Assertion (A): An ecosystem is a dynamic interaction between
biotic and abiotic components.
Reason (R): Abiotic components like temperature, light, and
water affect the distribution and survival of organisms in an ecosystem.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Ecosystems are dynamic because of the constant
interactions between biotic and abiotic factors, influencing the organisms'
distribution and survival.
Assertion (A): The primary producers in an ecosystem are the
plants and algae.
Reason (R): They are capable of converting solar energy into
chemical energy through photosynthesis.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Plants and algae are primary producers because
they can synthesize food through photosynthesis, which forms the base of the
energy flow in an ecosystem.
Assertion (A): Energy flows in an ecosystem in a unidirectional
manner.
Reason (R): The flow of energy is controlled by the second law
of thermodynamics, which states that energy decreases as it moves up trophic
levels.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Energy flows from producers to consumers in one
direction, and some energy is lost at each trophic level due to metabolic
processes, following the second law of thermodynamics.
Assertion (A): Decomposers play an important role in nutrient
cycling.
Reason (R): They break down dead organic matter into simple
inorganic substances, which are then available to plants.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Decomposers are essential for recycling nutrients,
converting dead organic matter into nutrients like nitrogen and phosphorus,
which plants can absorb.
Assertion (A): The producer in a forest ecosystem is primarily
responsible for the ecosystem’s productivity.
Reason (R): Producers capture solar energy through
photosynthesis and convert it into chemical energy.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Producers are the primary source of energy in any
ecosystem, as they convert solar energy into chemical energy, which supports all
other trophic levels.
Assertion (A): The number of trophic levels in an ecosystem is
limited.
Reason (R): The amount of energy decreases as it moves up
trophic levels, and insufficient energy is available to support many trophic
levels.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Energy loss at each trophic level limits the
number of trophic levels in an ecosystem, as higher levels have insufficient
energy to sustain many organisms.
Assertion (A): Biogeochemical cycles are crucial for
maintaining ecosystem stability.
Reason (R): These cycles recycle essential nutrients like
carbon, nitrogen, and phosphorus, making them available for organisms.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The cycling of nutrients ensures that essential
elements are continuously available for organisms, maintaining ecosystem
stability and productivity.
Assertion (A): The amount of biomass decreases as we move up
trophic levels in an ecosystem.
Reason (R): Energy is lost as heat during metabolic processes,
leading to less biomass at higher trophic levels.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Due to energy loss at each trophic level, the
amount of biomass decreases as we move from producers to higher consumers.
Assertion (A): The amount of energy passed from one trophic
level to the next is about 10%.
Reason (R): Energy is lost as heat, movement, and in metabolic
processes, limiting the amount transferred to the next trophic level.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: According to the 10% energy transfer rule, only
about 10% of the energy is passed on to the next trophic level, while the rest
is lost in various forms.
Assertion (A): A food web is a more realistic representation of
an ecosystem than a food chain.
Reason (R): In nature, organisms have multiple food sources and
are often part of multiple food chains.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: A food web accurately depicts the complex,
interconnected feeding relationships in an ecosystem, whereas a food chain
represents a linear sequence.
Assertion (A): The carbon cycle is a major biogeochemical cycle
in ecosystems.
Reason (R): Carbon is used by plants for photosynthesis and
released by animals during respiration.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The carbon cycle involves the movement of carbon
through various reservoirs, including the atmosphere, plants, animals, and soil,
and is essential for ecosystem functioning.
Assertion (A): The nitrogen cycle involves the process of
nitrogen fixation.
Reason (R): Nitrogen fixation is carried out by bacteria, which
convert atmospheric nitrogen into a usable form for plants.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Nitrogen fixation is the first step in the
nitrogen cycle, where nitrogen-fixing bacteria convert atmospheric nitrogen into
ammonia, making it available to plants.
Assertion (A): A pyramid of energy is always upright.
Reason (R): The energy available at each trophic level
decreases as we move up the pyramid due to energy loss.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The pyramid of energy is always upright because
the energy decreases at each trophic level, with producers having the most
energy and higher consumers having less.
Assertion (A): Primary productivity is the rate at which
producers in an ecosystem convert solar energy into chemical energy.
Reason (R): Primary productivity is influenced by environmental
factors such as temperature, light, and water availability.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Primary productivity reflects the efficiency of
producers in an ecosystem to convert solar energy into chemical energy,
influenced by abiotic factors like light and temperature.
Assertion (A): A pond is an example of a freshwater ecosystem.
Reason (R): Freshwater ecosystems are characterized by a low
concentration of dissolved salts.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: A pond is a freshwater ecosystem with minimal
dissolved salts, distinguishing it from marine ecosystems which have higher
salinity levels.
Assertion (A): A desert ecosystem is characterized by low
primary productivity.
Reason (R): Deserts have limited water availability and extreme
temperature conditions, which restrict plant growth.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Deserts have harsh conditions such as limited
water and extreme temperatures, which lead to low productivity compared to more
temperate ecosystems.
Assertion (A): Trophic efficiency refers to the percentage of
energy transferred from one trophic level to the next.
Reason (R): Trophic efficiency is typically around 10%, meaning
only 10% of the energy is passed to the next level.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Trophic efficiency is typically around 10% because
energy is lost during metabolism, movement, and heat generation at each trophic
level.
Assertion (A): In an aquatic ecosystem, the producers are
mostly phytoplankton.
Reason (R): Phytoplankton can photosynthesize and form the base
of the food chain in aquatic ecosystems.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Phytoplankton are the primary producers in aquatic
ecosystems, using sunlight to produce energy that supports higher trophic
levels.
Assertion (A): Ecosystem stability refers to an ecosystem's
ability to resist disturbances and return to its original state.
Reason (R): The resilience of an ecosystem is influenced by its
biodiversity and complexity.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Ecosystem stability is closely linked to
biodiversity and ecosystem complexity, which help an ecosystem recover from
disturbances.
Assertion (A): The water cycle is essential for maintaining the
balance in ecosystems.
Reason (R): Water is a necessary resource for all living
organisms, and its cycling ensures its continuous availability.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The water cycle ensures that water is continuously
recycled, making it available for plants and animals in ecosystems.
Assertion (A): In an aquatic ecosystem, light is a crucial
factor influencing primary productivity.
Reason (R): The availability of light determines the depth at
which photosynthesis can occur in water.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The depth of the photic zone, where light is
sufficient for photosynthesis, limits primary productivity in aquatic
ecosystems.
Assertion (A): A large population size ensures the stability of
an ecosystem.
Reason (R): Large populations can withstand environmental
fluctuations and disturbances better than small populations.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Larger populations have greater genetic diversity
and more resilience to environmental changes, contributing to the stability of
an ecosystem.
Assertion (A): In a forest ecosystem, the diversity of species
plays an important role in maintaining ecosystem balance.
Reason (R): Species diversity increases the interactions
between biotic components, leading to greater ecosystem productivity and
stability.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: A high level of species diversity ensures a more
complex food web and enhances ecosystem resilience.
Assertion (A): The net primary productivity (NPP) is always
lower than the gross primary productivity (GPP) in an ecosystem.
Reason (R): NPP represents the energy left after plants use
some of it for their own metabolism.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: GPP is the total energy captured by plants, while
NPP is the energy available for the next trophic level after the plant's own
energy requirements are subtracted.
Assertion (A): A detritus food chain is an example of
decomposers’ role in an ecosystem.
Reason (R): Detritus food chains begin with dead organic matter
and are dependent on decomposers for energy flow.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Detritus food chains depend on the decomposition
of dead organic matter, where decomposers like bacteria and fungi break it down.
Assertion (A): The species richness in an ecosystem generally
increases with habitat size.
Reason (R): Larger habitats provide more niches and resources
for different species.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Larger habitats can support more species by
offering more resources and niches, which leads to greater biodiversity.
Assertion (A): The primary consumers in an ecosystem are
herbivores.
Reason (R): Herbivores feed on plants, which are primary
producers in the ecosystem.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Herbivores feed directly on primary producers,
making them primary consumers in the food chain.
Assertion (A): A tropical rainforest is a highly productive
ecosystem.
Reason (R): Tropical rainforests receive abundant sunlight and
rainfall, which support high primary productivity.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The high levels of sunlight and rainfall in
tropical rainforests support lush vegetation and high primary productivity.
Assertion (A): The use of chemical pesticides can disturb the
ecological balance of an ecosystem.
Reason (R): Pesticides can kill non-target organisms, disrupt
food chains, and reduce biodiversity.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Pesticides can affect organisms beyond the
intended target, leading to a decline in biodiversity and disrupting food chains
in ecosystems.
Assertion (A): The amount of energy available in a system
decreases with each trophic level.
Reason (R): Energy is lost as heat during metabolism, so less
energy is available to higher trophic levels.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Energy is lost at each trophic level, and this
loss reduces the energy available to the next trophic level.
Assertion (A): The ecological succession leads to the
stabilization of an ecosystem over time.
Reason (R): Succession involves the gradual change in species
composition, resulting in a more stable community.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Ecological succession leads to a climax community
that is more stable and self-sustaining, reflecting the ecosystem's maturation.
Assertion (A): Primary succession occurs in a newly formed or
disturbed habitat, such as bare rock.
Reason (R): Primary succession begins with the colonization of
bare substrate by pioneer species like lichens.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Primary succession begins in areas with no
previous soil or life, and pioneer species initiate soil formation and
ecological development.
Assertion (A): The biosphere includes all living organisms and
the environment in which they live.
Reason (R): The biosphere consists of the lithosphere,
atmosphere, and hydrosphere, which support life.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The biosphere is the zone of life on Earth,
including land, air, and water, where organisms exist and interact.
Assertion (A): The energy pyramid represents the flow of energy
in an ecosystem.
Reason (R): The energy pyramid shows the decrease in energy as
it moves through the trophic levels.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The energy pyramid visualizes the decrease in
energy at each successive trophic level, with the largest amount of energy at
the producer level.
Assertion (A): An increase in biodiversity increases the
stability of an ecosystem.
Reason (R): Biodiversity enhances ecosystem resilience,
enabling it to recover from disturbances more quickly.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Greater biodiversity allows ecosystems to adapt to
changes and recover from disturbances, making them more stable.
Assertion (A): Nitrogen fixation is an essential process for
the nitrogen cycle.
Reason (R): Nitrogen-fixing bacteria convert atmospheric
nitrogen into a form usable by plants.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Nitrogen fixation is crucial because it makes
nitrogen available to plants in the form of ammonia, which is essential for
their growth.
Assertion (A): A carbon sink is any reservoir that stores
carbon.
Reason (R): Forests, oceans, and soil are examples of carbon
sinks that absorb more carbon than they release.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Carbon sinks like forests and oceans help mitigate
the effects of carbon dioxide in the atmosphere by absorbing more than they
release.
Assertion (A): The carbon cycle is essential for maintaining
the balance of carbon in ecosystems.
Reason (R): Carbon is continuously cycled between living
organisms, the atmosphere, and the Earth’s surface.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The carbon cycle ensures that carbon, a vital
element for life, is recycled within ecosystems, supporting plant and animal
growth.
Assertion (A): Energy flow in an ecosystem is unidirectional,
whereas matter is recycled.
Reason (R): Energy cannot be recycled due to its dissipation as
heat, but matter is reused in biogeochemical cycles.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Energy flows in one direction through trophic
levels, while matter (nutrients) is recycled through ecosystems in
biogeochemical cycles.
Assertion (A): An increase in the concentration of pollutants
in an ecosystem can lead to biomagnification.
Reason (R): Biomagnification occurs when pollutants accumulate
in organisms at higher trophic levels, becoming more concentrated.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Pollutants like pesticides and heavy metals
accumulate in the food chain, becoming more concentrated as they move up trophic
levels.
Assertion (A): Biotic factors play a more direct role in
shaping ecosystems than abiotic factors.
Reason (R): Biotic factors like species interactions directly
influence population dynamics and community structures.
Answer: (B) A is true, but R is false.
Explanation: While biotic factors influence ecosystems, abiotic
factors like temperature, sunlight, and water also play a crucial role in
determining ecosystem characteristics.
Assertion (A): In an aquatic ecosystem, the phytoplankton are
the primary producers.
Reason (R): Phytoplankton utilize sunlight to produce energy
through photosynthesis, forming the base of the food chain.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Phytoplankton are primary producers in aquatic
ecosystems, harnessing sunlight to produce organic compounds for higher trophic
levels.
Assertion (A): Decomposers play an important role in recycling
nutrients in an ecosystem.
Reason (R): Decomposers break down dead organic matter,
releasing nutrients back into the environment.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Decomposers like bacteria and fungi break down
organic matter, ensuring that nutrients are recycled and made available to
plants.
Assertion (A): The loss of biodiversity can lead to a decline
in ecosystem services.
Reason (R): A decrease in biodiversity can disrupt ecological
processes such as pollination, nutrient cycling, and climate regulation.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Biodiversity supports ecosystem services by
maintaining the processes that regulate climate, pollinate plants, and cycle
nutrients.
Assertion (A): Water is a vital resource in an ecosystem.
Reason (R): Water is necessary for the survival of all
organisms, and it regulates climate and supports metabolic functions.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Water is essential for life, supporting
biochemical processes, and is integral to the functioning of ecosystems.
Assertion (A): The energy flow in an ecosystem follows the 10%
law.
Reason (R): According to the 10% law, only 10% of the energy
from one trophic level is passed on to the next.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The 10% law states that only 10% of the energy is
transferred to the next trophic level, with the rest lost as heat.
Assertion (A): The ecological niche refers to the specific role
and position an organism has in its environment.
Reason (R): An organism's niche includes how it gets its food,
its habitat, and how it interacts with other species.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: An organism's niche defines its role in the
ecosystem, including its interactions with the environment and other organisms.
Assertion (A): The concept of a food chain is a simplified
representation of energy flow in an ecosystem.
Reason (R): A food chain shows the direct transfer of energy
from one trophic level to the next.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: A food chain represents a linear energy flow, but
ecosystems are more complex with interconnected food webs.
Assertion (A): Soil plays a significant role in maintaining
ecosystem functions.
Reason (R): Soil supports plant growth, provides nutrients, and
hosts a diverse range of organisms.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Soil is essential for plant growth and supports a
variety of organisms that contribute to nutrient cycling and ecosystem
productivity.
Assertion (A): The study of ecosystems requires an
understanding of both biotic and abiotic components.
Reason (R): Both biotic and abiotic components interact in a
dynamic way to shape ecosystems.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The interaction between living organisms (biotic)
and non-living factors (abiotic) determines the structure and function of
ecosystems.