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Biology · AFCAT

BA05 — Ecology & Environment

BA05 · AFCAT General Awareness — Biology ★ Moderate + Current Affairs Relevance

Ecology connects biology to current affairs — AFCAT links ecosystem science with environmental policies. Questions about greenhouse gases, ozone depletion, and conservation are increasingly common.

AFCAT Focus: Pyramid of energy ALWAYS upright (10% rule); numbers CAN be inverted; Rhizobium = nitrogen fixation in legume root nodules; in-situ = national park; ex-situ = zoo/seed bank; ozone destroyed by CFCs (Montreal 1987); global warming = CO₂, CH₄, N₂O; acid rain pH < 5.6.

Part 1 — Ecological Pyramids

1. Ecological Pyramids

Pyramid of Numbers:

●CAN be inverted — e.g. 1 tree → thousands of insects → few birds → 1 hawk

●Usually upright: grassland, forest ecosystems

●Represents number of organisms at each trophic level

Pyramid of Energy:

●ALWAYS upright — NEVER inverted

●Only 10% energy passes to each next level; 90% lost as heat

●Food chains rarely exceed 4–5 links (energy loss too great)

●Biomass pyramid: CAN invert in aquatic ecosystems

Part 2 — Environment & Nitrogen Cycle

2. Environmental Issues & Conservation

Global Warming

Cause

CO₂, CH₄, N₂O trap heat (greenhouse effect); deforestation; fossil fuels

Effect

Rising sea levels; extreme weather events; species extinction

AFCAT Key Point

Paris Agreement (2015)

Ozone Depletion

Cause

CFCs from ACs & fridges destroy stratospheric O₃ (ozone)

Effect

Increased UV-B radiation; skin cancer; cataracts

AFCAT Key Point

Montreal Protocol (1987)

Acid Rain

Cause

SO₂ + NO₂ (industry/vehicles) + water vapour → H₂SO₄ + HNO₃

Effect

Harms aquatic life; corrodes marble (Taj Mahal)

AFCAT Key Point

pH of acid rain < 5.6

Eutrophication

Cause

Excess N & P nutrients from fertilisers run into water bodies

Effect

Algal bloom; O₂ depletion; fish and aquatic life die

AFCAT Key Point

Water pollution problem

In-situ Conservation

Cause

Protect species in their NATURAL habitat

Effect

Species preserved in wild environment

AFCAT Key Point

National Parks, Sanctuaries, Biosphere Reserves

Ex-situ Conservation

Cause

Protect species OUTSIDE their natural habitat

Effect

Backup populations maintained

AFCAT Key Point

Zoos, Botanical Gardens, Seed Banks, Gene Banks

Nitrogen Cycle:

●Fixation: Rhizobium (legume root nodules) converts N₂ → NH₃. Also: Azotobacter (free-living), lightning.

●Nitrification: NH₃ → NO₂⁻ (Nitrosomonas) → NO₃⁻ (Nitrobacter). Nitrates = plant-usable form.

●Denitrification: NO₃⁻ → N₂ back to atmosphere. Cycle complete.

AFCAT PYQs — Ecology

Q1. Which ecological pyramid is ALWAYS upright?AFCAT PYQ

(a) Numbers

(b) Biomass

(d) Numbers and Biomass

✓ Answer: (c) Pyramid of Energy

The pyramid of energy is always upright — energy is always lost as heat at each trophic level (10% rule) and can never increase going upward. Numbers and Biomass can both invert under certain conditions.

Q2. Montreal Protocol (1987) was signed to protect:AFCAT PYQ

(a) Forests from deforestation

(b) Ozone layer from CFC damage

(d) Ocean from plastic

✓ Answer: (b) Ozone layer

CFCs from ACs and refrigerators destroy stratospheric ozone. Montreal Protocol (1987) phased out CFCs. Most successful environmental treaty. Contrast: Paris Agreement (2015) = climate change / CO₂.

Quick Memory Chart — BA05

Pyramids

Energy: ALWAYS upright; 10% rule
Numbers: CAN invert (tree → insects)
Biomass: CAN invert (aquatic)
90% energy lost as heat each step

Nitrogen

Rhizobium: N₂ fixation (legumes)
Azotobacter: free-living N₂ fixer
Nitrosomonas: NH₃ → NO₂⁻
Nitrobacter: NO₂⁻ → NO₃⁻ (usable)

Environment

Ozone: CFCs deplete; Montreal 1987
Global warming: CO₂ main GHG
Acid rain: SO₂+NO₂; pH < 5.6
In-situ: National Parks, Sanctuaries
Ex-situ: Zoo, Seed bank, Gene bank

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