📝 Chapter Notes & Revision

Ecosystem

🏫 MP BoardClass 12Biology

📐 Formula & Cheat Sheet (English)

Quick Revision Notes: Ecosystem

Class: 12th Biology (MP Board)

1. Introduction to Ecosystem

  • Ecosystem: A functional unit of nature where living organisms (biotic components) interact among themselves and with the physical environment (abiotic components).
  • Term coined by: A.G. Tansley (1935).
  • Types of Ecosystems:
    • Natural: Forest, grassland, desert (Terrestrial); Pond, lake, wetland, estuary, ocean (Aquatic).
    • Artificial (Man-made): Crop fields, aquarium.

2. Ecosystem Structure and Function

The interaction of biotic and abiotic components results in a physical structure that is characteristic for each type of ecosystem.

  • Abiotic Components: Light, temperature, water, soil, minerals, and atmospheric gases.
  • Biotic Components:
    • Producers (Autotrophs): Green plants, algae, cyanobacteria. They trap solar energy.
    • Consumers (Heterotrophs): Animals that feed on plants or other animals.
      • Primary Consumers (Herbivores): Cow, rabbit, grasshopper.
      • Secondary Consumers (Primary Carnivores): Frog, fox.
      • Tertiary Consumers (Top Carnivores): Lion, tiger, eagle.
    • Decomposers (Saprotrophs): Fungi and bacteria. They break down dead organic matter (detritus).

3. Key Ecological Processes (Functional Aspects)

  1. Productivity: Rate of biomass production.
  2. Decomposition: Breakdown of complex organic matter into inorganic substances.
  3. Energy Flow: Unidirectional movement of energy through trophic levels.
  4. Nutrient Cycling: Movement of nutrient elements through the biotic and abiotic components.

4. Productivity

  • Primary Productivity: Amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. Expressed as g^-2 yr^-1 or kcal m^-2 yr^-1.
    • Gross Primary Productivity (GPP): Total rate of photosynthesis and total organic matter produced.
    • Net Primary Productivity (NPP): GPP minus respiration losses (R).
      • NPP = GPP - R (Important Formula)
      • Note: NPP is the available biomass for consumption to heterotrophs (herbivores and decomposers).
  • Secondary Productivity: Rate of assimilation of food energy by consumers.

5. Decomposition

The process of breaking down complex organic matter into inorganic substances like carbon dioxide, water, and nutrients.

  • Detritus: Raw material for decomposition (dead remains of plants and animals, including faecal matter).
  • Steps of Decomposition:
    1. Fragmentation: Detritivores (e.g., earthworms) break detritus into smaller particles.
    2. Leaching: Water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
    3. Catabolism: Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.
    4. Humification: Leads to accumulation of a dark-colored amorphous substance called Humus. Humus is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.
    5. Mineralisation: The humus is further degraded by some microbes and release of inorganic nutrients is released.

6. Energy Flow

  • Energy from the sun flows in a unidirectional manner (Sun $\rightarrow$ Producers $\rightarrow$ Consumers $\rightarrow$ Decomposers).
  • 10% Law (Lindeman's Law): Only 10% of the energy is transferred from one trophic level to the next. The remaining 90% is lost to the environment as heat during respiration.
    • Example: If Producers have 1000 J, Primary Consumers get 100 J, Secondary get 10 J, and Tertiary get 1 J.

7. Ecological Pyramids

Graphical representation of trophic levels in an ecosystem based on number, biomass, or energy.

  1. Pyramid of Number: Can be upright (grassland ecosystem) or inverted (tree ecosystem / parasitic food chain).
  2. Pyramid of Biomass:
    • Usually upright in terrestrial ecosystems (mass of producers > mass of consumers).
    • Inverted in aquatic ecosystems (mass of phytoplankton < mass of zooplankton, as phytoplankton reproduce and turnover very fast).
  3. Pyramid of Energy: Always upright, because energy flow is unidirectional and decreases at every successive trophic level.

8. Ecological Succession

The gradual and predictable change in the species composition of a given area over a period of time.

  • Pioneer Species: The first species to colonize a bare area (e.g., lichens on rocks).
  • Climax Community: The final stable community that is in near equilibrium with the environment.
  • Types:
    • Primary Succession: Starts where no living organisms ever existed (e.g., bare rock, cooled lava). Very slow.
    • Secondary Succession: Starts in areas that have lost all the previous living organisms (e.g., abandoned farm lands, burned or cut forests). Faster than primary succession.
  • Hydrarch Succession: Takes place in wetter areas and progresses from hydric to mesic conditions.
  • Xerarch Succession: Takes place in dry areas and progresses from xeric to mesic conditions.

9. Nutrient Cycling (Biogeochemical Cycles)

Movement of nutrient elements through the various components of an ecosystem.

  • Types of Cycles:
    • Gaseous Cycles: Reservoir exists in the atmosphere (e.g., Nitrogen, Carbon cycle).
    • Sedimentary Cycles: Reservoir exists in Earth's crust/soil (e.g., Phosphorus, Sulphur cycle).
  • Carbon Cycle:
    • Mainly through photosynthesis and respiration.
    • Ocean stores vast amounts of carbon.
  • Phosphorus Cycle:
    • Rocks are the primary natural reservoir of phosphorus.
    • Does not have a significant gaseous phase in the atmosphere.