Are these practice questions for Organisms and Populations based on the CBSE pattern?

Yes. Every practice question is modeled on the CBSE Class 12 - Science Biology exam pattern — including MCQs, assertion-reason questions, and short-answer formats that frequently appear in CBSE papers.

Are the practice questions for Organisms and Populations free?

Yes. Every chapter includes free practice questions for Class 12 - Science students to get you started.

What types of questions are included?

The practice set for Organisms and Populations mainly includes MCQs and CBSE-style short-answer questions, with instant feedback on each answer. For full-length textbook practice, use the NCERT Solutions page.

Are the practice questions suitable for board exam preparation?

Yes. The questions test the same concepts and depth that CBSE asks in board exams. After finishing, also solve the NCERT and NCERT Exemplar exercises for Organisms and Populations for full coverage.

How many practice questions are there for Organisms and Populations?

The number scales with chapter length and concept density. Each chapter typically has 15-50 practice questions across MCQ and short-answer formats.

Organisms and Populations Class 12 Biology Practice Questions with Answers

easy

An orchid plant is found growing on the branch of a mango tree, but it does not draw any nutrients from the tree itself. Apply your knowledge of population interactions to classify this relationship and briefly justify your answer.

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easy

A plant species evolving in a habitat with a high population of grazing animals is found to have developed thorns on its stems and leaves. Apply your understanding of population interactions to explain the ecological significance of these thorns.

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easy

Define the term 'population' as used in ecology.

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easy

Name the four basic processes that cause fluctuations in the density of a population.

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easy

List three attributes that a population possesses but an individual organism does not.

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easy

A population of deer in a national park has a density of 500 individuals at time

t

. During the following year, the number of births is 100, deaths is 60, individuals that immigrated is 40, and individuals that emigrated is 30. Calculate the population density at time

t+1

.

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easy

Identify the ecological term for an organism that lives on the external surface of its host.

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easy

A population of 500 birds in a newly colonized island habitat has the following changes in one year: 100 births, 20 deaths, 50 new birds immigrating, and 30 birds emigrating. Formulate the equation for population change and calculate the final population density (

N_{t+1}

) and the net change in population size.

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medium

Create and label three distinct age pyramids representing (a) a rapidly growing population, (b) a stable population, and (c) a declining population. For each pyramid, justify its shape by explaining the relative proportions of pre-reproductive, reproductive, and post-reproductive individuals.

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medium

The prickly pear cactus became an invasive species in Australia. Propose a set of criteria that scientists should have evaluated before introducing the cactus-feeding moth to control the cactus population, to ensure it did not become a new ecological problem.

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medium

Name the ecological principle which states that two closely related species competing for the same resources cannot co-exist indefinitely.

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medium

A population of flour beetles has an intrinsic rate of natural increase (

r

) of

0.12

per week. If the initial population size (

N_0

) is 500, formulate the exponential growth equation for this population and calculate the projected population size (

N_t

) after 4 weeks. (Assume

e^{0.48} \approx 1.616

).

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medium

Describe the key characteristics of the exponential growth model in population ecology. Include the shape of the curve and the formula.

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medium

In a laboratory population of 200 fruit flies, 20 individuals died during a specific week. Calculate the death rate in the population for that period.

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medium

Define carrying capacity and state the variable used to represent it.

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medium

In a forest community, an ecologist is trying to determine the population density of a single, massive banyan tree and 200 small Parthenium plants in the same area. Compare and contrast the use of 'total number' versus 'percent cover or biomass' as a measure of population size in this scenario, and analyze which method is more meaningful.

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medium

Explain what an age pyramid is and what the shape of a pyramid with a broad base indicates about the population's growth status.

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medium

Compare and contrast the population interactions of predation and parasitism. Identify their key similarity and two distinct differences.

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medium

Compare and contrast ectoparasites and endoparasites. For each type, provide an example and describe one specific adaptation related to their parasitic lifestyle.

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medium

A single banyan tree has a much greater ecological impact than 200 Parthenium plants in the same area. Justify the use of biomass or per cent cover as a more meaningful measure of population density in this case, instead of total number.

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medium

Analyze why introducing a natural predator of an invasive plant species is often a more effective long-term control strategy than using herbicides.

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medium

Gause's 'Competitive Exclusion Principle' suggests that two species competing for the same limited resources cannot coexist. However, MacArthur's study on warblers showed five species coexisting on the same tree. Evaluate how 'resource partitioning' acts as a mechanism to circumvent competitive exclusion. Create a hypothetical example of resource partitioning for two competing species of squirrels in a forest.

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medium

In a pond, there were 50 lotus plants last year. Through reproduction, 10 new plants are added, taking the current population to 60. Calculate the birth rate.

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medium

A population of fish in a lake is growing according to the logistic model. The carrying capacity (

K

) of the lake is 1000 fish. The intrinsic rate of natural increase (

r

) is

0.1

per year. If the current population size (

N

) is 800 fish, calculate the population growth rate (

dN/dt

).

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medium

Create a hypothetical ecological scenario involving at least three different species where mutualism, commensalism, and predation are all occurring simultaneously. Clearly identify each species and describe the interactions, assigning +, -, or 0 to each species for each interaction.

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medium

Justify why interspecific competition is generally considered a (-, -) interaction, even though one species might be a superior competitor.

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medium

In a wetland, a population of 400 lotus plants existed at the start of a year. Over the year, 80 new plants were produced through reproduction, and 60 plants died. Calculate the per capita birth rate and death rate for this population for that year.

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medium

Explain the population interaction known as commensalism and provide two examples.

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medium

Analyze the growth status of three different human populations based on the following descriptions of their age pyramids:

A pyramid with a very broad base and a sharply tapering top.
A pyramid that is bell-shaped with relatively even distribution across young and adult age groups.
A pyramid that is urn-shaped with a narrow base and a wider middle section.

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medium

Propose a life history strategy for a newly discovered fish species that lives in a highly unstable, temporary pond environment that dries up unpredictably. Justify your choice of traits related to offspring number, offspring size, and breeding frequency to maximize its Darwinian fitness (high

r

value).

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medium

Examine the mutualistic relationship between a specific fig species and its partner wasp species. Explain how the interaction benefits both organisms and why it is a classic example of co-evolution.

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medium

Summarize five types of population interactions, specifying the effect on each of the two interacting species.

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medium

List two examples of morphological defenses and one example of a chemical defense in plants against herbivores.

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medium

Recall the equation for population density at time

t+1

and define each variable.

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medium

Critique the statement: 'A sparrow eating a seed is not a predator because it is a herbivore.'

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medium

Contrast the exponential and logistic models of population growth. Your answer should address the conditions for each, the shape of the growth curve, and the meaning of the key parameters in their respective equations.

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hard

Describe the logistic growth model. Explain why it is considered more realistic than the exponential growth model for most populations in nature.

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hard

A conservation agency introduces a small population of a critically endangered deer species into a large, protected national park with abundant resources and no natural predators. Evaluate which population growth model (exponential or logistic) would be more appropriate to predict the population size for the first 50 years versus the next 200 years. Justify your reasoning.

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hard

The text asks, 'Do you believe that an ideal parasite should be able to thrive within the host without harming it? Then why didn't natural selection lead to the evolution of such totally harmless parasites?' Critique this notion of an 'ideal parasite'. Argue whether a completely harmless parasite would still be considered a parasite and evaluate the evolutionary pressures that prevent this from being a common outcome.

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hard

Examine the validity of Gause's 'Competitive Exclusion Principle' in natural ecosystems. Analyze how two or more closely related species competing for the same limited resources can coexist, providing specific examples.

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hard

The Mediterranean orchid Ophrys employs 'sexual deceit' to attract a specific bee for pollination. Evaluate the evolutionary risks and benefits of such a highly specialized mutualistic relationship for both the orchid and the bee. Propose what might happen to the orchid population if the bee species faced a sudden decline due to a new disease.

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hard

You are tasked with estimating the population density of tigers in a national park and bacteria in a petri dish. Critique the use of a single method (like total count) for both. Design an appropriate and practical estimation strategy for each population, justifying why your chosen methods are more suitable.

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hard

If a bacterial population growing exponentially doubles its size in 5 hours, calculate its intrinsic rate of increase (

r

). (Given

\ln(2) = 0.693

)

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hard

Analyze the life history strategies of 'breeding once' (like Pacific salmon) versus 'breeding many times' (like most mammals). Explain how each strategy can maximize Darwinian fitness, and demonstrate how environmental conditions might favor one strategy over the other.

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hard

Design a field experiment to test Connell's 'competitive release' hypothesis using two competing barnacle species, Balanus (larger, superior) and Chathamalus (smaller, inferior), on a rocky sea coast.

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Organisms and PopulationsClass 12 Biology Practice Questions