Biogeochemical Cycles Practice Questions
39 free Biogeochemical Cycles practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Ecology is best defined as the study of:
- A The internal structure of cells
- B Interactions between organisms and environment
- C Classification and naming of all living organisms
- D Evolutionary history of species
Correct answer: Interactions between organisms and environment
Ecology focuses on relationships between organisms and their physical and biological environment. It examines how these interactions influence survival and distribution.
The functional unit of ecology is the:
- A Population
- B Community
- C Ecosystem
- D Biome
Correct answer: Ecosystem
An ecosystem includes both living organisms and non-living components interacting together. It represents energy flow and nutrient cycling.
Which level of organization includes only members of the same species?
- A Community
- B Population
- C Ecosystem
- D Biome
Correct answer: Population
A population consists of individuals of the same species living in a specific area. They can interbreed and share resources.
The movement of individuals into a population is called:
- A Emigration
- B Natality
- C Immigration
- D Mortality
Correct answer: Immigration
Immigration increases population size by adding new individuals. It affects population growth and genetic diversity.
Which term describes the role and position of a species in an ecosystem?
- A Habitat
- B Biome
- C Niche
- D Population density
Correct answer: Niche
An ecological niche describes how a species uses resources and interacts with others. It includes habitat, diet, and behavior.
Primary producers in an ecosystem are mainly:
- A Herbivores
- B Carnivores
- C Decomposers
- D Autotrophs
Correct answer: Autotrophs
Autotrophs produce organic food from inorganic substances. They form the base of food chains.
Energy transfer between trophic levels follows which rule?
- A 100% transfer
- B 50% transfer
- C 10% law
- D 5% law
Correct answer: 10% law
Only about 10% of energy is transferred to the next trophic level. The rest is lost as heat or metabolic processes.
Which pyramid always remains upright?
- A Pyramid of numbers
- B Pyramid of biomass
- C Pyramid of energy
- D Pyramid of productivity
Correct answer: Pyramid of energy
The pyramid of energy is always upright because energy decreases at each trophic level. Energy cannot be recycled.
A food web differs from a food chain because it:
- A Has fewer organisms
- B Shows multiple feeding relationships
- C Occurs only within aquatic ecosystems everywhere
- D Has only producers and consumers
Correct answer: Shows multiple feeding relationships
A food web consists of interconnected food chains. It reflects complex feeding relationships in ecosystems.
Which biotic interaction benefits both species involved?
- A Parasitism
- B Commensalism
- C Mutualism
- D Predation
Correct answer: Mutualism
Mutualism benefits both interacting species. Examples include pollinators and flowering plants.
Organisms that break down dead organic matter are called:
- A Producers
- B Consumers
- C Decomposers
- D Scavengers
Correct answer: Decomposers
Decomposers recycle nutrients by breaking down dead organisms. They play a vital role in nutrient cycling.
Which factor is density-dependent?
- A Earthquake
- B Flood
- C Competition
- D Drought
Correct answer: Competition
Competition increases as population density rises. It directly depends on the number of individuals.
Exponential population growth is represented by:
- A S-shaped curve
- B J-shaped curve
- C Linear curve
- D Bell-shaped curve
Correct answer: J-shaped curve
Exponential growth produces a J-shaped curve. It occurs when resources are unlimited.
Which ecological succession occurs on bare rock?
- A Secondary succession
- B Primary succession
- C Seasonal succession
- D Cyclic succession
Correct answer: Primary succession
Primary succession starts on lifeless substrates like bare rock. Pioneer species initiate ecosystem development.
Which biome receives the highest rainfall?
- A Tundra
- B Desert
- C Tropical rainforest
- D Grassland
Correct answer: Tropical rainforest
Tropical rainforests receive heavy rainfall throughout the year. This supports high biodiversity.
The gradual replacement of one plant community by another is known as:
- A Adaptation
- B Succession
- C Migration
- D Speciation
Correct answer: Succession
Ecological succession involves progressive changes in community composition. It leads to a stable climax community.
Which gas is released during respiration by organisms?
- A Oxygen
- B Nitrogen
- C Carbon dioxide
- D Hydrogen
Correct answer: Carbon dioxide
Respiration releases carbon dioxide as a waste product. It is part of the carbon cycle.
The variety of species within an ecosystem is called:
- A Population density
- B Biomass
- C Biodiversity
- D Productivity
Correct answer: Biodiversity
Biodiversity refers to species richness and variety. Higher biodiversity enhances ecosystem stability.
Which nutrient cycle lacks a gaseous phase?
- A Carbon cycle
- B Nitrogen cycle
- C Phosphorus cycle
- D Oxygen cycle
Correct answer: Phosphorus cycle
The phosphorus cycle does not include a gaseous phase. It mainly occurs through rocks, soil, and water.
Ecological balance refers to:
- A Constant, unchanging population size over time everywhere
- B Stable interaction of organisms and environment
- C The complete absence of predators
- D Equal energy at all trophic levels
Correct answer: Stable interaction of organisms and environment
Ecological balance maintains stable ecosystem functioning. It involves regulated interactions among organisms and their environment.
Which biogeochemical cycle governs the movement of the element found in CO2 and all organic molecules through the atmosphere, biosphere, and lithosphere?
- A Nitrogen cycle
- B Phosphorus cycle
- C Water cycle
- D Carbon cycle
Correct answer: Carbon cycle
The carbon cycle describes the movement of carbon among the atmosphere, living organisms, and the Earth. It plays a key role in energy flow and climate regulation.
Which process releases carbon dioxide back into the atmosphere from organisms?
- A Photosynthesis
- B Nitrogen fixation
- C Respiration
- D Erosion
Correct answer: Respiration
Respiration by plants and animals releases carbon dioxide into the atmosphere. It is part of the carbon cycle that balances photosynthesis.
Which form of nitrogen is directly usable by most plants?
- A Nitrogen gas
- B Ammonia
- C Nitrate
- D Nitrite
Correct answer: Nitrate
Plants primarily absorb nitrogen in the form of nitrate ions. These are converted into amino acids and proteins.
Which bacteria convert atmospheric nitrogen into ammonia?
- A Denitrifying bacteria
- B Ammonia-oxidizing bacteria
- C Nitrogen-fixing bacteria
- D Decomposers
Correct answer: Nitrogen-fixing bacteria
Nitrogen-fixing bacteria convert atmospheric nitrogen into ammonia. This process makes nitrogen available to living organisms.
Which process converts ammonia into nitrites and nitrates?
- A Denitrification
- B Nitrification
- C Assimilation
- D Ammonification
Correct answer: Nitrification
Nitrification is the process by which ammonia is oxidized to nitrites and then nitrates. It is carried out by nitrifying bacteria.
Which process returns nitrogen gas to the atmosphere?
- A Nitrogen fixation
- B Nitrification
- C Denitrification
- D Assimilation
Correct answer: Denitrification
Denitrification converts nitrates into nitrogen gas, returning it to the atmosphere. This process completes the nitrogen cycle.
Which biogeochemical cycle does not have a significant gaseous phase?
- A Global carbon cycle
- B Nitrogen cycle
- C Phosphorus cycle
- D Oxygen cycle
Correct answer: Phosphorus cycle
The phosphorus cycle lacks a gaseous phase and mainly occurs through rocks, soil, and water. It moves slowly compared to other cycles.
Which reservoir stores the largest amount of carbon on Earth?
- A Atmosphere
- B Ocean waters
- C Living organisms
- D Fossil fuels
Correct answer: Ocean waters
Ocean waters store the largest amount of carbon, mainly in dissolved forms like bicarbonates. They act as a major carbon sink.
Which process adds carbon dioxide to the atmosphere from burning fossil fuels?
- A Respiration
- B Combustion
- C Photosynthesis
- D Erosion
Correct answer: Combustion
Combustion of fossil fuels releases stored carbon as carbon dioxide. This contributes significantly to global warming.
Which organisms play a major role in nitrogen fixation in root nodules?
- A Cyanobacteria colonies
- B Fungi
- C Rhizobium bacteria
- D Protozoa
Correct answer: Rhizobium bacteria
Rhizobium bacteria live in root nodules of legumes and fix atmospheric nitrogen. They form a symbiotic relationship with plants.
Which process converts organic nitrogen into ammonia?
- A Nitrification
- B Ammonification
- C Denitrification
- D Assimilation
Correct answer: Ammonification
Ammonification is the breakdown of organic nitrogen into ammonia by decomposers. It occurs during decomposition of dead organisms.
Which element is a key component of ATP and DNA in the phosphorus cycle?
- A Carbon
- B Nitrogen gas
- C Oxygen
- D Phosphorus
Correct answer: Phosphorus
Phosphorus is essential for ATP, DNA, and RNA. It plays a crucial role in energy transfer and genetic material.
Which process releases phosphorus from rocks into the soil?
- A Weathering
- B Respiration
- C Combustion
- D Nitrification
Correct answer: Weathering
Weathering breaks down rocks and releases phosphorus into the soil. Plants absorb this phosphorus for growth.
Which process incorporates carbon into organic molecules in plants?
- A Respiration
- B Photosynthesis
- C Combustion
- D Microbial decomposition
Correct answer: Photosynthesis
Photosynthesis incorporates carbon dioxide into organic molecules like glucose. This forms the basis of food chains.
Which process transfers phosphorus from land to aquatic systems?
- A Evaporation
- B Runoff
- C Respiration
- D Uptake
Correct answer: Runoff
Runoff carries phosphorus from soil into rivers and lakes. This can lead to eutrophication in aquatic systems.
Which human activity most disrupts the nitrogen cycle?
- A Mining
- B Large-scale deforestation
- C Irrigation
- D Use of fertilizers
Correct answer: Use of fertilizers
Excessive use of fertilizers adds large amounts of nitrogen to ecosystems. This can cause pollution and imbalance in the nitrogen cycle.
Which carbon cycle process leads to long-term storage of carbon in the Earth?
- A Respiration
- B Photosynthesis
- C Combustion
- D Sedimentation
Correct answer: Sedimentation
Sedimentation stores carbon in sediments and fossil fuels over long periods. This acts as a long-term carbon reservoir.
Which form of phosphorus is absorbed by plants from soil?
- A Phosphate ions
- B Phosphine gas
- C Organic phosphorus
- D Phosphorus dioxide
Correct answer: Phosphate ions
Plants absorb phosphorus mainly as phosphate ions from the soil. These are used in energy transfer and growth processes.
Which cycle is most directly linked to climate change due to greenhouse gas accumulation?
- A Nitrogen cycle
- B Phosphorus cycle
- C Water cycle
- D Carbon cycle
Correct answer: Carbon cycle
The carbon cycle is closely linked to climate change because of carbon dioxide accumulation. Increased CO2 enhances the greenhouse effect.