38  Human and Environment Interaction

The environment comprises all the conditions — physical, chemical and biological — that surround a living organism. Human activity shapes the environment and is in turn shaped by it. The discipline that studies this two-way relationship is ecology.

38.1 Core Concepts

TipFoundational Vocabulary
Term Meaning
Environment Sum of physical, chemical and biological surroundings
Ecology Study of relationships among organisms and their environment
Ecosystem A community of living organisms (biotic) interacting with non-living components (abiotic)
Biosphere The thin layer of Earth where life exists
Biome Large region with characteristic climate and biota (forest, desert, tundra)
Habitat The specific place where an organism lives
Niche The functional role of a species in its ecosystem
Population All members of one species in an area
Community All populations of all species in an area

38.2 Components of an Ecosystem

TipTwo Working Components
  • Abiotic (non-living) — sunlight, temperature, water, soil, air, minerals.
  • Biotic (living) — producers, consumers, decomposers.
TipTrophic Levels — Who Eats What
Trophic level Role Examples
Producers (autotrophs) Make their own food via photosynthesis Plants, algae, cyanobacteria
Primary consumers (herbivores) Eat producers Rabbits, deer, cows
Secondary consumers (carnivores) Eat herbivores Snakes, frogs
Tertiary consumers (top carnivores) Eat carnivores Hawks, lions
Decomposers Break down dead matter Fungi, bacteria 

flowchart LR
  S[Sun] -->|Energy| P[Producers<br/>Plants]
  P --> H[Primary Consumer<br/>Herbivore]
  H --> C[Secondary Consumer<br/>Carnivore]
  C --> T[Tertiary Consumer<br/>Top carnivore]
  T --> D[Decomposers<br/>Fungi, bacteria]
  D --> P
    classDef default fill:#003366,color:#ffffff,stroke:#ffcc00,stroke-width:3px,rx:10px,ry:10px;

38.3 Food Chain and Food Web

TipFood Chain vs Food Web
  • Food chain — a single, linear path of energy flow (Grass → Rabbit → Fox).
  • Food web — interconnected food chains; multiple paths for energy flow.

The 10 % rule (Lindeman, 1942): only about 10 % of the energy at one trophic level is transferred to the next; the rest is lost as heat. This explains why food chains rarely have more than 4–5 levels.

38.4 Ecological Pyramids

TipThree Types of Ecological Pyramid
Pyramid Measures Direction
Pyramid of numbers Count of organisms at each level Usually decreasing upward
Pyramid of biomass Total mass at each level Usually decreasing; can be inverted in aquatic systems
Pyramid of energy Energy flow at each level Always upright (10 % rule)

38.5 Biogeochemical Cycles

Biogeochemical cycles describe the circulation of elements through living and non-living components.

TipFive Major Cycles
Cycle Key processes Major reservoir
Water (hydrological) Evaporation, condensation, precipitation, runoff Oceans
Carbon Photosynthesis, respiration, combustion, decomposition Atmosphere (CO₂), oceans, fossil fuels
Nitrogen Fixation, ammonification, nitrification, denitrification Atmosphere (78 % N₂)
Oxygen Photosynthesis, respiration Atmosphere (~21 % O₂)
Phosphorus Weathering, uptake, decomposition Rocks, sediments (no atmospheric form)
TipNitrogen Cycle — Key Steps
  1. Nitrogen fixation — atmospheric N₂ → ammonia (NH₃) by bacteria (Rhizobium) or lightning.
  2. Ammonification — organic N → ammonia by decomposers.
  3. Nitrification — NH₃ → NO₂⁻ → NO₃⁻ by Nitrosomonas and Nitrobacter.
  4. Assimilation — plants absorb nitrates.
  5. Denitrification — NO₃⁻ → N₂ back to atmosphere by Pseudomonas.

38.6 Biodiversity

Biodiversity is the variety of life at all levels — genes, species, ecosystems. Coined by E.O. Wilson (1988).

TipThree Levels of Biodiversity
  • Genetic diversity — within-species variation (different rice varieties).
  • Species diversity — number of species in an area.
  • Ecosystem diversity — variety of habitats (forest, wetland, desert).
TipBiodiversity Hotspots in India

A biodiversity hotspot (Norman Myers, 1988) is a region with at least 1,500 endemic vascular plant species and ≤ 30 % of original habitat remaining.

India hosts four hotspots:

  1. Western Ghats
  2. Eastern Himalaya
  3. Indo-Burma
  4. Sundaland (including Nicobar Islands)

Globally, 36 hotspots are recognised.

38.7 Conservation Strategies

TipIn-situ vs Ex-situ Conservation
Strategy Where Examples
In-situ (on-site) Within the natural habitat National parks, wildlife sanctuaries, biosphere reserves, sacred groves
Ex-situ (off-site) Outside the natural habitat Zoos, botanical gardens, seed banks, gene banks (e.g., NBPGR India)
TipIndian Protected Area Categories
  • Biosphere Reserves — 18 in India; e.g., Nilgiri, Sundarbans, Nanda Devi.
  • National Parks — over 100; e.g., Jim Corbett, Kanha, Kaziranga.
  • Wildlife Sanctuaries — 500+; less restrictive than national parks.
  • Conservation Reserves and Community Reserves — added by Wildlife (Protection) Amendment Act, 2002.
  • Tiger Reserves — under Project Tiger (1973).
  • Ramsar sites — wetlands of international importance.

38.8 Ecological Footprint and Carrying Capacity

TipTwo Working Concepts
  • Carrying capacity — maximum population an environment can sustain over the long term.
  • Ecological footprint — area of land and water needed to support a person/society’s resource use and waste absorption.

If humanity’s footprint exceeds Earth’s biocapacity, we are in overshoot — drawing down natural capital.

38.9 Anthropocene — A Working Idea

Geologists and earth scientists increasingly use Anthropocene (proposed by Crutzen, 2000) for the present geological epoch in which human activity has become a dominant influence on climate and the environment. The starting marker is debated — some propose the Industrial Revolution, others the post-1950 “Great Acceleration”.

38.10 Practice Questions

Q 01 Ecosystem Easy

An ecosystem consists of:

  • ALiving organisms only
  • BNon-living components only
  • CBiotic and abiotic components interacting
  • DOnly producers and consumers
View solution
Correct Option: C
An ecosystem combines biotic (living) and abiotic (non-living) components in interaction.
Q 02 10 % Rule Medium

According to Lindeman's "10 % rule", what fraction of energy is typically transferred from one trophic level to the next?

  • A90 %
  • B50 %
  • C10 %
  • D1 %
View solution
Correct Option: C
Roughly 10 % of energy moves up one trophic level; the rest is lost as heat. (Lindeman, 1942.)
Q 03 Pyramid of Energy Medium

Which ecological pyramid is *always* upright?

  • APyramid of numbers
  • BPyramid of biomass
  • CPyramid of energy
  • DAll three
View solution
Correct Option: C
The pyramid of energy is always upright because of the second law of thermodynamics — energy is lost at each level.
Q 04 Biodiversity Hotspots in India Medium

Which of the following is *not* a biodiversity hotspot in India?

  • AWestern Ghats
  • BEastern Himalaya
  • CIndo-Burma
  • DAravalli Range
View solution
Correct Option: D
India's four hotspots: Western Ghats, Eastern Himalaya, Indo-Burma, and Sundaland. The Aravalli is not a hotspot.
Q 05 Conservation Medium

Conservation of species in their natural habitat is called:

  • AEx-situ conservation
  • BIn-situ conservation
  • CCryopreservation
  • DTranslocation
View solution
Correct Option: B
In-situ = "in place" — protection within natural habitat (national parks, sanctuaries). Ex-situ = outside natural habitat.
Q 06 Nitrogen Fixation Medium

In the nitrogen cycle, the bacteria that fix atmospheric nitrogen in plant root nodules are:

  • ANitrobacter
  • BNitrosomonas
  • CRhizobium
  • DPseudomonas
View solution
Correct Option: C
Rhizobium bacteria form symbiotic associations with leguminous plant roots and fix N₂. Nitrosomonas/Nitrobacter do nitrification; Pseudomonas does denitrification.
Q 07 Biodiversity Easy

The term "biodiversity" was popularised by:

  • ACharles Darwin
  • BE.O. Wilson
  • CRachel Carson
  • DAldo Leopold
View solution
Correct Option: B
E.O. Wilson popularised "biodiversity" in 1988. The concept of "biodiversity hotspots" is from Norman Myers (1988).
Q 08 Project Tiger Medium

Project Tiger was launched in India in:

  • A1969
  • B1973
  • C1985
  • D2005
View solution
Correct Option: B
Project Tiger was launched in 1973 to protect the Bengal tiger.
ImportantQuick recall
  • Components: Biotic + Abiotic.
  • Trophic levels: Producer → Primary → Secondary → Tertiary → Decomposer.
  • Lindeman’s 10 % rule — energy lost at each level; pyramid of energy always upright.
  • Cycles: Water, Carbon, Nitrogen, Oxygen, Phosphorus (no atmospheric phase for phosphorus).
  • Nitrogen-fixing: Rhizobium; Nitrification: Nitrosomonas/Nitrobacter; Denitrification: Pseudomonas.
  • Biodiversity (E.O. Wilson 1988); 3 levels: Genetic, Species, Ecosystem.
  • India’s hotspots: Western Ghats, Eastern Himalaya, Indo-Burma, Sundaland.
  • Conservation: In-situ (national park) vs ex-situ (zoo, gene bank).
  • Project Tiger 1973.