Test: Environment- 3 Free Online Test 2026

 Statement 1 is correct:  Populations refer to groups of individuals of the same species living in a particular area.
 Statement 2 is incorrect:  Communities consist of multiple populations of different species living and interacting in the same area.
 Statement 3 is correct : Biomes are large scale ecological regions characterized by distinct climate, vegetation, and animal communities.
Supplementary Notes:

• Populations: Populations refer to groups of individuals of the same species living in a particular area. Ecologists study population dynamics, which involve factors such as population size, density, growth rates, and patterns of  dispersal. They investigate how populations interact with their environment, including factors like resource availability, competition, predation, and disease.
• Communities: Communities consist of multiple populations  of different species living and interacting in the same area. Ecologists study the composition, structure, and diversity of communities, as well as the interactions among species within them.
  They examine concepts such as competition, predation, mutualism, and the fl ow of energy  and nutrients through the community.
• Biomes: Biomes are large-scale ecological regions characterized by distinct climate, vegetation,  and animal communities. Ecologists study the distribution and characteristics of different biomes, such as forests, grasslands, deserts, and aquatic ecosystems.
  They investigate how abiotic factors, such as temperature, precipitation, and soil type, shape the structure and functioning of these ecosystems, as well as the adaptations of organisms to these conditions.

The size of a population for any species is not a static parameter. It keeps changing with time, depending on various factors including food availability, predation pressure, and adverse weather. In fact, it is these changes in population density that give us some idea of what is happening to the population – whether it is flourishing or declining. The density of a population in a given habitat during a given period fluctuates due to changes in four basic processes, two of which (natality and immigration) contribute to an increase in population density and two (mortality and emigration) to a decrease.

Statement 1 is incorrect: Natality and immigration contribute to an increase in population density.
Statement 2 is incorrect: Mortality and emigration contribute to a decrease in population density.

Factors influencing the population size of the species:

• Birth rate: The rate at which individuals are born into a population affects its size. Higher birth rates contribute to population growth, while lower birth rates can lead to population decline.
• Death rate: The rate at which individuals die within a population impacts its size. Higher death rates can result in population decline, while lower death rates contribute to population growth.
• Immigration: The movement of individuals into a population from other areas can increase its size. Immigration can introduce new individuals with reproductive potential, potentially boosting the population.
• Emigration: The movement of individuals out of a population can decrease its size. Emigration reduces the number of individuals available for reproduction and can lead to population decline.
• Resource availability: The availability of essential resources such as food, water, shelter, and habitat can significantly impact population size.
• Predation and competition: The presence of predators and the intensity of competition for resources can affect population size.
• Disease and parasites: The prevalence of diseases and parasites within a population can impact population size.
• Environmental factors: Environmental conditions, such as temperature, precipitation, and climate patterns, can influence population size.
• Genetic factors: Genetic diversity within a population plays a role in determining its size. Populations with low genetic diversity may be more susceptible to diseases or environmental changes, which can impact their viability.

All pairs are correctly matched.

Supplementary Notes:
Population density of Species:

• Natality refers to the number of births during a given period in the population that are added to the initial density.
• Mortality is the number of deaths in the population during a given period.
• Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.
• Emigration is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

Option (a) is correct.

Supplementary Notes:
Population interactions among species refer to various ways in which different organisms within an ecosystem interact with one another. These interactions include competition, predation, mutualism, commensalism, and parasitism, playing a vital role in shaping the structure and dynamics of ecological communities.

Statement 1 is incorrect: Intense competition can lead to resource partitioning, where species evolve to occupy different ecological niches to reduce competition.

Statement 2 is correct: Predation is a relationship in which one species (the predator) captures and feeds on another species (the prey).

Supplementary Notes:
Population interactions among species:

• Competition occurs when two or more species compete for limited resources.
• Predation is a relationship where one species captures and feeds on another, regulating the abundance and distribution of prey species.

Both statements are correct.

Supplementary Notes:

• Ecosystem Structure: Ecosystem structure refers to the physical and biological components that make up an ecosystem. It encompasses both the living organisms (biotic factors) and the non-living environment (abiotic factors).
• Producers: Producers, also known as autotrophs, are organisms capable of converting energy from the sun (or in some cases, chemicals) into organic matter through photosynthesis or chemosynthesis. They form the foundation of the food chain and include plants, algae, and certain bacteria.
• Consumers: Consumers, also known as heterotrophs, are organisms that obtain energy by consuming other organisms. They can be divided into different trophic levels based on their feeding habits. Primary consumers (herbivores) feed directly on producers, while secondary consumers (carnivores) feed on primary consumers. Tertiary consumers (top carnivores) occupy the highest trophic level in a food chain.
• Decomposers: Decomposers play a vital role in breaking down dead organisms and organic waste material, returning essential nutrients to the ecosystem. They include bacteria, fungi, and certain invertebrates like earthworms. Decomposers complete the nutrient cycle by converting complex organic matter into inorganic compounds that can be used again by producers.
• Physical Environment: The abiotic factors of an ecosystem include temperature, sunlight, water availability, soil composition, air quality, and geological features. These factors influence the distribution and abundance of organisms within the ecosystem.
   

• Statement 1 is incorrect:  Energy flows through an ecosystem in a unidirectional manner.
• Statement 2 is correct:  Nutrient cycling involves the movement and recycling of essential elements such as carbon, nitrogen, phosphorus, and others within the ecosystem.
• Statement 3 is correct:  Nutrient cycling ensures the availability of vital elements for the growth and development of organisms.

 Supplementary Notes:

• Ecosystem Function: Ecosystem function refers to the processes and interactions that occur within an ecosystem, allowing it to maintain its structure and perform various functions. These functions are crucial for the sustainability and resilience of the ecosystem. Some key ecosystem functions include:
•  Energy Flow: Energy flows through an ecosystem in a unidirectional manner. Producers capture solar energy and convert it into chemical energy through photosynthesis. This energy is then transferred to consumers as they feed on other organisms. Energy flow is essential for sustaining life within the ecosystem.
• Nutrient Cycling: Nutrient cycling involves the movement and recycling of essential elements such as carbon, nitrogen, phosphorus, and others within the ecosystem.
• Decomposers break down dead organic matter, releasing nutrients that are taken  up by plants and reused in the food chain. Nutrient cycling ensures the availability of vital elements for the growth and development of organisms.

Both statements  are correct. 
Supplementary Notes:

• Biodiversity: Ecosystems thrive on biodiversity, which refers to the variety of different species and their interactions within an ecosystem.  Biodiversity provides stability to ecosystems and contributes to their resilience. Different species play unique roles, such as pollination, seed dispersal, and pest control,  which are crucial for ecosystem function.
• Regulation of Environmental Conditions: Ecosystems help regulate environmental conditions. Forests, for example, act as carbon sinks, absorbing carbon dioxide from  the atmosphere and mitigating climate change.
   

Option (a) is correct: The important steps in the process of decomposition are fragmentation, leaching, catabolism,humification and mineralisation.

Supplementary Notes:

• Decomposition:Decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition.Dead plant remains such as leaves, bark, flowers and dead remains of animals,including fecal matter, constitute detritus, which is the raw material fordecomposition.The important steps in the process of decomposition are fragmentation, leaching, catabolism, humifi cation and mineralisation.

Both pairs are correct.

Supplementary Notes:

• Decomposition: Detritivores (e.g., earthworm) break down detritus into smaller particles. This processis called fragmentation.By the process of leaching, water soluble inorganic nutrients go down into the soilhorizon and get precipitated as unavailable salts.Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.This process is called as catabolism.

Statement 1 is correct: Humifi cation leads to accumulation of a dark coloured amorphous substance called humus.

Statement 2 is incorrect: Humus is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.

Supplementary Notes:

• Rate of Decomposition:Humification and mineralisation occur during decomposition in the soil. Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.Being colloidal in nature it serves as a reservoir of nutrients. The humus is further degraded by some microbes and release of inorganic nutrients occurs by the process known as mineralisation.

Statement 1 is incorrect: Decomposition is largely an oxygen-requiring process.
Statement 2 is correct: The rate of decomposition is controlled by chemical composition of detritus and climatic factors.

Supplementary Notes:

Process of decomposition: In a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water soluble substances like sugars. Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes.Warm and moist environment favour decomposition whereas low temperature and anaerobiosis inhibit decomposition resulting in build-up of organic materials.

Option (d) is correct: The producers in an aquatic ecosystem are various species likephytoplankton, algae and higher plants.

Supplementary Notes:

• Producers in an aquatic ecosystem: The green plants in the ecosystem are called producers. In a terrestrial ecosystem, major producers are herbaceous and woody plants. Likewise, producers in an aquatic ecosystem are various species like phytoplankton, algae and higher plants.

Option (a) is correct

An important characteristic of allcommunities is that composition andstructure constantly change orderly andsequentially in response to the changingenvironmental conditions.This gradual and fairly predictable changein the species composition of a given area iscalled ecological succession.Ecological Succession fi nally leads toan establishment of a relatively stablecommunity that is in near equilibriumwith the environment and is called climaxcommunity.The entire sequences of communities thatsuccessively change in a given area arecalled seres.The individual transitional communities arecalled seral stages or seral communities.In the successive seral stages there isa change in the diversity of species oforganisms, increase in the number of speciesand organisms as well as an increase in thetotal biomass.

Ecological Succession is of 2 types:

• Primary Succession: Successionwhich starts in areas where no livingorganisms ever existed is called primarysuccession. Examples of areas whereprimary succession occurs are newlycooled lava, bare rock, newly createdpond or reservoir etc. The species thatinvade a bare area are called pioneerspecies. The establishment of a newbiotic community is generally slow as ittakes natural processes several hundredto several thousand years to producefertile soil on bare rock.
• Secondary Succession: It begins inareas where natural biotic communitieshave been completely or partiallydestroyed such as in abandoned farmlands, burned or cut forests, lands thathave been fl ooded. Since some soil orsediment is present, secondary successionis faster than primary succession.

• Statement 1 is correct: Ecotone is a zone of junction between two or more diverse ecosystems. For e.g. the mangrove forests represent an ecotone between marine and terrestrial ecosystem. Ecotone also appear where one body of water meets another (e.g., estuaries and lagoons) or at the boundary between the water and the land (e.g., marshes, river bank etc.). It has the conditions intermediate to the adjacent ecosystems. Hence it is a zone of transition.
• Statement 2 is correct: It is linear as it shows progressive increase in species composition of one in coming community and a simultaneous decrease in species of the other outgoing adjoining community.
• Statement 3 is correct: It may be very narrow or quite wide. A well-developed ecotone contains some organisms which are entirely different from that of the adjoining communitie

Option (d) is correct
Anything that attempts to alter the balance of the ecosystem potentially threatens the health and existence of that ecosystem.
Some of these threats are: 
Habitat Destruction: Economic activities such as logging, mining, farming and construction often involve clearing out places with natural vegetative cover. Very often, tampering with one factor of the ecosystem can have a ripple effect on it and affect many more or all other factors of that ecosystem. For example, clearing a piece of forest for timber can expose the upper layers of the soil to the sun’s heat, causing erosion and drying. It can cause a lot of animals and insects that depended on the shade and moisture from the tree to die or migrate to other places.
Pollution: Water, land and air pollution all together play a crucial role in the health of ecosystems. Pollution may be natural or human-caused, but regardless they potentially release destructive agents or chemicals (pollutants) into the environments of living things.
Eutrophication: This is the enrichment of water bodies with plant biomass as a result of the continuous inflow of nutrients particularly nitrogen and phosphorus. Eutrophication of water fuels excessive plant and algae growth and also hurts water life, often resulting in the loss of fl ora and fauna diversity. “The known consequences of cultural eutrophication include blooms of bluegreen algae, tainted drinking water supplies, degradation of recreational opportunities, and hypoxia.
Invasive species: Any foreign species (biological) that fi nds its way into an ecosystem, either by natural or human introduction can have an effect on the ecosystem. If this alien has the ability to prey on vulnerable and native members of that ecosystem, they will be wiped out, sooner or later.
Overharvesting: Fish species, game and special plants all do fall victim from time to time as a result of over-harvesting or humans over-dependence on them. Overharvesting leads to the reduction in populations, community structures and distributions, with an overall reduction in recruitment.
UV Radiation: UV rays come in three main wavelengths: UVA, UVB and UVC. UVB and UVC are more destructive and can cause DNA and cell damage to plants and animals. Ozone depletion is one way that exposes living things to UVB and UVC and the harm caused can wipe lots of species, and affect ecosystems members including humans.

All the statements are correct:
Ecosystem restoration is the process of halting and reversing degradation, resulting in improved ecosystem services and recovered biodiversity. Ecosystem restoration encompasses a wide continuum of practices, depending on local conditions and societal choice.
Depending on objectives, restored ecosystems can follow different trajectories:
From degraded natural to more intact natural ecosystems (often by assisting natural regeneration) From degraded, modified ecosystems to more functional modified ecosystems (e.g. restoration of urban areas and farmlands) From modified ecosystems towards more natural ecosystems, providing that the rights and needs of people who depend on that ecosystem are not compromised. Various approaches for ecosystem restoration include:

• Ecological Restoration: Assisting the recovery of a terrestrial, freshwater or marine ecosystem that has been degraded, damaged, or destroyed.
• Forest and Landscape Restoration: Reversing the degradation of soils, agricultural areas, forests and watersheds thereby regaining their ecological functionality.

Restoration of Aquatic Production

• Ecosystems: Maintaining ecosystem structure and function to support food provisioning, while minimizing impacts, rather than restoring ecosystems to an initial state before production activity started.
• Regenerative Agriculture: Farming that uses soil conservation as the entry point to regenerate and contribute to multiple provisioning, regulating and supporting services.
• Rewilding: Rebuilding, following major human disturbance, a natural ecosystem by restoring natural processes and the complete or near complete food-web at all trophic levels as a self-sustaining and resilient ecosystem using biota that would have been present had the disturbance not occurred.

Statement 1 is correct: Moist deciduous forests are found throughout India except in the western and the north-western regions. The trees are tall, have broad trunks, branching trunks and roots to hold them firmly to the ground. Some of the taller trees shed their leaves in the dry season. There is a layer of shorter trees and evergreen shrubs in the undergrowth. These forests are dominated by sal and teak, along with mango, bamboo, and rosewood.

Statement 2 is incorrect: Tropical dry deciduous forests are found throughout the northern part of the country except in the North-East.

Statement 3 is incorrect: Tropical dry evergreen forests are found along Tamil Nadu, Andhra Pradesh and Karnataka Coast. 

• Tropical Wet Evergreen Forests: Wet evergreen forests are found along the
• Western Ghats, the Nicobar and Andaman Islands and all along the north-eastern region. It is characterized by tall, straight evergreen trees. The trees in this forest form a tier pattern: shrubs cover the layer closer to the ground, followed by the short structured trees and then the tall variety.
• Tropical Semi-evergreen Forests: Semievergreen forests are found in the Western Ghats, Andaman and Nicobar Islands, and the Eastern Himalayas. Such forests have a mixture of the wet evergreen trees and the moist deciduous trees. The forest is dense and is fi lled with a large variety of trees of both types.
• Tropical Dry Deciduous Forests: Dry deciduous forests are found throughout the northern part of the country except in the North-East. It is also found in Madhya Pradesh, Gujarat, Andhra Pradesh, Karnataka, and Tamil Nadu. The canopy of the trees does not normally exceed 25 metres. The common trees are the sal, a variety of acacia, and bamboo.
• Tropical Thorn Forests: This type is found in areas with black soil: North, West, Central, and South India. The trees do not grow beyond 10 metres. Spurge, caper, and cactus are typical of this region.
• Tropical Dry Evergreen Forests: Dry evergreens are found along Tamil Nadu, Andhra Pradesh and Karnataka coast. It is mainly hard-leaved evergreen trees with fragrant fl owers, along with a few deciduous trees.

Statement 1 is correct: The number of species surviving in the world today is the outcome of two processes viz. speciation and extinction.Speciation is the process by which new species are formed and evolution is the mechanism by which speciation is brought about. A species comprises of many populations. Often different populations of a species remain isolated due to some geographic barrier such as mountain, ocean, river, etc. Geographic isolation occurs when a physical barrier develops between two populations of a species.

Statement 2 is correct: The most common way a population undergoes speciation is by geographic isolation.

In nature, many species occupy the same habitat but they perform different functions.
Statement 1 is correct: The functional characteristics of a species in its habitat are referred to as “niche” in that common habitat. Habitat of a species is like its ‘address’ (i.e. where it lives) whereas niche can be thought of as its “profession” (i.e. activities and responses specifi c to the species).
The term niche means the sum of all the activities and relationships of a species by which it uses the resources in its habitat for its survival and reproduction.
A niche is unique for a species while many species share the habitat. Statement 2 is incorrect: No two species in a habitat can have the same niche. This is because if two species occupy the same niche they will compete with one another until one is displaced. For example, a large number of different species of insects may be pests of the same plant but they can co-exist as they feed on different parts of the same plant.
Another example is the vegetation of the forest. The forest can support a large number of plant species as they occupy different niches: the tall trees, the short trees, shrubs, bushes and grasses are all part of the forest but because of varying heights they differ in their requirements for sunlight and nutrients and so can survive together.
The most important resources in the niches of animals are food and shelter while in case of plants, they are moisture and nutrients (phosphorous and nitrogen).

Statement 1 is incorrect: In bioaccumulation, there is an increase in the concentration of a pollutant from the environment to the first organism in a food chain.
Statement 2 is incorrect:
Biomagnification can occur only if the pollutant is fat-soluble.
Bioaccumulation: In bioaccumulation, there is an increase in the concentration of a pollutant from the environment to the first organism in a food chain. Thus, it refers to how pollutants enter a food chain.
Biomagnification: In this, there is an increase in the concentration of a pollutant from one trophic level to another. Condition for bioaccumulation is the high level of pollutants in the environment. Condition for biomagnifications is that pollutants must be fat-soluble, long-lived, biologically active, etc.

Statement 1 is incorrect: Nutrient cycle of an ecosystem is not unidirectional. They are recycled back to physical environment.
The nutrient cycle is a concept that describes how nutrients move from the physical environment to the living organisms, and subsequently recycled back to the physical environment.
This movement of nutrients from the environment into plants and animals and again back to the environment is essential for life and it is the vital function of the ecology of any region.
Based on the replacement period a nutrient cycle is referred to as a Perfect or Imperfect cycle.
A perfect nutrient cycle is one in which nutrients are replaced as fast as they are Utilized. Most gaseous cycles are generally considered as perfect cycles.

• Statement 1 is correct: The pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton. The base of a pyramid is broad and it narrows down at the apex. One gets a similar shape, whether you express the food or energy relationship between organisms at different trophic level. Thus, relationship is expressed in terms of number, biomass or energy. The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer. 
• Statement 2 is correct: Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step. Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per unit area. Since only 10% of the energy is transferred from one trophic level to the next, fewer and fewer numbers of individuals can be sustained as we go up the ecological pyramid.

Statement 1 is incorrect:

• Corals generally flourish in clear tropical oceans usually between 30°N and 30°S of the equator. Corals generally flourish in clear tropical oceans usually between 30°N and 30°S of the equator.
• They grow best in the brightly lighted water about 5 to 10 meters deep.
• The suspended particles interfere with feeding. Corals live in saline water (27%). Coral reef can from to depth of 90 meters, but growth rate declines rapidly after 5 to 10 meters depths. The reef building corals are found within the 21°C isotherm. Corals are not found near the mouths of rivers.
• Temperature below 18°C causes their death. The stunning colours in corals come from marine algae called zooxanthellae, which live inside their tissues. These algae provide the corals with an easy food supply thanks to photosynthesis, which gives the corals energy, allowing them to grow and reproduce.
• When corals get stressed, from things such as heat or pollution, they react by expelling this algae, leaving a ghostly, transparent skeleton behind. This is known as ‘coral bleaching’. Some corals can feed themselves, but without the zooxanthellae most corals starve.
• Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. Not all bleaching events are due to warm water.

Both statements are correct Eugene Odum and others compiled a list of eight general ecological principles. These are: Adaptation, Behavior, Diversity, Emergent properties, Energy fl ow, Growth and development, Limits, and Regulation.

The adaptation is any attribute of the organism (morphological, physiological, and behavioural) that enables the organism to survive and reproduce in its habitat. Many adaptations have evolved over a long evolutionary time and are genetically fi xed.

Some of the examples are as follows:

• Morphological: Many desert plants have a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits (sunken) to minimise water loss through transpiration.
• Physiological: Many tribes live in the high altitude of Himalayas have a higher red blood cell count. Behavioural: Animals migrating temporarily to a less stressful habitat. According to Charles Darwin’s theory of evolution by natural selection, the organisms adapt to their environment so that they could persist and pass their genes onto the next generation. Adaptation differs from acclimatization. Both terms are about changes. However, acclimatization is the physiological adjustment to the new conditions but it does not entail increasing species diversity as adaptation does. For a trait to be considered as an adaptation, it has to be heritable, functional, and increases fitness.

Option (b) is correct:
All species are not equally important in each community.

• Species Diversity: Species diversity is determined not only by the number of species within a biological community—i.e., species richness—but also by the relative abundance of individuals in that community. Species richness is the number of species within a community or area. It does not take into account the distribution of species within the area or what is referred to as species evenness.
• Growth From and structure: Community can be analysed in terms of major growth forms like trees, shrubs, herbs etc. In each growth from as in trees, there may be different kinds of plants as-broad leave trees, evergreen trees etc. These different growth forms determine the structural pattern of a community.
• Dominance: All species are not equally important in each community. The nature of the community is determined by a few species in a community. These limited species have control and dominating infl uence in the community. Dominant species (plants/animals) playing crucial and unique role and highly effect community structure and function in relative to its abundance are called Keystone species
• Self-reliance: Each community has a group of autotrophic plants as well as heterotrophic animals. The autotrophic plants are self-dependent.
• Relative abundance: Different populations in a community exist in relative proportions and this idea is called as relative abundance.
• Trophic structure: Each community has a trophic structure that determines the fl ow of energy and material from plants to herbivores to carnivores.

Option (c) is correct
Supplementary Notes
Biodiversity Some important reasons that infl uence the pattern of Biodiversity are as follows:

• Speciation which is needed for species diversifi cation A relatively more constant and predictable environment that promotes niche specialization and lead to greater species diversity.
• More insolation contributes to higher productivity, in turn, contribute indirectly to greater diversity.
• The more complex ecosystem provides more food web i.e. many entry points for any organism.
• This, in turn, sustains the greater biodiversity. Niche similarity is not good, promotes high competition and leads to loss of biodiversity.