Key Concepts & Formulas

Provide 5-7 essential concepts for Biology Ecology:

10 Practice MCQs

Q1. Which of the following is NOT a greenhouse gas? A) CO₂ B) CH₄ C) N₂ D) N₂O

Answer: C) N₂

Solution:

• Greenhouse gases trap heat: CO₂ (carbon dioxide), CH₄ (methane), N₂O (nitrous oxide)
• N₂ (nitrogen gas) constitutes 78% of atmosphere but doesn’t trap heat
• Water vapor (H₂O) is also a greenhouse gas but not listed here

Shortcut: Remember “CON-M” for greenhouse gases: CO₂, O₃, N₂O, CH₄

Concept: Biology Ecology - Environmental pollution and greenhouse effect

Q2. In a grassland ecosystem, if there are 10,000 kg of grass (producers), how much energy will reach the tertiary consumers? A) 10 kg B) 100 kg C) 1,000 kg D) 10,000 kg

Answer: A) 10 kg

Solution:

• Energy transfer efficiency: 10% at each trophic level
• Grass (producers) → Primary consumers: 10,000 × 0.1 = 1,000 kg
• Primary → Secondary consumers: 1,000 × 0.1 = 100 kg
• Secondary → Tertiary consumers: 100 × 0.1 = 10 kg

Shortcut: For 10% rule: Divide original by 10^(number of transfers). Here: 10,000 ÷ 10³ = 10 kg

Concept: Biology Ecology - Energy flow in ecosystems and 10% law

Q3. Which biome is characterized by highest biodiversity? A) Tundra B) Tropical rainforest C) Temperate forest D) Desert

Answer: B) Tropical rainforest

Solution:

• Tropical rainforests: Cover 6% land but contain >50% of world’s species
• Temperature: 25-30°C, Rainfall: 200-450 cm annually
• 3 vertical layers: emergent, canopy, understory
• Amazon rainforest: ~40,000 plant species, 3,000 fish species

Shortcut: “TRF = Tons of Rainforest Fauna” - highest diversity

Concept: Biology Ecology - Biomes and biodiversity distribution

Q4. A lake has BOD of 20 ppm. What is its pollution status? A) Clean B) Slightly polluted C) Highly polluted D) Very highly polluted

Answer: C) Highly polluted

Solution:

• BOD classification: <5 ppm (clean), 5-17 ppm (slightly polluted), >17 ppm (highly polluted)
• 20 ppm indicates heavy organic pollution
• Causes: sewage, industrial waste, agricultural runoff
• Leads to eutrophication and fish death

Shortcut: “BOD 17 = Pollution heaven” - >17 ppm is highly polluted

Concept: Biology Ecology - Water pollution indicators

Q5. In nitrogen cycle, which bacteria convert NH₃ to NO₂⁻? A) Rhizobium B) Nitrosomonas C) Nitrobacter D) Azotobacter

Answer: B) Nitrosomonas

Solution:

• Nitrogen cycle steps: N₂ → NH₃ (Nitrogenase) → NO₂⁻ (Nitrosomonas) → NO₃⁻ (Nitrobacter)
• Rhizobium: N₂ fixation in legume root nodules
• Azotobacter: Free-living N₂ fixer in soil
• Denitrification: Pseudomonas (NO₃⁻ → N₂)

Shortcut: “Mono” for “Monas” - NH₃ to NO₂⁻ (single step)

Concept: Biology Ecology - Nitrogen cycle and bacterial roles

Q6. A population grows from 100 to 400 in 2 years. What is the intrinsic growth rate (r)? A) 0.346 B) 0.693 C) 1.386 D) 2.772

Answer: B) 0.693

Solution:

• Exponential growth: Nₜ = N₀e^(rt)
• 400 = 100e^(2r) → 4 = e^(2r)
• ln(4) = 2r → r = ln(4)/2 = 1.386/2 = 0.693

Shortcut: For doubling: r = ln(2)/t = 0.693/2 = 0.346 per year, but here quadrupled in 2 years

Concept: Biology Ecology - Population growth equations

Q7. Which ecological pyramid can NEVER be inverted? A) Pyramid of numbers B) Pyramid of biomass C) Pyramid of energy D) All can be inverted

Answer: C) Pyramid of energy

Solution:

• Energy pyramid: Always upright (energy decreases at each level)
• Biomass pyramid: Can invert (e.g., aquatic: phytoplankton < zooplankton)
• Numbers pyramid: Can invert (e.g., single tree supporting many insects)
• Energy loss: 90% at each trophic level due to respiration, heat

Shortcut: “Energy never lies” - always decreases, so pyramid always upright

Concept: Biology Ecology - Ecological pyramid types and exceptions

Q8. In a forest ecosystem, the GPP is 10,000 kcal/m²/year and respiration loss is 60%. What is the NPP? A) 4,000 B) 6,000 C) 16,000 D) 4,000

Answer: A) 4,000 kcal/m²/year

Solution:

• GPP (Gross Primary Productivity) = 10,000 kcal
• Respiration loss = 60% of GPP = 0.6 × 10,000 = 6,000 kcal
• NPP (Net Primary Productivity) = GPP - Respiration = 10,000 - 6,000 = 4,000 kcal

Shortcut: NPP = GPP × (1 - respiration %). Here: 10,000 × 0.4 = 4,000

Concept: Biology Ecology - Productivity calculations in ecosystems

Q9. A pollutant has biological half-life of 5 years. After 15 years, what % remains in organism? A) 12.5% B) 25% C) 50% D) 75%

Answer: A) 12.5%

Solution:

• Half-life formula: Remaining = Initial × (1/2)^(t/t½)
• After 15 years with 5-year half-life: 3 half-lives
• Remaining = 100% × (1/2)³ = 100% × 1/8 = 12.5%

Shortcut: Count half-lives: 15/5 = 3 → 1/2³ = 1/8 = 12.5%

Concept: Biology Ecology - Biomagnification and half-life calculations

Q10. In a park survey, species richness is 50 and total individuals is 500. Using Shannon index formula H = -Σ(pi × ln pi), where diversity is maximum, what is H value? (Given: ln 0.02 = -3.91) A) 1.95 B) 2.30 C) 3.91 D) 4.60

Answer: C) 3.91

Solution:

• Maximum diversity: all species equally abundant
• pi = 1/50 = 0.02 for each species
• H = -Σ(50 × 0.02 × ln 0.02) = -50 × 0.02 × (-3.91) = 3.91

Shortcut: For equal abundance: H = ln(S) = ln(50) ≈ 3.91

Concept: Biology Ecology - Biodiversity indices and calculations

5 Previous Year Questions

PYQ 1. Which of the following is a secondary pollutant? A) SO₂ B) CO C) O₃ D) NO₂ [RRB NTPC 2021 CBT-1]

Answer: C) O₃

Solution:

• Primary pollutants: Directly emitted (SO₂, CO, NO₂)
• Secondary pollutants: Formed by reaction (O₃ from NOx + VOCs in sunlight)
• Ozone (O₃) forms through: NO₂ + hv → NO + O; O + O₂ → O₃

Exam Tip: Remember “PO” - Primary = Original, Secondary = Synthesized

PYQ 2. The 10% energy transfer law was given by: A) Lindeman B) Elton C) Tansley D) Odum [RRB Group D 2022]

Answer: A) Lindeman

Solution:

• Lindeman (1942): 10% law of energy transfer
• Elton: Pyramid concept
• Tansley: Coined “ecosystem”
• Odum: Father of modern ecology

Exam Tip: “Lindeman’s Ten Percent” - direct association for energy law

PYQ 3. Which National Park is famous for one-horned rhinoceros? A) Jim Corbett B) Kaziranga C) Bandipur D) Ranthambore [RRB ALP 2018]

Answer: B) Kaziranga

Solution:

• Kaziranga National Park: Assam, 2,400+ one-horned rhinos (80% of world population)
• UNESCO World Heritage Site (1985)
• Area: 430 km², Brahmaputra river flows through

Exam Tip: “Kaziranga = K” for “K"era (rhino in Hindi) association

PYQ 4. BOD is measure of: A) Organic pollution B) Heavy metals C) Acidity D) Temperature [RRB JE 2019]

Answer: A) Organic pollution

Solution:

• BOD: Biochemical Oxygen Demand
• Measures oxygen required by microbes to decompose organic matter
• Higher BOD = More organic pollution

Exam Tip: “BOD = Biochemical” → biological → organic matter

PYQ 5. Which is NOT a greenhouse gas? A) Water vapor B) CO₂ C) O₂ D) CH₄ [RPF SI 2019]

Answer: C) O₂

Solution:

• Greenhouse gases: H₂O, CO₂, CH₄, N₂O, O₃
• O₂ (oxygen) doesn’t absorb infrared radiation
• Comprises 21% of atmosphere but no greenhouse effect

Exam Tip: Remember “CON-M” greenhouse gases, O₂ is life gas, not heat-trapping

Speed Tricks & Shortcuts

For Biology Ecology, provide exam-tested shortcuts:

Common Mistakes to Avoid

Quick Revision Flashcards

Topic Connections

How Biology Ecology connects to other RRB exam topics:

• Direct Link: Environmental Chemistry (pollutants, greenhouse gases), Indian Geography (biomes, national parks), Current Affairs (COP conferences, climate targets)
• Combined Questions: Ecology + Chemistry (ozone formation), Ecology + Geography (wildlife distribution), Ecology + Economics (carbon trading)
• Foundation For: Environmental Science applications, Climate change policies, Sustainable development goals, Wildlife conservation strategies