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Practice succession-and-change with 20 free MCQ questions covering environment-and-ecology. Detailed explanations in English and Hindi, perfect for UPSC, SSC, and competitive exam preparation.
Attempt the quiz above first, then review every question with its correct answer and a short explanation below.
Q1.The gradual and fairly predictable change in the species composition of a given area over time is known as:
Explanation: NCERT Class 12 Biology Chapter 14 states: 'An important characteristic of all communities is that their composition and structure constantly change in response to the changing environmental conditions. This gradual and fairly predictable change in the species composition... is called ecological succession.'
Q2.What is the term used for the entire sequence of communities that successively change in a given area during ecological succession?
Explanation: NCERT Chapter 14 defines Sere: 'The entire sequence of communities that successively change in a given area are called sere(s).' The individual transitional communities are termed seral stages or seral communities.
Q3.The final stable community that is in near equilibrium with the environment and does not change further unless the climate shifts is called the:
Explanation: In ecological succession, the climax community is the final, stable stage of vegetation. It remains in dynamic equilibrium with the local climate and has high species diversity and structural complexity (NCERT).
Q4.Which of the following represents an area where Primary Succession would take place?
Explanation: NCERT states: 'Primary succession starts where no living organisms ever existed before... newly cooled lava, bare rocks, newly created ponds or reservoirs.' Secondary succession starts in areas where natural biotic communities have been destroyed but soil is present (abandoned farms, burned forests).
Q5.Why is Primary Succession extremely slow compared to Secondary Succession?
Explanation: NCERT Class 12 Biology ponders: 'Establishing a new biotic community is generally slow. Before a biotic community of diverse organisms can become established, there must be soil. Depending mostly on the climate, it takes natural processes several hundred to several thousand years to produce fertile soil on bare rock.'
Q6.Which of the following is a classic example of an area undergoing Secondary Succession?
Explanation: Secondary succession begins in areas where natural biotic communities have been destroyed but some soil or sediment is already present. Abandoned agricultural fields, burned forests, and flooded areas are classic sites for secondary succession (NCERT).
Q7.During ecological succession, what general changes occur in the seral communities over time?
Explanation: As succession progresses, the transitional seral stages show a clear trend: an increase in the number of species, increase in total biomass, and an increase in the complexity of food webs and structural strata of the ecosystem (NCERT Chapter 14).
Q8.Which species are the first to invade a bare area and initiate ecological succession?
Explanation: NCERT Class 12 Biology defines: 'The species that invade a bare area are called pioneer species.' For example, lichens on bare rock or phytoplankton in a newly formed water body.
Q9.Which of the following is a key factor that determines the rate of secondary succession in a disturbed forest area?
Explanation: NCERT notes: 'Since soil is already present, the rate of secondary succession is much faster... The description of secondary succession at any stage is determined by the condition of the soil, availability of water, and the environment, as well as the seeds or other vegetative propagules active.'
Q10.Regardless of whether succession starts in water (hydrarch) or on dry land (xerarch), both pathways eventually lead to which common moisture condition?
Explanation: NCERT Class 12 Biology Chapter 14 states: 'Both hydrarch and xerarch successions lead to medium water conditions (mesic) – neither too dry (xeric) nor too wet (hydric).'
Q11.Succession that is driven by the organisms themselves altering the environmental conditions of their habitat (e.g. leaf litter changing soil chemistry) is termed:
Explanation: Autogenic succession is driven by the biotic components of the ecosystem. The living organisms modify their own physical environment (e.g., plants adding organic matter, shading soil, or changing pH), making it more suitable for new species and less suitable for themselves.
Q12.Succession that is driven by external abiotic factors, such as volcanic eruptions, forest fires, or climate shifts, is called:
Explanation: Allogenic succession is driven by abiotic external forces changing the habitat. Volcanic ash deposition, changes in water table from drought, or periodic fires force changes in species composition without the direct influence of resident organisms.
Q13.A succession that begins in an organic-rich environment (like a rotting log or sewage-polluted water) where decomposers dominate early stages is classified as:
Explanation: Heterotrophic succession starts with heterotrophic organisms (fungi, bacteria, detritivores) dominating because the substrate is rich in dead organic matter. In contrast, autotrophic succession starts with autotrophic green plants dominating early stages.
Q14.When a major disturbance like a forest fire or logging clears a climax community, it resets the ecological state. The recovery process that follows is:
Explanation: NCERT Class 12 Biology states that disturbances like forest fires or logging destroy the existing vegetation but leave the soil intact. This initiates secondary succession, which begins with fast-growing pioneer grasses and herbs before woody shrubs and trees reappear.
Q15.What is the biological term for the process of soil formation, which is a key limiting step during primary succession?
Explanation: Pedogenesis is the process of soil formation. In primary succession on bare rock, pedogenesis involves physical weathering of rocks by wind/water/frost, combined with chemical weathering by organic acids secreted by pioneer lichens, breaking down minerals into soil particles.
Q16.Which of the following parameters increases and reaches its maximum value during the mid-seral stages of succession, rather than in the climax community?
Explanation: Net Primary Productivity (NPP) is often highest in middle seral stages (young forests/shrublands) where fast-growing plants occupy all layers. In the climax community, respiration (R) increases to match gross primary productivity (P), so NPP (P-R) declines slightly and stabilizes.
Q17.In primary succession on bare rock, which organisms act as pioneer species?
Explanation: NCERT Class 12 Biology explicitly documents: 'For primary succession on rocks, these [pioneers] are usually lichens which are able to secrete acids to dissolve rock, helping in weathering and soil formation.'
Q18.Which of the following represents the correct sequence of stages in primary succession on bare rock (xerarch succession)?
Explanation: According to NCERT Chapter 14: Lichens are pioneers. They secrete acids to dissolve rocks and form a little soil. Next, bryophytes (mosses) establish, followed by herbs/grasses, then shrubs, and finally, trees that form the stable climax forest.
Q19.Why is the climax community of an ecosystem considered to be in near equilibrium with the environment?
Explanation: A climax community is self-perpetuating and stable because the species composing it are well-adapted to the local climate. The microclimate created by the forest allows its own seedlings to grow, maintaining the community indefinitely unless a major climatic shift or disturbance occurs.
Q20.The primary succession in a newly created freshwater pond begins with which of the following pioneer communities?
Explanation: NCERT Class 12 Biology states: 'In primary succession in water, the pioneers are the small phytoplanktons...'. They are replaced over time by rooted submerged plants, floating angiosperms, reed-swamp, marsh-meadow, scrub, and finally trees.
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