Chapter 11: Organisms and Populations Assertion-Reason Questions | biology Class 12 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): A population has birth rates and death rates, but an individual organism does not. Reason (R): Birth rate and death rate are per capita rates that describe changes in numbers with respect to the total population, and are meaningful only at the population level.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): Exponential population growth produces a J-shaped curve when population size is plotted against time. Reason (R): In exponential growth, resources are unlimited, allowing the population to grow at a constant rate proportional to its current size without any ceiling.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 3

Logic Check

Assertion (A): Logistic growth is considered more realistic than exponential growth for natural populations. Reason (R): In nature, resources are always unlimited, allowing populations to grow exponentially for prolonged periods.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 4

Logic Check

Assertion (A): The shape of an age pyramid with a narrow base indicates a declining population. Reason (R): A narrow base means fewer individuals in the pre-reproductive age group, resulting in fewer births in future generations.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): For a banyan tree in a community with many carrot grass plants, total number is the most appropriate measure of population density. Reason (R): Per cent cover or biomass is more meaningful when species differ greatly in size, as total number would underestimate the ecological role of the larger organism.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 6

Logic Check

Assertion (A): Predators in nature tend to be 'prudent' and do not overexploit their prey. Reason (R): If a predator is too efficient and overexploits its prey, the prey may go extinct, causing the predator to also face extinction due to lack of food.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 7

Logic Check

Assertion (A): Cuscuta is considered a parasitic plant. Reason (R): Cuscuta has lost its chlorophyll and leaves during evolution and derives nutrition from the host plant it parasitises.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): The interaction between an orchid growing on a mango tree and the mango tree is an example of mutualism. Reason (R): In commensalism, one species benefits while the other is neither harmed nor helped.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 9

Logic Check

Assertion (A): Gause's Competitive Exclusion Principle is universally applicable in all natural ecosystems. Reason (R): In reality, species facing competition may evolve mechanisms like resource partitioning to promote co-existence, making the principle not always applicable.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 10

Logic Check

Assertion (A): Mycorrhizal associations represent mutualism between fungi and higher plant roots. Reason (R): In mycorrhizae, the fungus benefits by getting energy-yielding carbohydrates from the plant, while the plant benefits by enhanced absorption of essential soil nutrients.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 11

Logic Check

Assertion (A): Natality and immigration increase population density, while mortality and emigration decrease it. Reason (R): In a newly colonised habitat, birth rates always exceed immigration as the primary driver of population growth.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 12

Logic Check

Assertion (A): Removal of the starfish Pisaster from the intertidal community led to an increase in species diversity. Reason (R): Pisaster, as a keystone predator, was reducing the intensity of interspecific competition among prey species, thereby maintaining biodiversity.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 13

Logic Check

Assertion (A): Brood parasitic birds have evolved eggs that mimic host eggs in size and colour. Reason (R): If the parasitic egg resembles the host egg, the host is less likely to detect and eject the foreign egg from its nest.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): The Ophrys orchid offers nectar and pollen as rewards to attract male bees for pollination. Reason (R): Ophrys uses sexual deceit — one petal mimics the female bee — to attract male bees for pseudocopulation-based pollination without offering any reward.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 15

Logic Check

Assertion (A): Pacific salmon is an example of an iteroparous organism. Reason (R): Iteroparous organisms breed only once in their lifetime and then die.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 16

Logic Check

Assertion (A): Population ecology links ecology to population genetics and evolution. Reason (R): Although individuals cope with environmental changes, natural selection operates at the population level to evolve desired traits.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 17

Logic Check

Assertion (A): Endoparasites tend to have simpler morphological and anatomical features than free-living organisms. Reason (R): Endoparasites rely entirely on their host for nutrition and protection, so many structural features like sense organs and locomotive systems are reduced, but reproductive potential is greatly enhanced.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 18

Logic Check

Assertion (A): In a sexually reproducing population, a group of individuals producing offspring only through asexual reproduction cannot be considered a population. Reason (R): Even groups of individuals resulting from asexual reproduction are generally considered a population for ecological study purposes.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 19

Logic Check

Assertion (A): Chemical substances like nicotine, caffeine, quinine, and opium are produced by plants primarily for human medicinal use. Reason (R): These chemicals actually evolved in plants as defences against grazers and browsers; their medicinal use by humans is secondary.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 20

Logic Check

Assertion (A): The female mosquito is considered a parasite because it feeds on human blood. Reason (R): A true parasite derives benefit from the host at the host's expense and depends on the host for completing essential life processes; the female mosquito uses blood only for reproduction and does not live on or in the host.

Reasoning Options

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Chapter sections

Chapter 11: Organisms and Populations | Assertion-Reason

Assertion (A): A population has birth rates and death rates, but an individual organism does not. Reason (R): Birth rate and death rate are per capita rates that describe changes in numbers with respect to the total population, and are meaningful only at the population level.

Assertion (A): Exponential population growth produces a J-shaped curve when population size is plotted against time. Reason (R): In exponential growth, resources are unlimited, allowing the population to grow at a constant rate proportional to its current size without any ceiling.

Assertion (A): Logistic growth is considered more realistic than exponential growth for natural populations. Reason (R): In nature, resources are always unlimited, allowing populations to grow exponentially for prolonged periods.

Assertion (A): The shape of an age pyramid with a narrow base indicates a declining population. Reason (R): A narrow base means fewer individuals in the pre-reproductive age group, resulting in fewer births in future generations.

Assertion (A): Predators in nature tend to be 'prudent' and do not overexploit their prey. Reason (R): If a predator is too efficient and overexploits its prey, the prey may go extinct, causing the predator to also face extinction due to lack of food.

Assertion (A): Cuscuta is considered a parasitic plant. Reason (R): Cuscuta has lost its chlorophyll and leaves during evolution and derives nutrition from the host plant it parasitises.

Assertion (A): The interaction between an orchid growing on a mango tree and the mango tree is an example of mutualism. Reason (R): In commensalism, one species benefits while the other is neither harmed nor helped.

Assertion (A): Gause's Competitive Exclusion Principle is universally applicable in all natural ecosystems. Reason (R): In reality, species facing competition may evolve mechanisms like resource partitioning to promote co-existence, making the principle not always applicable.

Assertion (A): Mycorrhizal associations represent mutualism between fungi and higher plant roots. Reason (R): In mycorrhizae, the fungus benefits by getting energy-yielding carbohydrates from the plant, while the plant benefits by enhanced absorption of essential soil nutrients.

Assertion (A): Natality and immigration increase population density, while mortality and emigration decrease it. Reason (R): In a newly colonised habitat, birth rates always exceed immigration as the primary driver of population growth.

Assertion (A): Removal of the starfish Pisaster from the intertidal community led to an increase in species diversity. Reason (R): Pisaster, as a keystone predator, was reducing the intensity of interspecific competition among prey species, thereby maintaining biodiversity.

Assertion (A): Brood parasitic birds have evolved eggs that mimic host eggs in size and colour. Reason (R): If the parasitic egg resembles the host egg, the host is less likely to detect and eject the foreign egg from its nest.

Assertion (A): The Ophrys orchid offers nectar and pollen as rewards to attract male bees for pollination. Reason (R): Ophrys uses sexual deceit — one petal mimics the female bee — to attract male bees for pseudocopulation-based pollination without offering any reward.

Assertion (A): Pacific salmon is an example of an iteroparous organism. Reason (R): Iteroparous organisms breed only once in their lifetime and then die.

Assertion (A): Population ecology links ecology to population genetics and evolution. Reason (R): Although individuals cope with environmental changes, natural selection operates at the population level to evolve desired traits.

Assertion (A): Chemical substances like nicotine, caffeine, quinine, and opium are produced by plants primarily for human medicinal use. Reason (R): These chemicals actually evolved in plants as defences against grazers and browsers; their medicinal use by humans is secondary.

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