BC06 — Ecology & Environment

📖 BC06 · CDS General Knowledge — Biology CDS Level

Ecology is the study of how organisms interact with each other and with their physical environment. CDS tests ecological pyramids (which can be inverted), food chains, nitrogen cycle steps, and conservation methods. These connect biology with current environmental affairs.

📌 CDS Focus: Ecological pyramid of numbers CAN be inverted (tree→insects); pyramid of energy is ALWAYS upright (10% energy transfer rule); nitrogen fixation by Rhizobium (bacteria in root nodules of legumes); biodiversity hotspot = area with exceptional biodiversity that is also threatened; in-situ conservation = wildlife sanctuary, national park; ex-situ = zoo, seed bank.

1. Ecosystem & Food Chains

Fig. 1 — Ecological Pyramids: Which Can Be Inverted?

2. Biogeochemical Cycles & Conservation

ConceptKey Facts for CDS Nitrogen FixationRhizobium (bacteria in root nodules of legumes: pea, soybean, groundnut) converts N₂ gas → ammonia (NH₃). Also by lightning, and free-living bacteria (Azotobacter, Clostridium). NitrificationAmmonia → Nitrites (by Nitrosomonas) → Nitrates (by Nitrobacter). Nitrates are the usable form for plants. Carbon CyclePhotosynthesis removes CO₂ from air; respiration, decomposition and burning return it. Deforestation increases CO₂ (greenhouse gas). In-situ conservationProtecting species in their NATURAL habitat. Methods: National Parks, Wildlife Sanctuaries, Biosphere Reserves, Sacred groves. India has 106 National Parks. Ex-situ conservationProtecting species OUTSIDE their natural habitat. Methods: Zoos, Botanical gardens, Seed banks, Gene banks. Example: Svalbard Global Seed Vault. Biodiversity hotspotsAreas with exceptional species richness AND high threat level. India has 4 hotspots: Western Ghats+Sri Lanka, Eastern Himalayas, Indo-Burma, Sundaland.

📝 CDS PYQs — Ecology

Q1. Which of the following ecological pyramids can be inverted? CDS PYQ

(a) Pyramid of energy only(b) Pyramid of numbers and biomass(c) Pyramid of energy and biomass(d) All three pyramids

✔ Answer: (b) Pyramid of numbers and biomass

The pyramid of energy is ALWAYS upright because energy flows in one direction and is lost at each step (10% rule). The pyramid of numbers can be inverted (e.g., 1 large tree supports thousands of insects). The pyramid of biomass can also be inverted in aquatic ecosystems (phytoplankton biomass is less than zooplankton because phytoplankton reproduce rapidly). This "which pyramid can be inverted" question appears in multiple CDS papers.

Q2. Rhizobium bacteria help in: CDS PYQ

(a) Decomposition of organic matter(b) Nitrogen fixation in legume root nodules(c) Carbon fixation in leaves(d) Conversion of nitrates to nitrogen gas

✔ Answer: (b) Nitrogen fixation

Rhizobium lives symbiotically in root nodules of leguminous plants (peas, beans, groundnut, soybean). It fixes atmospheric nitrogen (N₂) into ammonia (NH₃), which the plant can use to make proteins. In return, the plant provides sugars and a microaerobic environment for the bacteria. This mutualistic relationship is why legumes are used in crop rotation to naturally enrich soil nitrogen.

🧠 Quick Memory Chart — BC06

🌿 Pyramids

Energy: ALWAYS upright (10% rule)
Numbers: can invert (tree→insects)
Biomass: inverted in aquatic ecosystems
10% rule: only 10% energy transfers up
Short food chains = more energy available

⛛ Nitrogen Cycle

Fixation: Rhizobium (legumes), Azotobacter
Nitrification: Nitrosomonas→Nitrobacter
Denitrification: returns N₂ to atmosphere
Decomposers: fungi & bacteria
Lightning also fixes nitrogen

🌎 Conservation

In-situ: National Parks, Sanctuaries
Ex-situ: Zoo, Seed bank, Gene bank
India: 4 biodiversity hotspots
Western Ghats = richest hotspot in India
IUCN categories: extinct, critically endangered...

📝 Practice Exercise

E1. Conservation of species in their natural habitat is called:

(a) Ex-situ conservation(b) In-situ conservation(c) Gene banking(d) Captive breeding

E2. If 1000 kcal of energy is available at the producer level, how much reaches the secondary consumer?

(a) 100 kcal(b) 10 kcal(c) 1 kcal(d) 50 kcal

Answers:
E1 → (b) In-situ conservation [protecting species in their natural environment] | E2 → (b) 10 kcal [1000 → 100 (primary consumer, 10%) → 10 (secondary consumer, 10% of 100)]

📝 Mock Tests 🎯 Subject Quiz ✈️ Telegram