Assertion (A): The population density refers to the number of
individuals of a species per unit area or volume.
Reason (R): Population density is a measure of how crowded or
sparse a population is in a given habitat.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Population density provides insight into the
concentration of individuals in a habitat, which is directly related to resource
availability and habitat conditions.
Assertion (A): The age structure of a population significantly
affects its growth rate.
Reason (R): A population with a higher number of individuals in
the reproductive age group tends to grow faster.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The number of individuals in reproductive age
determines the reproductive potential of a population, thereby influencing its
growth rate.
Assertion (A): Biotic potential refers to the maximum
reproductive capacity of an organism under optimal environmental conditions.
Reason (R): The biotic potential is determined by factors like
the number of offspring per reproduction event, the frequency of reproduction,
and the age at which reproduction starts.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The biotic potential of a species is determined by
these reproductive factors, which influence its population growth in ideal
conditions.
Assertion (A): The carrying capacity of an environment is
constant.
Reason (R): Carrying capacity refers to the maximum population
size that can be supported by the environment's resources.
Answer: (B) A is false, but R is true.
Explanation: The carrying capacity is not constant; it can
change with fluctuations in resource availability, environmental changes, or
other factors.
Assertion (A): In a J-shaped curve, the population grows
exponentially.
Reason (R): Exponential growth occurs when resources are
abundant, and the population grows without any limiting factors.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Exponential growth occurs in ideal conditions,
where resources are unlimited, leading to an accelerating increase in population
size.
Assertion (A): The logistic growth curve shows a slow start,
followed by a rapid increase, and eventually levels off.
Reason (R): This leveling off happens when the population
reaches the carrying capacity of the environment.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: In logistic growth, population growth slows as
resources become limiting, and the population stabilizes at the carrying
capacity.
Assertion (A): In mutualism, both organisms benefit from the
interaction.
Reason (R): Mutualism is a type of symbiotic relationship where
both species contribute to the survival and reproduction of each other.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Mutualism is a relationship where both organisms
derive benefits, such as the interaction between bees and flowers.
Assertion (A): In commensalism, one organism benefits while the
other is neither helped nor harmed.
Reason (R): Commensalism is an interaction where one species
benefits from another without affecting the host.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: In commensalism, one species gains benefits, like
shelter or food, while the other remains unaffected.
Assertion (A): Intraspecific competition occurs between
individuals of the same species.
Reason (R): Intraspecific competition arises due to competition
for the same resources, such as food, shelter, and mates.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Intraspecific competition happens within a species
for limited resources, which can affect population size and distribution.
Assertion (A): The r-strategy involves organisms that reproduce
quickly and in large numbers.
Reason (R): r-strategists have short life spans, produce many
offspring, and provide little to no parental care.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: r-strategists thrive in unstable environments,
producing large numbers of offspring with minimal investment in individual care.
Assertion (A): The K-strategy involves organisms that reproduce
slowly and invest heavily in offspring care.
Reason (R): K-strategists are adapted to stable environments
where competition for resources is intense.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: K-strategists produce fewer offspring but invest
more time in their survival and development, which is advantageous in stable
environments.
Assertion (A): The competitive exclusion principle states that
two species cannot coexist if they compete for the same limiting resource.
Reason (R): The principle implies that one species will
outcompete the other, leading to the local extinction of the weaker competitor.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The competitive exclusion principle suggests that
when two species compete for identical resources, one will dominate, and the
other may be driven to extinction.
Assertion (A): The birth rate in a population is the number of
offspring born per unit time.
Reason (R): The birth rate is an important factor that
influences the growth of a population.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Birth rate directly affects population growth, as
higher birth rates lead to faster population increase.
Assertion (A): The death rate refers to the number of
individuals that die per unit time in a population.
Reason (R): The death rate helps in determining the overall
survival rate and longevity of a population.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The death rate influences the population size and
helps to understand the mortality trends within a population.
Assertion (A): The interaction between the predator and prey in
an ecosystem can regulate the population size of both species.
Reason (R): Predators control the prey population, while the
availability of prey influences the predator population.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Predator-prey relationships help to regulate the
population dynamics of both species, maintaining ecological balance.
Assertion (A): An ecological niche refers to the role or
function of an organism within its habitat.
Reason (R): The niche includes the organism's food sources,
behavior, and interactions with other species in the ecosystem.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The ecological niche defines how an organism fits
into the environment and interacts with biotic and abiotic factors.
Assertion (A): The "big bang" reproduction strategy is typical
of r-strategists.
Reason (R): This strategy involves producing a large number of
offspring in a short period, with minimal parental care.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: r-strategists, such as insects, often exhibit "big
bang" reproduction, where they produce numerous offspring with little parental
investment.
Assertion (A): The population of a species can grow
indefinitely if resources are unlimited.
Reason (R): Exponential growth occurs in ideal conditions where
resources are abundant and there are no limiting factors.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Exponential growth can only occur when resources
are unlimited and environmental resistance is absent, which is unrealistic over
long periods.
Assertion (A): The human population is experiencing exponential
growth.
Reason (R): Advances in medicine and technology have reduced
death rates and increased life expectancy, leading to rapid population growth.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Technological advancements and improved healthcare
have led to reduced mortality and increased reproduction, contributing to
exponential human population growth.
Assertion (A): The life history of a species refers to the
series of changes in the life cycle of an organism.
Reason (R): Life history includes strategies such as
reproductive rate, survival, and lifespan.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The life history concept covers how organisms are
adapted to their environments in terms of growth, reproduction, and survival
strategies.
Assertion (A): In a population, the sex ratio is defined as the
number of females per 1000 males.
Reason (R): A balanced sex ratio is essential for the
reproductive success of a population.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: A balanced sex ratio ensures that enough females
are available for reproduction, supporting the continuity of the population.
Assertion (A): The fundamental niche of a species is the total
ecological space that a species can occupy.
Reason (R): The realized niche is the actual space the species
occupies due to interactions with other species and environmental factors.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The fundamental niche represents the potential
range, while the realized niche is the actual range after considering
competition and other ecological interactions.
Assertion (A): The "J-shaped" curve in population growth
indicates exponential growth.
Reason (R): Exponential growth occurs when resources are
abundant, and the environment can support an increasing number of individuals.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Exponential growth occurs when there are no
limiting factors, and the population grows rapidly, forming a J-shaped curve.
Assertion (A): In a competitive relationship, two species
compete for the same resource.
Reason (R): The stronger competitor excludes the weaker one,
causing the weaker species to either adapt or move to another area.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: In competitive interactions, one species often
dominates, leading to competitive exclusion, where the weaker competitor either
adapts or is displaced.
Assertion (A): Density-dependent factors affect the growth rate
of a population as its size increases.
Reason (R): These factors include competition, predation,
disease, and food scarcity, which become more impactful as population density
rises.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Density-dependent factors increase in intensity as
the population size grows, limiting further population growth.
Assertion (A): In an ecological pyramid, the number of
organisms at higher trophic levels decreases as compared to the lower levels.
Reason (R): This decrease is due to energy loss between trophic
levels as per the 10% energy rule.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The number of individuals decreases at higher
trophic levels because energy is lost at each level, which limits the number of
organisms that can be supported.
Assertion (A): The habitat of an organism is the place where it
lives and survives.
Reason (R): The habitat provides the organism with necessary
resources such as food, water, and shelter.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The habitat is essential for an organism's
survival as it provides the required resources and conditions for living.
Assertion (A): The carrying capacity of an environment refers
to the maximum number of individuals that an environment can support
indefinitely.
Reason (R): It is determined by the availability of resources,
competition, and environmental conditions.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Carrying capacity is influenced by resource
availability and environmental factors that regulate population size.
Assertion (A): The principle of competitive exclusion states
that no two species can occupy the same ecological niche for a prolonged period.
Reason (R): One species will always outcompete the other for
resources, leading to the elimination of the weaker species.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Competitive exclusion leads to the dominance of
one species over the other in the same niche, ultimately forcing the weaker
competitor to either adapt or face extinction.
Assertion (A): An organism's reproductive strategy is
influenced by environmental factors.
Reason (R): Species in unstable environments tend to be
r-strategists, while those in stable environments tend to be K-strategists.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Environmental stability plays a crucial role in
determining whether a species adopts an r-strategy (many offspring, low
investment) or a K-strategy (few offspring, high investment).
Assertion (A): An ecological niche includes all the
interactions of an organism with its environment.
Reason (R): The niche encompasses the organism's use of
resources and its role in the ecosystem, including its interactions with other
organisms.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: An organism's niche involves not only its habitat
but also its interactions with other species and its role in nutrient cycling,
energy flow, etc.
Assertion (A): The "carrying capacity" of a population changes
over time.
Reason (R): Carrying capacity fluctuates due to environmental
changes such as food availability, climate conditions, and space.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Environmental changes can lead to shifts in the
carrying capacity of a population, making it more or less sustainable in a given
area.
Assertion (A): In a predator-prey relationship, the population
sizes of predators and prey are closely linked.
Reason (R): As the prey population decreases, predators have
less food, which leads to a decline in their population, and vice versa.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The predator-prey cycle shows interdependence,
where changes in one population directly influence the other.
Assertion (A): In a population with a high growth rate, the
number of deaths exceeds the number of births.
Reason (R): This leads to a declining population size, as more
individuals are dying than are being born.
Answer: (B) A is false, but R is true.
Explanation: In populations with a high growth rate, the birth
rate exceeds the death rate, leading to an increase in population size.
Assertion (A): Population growth follows a predictable pattern
in nature, usually starting slow and then accelerating.
Reason (R): This pattern is known as the logistic growth curve,
which represents population growth with environmental limits.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Logistic growth starts slowly, then accelerates
until it reaches the carrying capacity, where growth levels off.
Assertion (A): The growth of a population is limited by factors
such as food, space, and disease.
Reason (R): These limiting factors determine the carrying
capacity of the environment.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Limiting factors such as food availability and
disease regulate the growth rate and the maximum population size that an
environment can support.
Assertion (A): Density-independent factors can affect the
population size regardless of the population's density.
Reason (R): Factors such as natural disasters, weather, and
human activities are examples of density-independent factors.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Density-independent factors affect populations
regardless of their density, often causing sudden changes in population size.
Assertion (A): The ecological balance in an ecosystem is
maintained by the interaction of biotic and abiotic components.
Reason (R): These interactions regulate the population sizes
and distribution of organisms in an ecosystem.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The balance of species and resources in an
ecosystem is maintained by interactions between organisms and their environment.
Assertion (A): In a food web, the flow of energy and nutrients
follows a linear path from producers to consumers.
Reason (R): A food web represents complex interconnections
among different trophic levels in an ecosystem.
Answer: (B) A is false, but R is true.
Explanation: A food web is a network of interconnected food
chains, representing the complex relationships and energy flow among species in
an ecosystem.
Assertion (A): The primary productivity of an ecosystem is the
rate at which energy is stored in the form of organic matter.
Reason (R): This is mainly determined by factors like sunlight,
temperature, and availability of nutrients.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Primary productivity reflects the ability of
producers to convert solar energy into organic matter, influenced by
environmental conditions.
Assertion (A): r-strategists reproduce quickly and in large
numbers.
Reason (R): r-strategists thrive in unpredictable or changing
environments where early reproduction maximizes their survival.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: r-strategists invest in producing many offspring
quickly, which helps them exploit unstable environments.
Assertion (A): K-strategists produce fewer offspring but invest
more in raising them.
Reason (R): K-strategists thrive in stable environments where
competition is high, and resources are limited.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: K-strategists focus on quality over quantity,
producing fewer offspring with greater parental investment to ensure their
survival in competitive environments.
Assertion (A): The concept of "niche partitioning" is observed
when different species occupy different niches in the same environment.
Reason (R): Niche partitioning reduces competition and allows
species to coexist in the same habitat.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Niche partitioning allows multiple species to
coexist by minimizing direct competition for resources, each exploiting
different aspects of the environment.
Assertion (A): Intraspecific competition occurs within the same
species.
Reason (R): Intraspecific competition arises because members of
the same species have similar resource needs.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Intraspecific competition occurs when individuals
of the same species compete for limited resources, leading to natural selection
and adaptation.
Assertion (A): A high species diversity is usually an indicator
of a healthy and stable ecosystem.
Reason (R): High species diversity enhances ecosystem
resilience and productivity.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: High species diversity promotes stability and
ensures that ecosystems can withstand disturbances and continue to function
efficiently.
Assertion (A): Symbiosis refers to interactions between two
organisms of different species that live in close physical proximity.
Reason (R): These interactions can be mutualistic,
commensalistic, or parasitic.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Symbiotic relationships can be mutually
beneficial, neutral, or harmful, depending on how the organisms involved
interact with one another.
Assertion (A): The "boom and bust" population growth pattern is
typical in species with low reproductive rates.
Reason (R): Species with low reproductive rates usually have
fluctuating population sizes due to environmental factors.
Answer: (B) A is false, but R is true.
Explanation: "Boom and bust" patterns are typical of species
with high reproductive rates, where rapid growth is followed by sharp declines,
often due to resource depletion or environmental changes.
Assertion (A): The concept of "ecological succession" refers to
the process by which ecosystems evolve over time.
Reason (R): Ecological succession occurs when a disturbance
alters the composition of species in a habitat.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Ecological succession is the gradual process of
change and replacement of species in an ecosystem following a disturbance.
Assertion (A): Ecological pyramids are used to represent the
flow of energy and matter through trophic levels.
Reason (R): Energy decreases as it moves up the trophic levels
due to energy loss during metabolic processes.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Energy flows through ecosystems in a pyramid
shape, with each level losing energy as it moves up, explained by the second law
of thermodynamics.
Assertion (A): Predation is an interaction where one organism
kills and eats another organism.
Reason (R): Predation plays a vital role in regulating
population sizes and maintaining ecological balance.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Predation helps control prey populations, ensuring
that no single species becomes too dominant in an ecosystem.