🌸Chapter 12
Ecosystem
(Summary Notes)
1. Ecosystem – Definition
Ecosystem: Functional unit of nature where living organisms (biotic)
interact with non-living components (abiotic) to maintain energy flow
and nutrient cycling.
Examples: Forest, pond, grassland, desert, ocean.
Components of Ecosystem:
|
Component |
Definition |
Examples |
|
Biotic |
Living components |
Producers (plants, phytoplankton), Consumers (herbivores,
carnivores, omnivores), Decomposers (bacteria, fungi) |
|
Abiotic |
Non-living components |
Sunlight, water, soil, air, temperature |
NCERT Keywords: Functional unit, interactions, energy flow, nutrient
cycling.
2. Producers, Consumers, Decomposers
Producers (Autotrophs):
- Make their own food via photosynthesis.
- Examples: Grass, phytoplankton.
- Form base of food chain.
Consumers (Heterotrophs):
- Depend on producers or other
consumers for food.
- Types:
- Primary: Herbivores (Grasshopper, Cow)
- Secondary: Carnivores (Frog, Snake)
- Tertiary: Top carnivores (Hawk, Tiger)
- Omnivores: Eat both plants and animals
(Humans)
Decomposers:
- Break down dead organic matter
into inorganic nutrients.
- Examples: Fungi, Bacteria
- Role: Nutrient recycling, soil
fertility, energy flow.
Keywords: Autotroph, herbivore, carnivore, omnivore, nutrient
recycling.
3. Food Chain, Food Web, and Trophic
Levels
Food Chain: Linear energy flow
Example: Grass → Grasshopper → Frog → Snake → Hawk
Food Web: Interconnected food chains
Example: Grass → Grasshopper → Frog → Snake → Hawk; Grass → Rabbit → Fox
→ Hawk
Trophic Levels:
1.
Producers
2.
Primary
Consumers
3.
Secondary
Consumers
4.
Tertiary
Consumers
5.
Decomposers
10% Law of Energy Transfer: Only 10% energy is passed to next
trophic level; 90% lost as heat.
Keywords: Energy flow, trophic levels, 10% law.
4. Ecological Pyramids
|
Pyramid Type |
Definition |
Example |
Shape |
|
Number |
Shows number of organisms |
Tree → Insects |
Can be inverted |
|
Biomass |
Total biomass at each level |
Pond: Phytoplankton → Zooplankton |
Can be inverted |
|
Energy |
Energy content at each level |
Grassland |
Always upright |
Keywords: Biomass, inverted pyramid, energy pyramid, upright.
Diagram – Pyramid of Energy:
Tertiary Consumer (Hawk) ──► 1 kcal
Secondary Consumer (Snake) ──► 10 kcal
Primary Consumer (Grasshopper) ──► 100
kcal
Producer (Grass) ──► 1000 kcal
5. Ecological Succession
Definition: Gradual, predictable change in species composition over
time.
Types:
1.
Primary
Succession:
Starts on bare rock (no soil)
o Example: Lichen → Moss → Grass →
Shrubs → Trees → Climax
o Pioneer species: Lichens, Mosses
2.
Secondary
Succession:
Soil present after disturbance
o Example: Abandoned farmland → Grass
→ Shrubs → Trees → Climax
Climax Community: Stable, mature community; maintains biodiversity and
nutrient cycling.
Terms:
- Sere: Stage in succession
- Seral Community: Transitional stage
- Pioneer Species: First colonizers
Keywords: Succession, climax community, pioneer species, sere, seral
community.
Diagram – Primary Succession:
Bare Rock → Lichens → Moss → Grass →
Shrubs → Trees → Climax Forest
6. Biogeochemical Cycles
Carbon Cycle
- Pathway: Atmosphere CO₂ →
Photosynthesis → Plants → Animals → Respiration/Decomposition → CO₂
- Human Impact: Fossil fuel burning → ↑ CO₂ →
Global warming
Nitrogen Cycle
- Processes: Nitrogen fixation,
Nitrification, Assimilation, Ammonification, Denitrification
- Bacteria: Rhizobium (legumes),
Nitrosomonas, Nitrobacter
Phosphorus Cycle
- No gaseous phase
- Rocks → Soil → Plants → Animals
→ Decomposers → Soil
Hydrological Cycle
- Evaporation → Condensation →
Precipitation → Runoff → Groundwater → Oceans
Keywords: Nitrogen fixation, nitrification, ammonification,
denitrification, decomposition, nutrient cycling.
7. Human Impacts on Ecosystems
|
Human Activity |
Effect |
|
Deforestation |
Loss of biodiversity, ↑ CO₂ |
|
Fossil fuel burning |
Global warming |
|
Excess fertilizers |
Nitrogen leaching, eutrophication |
|
Pesticides |
Bioaccumulation, biomagnification |
|
Industrial emissions |
Acid rain, pollution |
Keywords: Global warming, acid rain, eutrophication,
biomagnification, deforestation.
8. Ecosystem Types
|
Ecosystem |
Characteristics |
Examples |
|
Forest |
Multi-layered, high biodiversity, high productivity |
Tropical rainforest, deciduous forest |
|
Grassland |
Dominated by grasses, moderate rainfall |
Prairies, savannas |
|
Desert |
Arid, xerophytes, low productivity |
Thar Desert, Sahara |
|
Aquatic |
Freshwater & marine, producers are phytoplankton |
Pond, lake, ocean |
Keywords: Biodiversity, productivity, aquatic, desert, forest,
grassland.
9. Conservation & Protection
Methods:
- Protected Areas: National parks, Wildlife
Sanctuaries, Biosphere Reserves
- CITES: Controls trade of endangered
species
- EDGE: Evolutionarily Distinct and
Globally Endangered species
- REDD: Reducing Emissions from
Deforestation and Forest Degradation
Keywords: Conservation, biodiversity hotspots, protected areas, REDD,
CITES.
10. Quick NCERT Definitions to
Remember
1.
Ecosystem: Functional unit of nature.
2.
Producer: Autotrophs that synthesize food.
3.
Consumer: Heterotrophs depending on others
for food.
4.
Decomposer: Organisms that recycle nutrients.
5.
Food
chain: Linear
sequence of energy transfer.
6.
Food
web: Interconnected food chains.
7.
Trophic
level: Position
in a food chain.
8.
Primary
productivity:
Energy captured by producers.
9.
Succession: Gradual change in community
composition.
10.
Climax
community: Stable
final stage of succession.
11.
Biogeochemical
cycle: Nutrient
cycling involving biotic & abiotic components.
11. Important NCERT Keywords for
Exams
- Autotroph, Heterotroph,
Herbivore, Carnivore, Omnivore
- Producer, Consumer, Decomposer
- Food chain, Food web, Trophic
level
- Pyramid of
numbers/biomass/energy
- Ecological succession, Sere,
Seral community, Climax community
- Biogeochemical cycles: Carbon,
Nitrogen, Phosphorus, Hydrological
- Eutrophication, Acid rain,
Global warming, Biomagnification
- Protected area, Biodiversity
hotspot, EDGE species, CITES, REDD
12. Important Diagrams to Remember
1.
Food
Chain: Grass →
Grasshopper → Frog → Snake → Hawk
2.
Food
Web: Multiple interconnected chains
3.
Pyramid
of Energy / Biomass / Numbers
4.
Primary
Succession:
Bare rock → Lichen → Moss → Grass → Shrubs → Trees
5.
Biogeochemical
Cycles: Carbon,
Nitrogen, Phosphorus, Water
