10% Rule' in ecology states that only about 10% of the energy consumed at one level is converted into biomass at the next level. The remaining 90% is lost as metabolic heat or through waste.
Which process in the nitrogen cycle involves the conversion of atmospheric nitrogen (N2) into ammonia (NH3) by specialized bacteria?
- A Nitrification
- B Denitrification
- C Nitrogen fixation
- D Ammonification
Correct answer: Nitrogen fixation
Nitrogen fixation is the essential process where atmospheric nitrogen is converted into a form plants can use. This is primarily performed by bacteria like Rhizobium living in root nodules or free-living cyanobacteria.
What is the primary difference between a food chain and a food web?
- A A food chain includes decomposers while a food web does not.
- B A food web shows multiple interconnected energy paths; a food chain is a single linear path.
- C A food chain only occurs in aquatic ecosystems.
- D A food web only includes abiotic factors.
Correct answer: A food web shows multiple interconnected energy paths; a food chain is a single linear path.
A food chain is a simplified, linear model showing who eats whom. In contrast, a food web accurately represents the complex network of feeding relationships found in real-world ecosystems.
Which of the following organisms is always found at the first trophic level of an ecosystem?
- A Herbivores
- B Detritivores
- C Autotrophs
- D Apex predators
Correct answer: Autotrophs
Autotrophs, or producers, form the base of every ecosystem by converting inorganic energy (usually sunlight) into organic matter. All other trophic levels depend on the energy captured by these organisms.
In the phosphorus cycle, what is the primary reservoir for phosphorus?
- A The atmosphere
- B Sedimentary rock
- C The ocean surface
- D Living plants
Correct answer: Sedimentary rock
Unlike the carbon and nitrogen cycles, the phosphorus cycle does not involve a significant gaseous phase in the atmosphere. Phosphorus is mainly released from rocks through weathering and erosion.
What occurs during the process of 'biological magnification' (biomagnification)?
- A Energy increases as it moves up the food chain.
- B The population of producers increases rapidly.
- C Toxins increase in concentration in the tissues of organisms at higher trophic levels.
- D Nutrients are recycled back into the soil by decomposers.
Correct answer: Toxins increase in concentration in the tissues of organisms at higher trophic levels.
Biomagnification happens when persistent chemicals, like mercury or DDT, are not metabolized and become more concentrated as they are passed from prey to predator. This often leads to toxic levels in top-tier predators.
Which type of ecological succession occurs on a surface where no soil previously existed, such as a new volcanic island?
- A Secondary succession
- B Primary succession
- C Climax succession
- D Cyclic succession
Correct answer: Primary succession
Primary succession begins in essentially lifeless areas where there is no soil. It starts with pioneer species like lichens that break down rock to help form the initial layers of soil.
The relationship between a remora fish and a shark, where the remora gets a free ride and scraps of food while the shark is unaffected, is an example of:
- A Mutualism
- B Parasitism
- C Commensalism
- D Competition
Correct answer: Commensalism
Commensalism is a symbiotic relationship where one species benefits while the other is neither helped nor harmed. The remora gains transportation and food, but the shark experiences no significant effect.
Which ecosystem has the highest Net Primary Productivity (NPP) per square meter?
- A Open ocean
- B Desert
- C Tropical rainforest
- D Tundra
Correct answer: Tropical rainforest
Tropical rainforests have high temperatures, abundant rainfall, and year-round sunlight, which facilitate rapid plant growth. This makes them some of the most productive ecosystems on Earth in terms of organic matter creation.
What is the term for a species that has a disproportionately large effect on its natural environment relative to its abundance?
- A Endangered species
- B Keystone species
- C Invasive species
- D Indicator species
Correct answer: Keystone species
A keystone species plays a critical role in maintaining the structure of an ecological community. If removed, the ecosystem would be dramatically different or cease to exist altogether, such as sea otters in kelp forests.
In the carbon cycle, which process removes carbon dioxide from the atmosphere?
- A Combustion
- B Respiration
- C Photosynthesis
- D Decomposition
Correct answer: Photosynthesis
Photosynthesis is the primary biological process that absorbs atmospheric CO2. Plants and algae use the carbon to build glucose, effectively sequestering it from the air.
What describes the 'niche' of an organism within an ecosystem?
- A The physical location where it lives.
- B Its role and the set of conditions it needs to survive and reproduce.
- C The total number of offspring it produces.
- D Its position on a map relative to the equator.
Correct answer: Its role and the set of conditions it needs to survive and reproduce.
An organism's niche includes its habitat, what it eats, when it is active, and how it interacts with other species. It is effectively the 'profession' or 'job' of the species in the environment.
Which biome is characterized by permafrost, extremely low temperatures, and little precipitation?
- A Taiga
- B Savanna
- C Tundra
- D Temperate grassland
Correct answer: Tundra
The tundra is a cold, treeless biome found in the Arctic or on high mountains. The presence of permafrost (permanently frozen subsoil) prevents deep root growth and restricts the types of vegetation that can survive.
What is the primary role of fungi and bacteria in an ecosystem's nutrient cycle?
- A Primary production
- B Transpiration
- C Decomposition
- D Carbon fixation
Correct answer: Decomposition
Decomposers break down dead organic matter and waste products. This process returns essential nutrients like nitrogen and phosphorus back to the soil, making them available for producers again.
An 'ectoparasite' is an organism that lives on which part of its host?
- A Inside the bloodstream
- B Within the digestive tract
- C On the external surface
- D In the muscle tissue
Correct answer: On the external surface
Ectoparasites, such as ticks, lice, and leeches, live and feed on the outside of their host. Endoparasites, by contrast, live inside the host's body.
The Competitive Exclusion Principle states that:
- A Two species can share the exact same niche indefinitely.
- B Two species competing for the same limiting resource cannot coexist in the same niche.
- C The larger species will always win a competition.
- D Predators always exclude prey from an ecosystem.
Correct answer: Two species competing for the same limiting resource cannot coexist in the same niche.
This principle suggests that if two species have identical niches, one will eventually be more efficient at utilizing resources and drive the other to local extinction or evolutionary change.
Which of the following is an abiotic factor that could limit the size of a population?
- A Disease
- B Predation
- C Amount of sunlight
- D Parasitism
Correct answer: Amount of sunlight
Abiotic factors are the non-living chemical and physical parts of the environment. Sunlight, temperature, and water availability are abiotic, whereas disease and predation are biotic (living) factors.
What happens during the process of 'transpiration'?
- A Animals release carbon dioxide through breathing.
- B Plants release water vapor into the atmosphere through their leaves.
- C Water evaporates from the surface of the ocean.
- D Clouds form from cooling water vapor.
Correct answer: Plants release water vapor into the atmosphere through their leaves.
Transpiration is essentially evaporation from plant leaves. It is a vital part of the water cycle that helps move water from the soil to the atmosphere and drives the upward movement of water in plants.
In a pyramid of numbers, what does each level represent?
- A The total energy available at that level.
- B The total dry weight of organisms.
- C The number of individual organisms at each trophic level.
- D The amount of carbon stored in each organism.
Correct answer: The number of individual organisms at each trophic level.
A pyramid of numbers displays the population size of each trophic level. While energy pyramids are always upright, pyramids of numbers can sometimes be inverted (e.g., thousands of insects feeding on a single large tree).