Ecology

227 questions

All types227 Multiple choice105 True / False13 Numeric8 Matching59 Ordering42

Match each environmental pollutant listed on the left with its primary ecological consequence and appropriate control intervention on the right. Which matching correctly pairs every pollutant with its specific environmental impact and remediation strategy?

Click a left item, then click its matching right item

Show answer & explanation

Answer

The correct pairing links each pollutant directly to its mechanism of environmental damage and corresponding abatement method: Crude oil spill pairs with mangrove pneumatophore smothering and microbial bioremediation; Agricultural nutrient run-off pairs with algal blooms, high BOD, and tertiary treatment/riparian buffers; Methylmercury pairs with trophic biomagnification and chemical precipitation sequestration; Sulfur dioxide and particulates pair with acid precipitation and wet scrubbers/electrostatic precipitators.

Each pollutant is accurately matched to its precise biological impact and control strategy: crude oil smothers coastal respiratory structures and is remediated by hydrocarbon-degrading bacteria; nutrient run-off causes algal blooms and high BOD controlled by tertiary treatment; methylmercury undergoes trophic biomagnification requiring chemical precipitation; and gaseous sulfur/particulate emissions cause acid deposition controlled by stack scrubbers and electrostatic precipitators.

Step-by-Step Solution

Identify the primary physical barrier effect of petroleum contamination in coastal wetlands

Crude oil forms an insoluble slick that blocks oxygen diffusion, chokes breathing roots (pneumatophores), and requires hydrocarbon-utilizing bacteria for biological cleanup.

Bioremediation relies on specialized microbes to metabolize complex hydrocarbon chains into non-toxic compounds.

Analyze the aquatic biological impact of inorganic plant fertilizer run-off

Nitrates and phosphates accelerate phytoplankton blooms. When algae die, decomposers consume dissolved oxygen, elevating BOD and creating hypoxic dead zones.

Eutrophication management requires nutrient reduction via tertiary wastewater treatment and vegetative catchment buffers.

Examine the ecological movement of persistent heavy metal toxins like methylmercury

Heavy metals are non-biodegradable and lipophilic, accumulating in organism tissues and magnifying up food chains to toxic concentrations in top predators.

Chemical precipitation and ion exchange prevent heavy metal ions from entering aquatic food webs.

Assess the atmospheric pathway of combustion flue gases

Sulfur dioxide reacts with water vapor forming acid rain, while particulate matter damages respiratory tissues. Industrial scrubbers and precipitators intercept these emissions at the stack source.

Flue-gas desulfurization and particulate capture prevent regional atmospheric deposition.

Key Concept

Pollutant classification based on chemical behavior, specific ecological impact mechanisms (physical suffocation, eutrophication/BOD, biomagnification, acid deposition), and targeted environmental engineering/bioremediation controls.

Question 82Question →

Match each environmental degradation challenge listed on the left with its most effective biological or ecological management strategy on the right.

Click a left item, then click its matching right item

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Answer

Topsoil erosion on steep slopes matches contour terracing and cover cropping; species isolation from fragmentation matches establishing ecological corridors; heavy metal bioaccumulation in water bodies matches phytoremediation and effluent treatment; timber depletion from clear-cutting matches selective logging and sustained-yield re-afforestation.

Each management strategy directly addresses the specific cause of resource degradation: physical soil control methods mitigate surface erosion on slopes; ecological corridors eliminate population isolation; phytoremediation removes chemical water pollutants; and selective logging with re-afforestation maintains sustainable forestry yields.

Step-by-Step Solution

Analyze agricultural soil degradation mechanisms on sloped terrain.

Identify physical physical measures (contour terracing, strip cropping) designed to break water flow momentum and anchor topsoil.

Water runoff on inclines mobilizes sediment into rivers unless physical barriers reduce kinetic energy.

Evaluate genetic and ecological impacts of habitat fragmentation.

Link genetic isolation of wildlife to habitat connectivity solutions (ecological corridors).

Connecting fragmented reserves allows movement of individuals across landscape barriers to prevent inbreeding depression.

Assess heavy metal remediation strategies in contaminated aquatic environments.

Pair toxic chemical bioaccumulation with biological extraction methods (phytoremediation).

Hyperaccumulating organisms biologically extract heavy metals from polluted aquatic habitats.

Examine sustainable forestry resource practices against timber overexploitation.

Match canopy destruction from clear-cutting with controlled harvesting (selective logging) and replanting (re-afforestation).

Selective logging maintains structural habitat diversity while re-afforestation replenishes extracted forest biomass.

Key Concept

Natural resource conservation management techniques tailored to specific physical, biological, and chemical ecological threats.

Question 83Question →

Match each ecological measuring instrument listed in Column A with the corresponding abiotic parameter it measures in Column B.

Click a left item, then click its matching right item

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Answer

Wind vane matches with direction of wind movement; Lux meter matches with intensity of light in a habitat; Rain gauge matches with amount of precipitation over a period; Maximum-minimum thermometer matches with daily temperature range and extremes.

Each instrument correctly corresponds to its specific environmental measurement: wind vanes indicate wind direction, lux meters measure light intensity, rain gauges record precipitation amount, and maximum-minimum thermometers capture daily temperature extremes.

Step-by-Step Solution

Identify the primary function of each ecological instrument.

Wind vane indicates wind direction; Lux meter quantifies light intensity; Rain gauge collects rainfall; Maximum-minimum thermometer measures extreme temperatures.

Abiotic environmental factors are quantified using specific instruments designed for physical measurements.

Pair each instrument from Column A to its matching abiotic factor in Column B.

All instruments are mapped correctly to their respective environmental measurement parameters.

Direct one-to-one mapping links each equipment item with its intended ecological variable.

Key Concept

Measurement of Abiotic Ecological Factors

Question 84Question →

Which of the following air pollutants reduces the oxygen-carrying capacity of human blood by binding with hemoglobin?

Carbon monoxide

Sulfur dioxide

Chlorofluorocarbon

Carbon dioxide

Show answer & explanation

Answer: Carbon monoxide

Answer

Carbon monoxide

Carbon monoxide combines with blood hemoglobin to form carboxyhemoglobin, severely diminishing the capacity of red blood cells to transport oxygen.

Step-by-Step Solution

Identify the biological mechanism of carbon monoxide toxicity in humans.

Carbon monoxide (

CO

) has an affinity for hemoglobin over 200 times greater than oxygen, forming carboxyhemoglobin.

This stable complex reduces the available hemoglobin sites for oxygen binding and inhibits oxygen release to tissues.

Key Concept

Air Pollutants and Biological Effects of Carbon Monoxide

Estimated Time:45s

Question 85Question →

Match each ecological pyramid phenomenon or energy flow concept on the left with its correct metabolic or thermodynamic explanation on the right. Which pairing correctly matches each concept to its underlying biological cause?

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Answer

The correct pairings match: (1) Inverted biomass pyramid in aquatic systems with producer turnover rate and rapid reproduction; (2) Invariably upright energy pyramid with Second Law of Thermodynamics heat loss; (3) Stepwise reduction in available energy with metabolic and waste loss of approximately 90% per level; (4) Biomagnification with non-biodegradable fat-soluble toxins concentrating in smaller higher-level biomasses.

Each ecological concept matches its precise biological mechanism: aquatic biomass inversion is caused by rapid turnover of primary producers; energy pyramids are strictly upright due to metabolic heat loss (Second Law of Thermodynamics); energy reduction across trophic levels stems from respiration and excretion losses (~90%); and biomagnification occurs because persistent toxins accumulate in fat tissue as biomass decreases at higher levels.

Step-by-Step Solution

Analyze standing crop vs. productivity in aquatic habitats

Recognize that phytoplankton productivity is high despite low standing biomass due to rapid population turnover, creating an inverted biomass pyramid.

Explains why biomass pyramids can be inverted while energy production rates remain normal.

Apply thermodynamic laws to ecological energy transfer

Establish that energy cannot be recycled and entropy increases via metabolic heat release during each conversion.

Demonstrates why energy pyramids are strictly upright in every natural ecosystem.

Examine trophic efficiency calculations

Relate energy loss across trophic levels to physiological processes like movement, excretion, and cellular respiration (~90% lost).

Calculates net energy available to secondary and tertiary consumers.

Trace toxic substance dynamics in trophic chains

Correlate fat-solubility and biological persistence with increased toxin concentration at apex trophic levels.

Defines the biological mechanism behind biomagnification.

Key Concept

Thermodynamic laws in energy flow, trophic efficiencies, ecological pyramid structures, and biological magnification.

Question 86Question →

During primary ecological succession on a newly emerged volcanic island, which of the following structural and functional shifts characterizes the transition from the pioneer stage to a climax community?

Accumulation of soil organic matter and increased species diversity, with gross primary productivity eventually balancing total community respiration

Rapid initial colonization by deep-rooted herbaceous species that draw nutrients from pre-existing topsoil reserves beneath the volcanic substrate

Pioneer bryophytes absorbing water and mineral salts rapidly through specialized internal xylem and phloem conductive tissues

Immediate dominance by large canopy trees that suppress soil formation by exhausting organic humus deposited by pioneer colonizers

Show answer & explanation

Answer: Accumulation of soil organic matter and increased species diversity, with gross primary productivity eventually balancing total community respiration

Answer

Accumulation of soil organic matter and increased species diversity, with gross primary productivity eventually balancing total community respiration

Primary succession on bare volcanic rock requires pioneer organisms to weather substrate and contribute organic humus, forming soil over time. This enables higher plant species to invade, leading to higher species richness, structural complexity, and an energy balance where gross primary production equals community respiration at climax equilibrium.

Step-by-Step Solution

Identify the type of succession described in the stem.

The scenario describes primary succession on a newly emerged volcanic island, which starts on bare rock substrate without pre-existing soil.

Determining whether succession is primary or secondary establishes the baseline environmental conditions (e.g., presence or absence of soil).

Trace ecological changes from pioneer species to the climax stage.

Pioneer colonizers (lichens/microorganisms) secrete acids that weather bare rock. As they die and decompose, organic matter mixes with weathered minerals to form thin soil, allowing mosses, herbs, shrubs, and eventually trees to establish sequentially.

Succession involves progressive soil formation, increase in species diversity, food web complexity, and total biomass over time.

Analyze energy dynamics and ecosystem maturity at the climax stage.

In a mature climax community, total primary productivity (gross primary productivity) stabilizes and matches the total respiratory demands of all organisms in the community (

P/R \approx 1

Climax ecosystems reach a homeostatic equilibrium between gross production and total community respiration.

Key Concept

Primary Ecological Succession and Climax Community Dynamics

Question 87Question →

An ecologist monitored a freshwater pond and recorded the following observations:

1. A group of *Oreochromis niloticus* (Tilapia) feeding on floating algae near the surface.
2. Water lilies absorbing dissolved mineral nutrients and solar radiation.
3. Decomposing bacteria breaking down organic detritus on the muddy bottom.
4. Variations in water temperature, pH, and dissolved oxygen concentration throughout the day.

Which ecological concept is best described by the structural and functional interaction of all these living organisms together with their non-living physical environment?

An ecosystem

An ecological niche

A biological community

A population

Show answer & explanation

Answer: An ecosystem

Answer

An ecosystem is the correct term representing the interactive system of biotic organisms and abiotic environmental factors.

An ecosystem is defined as a self-sustaining structural and functional unit formed by the interaction of a biological community (plants, animals, microorganisms) with its abiotic physical environment (water, light, temperature, chemical factors).

Step-by-Step Solution

Identify the components present in the pond observation.

The observations list biotic components (tilapia, water lilies, bacteria) and abiotic factors (temperature, pH, dissolved oxygen).

Determining whether both living organisms and physical environment are included helps define the level of ecological organization.

Distinguish between population, community, niche, and ecosystem.

A population includes one species; a community includes multiple interacting species; an ecological niche is a species' functional role; an ecosystem incorporates both the community and abiotic factors.

Comparing definitions isolates the unique requirement of abiotic-biotic integration.

Select the term that encompasses both biotic and abiotic interactions.

An ecosystem correctly describes this complete structural and functional unit.

The stem explicitly asks for the concept describing organisms interacting together with their non-living environment.

Key Concept

Levels of Ecological Organization and Ecosystem Components

Question 88Question →

Unlike pyramids of numbers or biomass, a pyramid of energy in a natural ecosystem can never be inverted. Which of the following best explains why a pyramid of energy always maintains an upright shape?

Energy is progressively lost as heat during metabolic processes at each successive trophic level

Primary producers always have lower total biomass than the primary consumers that feed on them

Energy accumulates and increases in total magnitude as it passes up the food chain

Decomposers continuously recycle dissipated heat energy back to autotrophs for photosynthesis

Show answer & explanation

Answer: Energy is progressively lost as heat during metabolic processes at each successive trophic level

Answer

A pyramid of energy is always upright because energy is progressively lost as heat through metabolic activities at each successive trophic level.

The correct answer correctly identifies that as energy flows from producers to higher trophic levels, a large percentage is lost as heat through respiration and metabolic activities. Consequently, less energy is available to support successive levels, ensuring the pyramid of energy is strictly upright in all ecosystems.

Step-by-Step Solution

Recall the second law of thermodynamics as applied to ecological energy flow.

Energy transformations are never 100% efficient, and a significant portion of usable energy is converted to unrecoverable heat at every transfer.

Organisms utilize energy for respiration, movement, and excretion, releasing heat energy into the surroundings.

Determine the direction of net energy availability across trophic levels.

Producers store the maximum total energy, while primary, secondary, and tertiary consumers receive exponentially smaller quantities of available energy.

Only about 10% of the energy stored in biomass at one level is converted to biomass at the next level.

Conclude why an energy pyramid cannot be inverted.

Since a higher trophic level can never contain more energy than the lower level supplying it, the energy pyramid must always remain upright.

An inverted energy pyramid would require energy creation from nothing, violating physical laws.

Key Concept

Thermodynamic energy loss and the non-inversion of pyramids of energy

Estimated Time:45s

Question 89Question →

A biology student investigating edaphic factors collected $100\text{ cm}^3$ of an undisturbed garden soil sample in a graduated cylinder and added $100\text{ cm}^3$ of water. After stirring thoroughly and allowing all trapped air bubbles to escape, the final settled volume of the soil-water mixture measured $160\text{ cm}^3$ . What is the percentage porosity of this soil sample?

40\%

60\%

25\%

16\%

Show answer & explanation

Answer: $40\%$

Answer

The percentage porosity of the garden soil sample is

40\%

Soil porosity represents the percentage of pore space (voids filled with air or water) within a given volume of soil. When

100\text{ cm}^3

of water is added to

100\text{ cm}^3

of dry soil, the expected combined volume without pores would be

200\text{ cm}^3

. The actual mixture volume of

160\text{ cm}^3

indicates that

40\text{ cm}^3

of air was displaced by water. Expressed as a percentage of the original

100\text{ cm}^3

soil volume, the porosity is

\frac{40\text{ cm}^3}{100\text{ cm}^3} \times 100\% = 40\%

Step-by-Step Solution

Calculate the theoretical total volume if no air spaces were present.

Theoretical volume =

\text{Volume of soil} + \text{Volume of water} = 100\text{ cm}^3 + 100\text{ cm}^3 = 200\text{ cm}^3

Water fills the pore spaces previously occupied by air in the soil sample.

Determine the volume of air spaces (pores) in the soil sample.

Volume of air spaces =

\text{Theoretical volume} - \text{Actual mixture volume} = 200\text{ cm}^3 - 160\text{ cm}^3 = 40\text{ cm}^3

The reduction in expected total volume corresponds directly to the volume of displaced air.

Calculate the percentage porosity using the ratio of pore space volume to initial soil volume.

\text{Percentage Porosity} = \left(\frac{\text{Volume of air spaces}}{\text{Initial volume of soil}}\right) \times 100\% = \left(\frac{40\text{ cm}^3}{100\text{ cm}^3}\right) \times 100\% = 40\%

Porosity measures the percentage of total soil volume occupied by pore spaces.

Key Concept

Soil Porosity Measurement (Edaphic Factor Analysis)

Question 90Question →

A marine biologist analyzed the ecological structure of a coastal reef ecosystem and categorized its functional components into four groups:

Component	Description
P	Unicellular phytoplankton performing carbon fixation in the photic zone
Q	Zooplankton and small herbivorous fish feeding on phytoplankton
R	Predatory fish consuming herbivorous aquatic organisms
S	Benthic bacteria and fungi decomposing organic fallout

During a seasonal survey, the standing crop biomass of component Q was recorded to be higher than that of component P. Which statement correctly evaluates the structural dynamics and thermodynamic principles of this ecosystem?

The ecosystem remains energetically stable because phytoplankton have a rapid turnover rate and high productivity, ensuring that the pyramid of energy remains upright despite an inverted biomass snapshot.

Energy flows bidirectionally between component P and component Q, causing the overall pyramid of energy to become permanently inverted in marine environments.

Component S operates as primary producers by ingesting solid detritus waste holozoically to synthesize new organic matter for component P.

The inverted biomass ratio between primary producers and primary consumers forces the ecosystem to restart via primary succession on bare rock substrate.

Show answer & explanation

Answer: The ecosystem remains energetically stable because phytoplankton have a rapid turnover rate and high productivity, ensuring that the pyramid of energy remains upright despite an inverted biomass snapshot.

Answer

In aquatic ecosystems, primary producers (phytoplankton) have a very high rate of reproduction and turnover. Even though their instantaneous standing crop biomass is lower than that of primary consumers (zooplankton), their cumulative rate of primary production supplies ample energy to sustain the consumer population. Thus, the pyramid of biomass appears inverted, while the pyramid of energy remains strictly upright and unidirectional.

Step-by-Step Solution

Analyze the functional roles of ecosystem components P, Q, R, and S.

P is the primary producer, Q is the primary consumer, R is the secondary consumer, and S represents the decomposers.

Establishing trophic roles is required to evaluate energy flow and biomass relationships.

Evaluate the relationship between standing crop biomass and energy flow in marine ecosystems.

Phytoplankton (P) reproduce and are consumed extremely rapidly. Although their standing crop biomass at any instant is small relative to zooplankton (Q), their total energy production over time is much larger.

Pyramids of standing crop biomass in aquatic systems can be inverted, but pyramids of energy are always upright due to the Second Law of Thermodynamics.

Identify the correct physical law governing energy pyramids.

Energy transfer is strictly unidirectional and decreases at successive trophic levels due to metabolic heat loss.

An inverted energy pyramid would violate fundamental laws of thermodynamics.

Key Concept

Standing crop biomass vs. energy flow in ecosystem structure

Question 91Question →

Match each organism or ecological role on the left with its corresponding trophic level or function in energy flow on the right.

Click a left item, then click its matching right item

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Answer

Green plants and phytoplankton match with Primary producers (Trophic Level 1); Herbivores such as grasshoppers match with Primary consumers (Trophic Level 2); Carnivores such as frogs match with Secondary consumers (Trophic Level 3); Saprophytic fungi and bacteria match with Decomposers recycling organic matter.

Organisms are categorized into trophic levels based on their source of energy: photosynthetic autotrophs are primary producers (Level 1), plant-eaters are primary consumers (Level 2), animal-eaters preying on herbivores are secondary consumers (Level 3), and decay organisms recycle organic matter as decomposers.

Step-by-Step Solution

Identify the energy-capturing organisms in an ecosystem.

Green plants and phytoplankton capture solar energy to synthesize food, placing them at Trophic Level 1 as primary producers.

Primary producers form the foundational trophic level in all food chains.

Identify organisms that directly feed on producers.

Herbivores such as grasshoppers consume plant matter directly, placing them at Trophic Level 2 as primary consumers.

Direct consumers of autotrophs occupy the second trophic position.

Identify organisms that prey on primary consumers.

Carnivores such as frogs feed on primary consumers (herbivores), placing them at Trophic Level 3 as secondary consumers.

Predators of herbivores occupy the third trophic position in energy transfer.

Identify organisms responsible for breaking down dead organic waste.

Saprophytic fungi and bacteria digest non-living organic matter, functioning as decomposers.

Decomposers facilitate nutrient recycling back into abiotic ecosystem pools.

Key Concept

Trophic level classification and functional roles in food chains

Question 92Question →

Which of the following ecological instruments is used by biologists to measure relative humidity in a terrestrial habitat?

Anemometer

Hygrometer

Hydrometer

Barometer

Show answer & explanation

Answer: Hygrometer

Answer

The hygrometer is the instrument used to measure relative humidity in an ecosystem.

The hygrometer is designed specifically to measure relative humidity by detecting moisture content in atmospheric air.

Step-by-Step Solution

Identify the abiotic factor described in the stem.

The target abiotic factor is relative humidity (the percentage of water vapour present in atmospheric air).

Choosing the correct measuring instrument requires matching it with the specific physical variable being quantified.

Match the factor with its standard measuring device.

Relative humidity is measured using a hygrometer (or wet-and-dry bulb psychrometer).

Hygrometers detect changes in humidity levels in ambient air.

Key Concept

Measurement of Abiotic Ecological Factors

Estimated Time:45s

Question 93Question →

In a terrestrial grassland ecosystem, the total energy fixed by green plants (producers) is measured at $20{}000\text{ kJ m}^{-2}\text{ yr}^{-1}$ . According to Lindeman's $10\%$ law of ecological efficiency, what amount of energy will be available to the secondary consumers in this ecosystem?

2{}000\text{ kJ m}^{-2}\text{ yr}^{-1}

200\text{ kJ m}^{-2}\text{ yr}^{-1}

20\text{ kJ m}^{-2}\text{ yr}^{-1}

20{}000\text{ kJ m}^{-2}\text{ yr}^{-1}

Show answer & explanation

Answer: $200\text{ kJ m}^{-2}\text{ yr}^{-1}$

Answer

The amount of energy available to secondary consumers is

200\text{ kJ m}^{-2}\text{ yr}^{-1}

Secondary consumers occupy the third trophic level. Beginning with

20{}000\text{ kJ m}^{-2}\text{ yr}^{-1}

at the producer level, primary consumers (level 2) obtain

10\%

of this energy (

2{}000\text{ kJ m}^{-2}\text{ yr}^{-1}

). Secondary consumers (level 3) retain

10\%

of the energy from primary consumers, which equals

200\text{ kJ m}^{-2}\text{ yr}^{-1}

Step-by-Step Solution

Identify the trophic level of secondary consumers.

Producers belong to Trophic Level 1, Primary Consumers to Trophic Level 2, and Secondary Consumers to Trophic Level 3.

Energy flows sequentially from producers to consumers across discrete trophic steps.

Calculate energy available at Trophic Level 2 (Primary Consumers).

20{}000\text{ kJ m}^{-2}\text{ yr}^{-1} \times 0.10 = 2{}000\text{ kJ m}^{-2}\text{ yr}^{-1}

Approximately

10\%

of net primary production is assimilated by herbivores, while

90\%

is lost as metabolic heat and unconsumed waste.

Calculate energy available at Trophic Level 3 (Secondary Consumers).

2{}000\text{ kJ m}^{-2}\text{ yr}^{-1} \times 0.10 = 200\text{ kJ m}^{-2}\text{ yr}^{-1}

Applying the

10\%

transfer efficiency once more determines the energy incorporated at the carnivore/secondary consumer level.

Key Concept

10% Law of Energy Transfer across Ecological Trophic Levels

Estimated Time:1m 15s

Question 94Question →

In an agricultural soil plot rich in decaying organic matter, ammonium ions are rapidly produced by decomposers. Soil biochemical analysis reveals that while ammonium is converted into nitrites ( $NO_2^-$ ), the subsequent transformation of nitrites into nitrates ( $NO_3^-$ ) is completely blocked, leading to a toxic buildup of nitrites. Which soil bacterium is deficient or inactive in this ecosystem?

Nitrobacter

Rhizobium

Clostridium

Pseudomonas

Show answer & explanation

Answer: Nitrobacter

Answer

Nitrobacter is the bacterium responsible for the second stage of nitrification, transforming nitrites (

NO_2^-

) into nitrates (

NO_3^-

Nitrobacter is the obligate aerobic chemoautotroph responsible for the second oxidation step in nitrification, converting nitrites (

NO_2^-

) into nitrates (

NO_3^-

). If Nitrobacter is inactive, nitrites accumulate because the pathway cannot proceed to completion.

Step-by-Step Solution

Identify the specific biochemical step that is blocked in the soil.

The reaction converting nitrites (

NO_2^-

) to nitrates (

NO_3^-

) is inhibited.

Ammonium has already been oxidized to nitrite, so the second stage of nitrification is where the block occurs.

Recall the micro-organism responsible for nitrite oxidation.

Nitrobacter chemoautotrophically oxidizes

NO_2^-

NO_3^-

Different nitrifying bacteria specialize in distinct steps of the nitrification pathway.

Match the missing biological function to the candidate bacteria.

Inactivity or absence of Nitrobacter leads directly to the accumulation of toxic nitrites.

Without Nitrobacter, nitrites cannot be converted to nitrates, which plants absorb for amino acid synthesis.

Key Concept

Nitrification Pathway and Microbial Roles

Estimated Time:1m 30s

Question 95Question →

Arrange the following ecological spatial units in order of increasing geographic scale and structural complexity, starting from the most localized micro-environment to the broadest regional ecological zone.

Drag items to arrange them in the correct order

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Answer

The correct sequence from smallest to largest ecological scale is Microhabitat, Habitat, Ecosystem, and Biome.

The correct sequence begins with the microhabitat, which is the most localized physical space (such as the space under a rotting log). This exists within a habitat, which describes the general physical environment where organisms live. Combining living communities in a habitat with non-living abiotic factors creates a functional ecosystem. Finally, a biome represents the broadest regional ecological zone defined by macro-climate and dominant vegetation.

Step-by-Step Solution

Identify the smallest and most localized physical environmental unit.

The Microhabitat is a specialized, small-scale physical location providing immediate specific microclimatic conditions.

Microhabitats exist as sub-units within larger habitat environments.

Identify the broader physical environment encompassing multiple micro-environments.

The Habitat is the natural address or localized area where populations of organisms live.

A habitat provides the overall living space for organisms across a community.

Integrate living biological communities with their non-living physical surroundings.

The Ecosystem incorporates all biotic factors interacting with abiotic factors (light, soil, water, temperature).

An ecosystem extends beyond physical space to include functional energy and nutrient interactions.

Determine the broad regional ecological classification.

The Biome encompasses major geographical zones sharing characteristic climate patterns and vegetation types.

Biomes are regional aggregations of similar ecosystems worldwide.

Key Concept

Hierarchy of Ecological Spatial Scale and Ecosystem Structure

Question 96Question →

Arrange the following procedural steps in the correct chronological order for determining the dissolved oxygen concentration of an aquatic sample using the Winkler titration method.

Drag items to arrange them in the correct order

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Answer

The correct procedural order for Winkler titration of dissolved oxygen is: 1) Collect water sample without air bubbles, 2) Add manganous sulfate and alkaline iodide-azide below surface, 3) Stopper, invert to mix, and allow precipitate to settle, 4) Add concentrated sulfuric acid to dissolve precipitate and release iodine, 5) Titrate liberated iodine against sodium thiosulfate with starch indicator until colorless.

The correct protocol begins with bubble-free sampling to avoid aeration error. Next, chemical fixation reagents (manganous sulfate and alkaline iodide-azide) are added to form a brown precipitate. After inverting and allowing settling, concentrated sulfuric acid is introduced to dissolve the precipitate and release free iodine proportional to oxygen concentration. Finally, titrating against sodium thiosulfate with a starch indicator yields a colorless end-point, accurately quantifying aquatic dissolved oxygen.

Step-by-Step Solution

Sample collection without atmospheric contact

Sample acquired at zero aeration.

Prevents artificial elevation or depletion of dissolved gases prior to chemical fixation.

Chemical fixation of dissolved gas

Formation of manganese hydroxide precipitate.

Converts volatile dissolved oxygen gas into a stable chemical compound.

Precipitation completion

Precipitate thoroughly settled at the bottle bottom.

Guarantees complete reaction between manganese ions and oxygen.

Iodine liberation via acidification

Clear golden-yellow free iodine solution.

Acidic environment dissolves the brown precipitate and liberates iodine in direct ratio to oxygen.

Quantitative titration end-point determination

Colorless end-point reached.

Sodium thiosulfate reduces iodine, and starch indicator pinpoints the exact completion of the reaction.

Key Concept

Winkler Method for Dissolved Oxygen Quantification

Question 97Question →

Which of the following ecological pyramids is always upright in shape across all functional natural ecosystems?

Pyramid of energy

Pyramid of numbers

Pyramid of biomass

Inverted pyramid of energy

Show answer & explanation

Answer: Pyramid of energy

Answer

The pyramid of energy is always upright in all natural ecosystems.

The pyramid of energy represents total energy productivity over time. Due to respiratory loss and incomplete assimilation, available energy decreases continuously from producers to consumers, making the pyramid strictly upright in all natural ecosystems.

Step-by-Step Solution

Analyze energy transfer efficiency across trophic levels.

According to ecological principles and the second law of thermodynamics, energy is lost as heat during cellular respiration at each consecutive transfer.

Only approximately 10% of energy stored in biomass is transferred to the next trophic level.

Evaluate the structural shape of different ecological pyramids.

Because energy flow is unidirectional and continuously decreases from producers to apex consumers, the pyramid of energy must always have its widest base at the primary producer level and taper upward.

Pyramids of numbers and biomass can occasionally be inverted, but pyramids of energy can never be inverted.

Key Concept

Unidirectional energy flow and thermodynamic energy loss in trophic levels

Question 98Question →

In ecological hierarchy, structural organization progresses from single organisms to higher ecological levels. Which of the following best defines an ecological population?

All the different species of plants and animals occupying the same geographical area

A group of individuals of the same species occupying a defined area at a specific time

The specific functional role and position an organism occupies within its ecosystem

A biological community interacting dynamically with its abiotic physical environment

Show answer & explanation

Answer: A group of individuals of the same species occupying a defined area at a specific time

Answer

An ecological population is defined as a group of organisms belonging to the same species living and interacting in a defined geographical area at a specific time.

An ecological population consists exclusively of individuals belonging to the same species co-existing within a specific area at the same time, allowing them to interact and interbreed.

Step-by-Step Solution

Identify the key defining criteria of a population in ecological hierarchy.

A population requires three main elements: individuals of the same species, a shared geographic location, and a specific timeframe.

Different species living together form a community, while abiotic interactions define an ecosystem.

Evaluate the option defining a group of single-species organisms in a specific area.

The statement describing individuals of the same species inhabiting a defined area at a specific time accurately matches the definition of a population.

This sets population apart from community (multi-species) and ecosystem (biotic + abiotic).

Key Concept

Definition of an Ecological Population

Estimated Time:45s

Question 99Question →

An agricultural soil receives ammonium-based fertilizer. Arrange the subsequent biological transformations and processes in their natural sequential order, starting from the conversion of ammonium ions and ending with the synthesis of plant proteins. What is the correct sequence of these steps?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order of steps is: Conversion of ammonium ions into nitrite ions by Nitrosomonas -> Oxidation of nitrite ions into nitrate ions by Nitrobacter -> Absorption of soluble nitrate ions from soil water by plant root hair cells -> Biochemical reduction and assimilation of absorbed nitrates into amino acids and structural proteins.

Nitrification occurs in two sequential steps: *Nitrosomonas* oxidizes ammonium ions into nitrite, and *Nitrobacter* oxidizes nitrite into nitrate. The dissolved nitrate is then absorbed by root hairs and assimilated into plant amino acids and proteins.

Step-by-Step Solution

Identify the initial step of nitrification.

Ammonium ions (

\text{NH}_4^+

) are first oxidized into nitrite ions (

\text{NO}_2^-

) by specialized nitrifying bacteria (*Nitrosomonas*).

Ammonium cannot be taken up efficiently by most plants until converted by nitrifying bacteria.

Determine the second phase of nitrification.

Nitrite ions are further oxidized to nitrate ions (

\text{NO}_3^-

) by *Nitrobacter*.

Nitrite is toxic to plants and must be converted to nitrate before plant uptake.

Identify the mechanism of plant uptake.

Plant root hairs absorb dissolved nitrate ions (

\text{NO}_3^-

) from the soil solution.

Nitrate is the primary soluble form of nitrogen utilized by higher plants.

Determine the final assimilation step.

Absorbed nitrates are incorporated into organic molecules, producing amino acids and proteins within plant tissues.

Inorganic nitrate must be biochemically converted into organic nitrogenous compounds for plant biomass growth.

Key Concept

Sequential Nitrification and Plant Nitrogen Assimilation

Question 100Question →

During the soil nitrogen cycle, which specific bacterium is directly responsible for converting ammonia ( $NH_3$ ) into nitrites ( $NO_2^-$ )?

Nitrosomonas

Nitrobacter

Rhizobium

Pseudomonas

Show answer & explanation

Answer: Nitrosomonas

Answer

Nitrosomonas is the chemoautotrophic bacterium responsible for converting ammonia (

NH_3

) into nitrites (

NO_2^-

) during the first phase of nitrification.

Nitrification occurs in two distinct biochemical steps. In the first step, Nitrosomonas oxidizes toxic ammonia (

NH_3

) produced by decomposers into nitrite (

NO_2^-

). Nitrobacter then converts these nitrites into nitrates (

NO_3^-

), which plants readily absorb.

Step-by-Step Solution

Identify the biological process in question

The two-step oxidation of ammonia to nitrates is called nitrification.

Nitrification converts toxic or inorganic waste products into usable plant nutrients.

Distinguish between the bacterial species involved in each phase of nitrification

The oxidation of ammonia (

NH_3

) to nitrite (

NO_2^-

) is performed by Nitrosomonas, whereas the oxidation of nitrite (

NO_2^-

) to nitrate (

NO_3^-

) is performed by Nitrobacter.

Each specific metabolic transformation requires specialized enzymatic machinery unique to distinct bacterial genera.

Key Concept

Bacterial Roles in Nitrification

Estimated Time:45s

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