Class 11 Geography Notes Chapter 15 (Life on the earth) – Fundamental of Physical Geography Book

Detailed Notes with MCQs of Chapter 15: Life on the Earth from our 'Fundamentals of Physical Geography' textbook. This chapter is crucial as it connects the physical environment we've studied so far with the living world, forming the basis of ecology and biogeography. Pay close attention, as these concepts frequently appear in various government examinations.

Chapter 15: Life on the Earth - Detailed Notes

1. Introduction: Ecology and Environment

• Ecology: The scientific study of the interactions between organisms and their physical (abiotic) environment. It examines how organisms are distributed, their abundance, and how they interact with each other and their surroundings.
  • Derived from the Greek words 'Oikos' (house/dwelling) and 'Logos' (study).
• Environment: Everything that surrounds an organism, including both living (biotic) and non-living (abiotic) components.
• Habitat: The specific physical place or environment where an organism or a biological population lives or occurs.

2. Ecological Systems (Ecosystems)

• Definition: An ecosystem is a functional unit of nature where living organisms (biotic components) interact among themselves and with the surrounding physical environment (abiotic components). It involves energy flow and nutrient cycling.

• Structure of Ecosystem:

  • Abiotic Components: Non-living parts.
    • Inorganic substances: Carbon, Nitrogen, Water, Oxygen, Calcium, Phosphorus, etc. involved in biogeochemical cycles.
    • Organic compounds: Proteins, Carbohydrates, Lipids – link biotic and abiotic components.
    • Climatic factors: Temperature, Light (energy source), Water (precipitation), Humidity, Wind.
    • Edaphic factors: Soil conditions (texture, structure, pH, mineral content).
  • Biotic Components: Living parts.
    • Producers (Autotrophs): Organisms that produce their own food, primarily through photosynthesis (e.g., green plants, algae, some bacteria). They form the base of the food chain.
    • Consumers (Heterotrophs): Organisms that obtain energy by feeding on other organisms.
      • Primary Consumers (Herbivores): Feed directly on producers (e.g., deer, grasshopper).
      • Secondary Consumers (Carnivores/Omnivores): Feed on primary consumers (e.g., fox, frog).
      • Tertiary Consumers (Top Carnivores/Omnivores): Feed on secondary consumers (e.g., lion, eagle).
      • Omnivores: Feed on both plants and animals (e.g., humans, bears).
    • Decomposers (Saprotrophs): Organisms that break down dead organic matter (detritus) from all trophic levels, returning nutrients to the soil (e.g., bacteria, fungi). Crucial for nutrient cycling.

• Functions of Ecosystem:

  • Energy Flow:
    • Unidirectional: Energy flows from the sun -> producers -> consumers -> decomposers. It is not recycled; energy is lost as heat at each transfer (follows the laws of thermodynamics).
    • Trophic Levels: Steps in the food chain where energy transfer occurs (Producer level, Primary consumer level, etc.). Only about 10% of energy is transferred from one trophic level to the next (10% Law).
  • Food Chain: A linear sequence of organisms where nutrients and energy are transferred as one organism eats another. (e.g., Grass -> Grasshopper -> Frog -> Snake -> Eagle).
  • Food Web: A network of interconnected food chains within an ecosystem, representing more realistic feeding relationships. Provides stability to the ecosystem.
  • Ecological Pyramids: Graphical representation of the relationship between different trophic levels in terms of numbers, biomass, or energy.
    • Pyramid of Numbers: Shows the number of individual organisms at different trophic levels. Usually upright (broad base of producers), but can be inverted (e.g., single large tree supporting many insects).
    • Pyramid of Biomass: Shows the total dry weight (biomass) of organisms at each trophic level. Usually upright in terrestrial ecosystems, but often inverted in aquatic ecosystems (phytoplankton biomass is less than zooplankton).
    • Pyramid of Energy: Shows the amount of energy flow at each trophic level. Always upright because energy is lost at each transfer.
  • Nutrient Cycling (Biogeochemical Cycles): The movement of essential elements (like Carbon, Nitrogen, Water, Phosphorus) through the biotic and abiotic components of an ecosystem.

3. Types of Ecosystems

• Terrestrial Ecosystems: Land-based (e.g., Forests, Grasslands, Deserts, Tundra).
• Aquatic Ecosystems: Water-based.
  • Freshwater: Ponds, Lakes, Rivers, Wetlands.
  • Marine: Oceans, Estuaries, Coral Reefs.

4. Biogeochemical Cycles

• The cyclical movement of chemical elements between organisms (bio) and the physical environment (geo). Essential for sustaining life.
• Water Cycle (Hydrological Cycle): Evaporation, Transpiration, Condensation, Precipitation, Runoff, Infiltration. Driven by solar energy.
• Carbon Cycle:
  • Carbon is the basis of organic molecules.
  • Reservoirs: Atmosphere (CO2), Oceans (dissolved CO2, carbonates), Fossil fuels, Rocks (limestone), Living organisms.
  • Processes: Photosynthesis (removes CO2), Respiration (releases CO2), Decomposition (releases CO2), Combustion (releases CO2), Ocean absorption/release.
• Oxygen Cycle:
  • Interlinked with Carbon and Water cycles.
  • Reservoirs: Atmosphere (O2), Lithosphere (oxides), Water (H2O).
  • Processes: Photosynthesis (releases O2), Respiration (consumes O2), Combustion (consumes O2), Decomposition (consumes O2), Photolysis of water vapour.
• Nitrogen Cycle:
  • Nitrogen is essential for proteins and nucleic acids. Atmospheric N2 (78%) is unusable by most organisms directly.
  • Processes:
    • Nitrogen Fixation: Conversion of atmospheric N2 into usable forms (ammonia, nitrates) by lightning, industrial processes, and nitrogen-fixing bacteria (e.g., Rhizobium in root nodules of legumes).
    • Nitrification: Conversion of ammonia to nitrites and then nitrates by nitrifying bacteria.
    • Assimilation: Uptake of nitrates/ammonia by plants.
    • Ammonification: Decomposition of organic matter back to ammonia by decomposers.
    • Denitrification: Conversion of nitrates back to gaseous N2 by denitrifying bacteria, returning it to the atmosphere.

5. Ecological Balance

• A state of dynamic equilibrium within a community of organisms where genetic, species, and ecosystem diversity remain relatively stable, subject to gradual changes through natural succession.
• Maintained by checks and balances: predator-prey relationships, competition, nutrient cycling, energy flow.
• Human activities (deforestation, pollution, introduction of invasive species, climate change) can severely disrupt ecological balance.

6. Biomes

• Definition: Large, distinct terrestrial regions characterized by similar climate (temperature, precipitation), soil, and dominant plant and animal communities. They are essentially large-scale ecosystems.

• Major Terrestrial Biomes:

  • Tropical Rainforest: High temperature, high rainfall throughout the year. Dense, multi-layered vegetation, extremely high biodiversity. (Amazon Basin, Congo Basin, Southeast Asia).
  • Tropical Deciduous Forest (Monsoon Forest): High temperature, seasonal rainfall (distinct wet and dry seasons). Trees shed leaves in the dry season. (India, Southeast Asia).
  • Temperate Evergreen Forest: Moderate temperature, adequate rainfall. Dominated by evergreen trees (needle-leaf or broad-leaf depending on location). (Mediterranean regions, parts of USA, China).
  • Temperate Deciduous Forest: Moderate temperature, distinct seasons (warm summer, cold winter), adequate rainfall. Broad-leaf deciduous trees (oak, maple). (Eastern USA, Western Europe, East Asia).
  • Boreal Forest (Taiga): Cold climate, long winters, short summers, moderate precipitation (mostly snow). Dominated by coniferous evergreen trees (pine, spruce, fir). (Canada, Siberia, Scandinavia).
  • Tundra: Extremely cold, low precipitation, permafrost (permanently frozen subsoil). Treeless, dominated by mosses, lichens, dwarf shrubs. Short growing season. (Arctic regions, high mountain tops - Alpine Tundra).
  • Tropical Grassland (Savanna): High temperature, distinct wet and dry seasons, seasonal rainfall insufficient for forests. Grasses with scattered trees. (Africa, parts of South America, Australia).
  • Temperate Grassland (Steppe/Prairie/Pampas/Veld): Moderate temperature, low to moderate rainfall, cold winters, warm summers. Dominated by grasses, few trees. (Central North America, Eurasia, South America, South Africa).
  • Desert (Hot and Cold): Very low precipitation (arid/semi-arid). Can be hot (Sahara, Thar) or cold (Gobi, Ladakh). Sparse, drought-adapted vegetation (succulents, shrubs) and nocturnal animals.

• Aquatic Biomes: Categorized based on salinity.

  • Freshwater: Lakes, ponds, rivers, streams, wetlands.
  • Marine: Oceans, coral reefs, estuaries.

7. Biodiversity and Conservation (Brief mention as per NCERT Ch 15 focus)

• Biosphere: The part of Earth where life exists – includes parts of the lithosphere, hydrosphere, and atmosphere. It's the sum of all ecosystems.
• The variety and variability of life forms within a given ecosystem, biome, or the entire Earth is crucial for ecological stability and provides essential resources (food, medicine, ecological services).
• Conservation efforts are needed to protect biodiversity from threats like habitat loss, pollution, climate change, and overexploitation.

Multiple Choice Questions (MCQs)

1. Which term describes the study of interactions between organisms and their physical environment?
   a) Biography
   b) Ecology
   c) Geology
   d) Hydrology

2. In an ecosystem, green plants are categorized as:
   a) Primary Consumers
   b) Decomposers
   c) Producers
   d) Secondary Consumers

3. Energy flow in an ecosystem is:
   a) Bidirectional
   b) Multidirectional
   c) Unidirectional
   d) Cyclical

4. Which biogeochemical cycle involves processes like Nitrogen Fixation, Nitrification, and Denitrification?
   a) Carbon Cycle
   b) Water Cycle
   c) Oxygen Cycle
   d) Nitrogen Cycle

5. A biome characterized by high temperatures, high rainfall throughout the year, and dense, multi-layered vegetation is:
   a) Savanna
   b) Tropical Rainforest
   c) Tundra
   d) Temperate Deciduous Forest

6. Which ecological pyramid is always upright?
   a) Pyramid of Numbers
   b) Pyramid of Biomass
   c) Pyramid of Energy
   d) Both a and b

7. Organisms that break down dead organic matter are known as:
   a) Autotrophs
   b) Herbivores
   c) Carnivores
   d) Decomposers (Saprotrophs)

8. The process by which atmospheric nitrogen (N2) is converted into usable ammonia (NH3) is called:
   a) Denitrification
   b) Nitrification
   c) Nitrogen Fixation
   d) Ammonification

9. A network of interconnected food chains within an ecosystem is called a:
   a) Trophic Level
   b) Food Web
   c) Ecological Pyramid
   d) Biome

10. Which of the following is an Abiotic component of an ecosystem?
    a) Bacteria
    b) Plants
    c) Temperature
    d) Fungi

Answer Key for MCQs:

1. b) Ecology
2. c) Producers
3. c) Unidirectional
4. d) Nitrogen Cycle
5. b) Tropical Rainforest
6. c) Pyramid of Energy
7. d) Decomposers (Saprotrophs)
8. c) Nitrogen Fixation
9. b) Food Web
10. c) Temperature

Make sure you understand these concepts thoroughly. Refer back to the textbook for diagrams and further details. Remember, understanding the interconnections between the physical environment and life is key. Good luck with your preparation!