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Ecology and Environment PYQs – Biology, SSC & Railway

168 Ecology and Environment (Biology) questions asked in recent SSC and Railway exams, newest first, with exam, date & shift, answers and solutions – page 2 of 2.

📚 168 questionsSSC 21 · Railway 147
12
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 2 · Waste management and biodegradable substances

Q101. A gardener buried five different substances in a garden: banana peels, newspaper, cotton cloth, plastic bottle and metal spoon. How many of the substances he buried were biodegradable?

  1. (a) Two
  2. (b) One
  3. (c) Four
  4. (d) Three
Answer & solution

Answer: (d) Three

Biodegradable substances are those that can decompose naturally by biological processes.
Banana peels, newspaper, and cotton cloth are biodegradable.
Plastic bottles and metal spoons are not biodegradable because they do not decompose easily.
So, the biodegradable substances are banana peels, newspaper, and cotton cloth.
Total biodegradable substances = 3.
Final answer: Option 4
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 1 · Pollution - effects on living beings

Q102. Even though people eat different types of food, they may still absorb harmful chemical residues. This is because ____________.

  1. (a) All plants produce natural pesticides
  2. (b) Food grains absorb only useful chemicals from soil
  3. (c) Pesticides are completely destroyed during cooking
  4. (d) Chemicals persist and accumulate via biomagnification
Answer & solution

Answer: (d) Chemicals persist and accumulate via biomagnification

Correct option: 4
People absorb harmful chemical residues because chemicals can persist in the environment.
These harmful chemicals accumulate along the food chain due to biomagnification.
Biomagnification leads to higher concentrations of toxic substances in organisms higher up the food chain, including humans.
Thus, even varied diets can contain harmful residues due to this accumulation process.
This explains why option 4 is correct.
Answer complete.
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 2 · Pollution - effects on living beings

Q103. When chemicals such as pesticides enter food chains and get more concentrated at higher levels, the process is known as ____.

  1. (a) Biodegradation
  2. (b) Photosynthesis
  3. (c) Eutrophication
  4. (d) Biological magnification
Answer & solution

Answer: (d) Biological magnification

The process where pesticides and other chemicals accumulate and increase in concentration at higher levels of the food chain is called biological magnification.
It causes higher animals to accumulate toxic substances, leading to ecological harm.
Hence, the correct term is Biological magnification.
Final answer: Option 4
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 3 · Pollution - effects on living beings

Q104. Which of the following best explains why humans have the highest concentration of harmful chemicals in their bodies?

  1. (a) They consume more pesticides directly than other organisms
  2. (b) They eat large quantities of contaminated animal products
  3. (c) They occupy the top trophic level in food chains
  4. (d) They are exposed to chemicals through air and water
Answer & solution

Answer: (c) They occupy the top trophic level in food chains

Option 3 is correct.
Humans are at the top trophic level in food chains.
Harmful chemicals accumulate through bioaccumulation and biomagnification.
Therefore, concentration of these chemicals increases as we go up the food chain.
This explains why humans have the highest concentration of harmful chemicals in their bodies.
Other options either describe exposure ways or sources, which are partial reasons.
Option 3 gives the clearest and most comprehensive explanation.
Hence, humans having the highest concentration is due to their position at the top trophic level.
Final answer: Option 3
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 3 · Trophic levels and the 10 percent law

Q105. Which of the following explains why most food chains do not exceed four trophic levels?

  1. (a) Decomposers consume all organisms at higher levels
  2. (b) Producers are rare in ecosystems
  3. (c) Only 10% of energy passes to the next level
  4. (d) Predators eat only herbivores
Answer & solution

Answer: (c) Only 10% of energy passes to the next level

Most food chains have limited trophic levels because of energy transfer efficiency.
Only about 10% of energy passes from one trophic level to the next.
This energy loss limits how many levels can be sustained.
Hence, food chains rarely exceed four trophic levels.
Correct answer: Option 3
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 1 · Pollution - effects on living beings

Q106. Why is biological magnification a health risk even with limited pesticide use?

  1. (a) Non-biodegradable pesticides are immediately excreted and do not persist
  2. (b) The toxicity of pesticides decreases as they move up the food chain
  3. (c) Non-biodegradable pesticides accumulate at successive trophic levels
  4. (d) Pesticides affect only soil microorganisms, not higher organisms
Answer & solution

Answer: (c) Non-biodegradable pesticides accumulate at successive trophic levels

Correct option: 3
Biological magnification occurs when non-biodegradable pesticides accumulate at successive trophic levels.
These pesticides do not break down easily and concentrate in organisms higher up the food chain.
Even limited use can lead to harmful levels in predators including humans.
This accumulation increases health risks as toxicity builds up in organisms.
Hence, non-biodegradable pesticides accumulating stepwise cause health hazards.
Final answer: Option 3
RRB JE CBT-1 2025-26 – 25 February 2026 · Waste management and biodegradable substances

Q107. What should be done in order to minimise waste production?

  1. (a) Change and adapt sustainable lifestyle
  2. (b) Use non-biodegradable products
  3. (c) Maximise plastic packaging of products
  4. (d) Increase plastic usage
Answer & solution

Answer: (a) Change and adapt sustainable lifestyle

Correct option is 1.
To minimise waste production, adopting and adapting a sustainable lifestyle is essential.
Using non-biodegradable products or increasing plastic usage only increases waste, so options 2, 3, and 4 are incorrect.
A sustainable lifestyle focuses on reducing demand on natural resources and waste generation.
Hence, the best way is to change and adapt sustainable lifestyle habits.
Answer complete.
RRB JE CBT-1 2025-26 – 25 February 2026 Shift 3 · Pollution - effects on living beings

Q108. Which of the following statements best explains why humans are severely affected by biological magnification?

  1. (a) Humans occupy the top trophic level in many food chains
  2. (b) Humans are best decomposers in food chain
  3. (c) Humans consume less food than other consumers in food chain
  4. (d) Humans can break down toxins
Answer & solution

Answer: (a) Humans occupy the top trophic level in many food chains

Humans are at the top trophic level in many food chains.
Biological magnification causes toxins to concentrate at higher trophic levels.
As top consumers, humans accumulate the highest levels of these toxins.
This leads to severe effects on human health due to toxin accumulation.
Therefore, option 1 is the correct explanation.
Final answer: Option 1
RRB JE CBT-1 2025-26 – 20 February 2026 · Waste management and biodegradable substances

Q109. Which of the following is an advantage of paper cups over plastic cups?

  1. (a) They are reusable
  2. (b) They are stronger
  3. (c) They are cheaper
  4. (d) They are biodegradable
Answer & solution

Answer: (d) They are biodegradable

Correct option: 4
Paper cups are biodegradable, which means they naturally decompose and do not harm the environment.
Plastic cups are not biodegradable and cause pollution.
Thus, paper cups have an environmental advantage over plastic cups.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 20 February 2026 · Waste management and biodegradable substances

Q110. Which of the following is an effect of non-biodegradable substances in water bodies?

  1. (a) Clogs drains and harms aquatic life
  2. (b) Helps plants grow
  3. (c) Water becomes fertile
  4. (d) Provides nutrients for fish
Answer & solution

Answer: (a) Clogs drains and harms aquatic life

Non-biodegradable substances do not decompose naturally.
They accumulate in water bodies and clog drains.
This leads to pollution and harms aquatic life.
Hence, the correct effect is clogging drains and harming aquatic life.
Final answer: Option 1
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 3 · Pollution - effects on living beings

Q111. A town replaces all plastic bags with cloth bags. Which chain reaction is expected in the ecosystem?

  1. (a) Reduced pollution and decreased biological magnification
  2. (b) Cloth bags cause soil toxicity
  3. (c) Plastic still enters the food chain
  4. (d) More plastic accumulates in water bodies
Answer & solution

Answer: (a) Reduced pollution and decreased biological magnification

Replacing plastic bags with cloth bags reduces plastic pollution.
Less plastic pollution leads to decreased biological magnification.
Biological magnification happens when toxins accumulate in organisms higher up the food chain.
Therefore, using cloth bags benefits the ecosystem by reducing pollution and biological magnification.
Final answer: Option 1
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 3 · Food chains and food webs

Q112. In a pond ecosystem, removal of phytoplankton would most directly affect ____________.

  1. (a) Abiotic components
  2. (b) Secondary consumers like fish-eating birds
  3. (c) Decomposers only
  4. (d) Primary consumers like zooplankton
Answer & solution

Answer: (d) Primary consumers like zooplankton

The removal of phytoplankton removes the primary producers in the pond ecosystem.
Phytoplankton are the main food source for primary consumers such as zooplankton.
Without phytoplankton, primary consumers like zooplankton will be directly affected as their food source disappears.
Abiotic components, secondary consumers, and decomposers are indirectly affected, but the most direct impact is on primary consumers.
Therefore, the correct answer is primary consumers like zooplankton.
Correct option is 4.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 1 · Waste management and biodegradable substances

Q113. Why are non-biodegradable substances harmful for the environment?

  1. (a) Causes no pollution in water
  2. (b) Needs heat and temperature for breakdown, releases harmful chemicals
  3. (c) Can be broken down by bacteria
  4. (d) Easily mixes with soil
Answer & solution

Answer: (b) Needs heat and temperature for breakdown, releases harmful chemicals

Option 2 is correct.
Non-biodegradable substances do not decompose easily.
They require heat and temperature for breakdown.
During this process, they release harmful chemicals.
These chemicals pollute the environment.
Hence, they are harmful to the environment.
Final answer: Option 2
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 3 · Waste management and biodegradable substances

Q114. Select the correct option regarding the following two statements labelled Assertion (A) and Reason (R).Assertion (A): Excess accumulation of biodegradable waste can also create environmental problems.Reason (R): Slow decomposition may lead to foul smell and spread of disease.

  1. (a) A is true, but R is false
  2. (b) A is false, but R is true
  3. (c) Both A and R are true, and R is the correct explanation of A
  4. (d) Both A and R are true, but R is not the correct explanation of A
Answer & solution

Answer: (c) Both A and R are true, and R is the correct explanation of A

Both Assertion (A) and Reason (R) are true.
Excess accumulation of biodegradable waste causes environmental problems like pollution and health hazards.
Slow decomposition of such waste leads to foul smell and spreads diseases.
Thus, Reason (R) correctly explains Assertion (A).
Final answer: Option 3
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 2 · Waste management and biodegradable substances

Q115. Select the correct option regarding the following two statements labelled Assertion (A) and Reason (R).
Assertion (A): Burning plastic waste is a safe method of disposal.
Reason (R): Burning plastic releases toxic gases harmful to humans and the environment.

  1. (a) Both assertion and reason are true, and reason correctly explains the assertion
  2. (b) Assertion is true, reason is false
  3. (c) Both assertion and reason are true, but reason does not correctly explain the assertion
  4. (d) Assertion is false, reason is true
Answer & solution

Answer: (d) Assertion is false, reason is true

Option 4 is correct.
Burning plastic waste is not a safe method of disposal.
This is because burning plastic releases toxic gases.
These gases are harmful to humans and the environment.
Hence, the assertion is false but the reason is true.
Therefore, the correct choice is Option 4.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 1 · Waste management and biodegradable substances

Q116. Which statement is correct regarding the definition of biodegradable substances?

  1. (a) Substances that are broken by physical process
  2. (b) Substances that are broken by chemical process
  3. (c) Substances that are broken by biological process
  4. (d) Substances that are broken by mechanical process
Answer & solution

Answer: (c) Substances that are broken by biological process

Correct option is 3.
Biodegradable substances are those that can be broken down by biological processes involving microorganisms.
These substances decompose naturally by the action of bacteria, fungi or other living organisms.
Physical, chemical or mechanical processes do not define biodegradability.
Hence, option 3 is correct.
Answer ends.
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 3 · Trophic levels and the 10 percent law

Q117. Why are terrestrial food chains usually limited to 4–5 trophic levels?

  1. (a) Plants produce less oxygen
  2. (b) Energy available decreases at higher trophic levels
  3. (c) Top predators eat less
  4. (d) Decomposers recycle all energy
Answer & solution

Answer: (b) Energy available decreases at higher trophic levels

The main reason terrestrial food chains have only 4–5 trophic levels is energy loss.
Energy decreases at each trophic level due to heat loss, respiration, and other metabolic activities.
Less energy is available to support organisms at higher levels, limiting chain length.
Therefore, longer chains cannot be supported because energy availability becomes too low.
Hence, energy available decreases at higher trophic levels is the correct reason.
Final answer: Option 2
SSC MTS 2025 – 18 February 2026 Shift 2 · Trophic levels and the 10 percent law

Q118. What happens to energy as it flows through different trophic levels in a food chain?

  1. (a) It is completely converted into chemical energy
  2. (b) It is entirely used by the organisms
  3. (c) It is stored indefinitely in all the trophic levels
  4. (d) Some energy is lost to the environment
Answer & solution

Answer: (d) Some energy is lost to the environment

The correct answer is option 4.
As energy flows through trophic levels in a food chain, approximately 90% of energy is lost to the environment as heat at each level (Lindeman's 10% rule). Only about 10% of the energy is transferred to the next trophic level. This is why food chains are typically short (3–4 levels) and why the number of organisms decreases at higher trophic levels.
Option 1 is incorrect: Energy cannot be completely converted to chemical energy; a large proportion is always lost as heat through metabolic activities.
Option 2 is incorrect: Organisms use only a fraction of the energy available; most is dissipated as heat, not fully utilised .
Option 3 is incorrect: Energy is never stored indefinitely across trophic levels; it continuously decreases, which is why energy pyramids taper towards the top.
SSC MTS 2025 – 17 February 2026 Shift 3 · Ecological terms (biome, niche, habitat, adaptation)

Q119. Which of the following statement is correct regarding endemic species?

  1. (a) They are exclusively found only in a specific geographic location
  2. (b) They are naturally found in multiple countries
  3. (c) They are always endangered
  4. (d) They are common to various continents
Answer & solution

Answer: (a) They are exclusively found only in a specific geographic location

Endemic species are those that are exclusively found in a specific geographic location and nowhere else naturally. For example, the Lion-tailed Macaque is endemic to the Western Ghats of India. They are NOT found in multiple countries, are not always endangered (though many are), and are not common to various continents.
Delhi Police Constable (Exe) 2025-26 – 4 January 2026 Shift 2 · Energy flow and ecological pyramids

Q120. What is the primary source of energy for almost all life on Earth?

  1. (a) Ocean tides
  2. (b) Geothermal energy
  3. (c) The Sun
  4. (d) Wind energy
Answer & solution

Answer: (c) The Sun

The Sun is the primary source of energy for almost all life on Earth. Plants capture solar energy through photosynthesis to produce food, forming the base of virtually all food chains and ecosystems.
(a) Incorrect: Ocean tides are caused by the gravitational pull of the Moon and Sun but are not a primary energy source for life.
(b) Incorrect: Geothermal energy supports some specialized ecosystems (like hydrothermal vents) but is not the primary energy source for most life on Earth.
(d) Incorrect: Wind energy is indirectly derived from the Sun but is not the primary energy source for life.
Delhi Police Constable (Exe) 2025-26 – 29 December 2025 Shift 2 · Energy flow and ecological pyramids

Q121. What is the primary source of energy for all living organisms on Earth?

  1. (a) The Moon
  2. (b) Volcanoes
  3. (c) The Sun
  4. (d) Ocean tides
Answer & solution

Answer: (c) The Sun

The Sun is the primary source of energy for all living organisms. Through photosynthesis, plants convert solar energy into chemical energy, which then flows through food chains to all other organisms. Without the Sun's energy, virtually no life would be possible on Earth.
(a) Incorrect: The Moon reflects sunlight but is not a primary energy source for life.
(b) Incorrect: Volcanoes provide geothermal energy, but this is not the primary source for most life.
(d) Incorrect: Ocean tides are driven by gravitational forces, not a primary energy source for organisms.
Delhi Police Constable (Exe) 2025-26 – 24 December 2025 Shift 1 · Sustainable development and Earth's spheres

Q122. How does the increasing global population affect environmental functions?

  1. (a) It aids in efficient resource utilization.
  2. (b) It strengthens the environmental functions.
  3. (c) It places immense pressure on environmental resources.
  4. (d) It leads to better resource management practices.
Answer & solution

Answer: (c) It places immense pressure on environmental resources.

The correct answer is It places immense pressure on environmental resources (Option 3).
An increasing global population leads to greater demand for food, water, energy, land, and natural resources. This overconsumption places immense pressure on environmental resources, leading to deforestation, biodiversity loss, water scarcity, pollution, and climate change.
Option 1: A larger population typically leads to overexploitation and inefficient use of resources, not more efficient utilization.
Option 2: Growing population generally weakens environmental functions by increasing pollution, habitat destruction, and resource depletion.
Option 4: Population growth tends to increase resource consumption and strain management systems rather than lead to better resource management.
Delhi Police Constable (Exe) 2025-26 – 23 December 2025 Shift 2 · Sustainable development and Earth's spheres

Q123. Which of the following is a direct result of unsustainable development?

  1. (a) Reduced global consumption
  2. (b) Enhanced resource regeneration
  3. (c) Environmental crisis and depletion of resources
  4. (d) Sustainable management of natural resources
Answer & solution

Answer: (c) Environmental crisis and depletion of resources

The correct answer is Environmental crisis and depletion of resources (Option 3).
Unsustainable development prioritises short-term economic gains over long-term ecological health, leading to environmental crises such as pollution, biodiversity loss, climate change, and depletion of natural resources like forests, water, and minerals.
Option 1 - Reduced global consumption: Unsustainable development is typically associated with increased consumption and overexploitation, not reduction.
Option 2 - Enhanced resource regeneration: Unsustainable development depletes resources faster than they can regenerate, not enhancing regeneration.
Option 4 - Sustainable management of natural resources: This is the goal of sustainable development, which is the opposite of unsustainable development.
SSC Stenographer 2025 – 8 December 2025 Shift 2 · Trophic levels and the 10 percent law

Q124. A forest ecosystem experiences a prolonged drought. Which trophic level would likely experience the most immediate and severe impact on its biomass?

  1. (a) Primary consumers
  2. (b) Secondary consumers
  3. (c) Tertiary consumers
  4. (d) Producers
Answer & solution

Answer: (d) Producers

Producers would face the most immediate and severe impact during a prolonged drought. The main reason is that they directly depend on natural resources like water, sunlight, and nutrients from the soil to perform photosynthesis. Without sufficient water, their growth and survival decline sharply, reducing the biomass at the very base of the food chain. Since producers form the foundation of all trophic levels, their reduction affects the entire ecosystem — leading to less food availability for primary consumers, which in turn cascades upward to secondary and tertiary consumers. Hence, the first and strongest impact of drought is seen on producers.
RRB NTPC UG CBT-1 2024-25 – 2 September 2025 Shift 3 · Waste management and biodegradable substances

Q125. Which State launched India' first PPP green waste processing plant?

  1. (a) Telangana
  2. (b) Madhya Pradesh
  3. (c) Chhattisgarh
  4. (d) Kerala
Answer & solution

Answer: (b) Madhya Pradesh

RRB NTPC UG CBT-1 2024-25 – 22 August 2025 Shift 3 · Sustainable development and Earth's spheres

Q126. Which of the following options best defines 'Sustainable Development'?

  1. (a) Maximising profits from natural resources
  2. (b) Using only renewable resources
  3. (c) Development that meets present needs without compromising future generations
  4. (d) Industrialisation without any restrictions
Answer & solution

Answer: (c) Development that meets present needs without compromising future generations

RRB NTPC UG CBT-1 2024-25 – 13 August 2025 Shift 2 · Ecological terms (biome, niche, habitat, adaptation)

Q127. What are endemic species?

  1. (a) Species found only in a particular area and nowhere else
  2. (b) Exotic animals brought from other countries
  3. (c) Species found in every forest
  4. (d) Species that have migrated recently
Answer & solution

Answer: (a) Species found only in a particular area and nowhere else

RRB NTPC UG CBT-1 2024-25 – 12 August 2025 Shift 3 · Waste management and biodegradable substances

Q128. Which of these is a part of solid waste management infrastructure?

  1. (a) Drainage tanks
  2. (b) Garbage collection and disposal
  3. (c) Electricity transmission lines
  4. (d) Sewage pipelines
Answer & solution

Answer: (b) Garbage collection and disposal

RRB NTPC UG CBT-1 2024-25 – 7 August 2025 Shift 1 · Sustainable development and Earth's spheres

Q129. Which of the following best describes 'intergenerational equity'?

  1. (a) Fair distribution of resources among present-day nations
  2. (b) Fair allocation of resources among various income groups
  3. (c) Equal economic opportunities for all age-based population groups
  4. (d) Fair use of resources to ensure availability for future generations
Answer & solution

Answer: (d) Fair use of resources to ensure availability for future generations

SSC Selection Post 2025 (Phase XIII) – 1 August 2025 Shift 3 · Biodiversity and its conservation (in-situ, ex-situ)

Q130. How have human-induced disturbances impacted terrestrial ecosystems?

  1. (a) Through increased vegetation growth
  2. (b) Through changes in land use
  3. (c) Through rising ocean temperatures
  4. (d) Through decreased atmospheric CO2 concentrations
Answer & solution

Answer: (b) Through changes in land use

Correct Answer: Option 2 – Through changes in land use
The primary way human activities disturb terrestrial ecosystems is through changes in land use – including deforestation, conversion of forests to agricultural land, urbanization, and mining. These directly destroy habitats and alter ecosystem structure and function.
Option 1 (Increased vegetation growth): While some areas have greening due to CO2 fertilization, the dominant human-induced disturbance is land use change, not vegetation increase.
Option 3 (Rising ocean temperatures): Ocean warming is a climate impact on marine ecosystems; not the primary mechanism for terrestrial ecosystem disturbance.
Option 4 (Decreased atmospheric CO2): Humans have significantly increased atmospheric CO2, not decreased it.
SSC Selection Post 2025 (Phase XIII) – 28 July 2025 Shift 3 · Ecological terms (biome, niche, habitat, adaptation)

Q131. Find the INCORRECT statement regarding the phenomenon of "Allelopathy" in plants.

  1. (a) Plants produce chemical compounds that help in growth of the plant
  2. (b) Chemical compound secreted by the roots of one plant blocks the germination of nearby seeds or inhibits the growth of neighboring plants
  3. (c) This phenomenon reduces the competition for nutrition
  4. (d) One of the example is Black walnut trees
Answer & solution

Answer: (a) Plants produce chemical compounds that help in growth of the plant

Correct Answer: Option 1 – Plants produce chemical compounds that help in growth of the plant (INCORRECT statement)
Allelopathy is a biological phenomenon where a plant produces biochemical compounds (allelochemicals) that INHIBIT or adversely affect the germination, growth, survival, or reproduction of other plants — NOT help the growth of the plant. The term 'allelopathy' comes from Greek: 'allelon' (of each other) + 'pathos' (to suffer). It is a form of chemical warfare between plants.
Option 2 (TRUE): Allelochemicals secreted by roots do block germination and inhibit growth of neighboring plants — this is the correct definition of allelopathy.
Option 3 (TRUE): By suppressing competitor plants, allelopathy reduces competition for water, nutrients, and light — giving the allelopathic plant a competitive advantage.
Option 4 (TRUE): Black walnut trees (Juglans nigra) produce juglone, a well-documented allelochemical that inhibits growth of many plants within the root zone — a classic example of allelopathy.
SSC Selection Post 2025 (Phase XIII) – 25 July 2025 Shift 1 · Ecosystem and its components

Q132. What term is used for organisms that break down dead plants and animals in an ecosystem?

  1. (a) Producers
  2. (b) Consumers
  3. (c) Decomposers
  4. (d) Parasites
Answer & solution

Answer: (c) Decomposers

Correct Answer: Option 3 – Decomposers
Decomposers are organisms (primarily bacteria and fungi) that break down dead organic matter (dead plants, animals, and waste) into simpler inorganic substances, returning nutrients to the soil. They play a critical role in nutrient cycling in ecosystems. Examples include fungi (Aspergillus, Rhizopus) and bacteria (Pseudomonas, Bacillus).
Option 1 (Producers): Autotrophs (plants, algae) that produce food through photosynthesis; do not break down dead matter.
Option 2 (Consumers): Heterotrophs (animals) that eat other organisms; do not specialize in breaking down dead matter.
Option 4 (Parasites): Organisms that live on/in a host and derive nutrition at the host's expense; not the same as decomposers.
SSC Selection Post 2025 (Phase XIII) – 25 July 2025 Shift 1 · Population ecology and growth

Q133. What is the term for the maximum population that an environment can sustain indefinitely?

  1. (a) Carrying capacity
  2. (b) Population density
  3. (c) Fertility rate
  4. (d) Dependency ratio
Answer & solution

Answer: (a) Carrying capacity

Correct Answer: Option 1 – Carrying capacity
Carrying capacity (K) is the maximum population size of a species that an environment can sustainably support indefinitely, given the food, water, habitat, and other resources available. It is a key concept in population ecology and conservation biology. When a population exceeds carrying capacity, resources become scarce, leading to increased mortality and reduced reproduction.
Option 2 (Population density): The number of individuals per unit area; not the maximum sustainable population size.
Option 3 (Fertility rate): The average number of children born per woman; a demographic measure, not an environmental limit.
Option 4 (Dependency ratio): The ratio of dependent population (children/elderly) to the working-age population; an economic/demographic measure, not an ecological concept.
RRB Technician Grade III 2024-25 – 30 December 2024 Shift 3 · Ecosystem and its components

Q134. Which of the following is NOT an abiotic component of the ecosystem?

  1. (a) Rainfall
  2. (b) Soil
  3. (c) Wind
  4. (d) Grass
Answer & solution

Answer: (d) Grass

Correct Answer: Option 4 — Grass
An ecosystem is a self-contained unit in which living organisms interact with one another and with their physical surroundings. It has two components. Biotic components are all the living things — producers (green plants), consumers (herbivores, carnivores, omnivores, parasites) and decomposers (bacteria and fungi). Abiotic components are the non-living physical and chemical factors — soil, water, air, wind, rainfall, temperature, light, humidity and minerals.
Grass is a green plant. It makes its own food by photosynthesis, so it is a producer — the first trophic level of every grassland food chain (grass → deer → lion). Being alive, it is a biotic, not an abiotic, component.
❌ Why the other options are incorrect
✗ Rainfall — a climatic (abiotic) factor; it decides the water available and hence the type of vegetation in a region.
✗ Soil — the non-living medium that supplies minerals and anchorage; it is an edaphic abiotic factor.
✗ Wind — a physical abiotic factor; it helps in pollination and seed dispersal but is itself non-living.
📌 SSC & Railway Exam Facts
• The term ecosystem was coined by A. G. Tansley in 1935.
• Producers → herbivores (primary consumers) → carnivores form a food chain; interlinked chains form a food web.
• Only about 10% of energy passes to the next trophic level — the 10 per cent law of Lindeman.
• A forest, ocean or lake is a natural ecosystem; a garden, crop field or aquarium is artificial.
• Ocean is the largest ecosystem; the flow of energy in an ecosystem is unidirectional.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 1 · Ecosystem and its components

Q135. In an ecosystem, physical factors like temperature, rainfall, wind, soil and minerals are:

  1. (a) living components
  2. (b) biotic components
  3. (c) decomposers
  4. (d) abiotic components
Answer & solution

Answer: (d) abiotic components

Correct Answer: Option 4 — abiotic components
An ecosystem is a self-sustaining unit in which living organisms interact with one another and with their physical surroundings. It has two components:
• Abiotic (non-living) components — the physical and chemical factors of the environment: temperature, rainfall, humidity, wind, light, soil, water, air and minerals. They decide which organisms can live in a place.
• Biotic (living) components — producers (green plants), consumers (herbivores, carnivores, omnivores, parasites) and decomposers (bacteria and fungi).
Since temperature, rainfall, wind, soil and minerals are all non-living, they are abiotic components.
❌ Why the other options are incorrect
✗ Living components — these are the organisms themselves; temperature, wind and minerals are clearly non-living.
✗ Biotic components — the biotic group covers only living things — plants, animals and microbes — not physical factors.
✗ Decomposers — a sub-group of the biotic component; bacteria and fungi that break down dead remains and return nutrients to the soil.
📌 SSC & Railway Exam Facts
• The term ecosystem was coined by A. G. Tansley (1935).
• Natural ecosystems — forest, grassland, lake, ocean; artificial (man-made) — crop field, garden, aquarium.
• The ocean is the largest ecosystem; the forest is the largest terrestrial ecosystem.
• Energy flow in an ecosystem is unidirectional, while nutrients move in cycles (biogeochemical cycles).
• Decomposers are also called saprophytes; without them nutrients would stay locked in dead bodies.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 1 · Trophic levels and the 10 percent law

Q136. Honey is produced by the honeybee. So, the honeybee is a _______.

  1. (a) primary consumer
  2. (b) producer
  3. (c) Decomposer
  4. (d) secondary consumer
Answer & solution

Answer: (a) primary consumer

Correct Answer: Option 1 — primary consumer
The honeybee feeds directly on the nectar and pollen of flowers, that is, directly on a producer (green plant). Any organism that eats a producer is a herbivore, and a herbivore occupies the second trophic level of a food chain and is called a primary consumer.
Honey is only the processed and stored food made by the bee from nectar — it is not food manufactured from carbon dioxide, water and sunlight. Making one's own food from inorganic raw materials is the job of an autotroph, and the honeybee cannot do that; it is a heterotroph.
A typical chain: Flower (producer) → Honeybee (primary consumer) → Bee-eater bird (secondary consumer) → Hawk (tertiary consumer).
❌ Why the other options are incorrect
✗ Producer — producers are autotrophs like green plants and algae that make food by photosynthesis; the bee only collects and concentrates food already made by the plant.
✗ Decomposer — bacteria and fungi that break down dead bodies and wastes into simple substances; the honeybee feeds on living flowers, not on dead matter.
✗ Secondary consumer — an animal that eats a primary consumer, i.e. a small carnivore like a frog or snake; the bee eats plant products, not animals.
📌 SSC & Railway Exam Facts
• Rearing of honeybees for honey and wax is apiculture; the common Indian species is *Apis cerana indica*.
• Honeybees are also the most important pollinating agents, which is vital for crop yield.
• Grazing food chain begins with a green plant; the detritus food chain begins with dead organic matter.
• Only about 10% of energy passes from one trophic level to the next — Lindeman's 10 per cent law.
• Sericulture — silkworm rearing; Pisciculture — fish farming; Apiculture — beekeeping.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 2 · Waste management and biodegradable substances

Q137. Which of the following is a biodegradable substance?

  1. (a) Glass
  2. (b) Plastic bag
  3. (c) Electric wire
  4. (d) Dead plant
Answer & solution

Answer: (d) Dead plant

Correct Answer: Option 4 — Dead plant
Substances that can be broken down into simple, harmless materials by the action of micro-organisms such as bacteria and fungi (the decomposers) are called biodegradable substances.
A dead plant is made of cellulose, proteins and other organic compounds, all of which decomposers can digest with their enzymes. Within weeks the plant rots and returns carbon, nitrogen and minerals to the soil, completing the biogeochemical cycles. This is exactly the principle used in making compost and vermicompost.
Substances that decomposers cannot break down are called non-biodegradable; they persist for hundreds of years, choke the soil and water, and cause biomagnification of toxins in food chains.
❌ Why the other options are incorrect
✗ Glass — made of fused silica (sand); no micro-organism has an enzyme to digest it, so it is non-biodegradable, though it is fully recyclable.
✗ Plastic bag — a synthetic polymer (polythene); its long carbon chains resist microbial attack and it may survive for hundreds of years, killing cattle and blocking drains.
✗ Electric wire — made of metal (copper/aluminium) with a plastic or rubber coating; both parts are non-biodegradable and form e-waste.
📌 SSC & Railway Exam Facts
• Biodegradable — food waste, paper, cotton, wool, leaves, cow dung, jute; Non-biodegradable — plastic, glass, metal, DDT, polythene, styrofoam.
• Decomposers (bacteria and fungi) are also called saprophytes; they are nature's cleaners.
• In Indian waste segregation, green bins are for biodegradable (wet) waste and blue bins for non-biodegradable (dry) waste.
• Concentration of harmful chemicals like DDT rising at each trophic level is biomagnification.
• The three R's of waste management are Reduce, Reuse and Recycle.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 3 · Energy flow and ecological pyramids

Q138. The energy transfer within the food web has a _______ pattern.

  1. (a) Unidirectional
  2. (b) Circular
  3. (c) Multidimensional
  4. (d) Bidirectional
Answer & solution

Answer: (a) Unidirectional

Correct Answer: Option 1 — Unidirectional
The flow of energy in a food chain or a food web is always unidirectional — it moves in one direction only, from the Sun → producers (green plants) → herbivores → carnivores. Energy captured by producers during photosynthesis never returns to the Sun, and energy passed on to a herbivore never flows back into the plant.
At every trophic level about 90% of the energy is lost as heat, respiration and other life processes, so only about 10% is passed on to the next level — this is Lindeman's 10% Law. Because of this steady loss, a food chain normally has only 3 or 4 trophic levels.
❌ Why the other options are incorrect
✗ Circular — matter and nutrients (carbon, nitrogen) do move in a circular way through cycles, but energy does not; it escapes as heat and cannot be recycled.
✗ Multidimensional — energy does not spread in many directions at a single feeding step; a food web only looks branched because many separate chains are interlinked.
✗ Bidirectional — energy never flows back from a consumer to a producer; a rabbit cannot return energy to the grass it ate.
📌 SSC & Railway Exam Facts
• The term ecosystem was coined by A.G. Tansley (1935); the food chain concept was given by Charles Elton.
• The 10% Law of energy transfer was given by Raymond Lindeman.
• Producers → primary consumers → secondary consumers → tertiary consumers form trophic levels T1–T4.
• Biomagnification — harmful chemicals such as DDT become more concentrated at higher trophic levels.
• Decomposers (bacteria and fungi) return nutrients to the soil and complete the nutrient cycle.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 3 · Waste management and biodegradable substances

Q139. Which of the following is NOT a suitable method to deal with non-biodegradable substances?

  1. (a) Throw them openly
  2. (b) Reuse them
  3. (c) Recycle them
  4. (d) Reduce their production
Answer & solution

Answer: (a) Throw them openly

Correct Answer: Option 1 — Throw them openly
Non-biodegradable substances such as plastics, polythene, glass, metal cans, DDT and e-waste cannot be broken down by decomposers (bacteria and fungi). Throwing them openly is therefore not a suitable method — they pile up in the environment for hundreds of years, choke drains, pollute soil and water, kill cattle and marine animals, and enter food chains through biomagnification.
The scientific way to handle such waste is the three R's — Reduce, Reuse and Recycle. Cutting down production, using an article again and again, and reprocessing it into new goods all reduce the load of waste on the ecosystem.
❌ Why the other options are incorrect
✗ Reuse them — a very good method; using a bottle or a bag again and again avoids fresh waste and needs no extra energy.
✗ Recycle them — plastics, glass and metals are reprocessed into new articles, saving raw material and energy.
✗ Reduce their production — cutting down the manufacture and use of such items is the best long-term solution.
📌 SSC & Railway Exam Facts
• Biodegradable wastes — vegetable peels, paper, cow dung, cotton; non-biodegradable — plastic, glass, DDT, aluminium.
• Biomagnification — pesticides such as DDT become more concentrated at each higher trophic level.
• Composting and vermicomposting (using earthworms) turn organic waste into manure.
• The Ganga Action Plan (1985) was launched to reduce river pollution.
• Reduce, Reuse, Recycle are the 3 R's of sustainable waste management.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 2 · Waste management and biodegradable substances

Q140. Which of the following statements is/are correct related to eco-system?
(i) Non-biodegradable substance harms the various members of eco-system.
(ii) Non-biodegradable substances break-down by biological processes.
(iii) Non-biodegradable substances never persist in the environment.

  1. (a) (i), (ii) and (iii)
  2. (b) Only (i)
  3. (c) Only (ii) and (iii)
  4. (d) Only (i) and (ii)
Answer & solution

Answer: (b) Only (i)

Correct Answer: Option 2 — Only (i)
Non-biodegradable substances are materials that cannot be broken down by the action of micro-organisms such as bacteria and fungi — examples are plastic, polythene, DDT, glass, metal cans and aluminium foil.
Statement (i) is correct: because they cannot be decomposed, these substances build up in soil and water, choke drains, are swallowed by cattle and marine animals, and pass up the food chain by biomagnification, harming many members of the ecosystem.
Statement (ii) is wrong — the very definition of non-biodegradable is that biological processes do not break them down.
Statement (iii) is wrong — such substances persist in the environment for decades or even centuries.
❌ Why the other options are incorrect
✗ (i), (ii) and (iii) — wrong, because (ii) and (iii) contradict the definition of a non-biodegradable substance.
✗ Only (ii) and (iii) — wrong; these are exactly the two false statements, and it also leaves out the true statement (i).
✗ Only (i) and (ii) — (i) is true but (ii) is false, so the pair cannot be correct.
📌 SSC & Railway Exam Facts
• Biodegradable wastes: vegetable peels, paper, cotton, cow dung, wood, jute.
• DDT entering a food chain is the classic example of biomagnification; its concentration is highest in the top consumer.
• Only about 10% of energy passes from one trophic level to the next — the 10 per cent law of Lindemann.
• Because energy is lost at each step, food chains generally have only 3 to 4 trophic levels.
• Reduce, Reuse, Recycle is the three-R approach to waste management.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 3 · Waste management and biodegradable substances

Q141. Which of the given statements is/are correct?
a) There are two types of waste: biodegradable and non-biodegradable.
b) We should collect dry waste and wet waste separately.

  1. (a) Only a)
  2. (b) Only b)
  3. (c) Both a) and b)
  4. (d) Neither a) nor b)
Answer & solution

Answer: (c) Both a) and b)

Correct Answer: Option 3 — Both a) and b)
Statement a) is correct. On the basis of whether micro-organisms can break them down, wastes are classified into two types — biodegradable wastes (vegetable peels, paper, cow dung, cotton, wood), which are decomposed by bacteria and fungi, and non-biodegradable wastes (plastic, polythene, glass, metal, DDT), which are not.
Statement b) is also correct. Waste should be segregated at source: the wet (biodegradable) waste can be turned into compost or biogas, while the dry (non-biodegradable) waste can be sent for recycling. Mixing the two makes both treatment and recycling difficult, which is why municipal bodies supply separate green and blue bins.
❌ Why the other options are incorrect
✗ Only a) — incomplete; separate collection of dry and wet waste is a correct and strongly recommended practice.
✗ Only b) — incomplete; the two-fold classification of waste in statement a) is a standard NCERT fact.
✗ Neither a) nor b) — clearly wrong, as both statements are scientifically true.
📌 SSC & Railway Exam Facts
• Green bin — wet/biodegradable waste; blue bin — dry/recyclable waste.
• Vermicomposting uses earthworms to turn organic waste into manure.
• Biogas is mainly methane (CH₄), obtained from cow dung in a gobar gas plant.
• Swachh Bharat Abhiyan was launched on 2 October 2014.
• The three Rs of waste management — Reduce, Reuse, Recycle.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · Waste management and biodegradable substances

Q142. Biodegradable material are broken down into simpler material by the action of which of the following?

  1. (a) Bacteria
  2. (b) Wind
  3. (c) Sunlight
  4. (d) Virus
Answer & solution

Answer: (a) Bacteria

Correct Answer: Option 1 — Bacteria
Biodegradable substances are those which can be broken down into simpler, harmless substances by the action of micro-organisms such as bacteria and fungi. These micro-organisms are the decomposers of the ecosystem. They secrete enzymes onto dead plant and animal matter, rot it, and return the nutrients to the soil so that plants can absorb them again.
Without decomposers the nutrient cycle would stop and dead bodies and wastes would pile up. Vegetable peels, paper, cotton, wood, cow dung and sewage are biodegradable; plastic, glass, aluminium cans, DDT and radioactive waste are non-biodegradable.
❌ Why the other options are incorrect
✗ Wind — wind only disperses and physically scatters waste; it cannot chemically break organic matter into simpler substances.
✗ Sunlight — sunlight can help dry or fade some materials, but decomposition of biodegradable waste is a biological action, not a purely physical one.
✗ Virus — a virus can multiply only inside a living host cell; it is not a decomposer and does not rot dead organic matter.
📌 SSC & Railway Exam Facts
• Decomposers — bacteria and fungi; they are also called micro-organisms of the soil.
• Biodegradable — food waste, paper, cotton, jute, cow dung. Non-biodegradable — plastic, glass, DDT, metals.
• Composting and vermicomposting (using earthworms) turn biodegradable waste into manure.
• Biogas is produced by the anaerobic decomposition of cow dung by bacteria; it is mainly methane (CH₄).
• Non-biodegradable pesticides show biomagnification along a food chain.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 3 · Waste management and biodegradable substances

Q143. Select the INCORRECT pair.

  1. (a) Plastic glass – non-biodegradable
  2. (b) Vegetable – biodegradable
  3. (c) Kulhad – non-biodegradable
  4. (d) Paper cup – biodegradable
Answer & solution

Answer: (c) Kulhad – non-biodegradable

Correct Answer: Option 3 — Kulhad – non-biodegradable
A kulhad is a cup made of baked clay (earthen ware). Since it is made of natural soil, a broken kulhad simply mixes back into the earth and is treated as an eco-friendly, biodegradable item. Calling it non-biodegradable is therefore the incorrect pair.
Biodegradable wastes are substances that are broken down into simple harmless matter by micro-organisms such as bacteria and fungi — vegetable peels, paper, cow dung, cotton and wood. Non-biodegradable wastes cannot be decomposed by microbes and stay in the environment for hundreds of years — plastics, polythene, glass, metals and DDT.
❌ Why the other options are incorrect
✗ Plastic glass – non-biodegradable — correct pairing; plastic is a polymer that microbes cannot decompose.
✗ Vegetable – biodegradable — correct pairing; vegetable matter is organic and rots quickly by microbial action.
✗ Paper cup – biodegradable — correct pairing; paper is made of cellulose from plants and is decomposed by microbes.
📌 SSC & Railway Exam Facts
• Green dustbins are for biodegradable waste and blue dustbins for non-biodegradable waste.
• Vermicomposting uses earthworms to convert organic waste into manure.
• Non-biodegradable pesticides like DDT cause biomagnification along the food chain.
• The 3 Rs of waste management are Reduce, Reuse and Recycle.
• Biogas (gobar gas) is mainly methane (CH₄) produced from cattle dung.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 1 · Waste management and biodegradable substances

Q144. Select the INCORRECT pair.

  1. (a) Plastic glass – non-biodegradable
  2. (b) Vegetable – biodegradable
  3. (c) Kulhad – non-biodegradable
  4. (d) Paper cup – biodegradable
Answer & solution

Answer: (c) Kulhad – non-biodegradable

Correct Answer: Option 3 — Kulhad – non-biodegradable
A kulhad is the traditional Indian cup made of baked clay (earthenware). Clay is a purely natural material; a discarded or broken kulhad simply crumbles and mixes back into the soil through weathering and the action of microorganisms. It is therefore a biodegradable article, and calling it non-biodegradable makes this pair incorrect.
Biodegradable substances are those which are broken down into simple, harmless substances by decomposers such as bacteria and fungi. Non-biodegradable substances resist this breakdown, persist in the environment for a very long time, pollute soil and water, and can enter food chains.
❌ Why the other options are incorrect
✗ Plastic glass – non-biodegradable — a correct pair; plastic is a man-made polymer that decomposers cannot break down, so it survives for hundreds of years.
✗ Vegetable – biodegradable — a correct pair; vegetable peels and leftovers rot quickly and are used to prepare compost and manure.
✗ Paper cup – biodegradable — a correct pair; paper is made of cellulose from wood pulp, which microbes readily decompose.
📌 SSC & Railway Exam Facts
• Biodegradable wastes — food and vegetable waste, paper, cotton, wool, wood, leather, jute, cow dung.
• Non-biodegradable wastes — plastic, polythene, glass, metals, DDT, synthetic fibres, aluminium foil.
• Harmful chemicals such as DDT keep increasing at each higher trophic level — this is biomagnification.
• Follow the 3R principle — Reduce, Reuse, Recycle; wet waste goes in the green bin and dry waste in the blue bin.
• Biodegradable waste rotting in the absence of air gives biogas (mainly methane) and useful manure.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 2 · Waste management and biodegradable substances

Q145. Which of the following is/are correct about non-biodegradable substances?
A. These substances are not broken down through biological processes.
B. These substances persist in the environment for a short period.
C. These substances may harm the various members of the ecosystem.

  1. (a) Both A and C
  2. (b) A, B and C
  3. (c) Only B
  4. (d) Both B and C
Answer & solution

Answer: (a) Both A and C

Correct Answer: Option 1 — Both A and C
Non-biodegradable substances are materials that decomposers such as bacteria and fungi cannot break down. Since no enzyme of any microbe acts on them, they stay in the environment almost unchanged.
Checking each statement:
• A is correct — they are not broken down by biological processes; plastic, glass and metals are not attacked by decomposers.
• B is wrong — they do not persist for a short period; they remain for decades or even centuries, which is precisely the problem.
• C is correct — they harm many members of the ecosystem: plastic chokes cattle and marine animals, blocks drains and soil pores, and pesticides like DDT pass up the food chain by biomagnification.
Hence only A and C are correct.
❌ Why the other options are incorrect
✗ A, B and C — includes B, which wrongly says these substances stay for only a short period.
✗ Only B — statement B is itself false, so it can never be the sole correct answer.
✗ Both B and C — again accepts the false statement B and leaves out the correct statement A.
📌 SSC & Railway Exam Facts
• Non-biodegradable — plastic, polythene, glass, metals, DDT, synthetic fibres, aluminium foil.
• Biodegradable — food and vegetable waste, paper, cotton, wool, wood, leather, jute, cow dung.
• Biomagnification — the rise in concentration of harmful chemicals at each higher trophic level; humans, being at the top, are worst affected.
• 3R principle — Reduce, Reuse, Recycle; segregate wet waste in green bins and dry waste in blue bins.
• Burning plastic releases poisonous gases such as dioxins; India has banned many single-use plastics.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 3 · Waste management and biodegradable substances

Q146. Which of the given substances is NOT biodegradable in nature?
A. Vegetable peels
B. Plastic bottles
C. Spoilt food

  1. (a) Only A
  2. (b) Only B
  3. (c) A, B and C
  4. (d) Both A and C
Answer & solution

Answer: (b) Only B

Correct Answer: Option 2 — Only B
Substances that are broken down by biological processes — by the action of micro-organisms such as bacteria and fungi — are called biodegradable. Substances that these decomposers cannot break down are non-biodegradable.
Plastic bottles are made of long-chain synthetic polymers for which no natural enzyme exists, so they persist in the soil and water for hundreds of years, choke drains, kill cattle and marine animals, and are the classic example of a non-biodegradable pollutant. Vegetable peels and spoilt food are organic wastes rich in carbohydrates and proteins; decomposers convert them into simple substances within days, which is why they are used to make compost.
❌ Why the other options are incorrect
✗ Only A — vegetable peels are biodegradable kitchen waste, easily rotted by bacteria and fungi.
✗ A, B and C — wrong, because peels and spoilt food are both readily decomposed; only the plastic is not.
✗ Both A and C — these two are exactly the biodegradable items, so they cannot be the answer.
📌 SSC & Railway Exam Facts
• Biodegradable — vegetable and fruit peels, paper, cotton, wool, cow dung, jute, wood.
• Non-biodegradable — plastics, polythene, glass, metals, DDT, aluminium cans, synthetic fibres.
• Non-biodegradable pesticides increase along a food chain — this is biomagnification.
• The 3 Rs of waste management are Reduce, Reuse and Recycle.
• Green dustbins are for biodegradable waste and blue dustbins for non-biodegradable waste.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 1 · Waste management and biodegradable substances

Q147. Which of the following statements is/are correct related to eco-system?
(i) Non-biodegradable substance harms the various members of eco-system.
(ii) Non-biodegradable substances break-down by biological processes.
(iii) Non-biodegradable substances never persist in the environment.

  1. (a) (i), (ii) and (iii)
  2. (b) Only (i) and (ii)
  3. (c) Only (i)
  4. (d) Only (ii) and (iii)
Answer & solution

Answer: (c) Only (i)

Correct Answer: Option 3 — Only (i)
Non-biodegradable substances are materials that cannot be broken down by decomposers such as bacteria and fungi — for example plastic, polythene, glass, metal and DDT.
Checking each statement:
• (i) is correct — such substances may be inert and persist for a long time, or they may harm the various members of the ecosystem, choking drains, killing cattle and marine life, and entering food chains.
• (ii) is wrong — it is biodegradable substances that are broken down by biological processes; non-biodegradable ones are not.
• (iii) is wrong — these substances do persist in the environment, often for hundreds of years.
Hence only statement (i) is correct.
❌ Why the other options are incorrect
✗ (i), (ii) and (iii) — statements (ii) and (iii) contradict the very definition of a non-biodegradable substance.
✗ Only (i) and (ii) — (ii) wrongly says non-biodegradable substances are broken down biologically.
✗ Only (ii) and (iii) — both statements are false, and this option also leaves out the true statement (i).
📌 SSC & Railway Exam Facts
• Biodegradable — vegetable peels, paper, cotton, cow dung, leaves; Non-biodegradable — plastic, glass, metal, DDT.
• Decomposers (bacteria and fungi) are also called saprophytes; they recycle nutrients back to the soil.
• Increase of harmful chemicals at successive trophic levels is biomagnification.
• Waste management follows the 4 R's — Refuse, Reduce, Reuse, Recycle.
• The term ecosystem was coined by A. G. Tansley (1935); ocean is the largest ecosystem.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 2 · Waste management and biodegradable substances

Q148. Select the INCORRECT pair.

  1. (a) Rice – digested in our body
  2. (b) Coal – digested in our body
  3. (c) Protein – digested in our body
  4. (d) Plastic – does not breakdown by the action of bacteria
Answer & solution

Answer: (b) Coal – digested in our body

Correct Answer: Option 2 — Coal – digested in our body
Coal cannot be digested by the human body. Digestion happens only when a specific enzyme is available for a specific substance, because enzymes are highly specific in action — a key fits only its own lock. Our alimentary canal has amylase for starch, pepsin and trypsin for proteins and lipase for fats, but there is no enzyme for coal, which is chemically almost pure carbon.
Substances that living organisms and decomposer micro-organisms can break down are called biodegradable; those they cannot break down, such as coal, plastic, glass and DDT, are non-biodegradable and stay in the environment for centuries.
❌ Why the other options are incorrect
✗ Rice – digested in our body — a correct pair; rice is starch, digested by salivary amylase (ptyalin) and pancreatic amylase into glucose.
✗ Protein – digested in our body — a correct pair; proteins are digested by pepsin in the stomach and trypsin in the small intestine into amino acids.
✗ Plastic – does not breakdown by the action of bacteria — a correct pair; plastic is a non-biodegradable man-made polymer that bacteria cannot attack.
📌 SSC & Railway Exam Facts
• Biodegradable wastes — paper, food waste, cotton, wool, wood, cow dung; non-biodegradable — plastic, polythene, glass, metal cans, DDT.
• Decomposers (bacteria and fungi) are called nature's cleaners because they recycle biodegradable matter.
• Non-biodegradable pesticides build up along a food chain — this is biomagnification.
• The three R's of waste management are Reduce, Reuse and Recycle.
• Enzymes are biological catalysts and are mostly proteins; they work best at a specific pH and temperature.
RRB Technician Grade III 2024-25 – 20 December 2024 Shift 2 · Trophic levels and the 10 percent law

Q149. Which of the following is correct about trophic levels in a food chain?

  1. (a) The herbivores or the secondary consumers come at the second level.
  2. (b) The heterotrophs fix up the solar energy and make it available for herbivores or other consumers.
  3. (c) The autotrophs or the producers are at the first trophic level.
  4. (d) The Larger carnivores or the tertiary consumers form the third trophic level.
Answer & solution

Answer: (c) The autotrophs or the producers are at the first trophic level.

Correct Answer: Option 3 — The autotrophs or the producers are at the first trophic level.
Each step of a food chain where energy transfer takes place is called a trophic level. The correct arrangement is:
• First trophic level (T1) — Producers / autotrophs (green plants, algae) that trap solar energy and convert it into chemical energy by photosynthesis.
• Second trophic level (T2) — Herbivores / primary consumers (deer, grasshopper).
• Third trophic level (T3) — Small carnivores / secondary consumers (frog, snake).
• Fourth trophic level (T4) — Larger carnivores / tertiary consumers (hawk, lion).
❌ Why the other options are incorrect
✗ Option 1 — herbivores at the second level are primary consumers, not secondary consumers.
✗ Option 2 — autotrophs, not heterotrophs, fix solar energy. Heterotrophs cannot make their own food.
✗ Option 4 — larger carnivores / tertiary consumers occupy the fourth trophic level, not the third.
📌 SSC & Railway Exam Facts
• The term trophic level was given by Raymond Lindeman.
• Only about 10% of energy passes to the next trophic level — the 10 per cent law of Lindeman.
• Because of this heavy loss, food chains usually have only 3 to 4 trophic levels.
• Energy flow in an ecosystem is unidirectional, while nutrients are recycled.
• Harmful chemicals like pesticides increase at each higher level — this is biomagnification.
RRB Technician Grade III 2024-25 – 20 December 2024 Shift 2 · Ecosystem and its components

Q150. Which of the following is/are correct regarding the components of an ecosystem?
A. Living organisms - Abiotic Component
B. Soil - Biotic component
C. Minerals - Abiotic component

  1. (a) Only C
  2. (b) B and C
  3. (c) Only B
  4. (d) Both A and C
Answer & solution

Answer: (a) Only C

Correct Answer: Option 1 — Only C
An ecosystem has two components:
• Biotic components — all living things: producers (green plants), consumers (herbivores, carnivores, omnivores, parasites) and decomposers (bacteria, fungi).
• Abiotic components — all non-living physical and chemical factors: soil, water, air, light, temperature, humidity and minerals.
Checking each statement:
• A is wrong — living organisms are biotic, not abiotic.
• B is wrong — soil is abiotic, not biotic.
• C is correct — minerals are indeed abiotic.
So only statement C is correct.
❌ Why the other options are incorrect
✗ B and C — B wrongly calls soil a biotic component.
✗ Only B — soil is abiotic, so B by itself is false.
✗ Both A and C — A wrongly calls living organisms abiotic.
📌 SSC & Railway Exam Facts
• The term ecosystem was coined by A. G. Tansley (1935).
• Decomposers are also called saprophytes; they return nutrients to the soil.
• A garden, pond or aquarium is an artificial (man-made) ecosystem; a forest, lake or ocean is a natural ecosystem.
• Ocean is the largest ecosystem on Earth.
• The study of the interaction of organisms with their environment is called ecology.
RRB Technician Grade III 2024-25 – 20 December 2024 Shift 3 · Waste management and biodegradable substances

Q151. Which of the following non-biodegradable substances may be inert and simply persist in the environment for a long time or may harm the various members of the eco-system?

  1. (a) Paper made material
  2. (b) Plastic made material
  3. (c) Clay made material
  4. (d) Plant leaves made material
Answer & solution

Answer: (b) Plastic made material

Correct Answer: Option 2 — Plastic made material
Plastic is a man-made polymer that decomposers such as bacteria and fungi cannot break down, so it is non-biodegradable. Discarded plastic either stays inert in the environment for hundreds of years or releases harmful substances that damage the various members of the ecosystem — it chokes drains, kills cattle and marine animals that swallow it, and its additives enter food chains.
Because it does not decompose, plastic also accumulates through the food chain and cannot be returned to the soil as nutrients, unlike biodegradable waste.
❌ Why the other options are incorrect
✗ Paper made material — made from cellulose of wood; micro-organisms digest cellulose, so paper is biodegradable and can also be recycled.
✗ Clay made material — clay is a natural earth material; broken clay objects mix back into the soil and are not a persistent toxic pollutant like plastic.
✗ Plant leaves made material — leaves are purely organic and are quickly turned into humus by decomposers; they are the classic example of biodegradable waste.
📌 SSC & Railway Exam Facts
• Biodegradable — food waste, paper, cotton, leaves, cow dung; Non-biodegradable — plastic, glass, metal, DDT, polythene.
• The build-up of non-degradable chemicals at higher trophic levels is called biomagnification.
• Waste management follows the 4 R's — Refuse, Reduce, Reuse, Recycle.
• Vermicomposting uses earthworms to convert biodegradable waste into manure.
• 5 June is celebrated as World Environment Day.
RRB Technician Grade III 2024-25 – 20 December 2024 Shift 3 · Waste management and biodegradable substances

Q152. Kulhads are disposable cups made of clay. A little thought shows that making these kulhads on a large scale would result in:

  1. (a) choking the sewage line
  2. (b) large remains collected in environment
  3. (c) losing the fertile top-soil
  4. (d) Unhygienic of its use
Answer & solution

Answer: (c) losing the fertile top-soil

Correct Answer: Option 3 — losing the fertile top-soil
Kulhads are disposable cups moulded from clay. Clay for pottery is dug out from the top-soil — the uppermost layer of soil that is rich in humus and minerals and supports plant growth. If kulhads are manufactured on a very large scale, enormous quantities of this fertile top-soil would be removed, which is why the practice cannot be considered environment-friendly.
Top-soil takes hundreds of years to form, so its loss means reduced soil fertility and greater risk of soil erosion. Hence the NCERT conclusion: for a very large population, disposable paper cups are a better option than kulhads.
❌ Why the other options are incorrect
✗ choking the sewage line — this is the typical problem of plastic and polythene waste, not of clay cups, which break up and settle.
✗ large remains collected in environment — clay is a natural earth material that merges back into the soil; it does not pile up as persistent waste.
✗ Unhygienic of its use — kulhads are actually hygienic, because each cup is used only once and then discarded.
📌 SSC & Railway Exam Facts
• Disposable plastic/thermocol cups are non-biodegradable, whereas paper cups are biodegradable.
• Top-soil is the most fertile layer, rich in humus, and is protected by vegetation cover.
• Removal of top-soil leads to soil erosion and desertification.
• The 4 R's of waste management are Refuse, Reduce, Reuse and Recycle.
• Reuse (e.g. refilling glass jars) is even better than recycling, because recycling itself needs energy.
RRB JE CBT-1 2024-25 – 18 December 2024 Shift 1 · Waste management and biodegradable substances

Q153. Which of the following can be broken down by biological processes?

  1. (a) Vegetable peels
  2. (b) Milk packets
  3. (c) Aluminium foil
  4. (d) Plastic bottles
Answer & solution

Answer: (a) Vegetable peels

Answer: Option 1 — Vegetable peels
Vegetable peels are plant matter that bacteria and fungi (decomposers) break down — so they are biodegradable.
Milk packets, aluminium foil and plastic bottles are not broken down by microbes.
Revision note — Biodegradable and non-biodegradable substances
• Biodegradable: broken down by biological processes — vegetable peels, paper, wood, cotton, dry leaves, dead animals.
• Non-biodegradable: remain for long periods — plastics, polythene, glass, aluminium, DDT, styrofoam.
• Microbes act through enzymes, which are specific — they cannot break plastics.
• Non-biodegradable chemicals like DDT concentrate up the food chain — biological magnification.
• 3Rs: Reduce, Reuse, Recycle; kitchen waste can be turned into compost or biogas.
Also asked from this topic: an example of biodegradable waste (dead animals); the commonest non-biodegradable waste (plastic); an example of "reducing" in waste management (switching from plastic bags to jute bags).
RRB JE CBT-1 2024-25 – 18 December 2024 Shift 1 · Waste management and biodegradable substances

Q154. Which of the following substances will take the longest time to degrade naturally in the environment?

  1. (a) Cardboard box
  2. (b) Paper
  3. (c) Leather
  4. (d) Leaves
Answer & solution

Answer: (c) Leather

Answer: Option 3 — Leather
Leather is biodegradable, but tanning cross-links its protein fibres so microbes break it down very slowly — it can take decades.
Paper, cardboard and leaves are plant cellulose and rot within weeks to a few months.
Revision note — Biodegradable and non-biodegradable waste (Class 10)
• Biodegradable: broken down by bacteria and fungi (decomposers) — food waste, paper, leaves, cotton, wood, leather, dead animals.
• Non-biodegradable: cannot be broken down by microbes — plastics, polythene, glass, aluminium cans, DDT, many metals.
• Non-biodegradable chemicals such as DDT build up along food chains — biological magnification; the top consumer gets the highest dose.
• Rough decay times: paper and leaves — weeks to months; cotton cloth — months; leather — decades; plastic — hundreds of years; glass — practically never.
• 3 Rs: Reduce (e.g. jute bag instead of plastic), Reuse, Recycle.
Also asked from this topic: the commonest non-biodegradable waste (plastic); an example of biodegradable waste (dead animals, food scraps); an example of "reduce" (jute bags instead of plastic).
RRB JE CBT-1 2024-25 – 18 December 2024 Shift 1 · Waste management and biodegradable substances

Q155. Which attribute of a paper cup makes it better than a plastic cup for our environment?

  1. (a) Disposable
  2. (b) Non-biodegradable
  3. (c) Biodegradable
  4. (d) Not disposable
Answer & solution

Answer: (c) Biodegradable

Answer: Option 3 — Biodegradable
A paper cup is made of paper (cellulose), which bacteria and fungi break down into harmless substances.
A plastic cup is non-biodegradable — it stays in soil and water for hundreds of years.
Revision note — Biodegradable and non-biodegradable substances
• Biodegradable: broken down by biological processes (microorganisms) — paper, vegetable peels, food waste, dry leaves, cotton, wood, dead animals.
• Non-biodegradable: not broken down by microbes — plastics, polythene, glass, aluminium cans, DDT, many pesticides.
• Non-biodegradable chemicals such as DDT enter food chains and show biological magnification — highest at the top trophic level.
• Plastics clog drains, harm aquatic and grazing animals and choke soil.
• 3 Rs: Reduce (use less), Reuse (use again), Recycle (reprocess into new products).
• Kulhads (disposable clay cups) were once suggested for trains; making them on a large scale would waste fertile top soil.
Do not mix these up
• Disposable vs biodegradable — both paper and plastic cups are disposable; only the paper cup is biodegradable.
Also asked from this topic: a common non-biodegradable waste (plastic); an effect of non-biodegradable substances in water bodies (they clog drains and harm aquatic life).
RRB JE CBT-1 2024-25 – 18 December 2024 Shift 1 · Waste management and biodegradable substances

Q156. What term can be used for substances that are broken down by biological processes?

  1. (a) Biodegradable
  2. (b) Recyclable
  3. (c) Compostable
  4. (d) Non-biodegradable
Answer & solution

Answer: (a) Biodegradable

Answer: Option 1 — Biodegradable
Substances that microorganisms (bacteria, fungi) can break down by biological processes are called biodegradable.
Revision note — Biodegradable and non-biodegradable substances
• Biodegradable: broken down by decomposers — food waste, paper, cotton, wood, leaves, animal dung.
• Non-biodegradable: inert to microbes — plastic, glass, metal cans, DDT; they persist and pile up.
• Decomposers (bacteria, fungi) return nutrients to the soil and are part of every ecosystem.
• Biological magnification: non-biodegradable chemicals build up along the food chain, highest in top consumers.
• Enzymes are specific — the enzymes of decomposers act only on certain substances, so plastic is not digested.
• Compostable waste is biodegradable waste that turns into manure (compost) under controlled conditions.
Do not mix these up
• Biodegradable vs recyclable — recyclable means reprocessed by humans into new products (glass, metals); biodegradable means broken down by living organisms.
Also asked from this topic: which is biodegradable waste (dead animals); an advantage of paper cups over plastic cups (they are biodegradable).
RRB JE CBT-1 2024-25 – 18 December 2024 Shift 1 · Ecosystem and its components

Q157. What would happen to dead plants and animals if decomposers were absent from an ecosystem?

  1. (a) They would be eaten by consumers.
  2. (b) They would persist, and the natural replenishment of soil would be hindered.
  3. (c) They would quickly turn into soil.
  4. (d) They would become producers.
Answer & solution

Answer: (b) They would persist, and the natural replenishment of soil would be hindered.

Answer: Option 2 — They would persist, and the natural replenishment of soil would be hindered.
Decomposers (bacteria and fungi) break dead remains into simple inorganic substances that go back to the soil.
Without them, dead bodies would pile up and nutrients would not return to the soil.
Revision note — Decomposers and the ecosystem
• An ecosystem has biotic parts (producers, consumers, decomposers) and abiotic parts (air, water, soil, light, temperature).
• Decomposers break complex organic matter → simple inorganic substances; they are the natural cleaners.
• They recycle nutrients so that producers can use them again.
• Materials broken down by microbes are biodegradable; plastics and DDT are non-biodegradable.
• Energy flows one way; nutrients cycle — decomposers close the nutrient cycle.
Do not mix these up
• Decomposers vs scavengers — vultures and jackals eat carcasses (consumers); bacteria and fungi chemically break down dead matter.
Also asked from this topic: the organisms that break down dead plants and animals (decomposers); the main role of decomposers (recycle nutrients back into the soil).
RRB JE CBT-1 2024-25 – 18 December 2024 Shift 1 · Trophic levels and the 10 percent law

Q158. What role do green plants and certain bacteria play in an ecosystem?

  1. (a) Consumers
  2. (b) Producers
  3. (c) Parasites
  4. (d) Decomposers
Answer & solution

Answer: (b) Producers

Answer: Option 2 — Producers
Green plants and certain bacteria (such as cyanobacteria) make their own food from simple substances using sunlight — they are autotrophs.
So they are the producers of an ecosystem.
Revision note — Producers and trophic levels
• Producers = autotrophs; they fix solar energy by photosynthesis (some bacteria use chemosynthesis).
• They form the first trophic level; all other organisms depend on them.
• Herbivores are primary consumers; carnivores are secondary/tertiary consumers.
• Decomposers (bacteria, fungi) are saprophytes that break down dead matter.
• 10 percent law: only about 10% of energy passes to the next trophic level.
• Energy flow is unidirectional; a grassland pyramid of numbers is upright (grass most numerous).
Do not mix these up
• Producers vs decomposers — both can be bacteria; producers make food, decomposers break down dead matter.
Also asked from this topic: the group that captures solar energy in a garden ecosystem (plants); the organisms NOT classified as consumers (producers); the trophic level hit hardest by a drought (producers).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 1 · Waste management and biodegradable substances

Q159. Which of the following materials is likely to be non-biodegradable?

  1. (a) Paper
  2. (b) Plastic
  3. (c) Vegetable peels
  4. (d) Wood
Answer & solution

Answer: (b) Plastic

Answer: Option 2 — Plastic
Plastic cannot be broken down by microorganisms (bacteria, fungi), so it stays in the environment for hundreds of years.
Paper, wood and vegetable peels are all plant material that decomposers break down.
Revision note — Biodegradable and non-biodegradable substances
• Biodegradable: broken down by biological processes (decomposers) — paper, wood, cotton, food waste, dry leaves, dead animals.
• Non-biodegradable: not broken down by microbes — plastics, polythene, glass, aluminium cans, DDT, styrofoam.
• Non-biodegradable chemicals like DDT pass up the food chain and concentrate at each level — biological magnification.
• Microbes lack the enzymes needed to break the long carbon chains of plastics.
• Waste management rests on the 3Rs — Reduce, Reuse, Recycle.
Also asked from this topic: an example of biodegradable waste (dead animals); the advantage of paper cups over plastic cups (they are biodegradable).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 1 · Waste management and biodegradable substances

Q160. Which of the following is an effective method to reduce plastic waste?

  1. (a) Recycling and reusing plastic materials
  2. (b) Using disposable plastic bags
  3. (c) Dumping plastic waste in landfills
  4. (d) Burning plastic waste
Answer & solution

Answer: (a) Recycling and reusing plastic materials

Answer: Option 1 — Recycling and reusing plastic materials
Reusing keeps a plastic item in use longer and recycling turns plastic waste into new products — both cut the plastic that ends up as waste.
Burning releases toxic gases; landfills only store plastic that never decomposes.
Revision note — Managing plastic and other waste
• The 3Rs: Reduce (use less — cloth or jute bags), Reuse (use again), Recycle (reprocess into new items).
• Plastic is non-biodegradable; it can last hundreds of years in soil and water.
• Burning plastic releases harmful gases such as dioxins and carbon monoxide.
• Plastic in drains and water bodies clogs drains and harms aquatic animals.
• India's Plastic Waste Management Rules banned identified single-use plastic items from 1 July 2022 and place Extended Producer Responsibility (EPR) on producers.
Do not mix these up
• Reduce vs reuse — carrying a jute bag instead of taking a plastic bag is reducing; using an old bucket to store things is reusing.
Also asked from this topic: an example of "reducing" in waste management (switching from plastic bags to jute bags); a good waste-management practice (use reusable and recyclable products).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 1 · Ecosystem and its components

Q161. Which of the following is a natural ecosystem?

  1. (a) Aquarium
  2. (b) Forest
  3. (c) Crop field
  4. (d) Garden
Answer & solution

Answer: (b) Forest

Answer: Option 2 — Forest
A forest develops and sustains itself without human help, so it is a natural ecosystem.
Aquariums, crop fields and gardens are set up and maintained by humans — artificial (man-made) ecosystems.
Revision note — Ecosystem
• Ecosystem = all living organisms of an area + the non-living surroundings, interacting as one unit.
• Biotic components: producers (green plants), consumers (herbivores, carnivores, omnivores, parasites), decomposers (bacteria, fungi).
• Abiotic components: temperature, rainfall, wind, soil, minerals, water, light.
• Natural ecosystems: forests, ponds, lakes, rivers, grasslands, deserts, oceans.
• Artificial ecosystems: gardens, crop-fields, aquariums, parks, zoos.
• Decomposers return nutrients to the soil; they are missing or controlled in an aquarium, so it must be cleaned regularly.
Do not mix these up
• Garden vs forest — both have plants and animals, but the garden needs human care; the forest does not.
Also asked from this topic: an example of an artificial ecosystem (crop-field); the role of decomposers (recycling nutrients back into the soil); an abiotic component of an ecosystem (soil).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 2 · Waste management and biodegradable substances

Q162. Thermocol disposables are being widely used in parties and restaurants. By promoting this practice ________.

  1. (a) we are increasing non-biodegradable waste
  2. (b) we are increasing the hygiene concern in us
  3. (c) we are reducing expenses; disposables are cheap to use
  4. (d) we are making the waste biodegradable
Answer & solution

Answer: (a) we are increasing non-biodegradable waste

Answer: Option 1 — we are increasing non-biodegradable waste
Thermocol is expanded polystyrene, a plastic that microorganisms cannot break down.
Every discarded plate or cup adds to non-biodegradable waste that stays for hundreds of years.
Revision note — Biodegradable and non-biodegradable substances
• Biodegradable: broken down by decomposers (bacteria, fungi) — paper, cotton, wood, food waste, dead animals.
• Non-biodegradable: not broken down by microbes — plastics, polythene, thermocol (styrofoam), glass, aluminium cans, DDT.
• Non-biodegradable waste clogs drains, harms aquatic animals, and burning it releases toxic gases.
• Chemicals like DDT concentrate up the food chain — biological magnification.
• Better choice at parties: kulhads, leaf plates (pattals), steel or washable crockery.
• Waste management rests on the 3Rs — Reduce, Reuse, Recycle.
Also asked from this topic: an advantage of paper cups over plastic cups (they are biodegradable); the effect of non-biodegradable substances in water bodies (they clog drains and harm aquatic life).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 2 · Ecosystem and its components

Q163. Which of the following categories are NOT a class of consumers?

  1. (a) Producers
  2. (b) Carnivores
  3. (c) Parasites
  4. (d) Herbivores
Answer & solution

Answer: (a) Producers

Answer: Option 1 — Producers
Producers (green plants, some bacteria) make their own food by photosynthesis, so they are not consumers.
Herbivores, carnivores and parasites all depend on other organisms for food — they are consumers.
Revision note — Components of an ecosystem
• Biotic components: producers, consumers and decomposers.
• Producers are autotrophs — they fix solar energy; they form the first trophic level.
• Herbivores = primary consumers (2nd level); small carnivores = secondary consumers; large carnivores = tertiary consumers.
• Omnivores eat both plants and animals; parasites live on a host and draw food from it — still consumers.
• Decomposers (bacteria and fungi) break down dead remains and return nutrients to the soil.
• Abiotic components: sunlight, temperature, water, air, soil, minerals.
Do not mix these up
• Producers vs decomposers — both are outside the consumer chain; producers make food, decomposers break down dead matter.
Also asked from this topic: the group that depends solely and directly on producers for food (herbivores); what herbivores are in a food web (primary consumers).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 2 · Ecosystem and its components

Q164. Garden is an ecosystem because:

  1. (a) it has only biotic components like plants, trees and flowers
  2. (b) the living organisms in it interact with each other and are affected by abiotic components
  3. (c) the living organisms in it interact with each other and are not affected by abiotic components
  4. (d) it has both plants, trees and animals like insects, frogs, birds, etc., as biotic components
Answer & solution

Answer: (b) the living organisms in it interact with each other and are affected by abiotic components

Answer: Option 2 — the living organisms in it interact with each other and are affected by abiotic components
An ecosystem is the biotic community together with its abiotic surroundings, interacting as one unit.
A garden has plants, insects, birds and microbes that interact with each other and with soil, water, light and air.
Revision note — Ecosystem
• Definition: all living organisms of an area plus the physical factors (temperature, rainfall, wind, soil, minerals) they interact with.
• Biotic components: producers, consumers, decomposers.
• Abiotic components: sunlight, temperature, water, air, soil, minerals.
• Natural ecosystems: forests, ponds, lakes, grasslands, deserts.
• Artificial (human-made) ecosystems: gardens, crop-fields, aquariums.
• The Sun is the ultimate source of energy for every ecosystem.
Do not mix these up
• Community vs ecosystem — a community is only the living organisms; an ecosystem adds the non-living environment.
Also asked from this topic: the best definition of an ecosystem (interaction of biotic and abiotic components); an example of an abiotic factor (soil); an example of an artificial ecosystem (crop-field).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 2 · Waste management and biodegradable substances

Q165. Why do non-biodegradable wastes cause environmental problems?

  1. (a) They are toxic to plants only.
  2. (b) They can be easily recycled.
  3. (c) They increase soil fertility.
  4. (d) They remain in the environment for a long time.
Answer & solution

Answer: (d) They remain in the environment for a long time.

Answer: Option 4 — They remain in the environment for a long time.
Decomposers (bacteria, fungi) cannot break these substances down.
They persist for years, pile up and harm soil, water and living beings.
Revision note — Non-biodegradable wastes
• Examples: plastics, polythene, glass, metals (aluminium cans), DDT, styrofoam.
• Microbes lack the enzymes to digest them, so they stay inert in nature.
• Plastics clog drains, choke animals and cut soil aeration and water seepage.
• Chemicals like DDT and mercury build up along the food chain — biological magnification; highest at the top consumer (humans).
• Remedy: the 3Rs — Reduce, Reuse, Recycle; segregate waste into wet (green bin) and dry (blue bin).
Also asked from this topic: the main concern with non-biodegradable waste (it accumulates and causes pollution); the advantage of paper cups over plastic cups (they are biodegradable).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 2 · Waste management and biodegradable substances

Q166. Rashi wants to make compost for her kitchen garden. She plans to use kitchen wastes. Which set of articles is best suited for her work?

  1. (a) Peels of fruits, leftover vegetables, plastic waste, thermocol cups.
  2. (b) Peels of fruits, leftover vegetables, paper, packing sheets.
  3. (c) Peels of fruits, leftover vegetables, paper, torn cotton clothes.
  4. (d) Peels of fruits, leftover vegetables, plastic waste, old mobile phone.
Answer & solution

Answer: (c) Peels of fruits, leftover vegetables, paper, torn cotton clothes.

Answer: Option 3 — Peels of fruits, leftover vegetables, paper, torn cotton clothes.
Compost is made by microbes decomposing organic waste.
Every item in this set is biodegradable — plant matter or natural fibre.
Revision note — Composting
• Composting — conversion of biodegradable kitchen and garden waste into manure (humus) by bacteria and fungi.
• Suitable: fruit and vegetable peels, leftover food, dry leaves, paper, cotton cloth, cow dung.
• Not suitable: plastic, polythene, thermocol, glass, metal, e-waste — they are non-biodegradable.
• Vermicomposting uses red worms (Eisenia fetida) to speed up composting.
• Compost improves soil fertility, water-holding capacity and aeration, and cuts landfill waste.
Also asked from this topic: why composting is environmentally beneficial (it converts organic waste into useful manure); an example of biodegradable waste (dead animals).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 2 · Pollution - effects on living beings

Q167. What impact does human activities have on the environment?

  1. (a) They help in waste disposal
  2. (b) No impact
  3. (c) They contribute to environmental pollution
  4. (d) Only a positive impact
Answer & solution

Answer: (c) They contribute to environmental pollution

Answer: Option 3 — They contribute to environmental pollution
Burning fuels, industry, vehicles, deforestation, plastics and chemical use add pollutants to air, water and soil faster than nature can clean them.
Revision note — Human activities and the environment
• Air pollution: burning fossil fuels releases CO_(2), SO_(2), NO_(x) and particulates; CO_(2) drives the greenhouse effect.
• Water pollution: industrial effluents, sewage and fertiliser run-off; excess nutrients cause eutrophication.
• Soil pollution: pesticides, plastics and non-biodegradable waste; DDT shows biological magnification.
• Deforestation causes soil erosion, floods and loss of biodiversity.
• CFCs from refrigerators and aerosols deplete the ozone layer.
• Remedies: the 3Rs (Reduce, Reuse, Recycle), renewable energy, afforestation.
Also asked from this topic: the main human source of carbon dioxide emissions (burning of fossil fuels); the activity that upsets the balance between soil formation and soil erosion (deforestation).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 2 · Waste management and biodegradable substances

Q168. Mohan went to a cafe and ordered a soft drink. The waiter brought his order in a plastic glass with a plastic straw. Mohan, being environment friendly, is not happy as:

  1. (a) plastic glass and plastic straw is non biodegradable and persists in soil for a long time
  2. (b) a plastic glass and plastic straw does not add to the standard of the cafe
  3. (c) plastic glass and plastic straw spoils the taste of the drink
  4. (d) the plastic glass and plastic straw were not of his favourite colour
Answer & solution

Answer: (a) plastic glass and plastic straw is non biodegradable and persists in soil for a long time

Answer: Option 1 — plastic glass and plastic straw is non biodegradable and persists in soil for a long time
Plastic cannot be broken down by decomposers (bacteria, fungi), so a used glass and straw stay in the soil and water for hundreds of years.
Single-use items like these are the easiest plastic to avoid.
Revision note — Non-biodegradable waste
• Biodegradable: broken down by microbes — paper, cotton, food waste, leaves, dead animals.
• Non-biodegradable: not broken down by microbes — plastic, polythene, glass, aluminium cans, DDT.
• Plastic clogs drains, chokes animals that swallow it and releases toxic gases (dioxins) when burnt.
• India banned identified single-use plastic items, including plastic straws, from 1 July 2022.
• Eco-friendly substitutes: paper or bamboo straws, glass, steel or kulhad (clay) cups.
• Waste management rests on the 3Rs — Reduce, Reuse, Recycle.
Also asked from this topic: an example of biodegradable waste (dead animals); what non-biodegradable waste does in water bodies (clogs drains and harms aquatic life).
12

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