Class 11 Geography: Life on the Earth (Biosphere)
A. Multiple Choice Questions (MCQs) - 1 Mark Each (Total: 15 Marks)
The narrow zone of contact between the lithosphere, hydrosphere, and atmosphere, where life exists, is called the:
a) Stratosphere
b) Biosphere
c) Mesosphere
d) Troposphere
Answer: b) Biosphere
Hint: This is the realm of living organisms.
Rationale: The biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, hydrosphere, and atmosphere.
Which of the following forms the base of almost all food chains in an ecosystem?
a) Primary Consumers
b) Decomposers
c) Producers
d) Tertiary Consumers
Answer: c) Producers
Hint: These organisms create their own food.
Rationale: Producers (autotrophs), primarily green plants and algae, synthesize their own food through photosynthesis, forming the base of the food chain from which all other organisms derive energy.
In an ecosystem, bacteria and fungi primarily act as:
a) Producers
b) Primary Consumers
c) Secondary Consumers
d) Decomposers
Answer: d) Decomposers
Hint: Their role involves breaking down dead organic matter.
Rationale: Decomposers (saprotrophs) like bacteria and fungi break down dead organic matter and waste products, returning nutrients to the soil and atmosphere for reuse by producers.
Which biogeochemical cycle involves the conversion of atmospheric nitrogen into usable forms by bacteria in the soil?
a) Carbon Cycle
b) Oxygen Cycle
c) Nitrogen Cycle
d) Water Cycle
Answer: c) Nitrogen Cycle
Hint: This cycle is crucial for plant growth and involves atmospheric fixation.
Rationale: The Nitrogen Cycle involves processes like nitrogen fixation, where atmospheric nitrogen is converted into ammonia by certain bacteria, making it available for plants.
The total variety of life on Earth, at all its levels, is termed as:
a) Ecosystem
b) Biome
c) Biodiversity
d) Habitat
Answer: c) Biodiversity
Hint: This term encompasses genetic, species, and ecosystem diversity.
Rationale: Biodiversity refers to the variety of life on Earth at all its levels, from genes to ecosystems, including the ecological and evolutionary processes that sustain it.
Which of the following is NOT an abiotic component of an ecosystem?
a) Sunlight
b) Water
c) Plants
d) Soil
Answer: c) Plants
Hint: Abiotic components are non-living.
Rationale: Plants are living organisms and thus are biotic components. Sunlight, water, and soil are non-living (abiotic) components.
The flow of energy in an ecosystem is generally:
a) Cyclic
b) Unidirectional
c) Random
d) Downwards
Answer: b) Unidirectional
Hint: Energy moves from one trophic level to the next without returning.
Rationale: Energy flows from producers to consumers (herbivores, carnivores) and eventually to decomposers. A significant portion of energy is lost as heat at each trophic level, making the flow unidirectional.
Which of the following greenhouse gases is primarily released by the burning of fossil fuels?
a) Methane (CH 4 )
b) Nitrous Oxide (N 2O)
c) Carbon Dioxide (CO 2)
d) Water Vapor (H 2 O)
Answer: c) Carbon Dioxide (CO 2 )
Hint: This gas is a major product of combustion.
Rationale: Carbon dioxide is the primary greenhouse gas released into the atmosphere from the combustion of fossil fuels (coal, oil, natural gas) for energy.
Areas characterized by specific climate conditions and distinct vegetation types, such as grasslands or tropical rainforests, are called:
a) Habitats
b) Niches
c) Biomes
d) Communities
Answer: c) Biomes
Hint: These are large ecological regions defined by dominant plant and animal life.
Rationale: Biomes are large geographical areas characterized by similar climate, soil, plants, and animals, representing major ecological communities on Earth.
The process by which green plants convert light energy into chemical energy, creating their own food, is known as:
a) Respiration
b) Transpiration
c) Photosynthesis
d) Decomposition
Answer: c) Photosynthesis
Hint: This is the fundamental process of energy capture in producers.
Rationale: Photosynthesis is the biochemical process by which producers (plants, algae, cyanobacteria) use sunlight, water, and carbon dioxide to create glucose (food) and oxygen.
What is meant by 'Ecological Balance'?
a) The number of species in an ecosystem.
b) The stability of an ecosystem over time.
c) The complete absence of human interference.
d) The rate of energy flow in a food web.
Answer: b) The stability of an ecosystem over time.
Hint: It refers to the state where species populations and their environment are relatively stable.
Rationale: Ecological balance refers to a state of dynamic equilibrium within a community of organisms where species populations remain relatively stable, responding to environmental changes without major shifts or collapses.
Which of the following human activities directly leads to a significant loss of biodiversity?
a) Sustainable agriculture
b) Protected area establishment
c) Deforestation
d) Recycling programs
Answer: c) Deforestation
Hint: This activity directly destroys habitats.
Rationale: Deforestation involves the clearing of forests for other land uses, leading to habitat loss, fragmentation, and direct destruction of species, thus significantly contributing to biodiversity loss.
The role or function of a species within an ecosystem, including what it eats and how it interacts with other species, is its:
a) Habitat
b) Community
c) Niche
d) Biome
Answer: c) Niche
Hint: This is often described as a species' 'profession' in its environment.
Rationale: A species' niche describes its specific role, adaptations, and interactions within its ecosystem, encompassing its use of resources and its interactions with other species.
The largest reservoir of carbon on Earth is found in:
a) The atmosphere
b) Oceans
c) Plants and animals
d) Fossil fuels
Answer: b) Oceans
Hint: This massive body of water acts as a huge carbon sink.
Rationale: Oceans hold the largest active reservoir of carbon on Earth, largely in dissolved inorganic carbon, which constantly exchanges with the atmosphere. Fossil fuels represent a large, but largely sequestered, reservoir until extracted.
What is the ultimate source of energy for almost all ecosystems on Earth?
a) Geothermal energy
b) Solar energy
c) Chemical energy
d) Tidal energy
Answer: b) Solar energy
Hint: Think about where producers get their energy.
Rationale: Sunlight is the ultimate source of energy for most ecosystems, as producers (plants, algae) convert solar energy into chemical energy through photosynthesis, which then flows through the food chain.
B. Short Answer Questions (2-3 Marks Each) - (Total: 20-30 Marks)
Define 'ecosystem' and list its two main components.
Answer: An ecosystem is a community of living organisms (biotic components) interacting with their non-living physical environment (abiotic components) as a functional unit. Its two main components are Biotic Components (e.g., producers, consumers, decomposers) and Abiotic Components (e.g., sunlight, water, temperature, soil, air).
Explain the concept of 'Trophic Levels' in a food chain.
Answer: Trophic levels describe the position an organism occupies in a food chain. Energy flows upwards from one level to the next. The main trophic levels are:
Producers (autotrophs, e.g., plants) at the base.
Primary Consumers (herbivores, e.g., deer) feeding on producers.
Secondary Consumers (carnivores, e.g., wolf) feeding on primary consumers.
Tertiary Consumers (top carnivores, e.g., tiger) feeding on secondary consumers.
Decomposers act on all levels.
Briefly describe the role of decomposers in an ecosystem.
Answer: Decomposers (primarily bacteria and fungi) play a crucial role in an ecosystem by breaking down dead organic matter (dead plants, animals, and waste products). This process releases inorganic nutrients back into the soil, water, and atmosphere, making them available for uptake by producers. Without decomposers, nutrient cycling would cease, and dead material would accumulate.
What is 'Biodiversity'? State two reasons why it is important.
Answer: Biodiversity refers to the total variety of life on Earth, encompassing genetic diversity (within a species), species diversity (number and abundance of different species), and ecosystem diversity (variety of habitats and ecological communities).
Importance 1: Provides essential ecosystem services like oxygen production, water purification, soil fertility, pollination, and climate regulation.
Importance 2: Source of food, medicine, raw materials, and genetic resources for agriculture and industry. It also holds aesthetic and cultural value.
Explain the concept of 'Ecological Balance'.
Answer: Ecological balance refers to a state of dynamic equilibrium within an ecosystem, where the populations of different species remain relatively stable over time, and the abiotic components also show relative stability. It implies a harmonious relationship between biotic and abiotic factors, allowing the ecosystem to sustain itself and perform its functions without drastic changes, even while adapting to minor disturbances.
How do human activities contribute to the increase of carbon dioxide in the atmosphere?
Answer: Human activities primarily increase atmospheric carbon dioxide (CO 2) through:
Burning of Fossil Fuels: Combustion of coal, oil, and natural gas for energy production (electricity, transport, industry) releases large amounts of stored carbon as CO 2.
Deforestation: Forests act as carbon sinks, absorbing CO 2. Cutting down and burning trees releases the stored carbon back into the atmosphere and reduces the Earth's capacity to absorb future CO 2.
Differentiate between a food chain and a food web.
Answer: A food chain is a simple, linear sequence showing how energy is transferred from one organism to another, starting from a producer and moving through different trophic levels (e.g., grass -> deer -> wolf). A food web is a more complex and realistic representation, consisting of interconnected food chains within an ecosystem. It shows that most organisms consume or are consumed by more than one type of organism, illustrating the multiple pathways of energy flow.
What is the significance of the Oxygen Cycle for life on Earth?
Answer: The Oxygen Cycle is vital because oxygen is essential for the respiration of most living organisms (animals, humans, plants at night). It also forms the ozone layer (O3) in the stratosphere, which protects life from harmful ultraviolet radiation. The cycle maintains the balance of oxygen in the atmosphere, primarily through photosynthesis (which releases oxygen) and respiration/combustion (which consume oxygen).
Define a 'Biome' and give two examples of terrestrial biomes.
Answer: A Biome is a large geographical area characterized by specific climate conditions (temperature and precipitation) that support a distinct type of vegetation and associated animal life. It is essentially a large ecological region.
Two examples of terrestrial biomes are:
Tropical Rainforest: Characterized by high temperatures and abundant rainfall year-round, leading to dense, multi-layered vegetation and high biodiversity.
Desert: Characterized by extremely low precipitation, high diurnal temperature ranges, and sparse, drought-adapted vegetation (e.g., cacti, succulents).
Explain how 'Transpiration' is linked to the water cycle.
Answer: Transpiration is the process by which water vapor is released from plants, primarily through their leaves, into the atmosphere. It is a significant component of the water cycle, acting as a major pathway for water to move from the land surface back into the atmosphere, contributing to atmospheric humidity and cloud formation, similar to evaporation from water bodies.
C. Long Answer Questions (5-6 Marks Each) - (Total: 10-12 Marks)
Describe the Carbon Cycle in detail, explaining its various reservoirs and the processes involved in the movement of carbon. Discuss the human impact on this cycle.
Answer:
The Carbon Cycle is a biogeochemical cycle that describes the movement of carbon through the Earth's atmosphere, oceans, land, and living organisms. Carbon is a fundamental building block of all organic life.
Major Carbon Reservoirs:
Atmosphere: Carbon exists primarily as carbon dioxide (CO 2), and also as methane (CH 4 ).
Oceans: The largest active reservoir, containing dissolved CO 2 , carbonic acid, and carbonate ions. It also includes marine life and sediments.
Land (Terrestrial Biosphere): Stored in living organisms (plants, animals), dead organic matter in soils (humus), and biomass.
Lithosphere (Earth's Crust): Vast amounts of carbon stored over geological timescales in sedimentary rocks (e.g., limestone) and fossil fuels (coal, oil, natural gas).
Processes Involved in Carbon Movement:
Photosynthesis: The primary process by which carbon moves from the atmosphere to the biosphere. Green plants (producers) absorb atmospheric CO2(or dissolved CO 2 in water) and convert it into organic compounds (sugars) using sunlight.
CO 2 + Water + Light Energy → Glucose + Oxygen
Respiration: All living organisms (plants, animals, microbes) release CO2 back into the atmosphere (or water) through cellular respiration as they break down organic compounds for energy.
Glucose + Oxygen → CO 2+ Water + Energy
Decomposition: Decomposers (bacteria and fungi) break down dead organic matter, releasing CO 2(and CH 4 in anaerobic conditions) into the atmosphere and contributing to soil carbon.
Ocean Absorption and Release: Oceans absorb CO2 from the atmosphere (carbonic acid formation), and release it when water warms or due to biological processes. Marine organisms use dissolved carbon to build shells and skeletons, which eventually form sedimentary rocks like limestone on the ocean floor.
Sedimentation and Burial: Over geological time, dead organic matter can be buried and compressed, forming fossil fuels (coal, oil, gas) or incorporated into sedimentary rocks. This sequesters carbon away from the active cycle.
Volcanic Activity: Volcanoes release CO 2 into the atmosphere, derived from the Earth's interior.
Human Impact on the Carbon Cycle:
Human activities have significantly altered the natural carbon cycle, leading to an imbalance:
Burning of Fossil Fuels: The combustion of coal, oil, and natural gas for electricity generation, transportation, and industry releases vast amounts of carbon (that was stored for millions of years) rapidly into the atmosphere as CO 2 . This is the largest anthropogenic source of atmospheric CO 2
.
Deforestation and Land-Use Change: Clearing forests for agriculture, urbanization, or timber removes significant carbon sinks. Burning trees also releases stored carbon. This reduces the Earth's capacity to absorb atmospheric CO 2 .
Industrial Processes: Some industrial processes (e.g., cement production) also release CO 2.
The increased concentration of CO2 in the atmosphere due to these human activities enhances the greenhouse effect, leading to global warming and climate change, with far-reaching environmental consequences.
2-What is biodiversity? Discuss its different levels and explain the major threats to biodiversity caused by human activities.
Answer:
Biodiversity (or biological diversity) is the total variety of life on Earth. It encompasses the variability among living organisms from all sources, including terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they are part. This includes diversity within species, between species, and of ecosystems.
Levels of Biodiversity:
Genetic Diversity: This refers to the variation in genes within a single species. It allows species to adapt to changing environments and diseases. A species with high genetic diversity is more resilient than one with low genetic diversity.
Example: Different varieties of rice (basmati, japonica, indica) or different breeds of dogs (Poodle, Bulldog, German Shepherd) within the species Canis familiaris.
Species Diversity: This refers to the variety of different species within a particular region or ecosystem. It is often measured by the number of species (species richness) and the relative abundance of those species (species evenness).
Example: A tropical rainforest has higher species diversity than a desert or a tundra biome.
Ecosystem Diversity: This refers to the variety of different habitats, communities, and ecological processes within a given area or across the planet. It involves the diversity of biomes (forests, grasslands, wetlands, oceans, deserts) and the complex interactions between their biotic and abiotic components.
Example: A region containing forests, rivers, grasslands, and mountains exhibits high ecosystem diversity.
Major Threats to Biodiversity Caused by Human Activities:
Human activities are the primary drivers of biodiversity loss, leading to what is often referred to as the 'sixth mass extinction'. The major threats include:
Habitat Loss and Fragmentation: This is the single greatest threat. As human populations expand, natural habitats are destroyed or broken into smaller, isolated patches for agriculture, urbanization, infrastructure development (roads, dams), and resource extraction (mining, logging). This reduces the space available for species, isolates populations, and disrupts ecosystems.
Example: Clearing of tropical rainforests for cattle ranching or palm oil plantations leads to the immediate loss of countless species.
Pollution: Environmental pollution from various sources contaminates air, water, and soil, harming organisms and ecosystems.
Examples: Industrial effluents and agricultural runoff (pesticides, fertilizers) pollute aquatic ecosystems, leading to eutrophication and dead zones. Plastic pollution in oceans harms marine life. Air pollution (acid rain) damages forests and aquatic systems.
Overexploitation: Unsustainable harvesting of resources, such as overfishing, overhunting, illegal poaching, and excessive logging, can deplete species populations faster than they can reproduce, leading to decline or extinction.
Example: Depletion of fish stocks due to commercial overfishing, or the near extinction of rhinos due to poaching for their horns.
Invasive Alien Species: The introduction of non-native (alien) species into new environments, either accidentally or intentionally, can disrupt native ecosystems. Invasive species often outcompete native species for resources, prey on them, or introduce diseases, leading to population declines and extinctions of native species.
Example: The introduction of water hyacinth (an aquatic plant) has choked many native aquatic ecosystems in tropical regions.
Climate Change: Human-induced climate change (primarily from greenhouse gas emissions) alters global temperatures, precipitation patterns, and sea levels. This forces species to adapt or migrate, but many cannot cope with the rapid changes, leading to habitat shifts, reduced reproductive success, and increased extinction risk.
Examples: Coral bleaching due to rising ocean temperatures, melting polar ice affecting polar bear habitats, and shifts in species distribution.
Co-extinctions: The extinction of one species can lead to the extinction of another species that depends on it (e.g., a specific pollinator or parasite).
Addressing these threats requires a combination of conservation efforts, sustainable resource management, policy changes, and global cooperation.
