During the process of ecological succession the changes that take place in communities are:

• (a) orderly and sequential
• (b) random
• (c) very quick
• (d) not influenced by the physical environment

Correct Answer: (a) orderly and sequential

During ecological succession, the changes that take place in communities are orderly and sequential. Ecological succession is a predictable process where communities change in a specific sequence over time, with each stage creating conditions favorable for the next stage until a stable climax community is reached.

Climax community is in a state of:

• (a) non-equilibrium
• (b) equilibrium
• (c) disorder
• (d) constant change

Correct Answer: (b) equilibrium

A climax community is in a state of equilibrium. It represents the final, stable stage of ecological succession where the community composition remains relatively constant over time, with birth rates and death rates balanced, and energy input equals energy output.

Among the following biogeochemical cycles which one does not have losses due to respiration?

• (a) Phosphorus
• (b) Nitrogen
• (c) Sulphur
• (d) All of the above

Correct Answer: (a) Phosphorus

The phosphorus cycle does not have losses due to respiration. Unlike carbon, nitrogen, and sulfur cycles where gaseous forms are released during respiration, phosphorus exists mainly in solid form and moves through sedimentary cycles without atmospheric gaseous phases during respiration.

If the carbon atoms fixed by producers have already passed through three species, the trophic level of the last species would be:

• (a) scavenger
• (b) tertiary consumer
• (c) tertiary producer
• (d) secondary consumer

Correct Answer: (b) tertiary consumer

If carbon atoms fixed by producers have passed through three species, the sequence would be: Producers → Primary consumer → Secondary consumer → Tertiary consumer. Therefore, the last species would be a tertiary consumer, representing the fourth trophic level.

Humans benefit from ecosystems because ecosystems provide:

• (a) buffers from natural disasters such as floods
• (b) maintenance of a clean water supply
• (c) climate moderation
• (d) All of the above

Correct Answer: (d) All of the above

Humans benefit from ecosystems through multiple ecosystem services including: buffers from natural disasters (wetlands prevent floods), maintenance of clean water supply (natural filtration), and climate moderation (forests regulate temperature and humidity). All these services are crucial for human survival and well-being.

Edaphic factor refers to:

• (a) water
• (b) soil
• (c) relative humidity
• (d) altitude

Correct Answer: (b) soil

Edaphic factor refers to soil-related environmental factors that affect plant growth and distribution. These include soil pH, nutrient content, soil texture, water-holding capacity, and other soil properties that influence ecosystem structure and function.

The sequence of communities of primary succession in water is:

• (a) phytoplankton, sedges, free-floating hydrophytes, rooted hydrophytes, grasses and trees
• (b) phytoplankton, free-floating hydrophytes, rooted hydrophytes, sedges, grasses and trees
• (c) free-floating hydrophytes, sedges, phytoplankton, rooted hydrophytes, grasses and trees
• (d) phytoplankton, rooted submerged hydrophytes, floating hydrophytes, reed swamp, sedges, meadow and trees

Correct Answer: (d) phytoplankton, rooted submerged hydrophytes, floating hydrophytes, reed swamp, sedges, meadow and trees

In aquatic primary succession (hydrosere), the sequence begins with phytoplankton in open water, followed by rooted submerged plants, then floating plants, followed by emergent vegetation (reed swamp), sedges in marshy areas, meadow formation, and finally terrestrial forest community.

The reservoir for the gaseous type of biogeochemical cycle exists in:

• (a) stratosphere
• (b) atmosphere
• (c) ionosphere
• (d) lithosphere

Correct Answer: (b) atmosphere

The reservoir for gaseous biogeochemical cycles (like carbon, nitrogen, oxygen, and sulfur cycles) exists in the atmosphere. The atmosphere serves as the main storage and exchange medium for gaseous forms of these elements.

Assertion: In a food chain the members of the successive trophic levels are fewer.

Reason: Number of organisms at any trophic level is independent of the availability of organisms which serve as food at the lower level.

Correct Answer: (d) Assertion is wrong statement but reason is correct statement

The assertion is incorrect because generally, the number of organisms decreases at successive trophic levels due to energy transfer efficiency (10% rule), but this is not always true (inverted pyramids exist). The reason is also incorrect as the number of organisms at any trophic level is very much dependent on the availability of food organisms at lower levels.

Assertion: Ecological succession occurs when older communities of plants and animals are replaced by newer communities.

Reason: The natural process of replacement of one vegetation community in a given habitat by the other vegetation community.

Correct Answer: (a) Both assertion and reason are correct statements and reason is correct explanation for assertion

Both the assertion and reason are correct. Ecological succession is indeed the replacement of older communities by newer ones, and the reason correctly explains this process as the natural replacement of vegetation communities in a habitat.

Assertion: Vertical distribution of different species occupying different levels is called stratification.

Reason: Trees occupy top vertical strata, shrubs the second, herbs and grasses occupy the bottom layers.

Correct Answer: (b) Both assertion and reason are correct statements but reason is not correct explanation for assertion

Both statements are correct. Stratification is indeed the vertical distribution of species at different levels, and the reason correctly describes the typical arrangement. However, the reason doesn't explain what stratification is—it merely gives an example of stratification.

Assertion: The decomposers feed on detritus, or decaying organic matter, derived from all levels.

Reason: At each level of energy flow in the food web, energy is lost to respiration.

Correct Answer: (b) Both assertion and reason are correct statements but reason is not correct explanation for assertion

Both statements are factually correct. Decomposers do feed on detritus from all trophic levels, and energy is lost at each level through respiration. However, the reason doesn't explain why decomposers feed on detritus from all levels—these are independent facts about ecosystem functioning.

Assertion: In a terrestrial ecosystem, detritus food chain is the major conduit for energy flow.

Reason: Solar energy is the direct source for energy supply in a detritus food chain.

Correct Answer: (c) Assertion is correct statement but reason is wrong statement

The assertion is correct—in terrestrial ecosystems, the detritus food chain handles a larger fraction of energy flow than the grazing food chain. However, the reason is incorrect because solar energy is not the direct source for detritus food chains; they depend on dead organic matter that originally derived from solar energy through photosynthesis.

Assertion: A network of food chains existing together in an ecosystem is known as a food web.

Reason: An animal like kite cannot be part of a food web.

Correct Answer: (c) Assertion is correct statement but reason is wrong statement

The assertion is correct—a food web is indeed a network of interconnected food chains in an ecosystem. However, the reason is wrong because animals like kites (scavengers) are very much part of food webs, as they feed on dead animals and play important ecological roles.

Assertion: In open water zone up to the depth to which light can penetrate is called photic zone.

Reason: The photic zone contains autotrophs.

Correct Answer: (b) Both assertion and reason are correct statements but reason is not correct explanation for assertion

Both statements are correct. The photic zone is indeed the upper layer of water where light penetrates, and it does contain autotrophs (like phytoplankton). However, the reason doesn't explain what defines the photic zone—the presence of light is what defines it, not the presence of autotrophs.

Assertion: Net primary productivity is gross primary productivity minus respiration.

Reason: Secondary productivity is produced by heterotrophs.

Correct Answer: (b) Both assertion and reason are correct statements but reason is not correct explanation for assertion

Both statements are factually correct. Net primary productivity is indeed GPP minus respiration, and secondary productivity is produced by heterotrophs (consumers). However, these are independent definitions and the reason doesn't explain the assertion.

Assertion: Primary succession takes a very long time.

Reason: Soil is absent at the time of beginning of primary succession.

Correct Answer: (a) Both assertion and reason are correct statements and reason is correct explanation for assertion

Both statements are correct, and the reason explains the assertion. Primary succession takes a very long time precisely because it starts from bare rock or substrate where soil is absent, and soil formation is a slow process that can take hundreds to thousands of years.

Assertion: Pyramid of energy is always upright.

Reason: When energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step.

Correct Answer: (a) Both assertion and reason are correct statements and reason is correct explanation for assertion

Both statements are correct, and the reason perfectly explains the assertion. The pyramid of energy is always upright because at each trophic level, approximately 90% of energy is lost as heat during metabolism and other processes, leaving only about 10% to be transferred to the next level.

Study the diagram given below and answer the questions that follow.

Name the biogeochemical (nutrient) cycle shown above.

Answer: Carbon Cycle

The biogeochemical cycle shown in the diagram is the carbon cycle. This cycle shows the movement of carbon between the atmosphere, biosphere, hydrosphere, and geosphere through processes like photosynthesis, respiration, combustion, and oceanic exchange.

Name an activity of the living organisms not depicted in the cycle by which this nutrient is returned to the atmosphere.

Answer: Microbial decomposition of organic matter

An activity of living organisms not depicted in the cycle by which carbon is returned to the atmosphere is microbial decomposition of organic matter. Decomposer microorganisms break down dead plant and animal material, releasing CO₂ back into the atmosphere through cellular respiration.

How would the flow of the nutrient in the cycle be affected due to large scale deforestation? Explain giving reasons.

Answer: Carbon cycle disruption leading to atmospheric CO₂ accumulation

Due to large scale deforestation, the flow of carbon in the cycle would be severely disrupted because:

• Plants are the major consumers of atmospheric CO₂ through photosynthesis
• Removal of forests reduces the carbon sink capacity of terrestrial ecosystems
• Less CO₂ is being absorbed from the atmosphere
• This leads to accumulation of carbon dioxide in the atmosphere
• Enhanced greenhouse effect and climate change
• Reduced carbon storage in biomass and soil

Name an omnivore which occurs in both grazing food chain and the decomposer food chain.

Answer: Sparrow or Crow

An omnivore that occurs in both grazing food chain and decomposer food chain is sparrow or crow. These birds feed on seeds, grains, and insects (grazing food chain) as well as on dead organic matter and detritus (decomposer food chain).

Standing crop and biomass are related to each other, how?

Standing crop is measured as the mass (biomass) of living organisms or the number of plants in a unit area. Biomass of a species is the mass of the standing crop, expressed as fresh or dry weight. Thus, standing crop represents the total amount of biomass present at any given time in an ecosystem.

All the primary productivity is not available to a herbivore. Give one reason.

All the primary productivity is not available to herbivores because a considerable amount is utilized by the plants themselves for respiration. Plants use much of their produced energy for their own metabolic processes, growth, and maintenance, leaving only a portion available for herbivores to consume.

Differentiate between standing state and standing crop in an ecosystem.

Why is the pyramid of biomass inverted in a pond ecosystem?

The pyramid of biomass is inverted in a pond ecosystem because the biomass of fish (consumers at higher trophic levels) is far larger than that of the producers (phytoplankton). Although phytoplankton have high productivity, their individual biomass is very small and they have rapid turnover rates, while fish accumulate biomass over longer periods.

Mention the role of pioneer species in primary succession on rocks.

The role of pioneer species in primary succession on rocks is to invade bare areas and pave the way for other species. Pioneer species like lichens break down rocks through physical and chemical weathering, contribute organic matter, help in soil formation, and create favorable conditions for the establishment of subsequent plant communities.

Why is a food web formed in nature?

A food web is formed in nature because many organisms occupy positions in different food chains and several food chains become interconnected. Most organisms have varied diets and can feed at multiple trophic levels, creating complex feeding relationships that form a web-like structure rather than simple linear chains.

What is a detritus food chain made up of? How do they meet their energy and nutritional requirements?

Composition: A detritus food chain is made up of dead plant and animal remains and their fecal matter, collectively known as detritus.

Energy and nutritional requirements: Decomposers in this chain (like bacteria, fungi, earthworms) obtain energy and nutrients by decomposing the dead organic materials through enzymatic breakdown, releasing stored chemical energy and recycling nutrients back to the ecosystem.

Define mineralisation.

Mineralisation is the process in which humus is degraded by certain microorganisms, leading to the release of inorganic nutrients into the soil. This process converts complex organic compounds in humus back into simple inorganic forms that can be readily absorbed by plant roots.