301. Which statement correctly distinguishes gaseous nutrient cycles from sedimentary nutrient cycles?
ⓐ. Gaseous cycles have consumers as the major reservoir, whereas sedimentary cycles have producers as the reservoir
ⓑ. Gaseous cycles have atmosphere or hydrosphere as the major reservoir, whereas sedimentary cycles have Earth’s crust as the major reservoir
ⓒ. Gaseous cycles operate only in aquatic ecosystems, whereas sedimentary cycles operate only in terrestrial ecosystems
ⓓ. Gaseous cycles are one-way, whereas sedimentary cycles are always circular
Correct Answer: Gaseous cycles have atmosphere or hydrosphere as the major reservoir, whereas sedimentary cycles have Earth’s crust as the major reservoir
Explanation: Nutrient cycles are classified by the location of their major reservoir. In gaseous cycles, the main store lies in the atmosphere or hydrosphere, while in sedimentary cycles it lies in rocks and the Earth's crust. This difference helps explain why carbon and phosphorus are placed in different categories. The classification is based on reservoir location, not on habitat alone.
302. Which of the following is the best example of a sedimentary nutrient cycle?
ⓐ. Carbon cycle
ⓑ. Oxygen cycle
ⓒ. Nitrogen cycle
ⓓ. Phosphorus cycle
Correct Answer: Phosphorus cycle
Explanation: The phosphorus cycle is classically treated as a sedimentary cycle because its major reservoir is in rocks and Earth's crust. It does not have a major atmospheric phase like gaseous cycles do. Phosphorus enters ecosystems through weathering and then moves through living organisms and the environment. This crust-based storage is the key reason for its classification.
303. Why is nutrient movement in ecosystems called cyclic?
ⓐ. Released nutrients can return to the abiotic environment and be used again by organisms
ⓑ. Nutrients always move upward from carnivores to producers
ⓒ. Nutrients disappear completely after passing through one trophic level
ⓓ. Nutrients are transformed into energy at the end of each food chain
Correct Answer: Released nutrients can return to the abiotic environment and be used again by organisms
Explanation: Nutrients do not move in a single one-way path and vanish. After being incorporated into organisms, they can return to soil, water, or air through waste, death, and decomposition. From there they become available again for uptake by producers. This repeated reuse is why the process is described as cyclic.
304. A nutrient element whose major reservoir is mainly in air and water would be classified under which type of nutrient cycle?
ⓐ. Detritus cycle
ⓑ. Trophic cycle
ⓒ. Gaseous cycle
ⓓ. Standing crop cycle
Correct Answer: Gaseous cycle
Explanation: Gaseous cycles are defined by having their main reservoir in the atmosphere or hydrosphere. Nutrients stored largely in air or water therefore belong to this category. Carbon is the standard example used for this type of cycle. The name reflects reservoir location rather than the organisms involved.
305. Which statement best defines ecosystem services?
ⓐ. They are the number of species present in an ecosystem
ⓑ. They are the energy losses occurring at each trophic level
ⓒ. They are the dead organic remains used in decomposition
ⓓ. They are the products and benefits that arise from ecosystem processes
Correct Answer: They are the products and benefits that arise from ecosystem processes
Explanation: Ecosystem services are useful outcomes generated by normal ecosystem functioning. They are not separate from ecological processes but emerge from them. Such services can directly or indirectly support human life and well-being. The term therefore links ecology with practical benefit.
306. Which of the following is specifically cited as an ecosystem service provided by forests?
ⓐ. Purification of air and water
ⓑ. Fixation of all atmospheric nitrogen
ⓒ. Transfer of 10% energy to each trophic level
ⓓ. Conversion of every nutrient cycle into a gaseous cycle
Correct Answer: Purification of air and water
Explanation: Forests help maintain environmental quality by contributing to the purification of air and water. This is one of the clearest examples of an ecosystem service linked to human welfare. The benefit arises from ecosystem functioning rather than from a manufactured process. It shows how natural systems support everyday life.
307. Which situation best illustrates an ecosystem service?
ⓐ. A food chain showing fewer organisms at higher trophic levels
ⓑ. Humus forming in soil after decomposition
ⓒ. A forest improving water quality and helping cleanse the surrounding air
ⓓ. A carnivore feeding on a herbivore in a grazing food chain
Correct Answer: A forest improving water quality and helping cleanse the surrounding air
Explanation: An ecosystem service is recognized when an ecological process produces a useful benefit for humans. Forests can improve air quality and help maintain cleaner water, so this is a direct service example. The other options describe ecological processes or relationships but do not state a human-linked benefit clearly. The key idea is beneficial output from ecosystem functioning.
308. Why are ecosystem services important to humans?
ⓐ. They stop all decomposition in natural habitats
ⓑ. They connect ecosystem functioning with human welfare
ⓒ. They remove the need for producers in food chains
ⓓ. They make energy flow cyclic like nutrients
Correct Answer: They connect ecosystem functioning with human welfare
Explanation: Ecosystem services show that natural ecological processes are not only biologically important but also useful to people. Clean air, cleaner water, and other benefits arise from functioning ecosystems. This creates a direct link between ecological stability and human well-being. The concept helps explain why healthy ecosystems matter beyond academic study.
309. Which statement about ecosystem services is correct?
ⓐ. They arise from normal ecological processes and can provide useful benefits to people
ⓑ. They are limited only to predator-prey relationships
ⓒ. They refer only to the number of producers in a forest
ⓓ. They occur only in artificial ecosystems maintained by humans
Correct Answer: They arise from normal ecological processes and can provide useful benefits to people
Explanation: Ecosystem services emerge from the regular operation of ecosystems such as nutrient cycling, vegetation growth, and water or air purification. These processes can produce outcomes valuable to human life. The idea is broader than any single food relationship or population count. Natural ecosystems are especially important sources of such services.
310. If a forest cover in a region is severely reduced, which consequence most directly reflects loss of an ecosystem service?
ⓐ. Increase in trophic levels from three to five
ⓑ. Complete stoppage of nutrient cycling
ⓒ. Reduced natural purification of air and water
ⓓ. Permanent inversion of the energy pyramid
Correct Answer: Reduced natural purification of air and water
Explanation: Forests contribute to environmental quality by helping filter air and maintain cleaner water systems. When forest cover declines, this beneficial function is weakened. That reduction represents loss of an ecosystem service. The effect is therefore understood in terms of diminished human and environmental benefit.
311. Which statement best links ecosystem processes to ecosystem services?
ⓐ. Ecosystem services replace the need for ecological processes
ⓑ. Ecosystem services are useful outcomes generated by ecosystem functioning
ⓒ. Ecosystem services occur only when food chains are absent
ⓓ. Ecosystem services are unrelated to nutrient cycling and decomposition
Correct Answer: Ecosystem services are useful outcomes generated by ecosystem functioning
Explanation: Ecosystem services do not exist independently of ecosystem processes. They arise because processes such as production, decomposition, cycling, and regulation keep ecosystems functioning. When these processes operate well, benefits useful to humans can result. This makes ecosystem services a practical expression of ecological functioning.
312. A town near a healthy forest receives cleaner water and better air quality than a nearby deforested region. This most clearly demonstrates
ⓐ. ecological succession
ⓑ. standing crop
ⓒ. secondary productivity
ⓓ. ecosystem services
Correct Answer: ecosystem services
Explanation: The example shows a direct human benefit coming from a functioning ecosystem. Cleaner water and better air quality are outcomes of ecological processes operating in the forest. Such benefits are described as ecosystem services. The term captures the connection between ecosystem health and human welfare.
313. Which statement best defines secondary productivity?
ⓐ. It is the total organic matter produced by plants during photosynthesis
ⓑ. It is the amount of detritus accumulated in an ecosystem
ⓒ. It is the rate at which consumers form new organic matter from assimilated food
ⓓ. It is the total standing crop of producers at a given time
Correct Answer: It is the rate at which consumers form new organic matter from assimilated food
Explanation: Secondary productivity refers to biomass formation by heterotrophs rather than by autotrophs. Consumers build new tissues only after obtaining and assimilating food from other organisms. The idea is therefore linked with consumer growth and biomass gain over time. It is a rate measure, not just a one-time standing amount.
314. Which set includes the major factors that directly influence primary productivity?
ⓐ. Plant species, nutrient availability, and photosynthetic capacity
ⓑ. Number of top carnivores, humidity, and food-web length
ⓒ. Decomposer diversity, mineralisation rate, and stratification
ⓓ. Trophic level, biomass pyramid, and omnivore abundance
Correct Answer: Plant species, nutrient availability, and photosynthetic capacity
Explanation: Primary productivity depends strongly on the producers themselves and the conditions that support photosynthesis. Different plant species vary in efficiency, nutrient supply affects growth, and photosynthetic capacity determines how effectively light can be used. These factors directly influence the rate of organic matter formation. The other options include ecological features that do not directly determine producer productivity in the same way.
315. Two grassland plots receive similar sunlight and rainfall, but Plot X has nutrient-rich soil and highly efficient producer species, while Plot Y has poor soil and less efficient producer species. Which plot is likely to show higher primary productivity?
ⓐ. Plot Y, because lower nutrients reduce respiration losses
ⓑ. Both plots, because sunlight alone decides productivity
ⓒ. Plot Y, because poor soil prevents consumer losses
ⓓ. Plot X, because better nutrient supply and efficient producers favour greater biomass formation
Correct Answer: Plot X, because better nutrient supply and efficient producers favour greater biomass formation
Explanation: When major limiting factors are more favorable, producers can usually photosynthesize and grow more effectively. Nutrient-rich conditions support synthesis of cellular materials, and efficient producer species convert available resources into biomass more successfully. Since the two plots receive similar sunlight and rainfall, the soil and producer differences become more important. That makes Plot X the more productive one.
316. Which figure best represents the approximate annual contribution of terrestrial ecosystems to the biosphere's net primary productivity?
ⓐ. About 55 billion tons of dry organic matter
ⓑ. About 115 billion tons of dry organic matter
ⓒ. About 170 billion tons of dry organic matter
ⓓ. About 225 billion tons of dry organic matter
Correct Answer: About 115 billion tons of dry organic matter
Explanation: The annual net primary productivity of the biosphere is about 170 billion tons of dry organic matter, and oceans contribute about 55 billion tons. The remaining contribution comes mainly from land ecosystems. Subtracting 55 from 170 gives about 115 billion tons. This shows that land contributes a major share of global NPP.
317. Which statement best explains why primary productivity varies from one ecosystem to another?
ⓐ. All ecosystems contain the same producer species but differ in top carnivores
ⓑ. Variation occurs only because energy pyramids are shaped differently
ⓒ. It varies because producer species, nutrient availability, and photosynthetic capacity differ among ecosystems
ⓓ. It varies only with the number of decomposers present
Correct Answer: It varies because producer species, nutrient availability, and photosynthetic capacity differ among ecosystems
Explanation: Ecosystems are not equally productive because their producers and environmental conditions are not identical. Different plant communities vary in structure and efficiency, while nutrient supply and photosynthetic ability affect the rate of biomass formation. These differences produce real variation in primary productivity. Consumer abundance alone cannot explain this pattern.
318. Fill in the blank in the most accurate way:
The rate of formation of new organic matter by consumers is called ______.
ⓐ. net primary productivity
ⓑ. standing crop
ⓒ. mineralisation
ⓓ. secondary productivity
Correct Answer: secondary productivity
Explanation: Secondary productivity belongs to the consumer side of ecosystem function. It measures how rapidly heterotrophs convert assimilated food into new biomass. This distinguishes it from primary productivity, which is performed by producers. The term therefore refers to consumer growth as a rate.
319. Oceans cover about 70% of Earth’s surface, yet their annual net primary productivity is about
ⓐ. 170 billion tons of dry organic matter
ⓑ. 115 billion tons of dry organic matter
ⓒ. 85 billion tons of dry organic matter
ⓓ. 55 billion tons of dry organic matter
Correct Answer: 55 billion tons of dry organic matter
Explanation: Although oceans occupy most of the planet’s surface, their annual contribution to global net primary productivity is about 55 billion tons of dry organic matter. This shows that area alone does not determine total productivity. The figure is lower than the total biosphere value and leaves a large remaining share to land ecosystems. It is a useful comparison point in global productivity questions.
320. If the biosphere produces about 170 billion tons of dry organic matter annually and oceans contribute about 55 billion tons, the remaining contribution is mainly from land and is approximately
ⓐ. 55 billion tons
ⓑ. 115 billion tons
ⓒ. 170 billion tons
ⓓ. 225 billion tons
Correct Answer: 115 billion tons
Explanation: The remaining contribution from land can be estimated by simple subtraction. When 55 billion tons from oceans are removed from the total of 170 billion tons, about 115 billion tons remain. This indicates that terrestrial ecosystems contribute a substantial share of global productivity. The calculation helps interpret the ocean-versus-land contrast numerically.
