NCERT Class 11 Part 1 Chapter 15: Life on Earth YouTube Lecture Handouts

Glide to success with Doorsteptutor material for UGC : Get detailed illustrated notes covering entire syllabus: point-by-point for high retention.

Get video tutorial on: Examrace YouTube Channel

NCERT Class 11 Part 1 Geography Chapter 15: Life on Earth


  • Lithosphere
  • Atmosphere
  • Hydrosphere
  • Affected by atmospheric elements like temperature, rain, sunlight and moisture

Environment and Ecosystem

  • Environment – biotic and abiotic
  • Diversity brings in balance
  • Ecological systems – interaction of group of elements with abiotic factors within particular habitat result in energy flow and material cycling
  • Ecology made from oikos meaning “house” and logy “means” “study of” – Ernst Haeckal used term oekologie in 1869 – scientific study of interaction between life form and physical features
  • Habitat – totality of physical and chemical factors that constitute the environment
  • Ecological Adaptation – plants and animals get adapted through evolution

Types of Ecosystem

  • Ecosystem can be terrestrial and aquatic
  • Biome – plant and animal community covering large area and boundaries are set by climate – assemblage of plants and animals interacting in specific conditions
  • Examples – forest, grassland, desert and tundra
  • Aquatic – marine (ocean, coastal and coral reef) and freshwater (lakes, ponds, stream and bog)

Structure and Function of Ecosystem

  • Abiotic – temperature, train, humidity
  • Biotic – flora and fauna
  • Primary consumer, secondary consumer and decomposer
  • Food chain – detritus and grazing
  • Flow of energy
  • Food web

Types of Biomes

  • Forest – tropical (equatorial-acidic and poor in nutrient and deciduous-rich in nutrient) , temperate and boreal
  • Desert – hot dry, semiarid, coastal and cold
  • Aquatic – freshwater and marine
  • Grassland – tropical savanna (warm hot climate – thin humus) and temperate steppe (hot summer and cold winter – rich in bases)
  • Altitudinal – slope is major factor, temperature and precipitation vary

Biogeochemical Cycles

  • Sun as main source of energy, life starts with photosynthesis
  • Living organisms exist in various associations
  • Balance is maintained by cyclic passage of plant and animal tissues
  • Cyclic movement of chemical substance of biosphere between organism and environment
  • Cycle can be gaseous and sedimentary
  • Water cycle – hydrological cycle – precipitation, evaporation and condensation takes place

Carbon Cycle

A Carbon Cycle
  • Biosphere has half million carbon compounds
  • Start with photosynthesis; glucose many be converted sucrose, starch and cellulos
  • released by leaves
  • Oxygen Cycle
  • Oxygen generation – plants and sunlight
  • Oxygen consumption – respiration, decomposition, rusting and combustion

Nitrogen Cycle

A Nitrogen Cycle
  • 79 % of gases with amino acid, nucleic acid, protein, vitamin, pigments
  • 90 % of fixed nitrogen is biological. Nitrogen can only be used when fixed.
  • Can also be fixed by lightning and radiation; green plants can assimilate it
  • Dead plants excrete nitrogenous waste which is converted to nitrites and finally nitrates
  • From nitrate to free nitrogen is denitrification
  • Other Cycles are potassium, calcium, Sulphur and phosphorus – from mineral salts dissolved, weathering, sedimentation and death of organisms

Ecological Balance

  • State of dynamic equilibrium within community of organisms in a habitat
  • Gradual changes occur by natural succession
  • Competition and cooperation coexists
  • Balance attained by species dependent on food and sustenance
  • Clearing of forest brings changes; change is due to competition and called as succession
  • Ecological balance can be disturbed by new species, natural hazard and human interference – this can lead to calamities like landslides, disease and floods
  • Knowledge and understanding of factors provides a base for protection and conservation of ecosystem

Developed by: