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Our Environment

NCERT Class 10 · Science Based on NCERT Class 10 Science textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explores the interactions between living organisms and their physical surroundings, forming ecosystems. It explains how energy flows through food chains and webs, the impact of human activities like pesticide use and ozone depletion, and the critical difference between biodegradable and non-biodegradable waste. The one big idea a student must walk away with is that all components of an environment are interdependent, and human actions can disrupt this delicate balance, leading to problems like biological magnification and ozone layer depletion.
Key Concepts (16)
Ecosystem
An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals, all interacting with each other and maintaining a balance in nature.
e.g. A garden with plants, animals, soil, and sunlight is an ecosystem.
Biotic components
The living organisms in an ecosystem, such as plants, animals, and microorganisms.
e.g. Trees, frogs, insects, and bacteria in a garden.
Abiotic components
The non-living physical factors in an ecosystem, such as temperature, rainfall, wind, soil, and minerals.
e.g. Sunlight, water, and soil in a pond.
Natural ecosystem
An ecosystem that occurs naturally without human intervention, such as forests, ponds, and lakes.
e.g. A forest ecosystem.
Artificial ecosystem
A human-made ecosystem, such as gardens, crop-fields, and aquariums.
e.g. An aquarium set up in a home.
Producers
All green plants and certain bacteria which can produce food by photosynthesis from inorganic substances using the radiant energy of the Sun in the presence of chlorophyll.
e.g. Grass, wheat, and mango trees.
Consumers
Organisms which consume the food produced, either directly from producers or indirectly by feeding on other consumers.
e.g. Herbivores like goats, carnivores like lions, and omnivores like humans.
Decomposers
Microorganisms, comprising bacteria and fungi, that break-down the complex organic substances of dead remains and waste products into simple inorganic substances that go into the soil and are used up once more by the plants.
e.g. Bacteria and fungi breaking down a dead leaf.
Food chain
A series of organisms taking part at various biotic levels, feeding on one another, forming a chain.
e.g. Grass → Goat → Human.
Trophic level
Each step or level of the food chain forms a trophic level.
e.g. Producers are at the first trophic level, herbivores at the second.
Food web
A series of branching lines showing the feeding relationships in an ecosystem, where each organism is generally eaten by two or more other kinds of organisms.
e.g. In a grassland, grass is eaten by both rabbits and insects, which are then eaten by foxes and birds.
Biological magnification
The phenomenon where non-degradable chemicals like pesticides get accumulated progressively at each trophic level, with the maximum concentration in organisms at the top level.
e.g. DDT in water is absorbed by algae, then concentrated in fish, and further concentrated in birds that eat the fish.
Ozone (O3)
A molecule formed by three atoms of oxygen, which at higher levels of the atmosphere shields the surface of the earth from ultraviolet (UV) radiation from the Sun.
e.g. The ozone layer in the stratosphere.
Chlorofluorocarbons (CFCs)
Synthetic chemicals used as refrigerants and in fire extinguishers that are linked to the depletion of the ozone layer.
e.g. CFCs used in old refrigerators and air conditioners.
Biodegradable substances
Substances that are broken down by biological processes (action of bacteria or other saprophytes).
e.g. Fruit peels, cake, wood, and grass.
Non-biodegradable substances
Substances that are not broken down by biological processes and persist in the environment for a long time or may harm the ecosystem.
e.g. Plastics, empty medicine bottles, and broken footwear.
Formulas & Equations (4)
O2 → (UV radiation) → O + O
Reads as: Oxygen molecule is split by UV radiation into two free oxygen atoms.
Variables: O2 = molecular oxygen; O = free oxygen atom; UV = ultraviolet radiation.
Use when: Explaining the first step of ozone formation in the atmosphere.
⚠ Students often write O2 splitting into O3 directly, forgetting the intermediate free oxygen atoms.
O + O2 → O3
Reads as: A free oxygen atom combines with an oxygen molecule to form ozone.
Variables: O = free oxygen atom; O2 = molecular oxygen; O3 = ozone.
Use when: Explaining the second step of ozone formation.
⚠ Students forget to mention that this reaction requires a third molecule (like N2) to carry away excess energy, though not explicitly in NCERT, they should not write it as a simple collision without energy transfer context.
Energy captured by producers = 1% of sunlight energy
Reads as: Green plants in a terrestrial ecosystem capture about one percent of the energy of sunlight that falls on their leaves.
Variables: No variables; it is a fixed percentage.
Use when: Explaining energy flow and the inefficiency of energy capture at the producer level.
⚠ Students often write that plants capture 10% of sunlight, confusing it with the 10% law for trophic transfer.
10% Law: Energy transferred to next trophic level = 10% of energy in the previous trophic level
Reads as: An average of 10 percent of the food eaten is turned into its own body and made available for the next level of consumers.
Variables: No variables; it is a general rule of thumb.
Use when: Explaining why food chains generally have only 3-4 trophic levels and why energy diminishes at each step.
⚠ Students think 10% of the energy is transferred from the Sun to producers, but it is 10% of the energy in the organism's body that is passed to the next trophic level.
How It Works
Flow of energy in an ecosystem
  1. Step 1: Autotrophs (producers) capture about 1% of the solar energy falling on their leaves and convert it into chemical energy (food) through photosynthesis.
  2. Step 2: Primary consumers (herbivores) eat the producers and use most of the energy for digestion, work, and growth, losing a great deal as heat to the environment.
  3. Step 3: Only about 10% of the food eaten by a consumer is turned into its own body and made available for the next level of consumers.
  4. Step 4: This 10% transfer continues at each trophic level, so very little usable energy remains after four trophic levels.
  5. Step 5: The flow of energy is unidirectional — it does not revert back to the previous level or to the solar input.
💡 Energy flow is unidirectional and diminishes at each trophic level; it is not recycled like matter.
Formation and depletion of ozone layer
  1. Step 1: High-energy UV radiation from the Sun splits some molecular oxygen (O2) into free oxygen atoms (O).
  2. Step 2: These free oxygen atoms combine with molecular oxygen (O2) to form ozone (O3).
  3. Step 3: The ozone layer at higher levels of the atmosphere shields the Earth's surface from harmful UV radiation.
  4. Step 4: In the 1980s, the amount of ozone began to drop sharply due to synthetic chemicals like chlorofluorocarbons (CFCs) used as refrigerants and in fire extinguishers.
  5. Step 5: In 1987, the United Nations Environment Programme (UNEP) forged an agreement to freeze CFC production at 1986 levels, and it is now mandatory to make CFC-free refrigerators.
💡 Ozone at ground level is a pollutant, but in the stratosphere it is essential for life; CFCs are the main cause of its depletion.
Biological magnification
  1. Step 1: Pesticides and other non-degradable chemicals are used to protect crops from diseases and pests.
  2. Step 2: These chemicals are washed down into the soil or into water bodies.
  3. Step 3: From the soil, they are absorbed by plants along with water and minerals; from water bodies, they are taken up by aquatic plants and animals.
  4. Step 4: As these chemicals are not degradable, they get accumulated progressively at each trophic level.
  5. Step 5: Human beings, occupying the top level in any food chain, accumulate the maximum concentration of these chemicals in their bodies.
💡 The concentration of the chemical increases at each trophic level, not the amount of the chemical itself.
Decomposition by decomposers
  1. Step 1: When an organism dies, microorganisms (bacteria and fungi) act on the dead remains and waste products.
  2. Step 2: These decomposers break down complex organic substances into simple inorganic substances.
  3. Step 3: These simple inorganic substances go into the soil and are used up once more by the plants.
  4. Step 4: This process ensures natural replenishment of the soil.
💡 Decomposers are essential for recycling matter; without them, dead matter would accumulate and soil fertility would decline.
Exam Traps — Don't Make These Mistakes
⚠ Confusing '10% law' with energy captured by producers
✗ Plants capture 10% of sunlight energy.
→ The chapter clearly states that green plants capture about 1% of the energy of sunlight that falls on their leaves. The 10% law applies to the transfer of energy from one trophic level to the next, not from the Sun to producers.
✓ Green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers.
⚠ Ozone is always good
✗ Ozone is beneficial for the environment.
→ The chapter states that ozone (O3) is a deadly poison. It is only beneficial at higher levels of the atmosphere where it shields us from UV radiation. At ground level, it is a harmful pollutant.
✓ Ozone at higher levels of the atmosphere shields the Earth from UV radiation, but at ground level it is a deadly poison and harmful to living organisms.
⚠ Decomposers are consumers
✗ Decomposers are a type of consumer because they eat dead matter.
→ Consumers obtain food by feeding on producers or other consumers. Decomposers break down dead remains and waste products into simple inorganic substances, which is a different process. They are a separate category.
✓ Decomposers are microorganisms (bacteria and fungi) that break down complex organic substances from dead remains and waste into simple inorganic substances, returning them to the soil.
⚠ Biological magnification means more chemical is added at each level
✗ The amount of pesticide increases at each trophic level because more is eaten.
→ The amount of the chemical does not increase; the concentration (amount per unit body weight) increases because the chemical is non-degradable and accumulates, while the organism's body mass does not increase proportionally.
✓ Non-degradable chemicals get accumulated progressively at each trophic level, leading to higher concentration in organisms at higher trophic levels, a phenomenon known as biological magnification.
⚠ All waste is biodegradable if given enough time
✗ Plastics will eventually break down if buried for a very long time.
→ The chapter states that many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes under ambient conditions. They persist for a long time and are non-biodegradable.
✓ Non-biodegradable substances like plastics are not broken down by biological processes and persist in the environment for a long time, causing pollution.
⚠ Food chain and food web are the same
✗ A food web is just a longer food chain.
→ A food chain is a single linear series of organisms feeding on one another. A food web is a network of many interconnected food chains, showing that each organism is generally eaten by two or more other kinds of organisms.
✓ A food chain is a single series of organisms feeding on one another, while a food web consists of many branching and interconnected food chains.
Compare & Contrast
Ability to be broken down by biological processes
Biodegradable substances
Non-biodegradable substances
Biodegradable substances are broken down by bacteria and other saprophytes into simple inorganic substances, while non-biodegradable substances are not broken down by biological processes and persist in the environment.
Structure of feeding relationships
Food chain
Food web
A food chain is a single linear sequence of organisms feeding on one another, whereas a food web is a complex network of many interconnected food chains.
Origin or creation
Natural ecosystem
Artificial ecosystem
A natural ecosystem occurs naturally without human intervention (e.g., forest, pond), while an artificial ecosystem is created and maintained by humans (e.g., garden, aquarium).
Exam Focus
Marks pattern: This chapter typically appears in board exams as: 2-3 MCQs (1 mark each), 1 Very Short Answer (1 mark), 1 Short Answer (2-3 marks), and 1 Long Answer (5 marks) on topics like food chain/energy flow or ozone depletion.
Most asked: Trophic levels and 10% energy transfer law · Biological magnification · Ozone layer formation and depletion by CFCs · Biodegradable vs non-biodegradable substances · Role of decomposers in the ecosystem
Don't skip: Draw a food chain with at least three trophic levels and explain the energy flow using the 10% law.; Explain biological magnification with an example and its effect on human beings.; Describe the formation of ozone and the role of CFCs in its depletion. What steps have been taken to limit this damage?
One-Line Revision (read aloud before the exam)
  1. An ecosystem consists of biotic (living) and abiotic (non-living) components interacting with each other.
  2. Producers (green plants) capture about 1% of sunlight energy and convert it into chemical energy.
  3. Only 10% of the energy from one trophic level is transferred to the next trophic level.
  4. Food chains generally have only 3-4 trophic levels due to the loss of energy at each step.
  5. Decomposers (bacteria and fungi) break down dead organic matter into simple inorganic substances, recycling nutrients.
  6. Biological magnification is the progressive accumulation of non-degradable pesticides at each trophic level.
  7. Ozone (O3) at higher levels of the atmosphere shields the Earth from harmful UV radiation.
  8. Ozone is formed when UV radiation splits O2 into free oxygen atoms, which then combine with O2 to form O3.
  9. Chlorofluorocarbons (CFCs) used in refrigerators and fire extinguishers deplete the ozone layer.
  10. The 1987 UNEP agreement froze CFC production at 1986 levels, and now CFC-free refrigerators are mandatory.
  11. Biodegradable substances are broken down by biological processes; non-biodegradable substances are not.
  12. Non-biodegradable wastes like plastics persist in the environment and cause pollution.
  13. Energy flow in an ecosystem is unidirectional and does not revert back to the previous level.
  14. A food web is a network of interconnected food chains, showing multiple feeding relationships.
  15. Human activities like pesticide use and waste generation significantly impact the environment.

MCQs — 10 Questions with Answers

Q1. A student sets up an aquarium with fish, aquatic plants, water, and an aerator. After two weeks, the student notices the water becomes cloudy and fish appear stressed. Which ecosystem component is MOST likely responsible for this problem if the aquarium is not cleaned?

  • A. Decomposers breaking down dead matter are producing toxic byproducts faster than they can be removed ✓
  • B. Producers are consuming all the oxygen at night
  • C. Primary consumers are eating all available food
  • D. The abiotic factor of temperature has increased

Answer: A — Decomposers (bacteria and fungi) break down dead matter, and in an uncleaned aquarium, their metabolic byproducts accumulate, causing water quality to deteriorate and stress organisms; students often incorrectly blame producers or temperature without understanding decomposer waste accumulation.

Q2. In a pond ecosystem, algae produce 10,000 kJ of energy. If small fish eat the algae and large fish eat the small fish, approximately how much energy is available to the large fish at the tertiary consumer level?

  • A. 100 kJ
  • B. 1,000 kJ
  • C. 10 kJ ✓
  • D. 500 kJ

Answer: C — Energy transfer follows the 10% rule: algae (10,000 kJ) → small fish (1,000 kJ) → large fish (100 kJ); most students incorrectly apply 10% only once or forget the cumulative loss across multiple trophic levels.

Q3. A farmer removes all decomposer organisms from the soil using chemical treatment. What will be the MOST immediate consequence for plant growth in this ecosystem?

  • A. Plants will grow faster because they don't have to compete with decomposers
  • B. Complex organic substances from dead organisms will not be broken down into simple inorganic nutrients available for plant uptake ✓
  • C. Photosynthesis will increase because decomposers no longer consume glucose
  • D. The abiotic factor of soil temperature will increase significantly

Answer: B — Decomposers convert complex organic matter into simple inorganic substances that plants need for nutrition; without them, the nutrient cycle breaks down, and students commonly overlook decomposer role in nutrient cycling rather than competing with plants.

Q4. A forest ecosystem contains grass (producer), rabbits (primary consumer), foxes (secondary consumer), and bacteria (decomposer). If all grass is removed from this ecosystem, which organism will be affected FIRST and MOST SEVERELY?

  • A. Foxes, because they lose their food source
  • B. Bacteria, because they have no dead matter to decompose
  • C. Rabbits, because grass is their direct food source ✓
  • D. All organisms equally, because the entire food chain collapses

Answer: C — Rabbits depend directly on grass for energy and nutrients; their population collapses first, which subsequently affects foxes; students often think apex predators are most vulnerable, missing the trophic level concept.

Q5. A student observes an aquarium where fish waste accumulates at the bottom. The student adds aquatic plants to the aquarium. After one week, the waste is reduced. Which process BEST explains this improvement?

  • A. Plants consume fish waste as food through their roots
  • B. Plants use nutrients from decomposed waste products and reduce overall waste accumulation through nutrient cycling ✓
  • C. Plants directly absorb solid waste particles
  • D. Fish produce less waste when plants are present

Answer: B — Aquatic plants as producers take up inorganic nutrients released by decomposer breakdown of waste, supporting nutrient cycling; students mistakenly believe plants eat solid waste or that their presence changes fish metabolism rather than understanding nutrient recycling.

Q6. Assertion (A): A food chain in a terrestrial ecosystem rarely exceeds four trophic levels. Reason (R): Energy is lost as heat and through metabolic processes at each trophic level, so insufficient usable energy remains after four levels. Choose the correct option:

  • A. Both A and R are true and R is the correct explanation of A ✓
  • B. Both A and R are true but R is not the correct explanation of A
  • C. A is true but R is false
  • D. A is false but R is true

Answer: A — The energy loss at each step (following the 10% rule) directly explains why long food chains cannot be sustained; this is the foundational principle linking energy flow to food chain structure.

Q7. Assertion (A): Green plants capture approximately 1% of the solar energy that falls on their leaves. Reason (R): The remaining 99% of solar energy is reflected back into space and does not interact with Earth's atmosphere. Choose the correct option:

  • A. Both A and R are true and R is the correct explanation of A
  • B. Both A and R are true but R is not the correct explanation of A
  • C. A is true but R is false ✓
  • D. A is false but R is true

Answer: C — While plants do capture ~1% of incident solar energy, the remaining 99% is not all reflected to space—much is absorbed as heat by soil, water, and atmosphere; students confuse energy capture efficiency with energy reflection.

Q8. Assertion (A): Decomposers are not considered consumers because they do not eat other organisms directly. Reason (R): Decomposers break down dead organic matter and are essential for nutrient cycling in ecosystems. Choose the correct option:

  • A. Both A and R are true and R is the correct explanation of A
  • B. Both A and R are true but R is not the correct explanation of A ✓
  • C. A is true but R is false
  • D. A is false but R is true

Answer: B — Both statements are accurate, but R does not explain why decomposers are not classified as consumers—they are excluded from consumer classification because they use extracellular digestion and obtain energy from dead matter, not because of their role in nutrient cycling.

Q9. A scientist measures energy content at different trophic levels in a forest: Grass = 50,000 kJ, Herbivores = 5,000 kJ, Carnivores = 500 kJ. Which conclusion is MOST accurate based on this data?

  • A. Each trophic level has exactly 10% of the energy of the previous level, confirming the 10% rule
  • B. Energy decreases by different percentages at each level, suggesting the 10% rule is only an average ✓
  • C. Carnivores are more energy-efficient than herbivores
  • D. The ecosystem is not self-sustaining due to energy loss

Answer: B — The data shows grass→herbivores is exactly 10%, but herbivores→carnivores is also exactly 10%; however, the 10% rule stated in the chapter is described as an 'average value,' meaning variation occurs; students may oversimplify by seeing perfect 10% ratios rather than understanding it as an average principle.

Q10. A student observes a food web diagram showing: Plants → Insects → Frogs → Snakes, and Plants → Grasshoppers → Snakes. If all insects suddenly die due to pesticide use, which organism will experience the GREATEST immediate energy shortage?

  • A. Snakes, because they lose two food sources
  • B. Frogs, because insects are their only food source shown ✓
  • C. Grasshoppers, because they compete with insects
  • D. Plants, because they lose consumers

Answer: B — Frogs depend exclusively on insects in this food web for energy, while snakes still have grasshoppers as an alternative source; students often overlook that organisms with single food sources are more vulnerable than those with multiple sources (food web advantage).

Flashcards

What is an ecosystem?

An ecosystem is all living organisms (biotic components) and non-living factors (abiotic components like temperature, soil, rainfall) in an area that interact with each other.

Define the three categories of organisms in an ecosystem.

Producers are green plants that make food via photosynthesis; consumers are organisms that eat producers or other consumers; decomposers are bacteria and fungi that break down dead matter into inorganic substances.

What is a food chain?

A food chain is a linear sequence of organisms where each organism is eaten by the next, showing the flow of energy from producers through various consumer levels.

What percentage of energy is transferred from one trophic level to the next?

Only 10% of the food energy consumed at one trophic level becomes available for the next trophic level; the remaining 90% is lost as heat, digestion, and work.

Why do food chains rarely exceed four trophic levels?

Energy loss at each level (90% lost) means very little usable energy remains after four steps, making longer food chains unable to support viable populations.

What is the difference between a food chain and a food web?

A food chain is a single linear path of energy flow, while a food web shows multiple interconnected food chains where organisms eat and are eaten by many different species.

How much solar energy do green plants capture?

Green plants capture approximately 1% of the solar energy that falls on their leaves and convert it into chemical energy stored in food.

What is a trophic level?

A trophic level is each step in a food chain, where producers are at level 1, primary consumers at level 2, secondary consumers at level 3, and tertiary consumers at level 4.

What role do decomposers play in an ecosystem?

Decomposers break down dead organisms and waste products into simple inorganic substances that return to the soil for plants to reuse, recycling nutrients but not energy.

Why is energy flow through an ecosystem unidirectional?

Energy captured by autotrophs does not revert to sunlight, and energy passing to herbivores does not return to autotrophs; it only moves forward and is lost as heat at each step.

Important Board Questions

Define an ecosystem. Name the biotic and abiotic components of an ecosystem. [2 marks]

State that ecosystem = living organisms + non-living environment interacting together. List biotic as plants/animals/microorganisms and abiotic as temperature/rainfall/soil/wind/minerals.

Explain why only 10% of energy is transferred from one trophic level to the next. What happens to the remaining 90% of energy? [3 marks]

State that when organisms eat food, much energy is lost—explain three uses: heat release to environment, energy used in digestion, and energy used for work/movement. Only remainder (10%) goes to body growth and reproduction for next level consumption.

With the help of an example, explain why food chains in nature are generally limited to only three or four steps. Draw a diagram showing energy flow through a food chain with all trophic levels and explain the 10% rule. [5 marks]

Draw a complete food chain (e.g., grass → grasshopper → bird → hawk) showing each organism with trophic level labels. Calculate energy at each level using 10% rule (if 100 units at producer level, 10 at primary consumer, 1 at secondary, 0.1 at tertiary). Explain that after level 4, energy becomes too low to support viable populations, making longer chains impossible. Emphasize unidirectional flow and energy loss mechanism.

Assertion-Reason Questions for Our Environment

Q1. Assertion (A):

Decomposers are essential for the survival of an ecosystem.

Reason (R):

Decomposers break down dead organic matter into simple inorganic substances that are returned to the soil for plants to use.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both the assertion and reason are true, and the reason correctly explains why decomposers are essential. Without decomposers, nutrients would not be recycled and would accumulate as dead matter, eventually collapsing the ecosystem. The reason provides the exact mechanism that makes the assertion true.

Q2. Assertion (A):

Food webs are more realistic representations of energy flow in ecosystems than food chains.

Reason (R):

Food webs show that organisms exist in isolation and do not interact with multiple species.

Answer: C — A is true but R is false — The assertion is true; food webs better represent real ecosystems because organisms feed on and are eaten by multiple species. However, the reason is false because food webs actually show that organisms interact extensively with multiple species, not in isolation. The reason contradicts the correct explanation.

Q3. Assertion (A):

Green plants capture only 1% of the solar energy that falls on their leaves.

Reason (R):

The remaining 99% of solar energy is used by herbivores and carnivores for their activities.

Answer: C — A is true but R is false — The assertion is true based on the study material. However, the reason is false because the remaining 99% is not used by consumers; instead, it is reflected or absorbed without being converted to chemical energy that organisms can use. Only the 1% captured by plants is available for consumers.

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Case-Based Questions (CBQ) for Our Environment

Case Study:

A biology teacher created a controlled study of a pond ecosystem by dividing it into two sections. In Section A, all aquatic plants were removed. In Section B, plants were maintained. After 4 weeks, Section A showed a decline in fish population and accumulation of dead algae, while Section B maintained stable fish populations and clear water. The teacher measured oxygen levels and found Section A had significantly lower dissolved oxygen compared to Section B.

Q1. What is the role of aquatic plants in maintaining dissolved oxygen levels in the pond?

  • A. They consume oxygen produced by fish
  • B. They produce oxygen through photosynthesis during the day ✓
  • C. They decompose dead matter to release oxygen
  • D. They store oxygen in their roots for later use

Answer: B

Q2. Why did Section A experience a decline in fish population?

  • A. Fish migrated to other ponds
  • B. Dead algae poisoned the water
  • C. Lack of oxygen and food due to absence of plants as producers ✓
  • D. Excessive growth of decomposers

Answer: C

Q3. What would be the trophic level of algae and aquatic plants in this pond ecosystem?

  • A. Secondary consumers
  • B. Primary consumers
  • C. Producers ✓
  • D. Decomposers

Answer: C

Q4. Based on the experimental results, which statement best explains the importance of biotic components in an ecosystem?

  • A. Biotic components are unrelated to ecosystem stability
  • B. Biotic components like plants are essential for producing energy and oxygen that support other organisms ✓
  • C. Only fish are important for ecosystem survival
  • D. Decomposers alone can maintain an ecosystem

Answer: B

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Previous Year Questions (PYQ) for Our Environment

Real CBSE board exam questions from past papers — free to attempt.

CBSE 2026 · Set 31/4/1 · 1 mark

Given below are some of the statements regarding our environment: (i) Change in our life-styles have resulted in greater amounts of waste material generation. (ii) Changes in attitude have resulted in use of more disposable things. (iii) Changes in packaging has resulted in much of our waste becoming non-biodegradable. (iv) Organic farming. Which amongst these is not leading to any damage of environment?

  • (i), (ii), (iii)
  • (iv)
  • (i) and (iii)
  • (ii) and (iv)

CBSE 2026 · Set 31/4/1 · 1 mark

Assertion (A): Highest percentage of pesticides is found in tertiary consumers in a food chain. Reason (R): Chemicals / pesticides get accumulated progressively at each trophic level.

  • Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
  • Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
  • Assertion (A) is true, but Reason (R) is false.
  • Assertion (A) is false, but Reason (R) is true.

CBSE 2026 · Set 31/4/1 · 2 marks

Explain why food chains generally consist of three or four steps.

CBSE 2026 · Set 31/4/2 · 1 mark

In terms of various trophic levels of a food chain, which of the following organisms belong to the same level?

  • Snake and Grasshopper
  • Grass and tree
  • Lizard and elephant
  • Bacteria and grass

CBSE 2026 · Set 31/4/3 · 2 marks

What are decomposers? List two important roles they play in the environment.

CBSE 2026 · Set 31/5/1 · 1 mark

Which of the following is a non-biodegradable pollutant?

  • Paper
  • DDT
  • Wood
  • Vegetable peel

CBSE 2026 · Set 31/5/1 · 1 mark

In an ecosystem, the decomposers perform an important role. Select the option indicating the role of decomposers.

  • Convert inorganic materials to simpler forms
  • Break down complex organic substances to simple inorganic substances.
  • Break down inorganic substances into organic substances.
  • Do not act on organic compounds.

CBSE 2026 · Set 31/5/1 · 3 marks

(a) Mention any one harmful effect of using plastic bags on the environment. Suggest better alternatives to the usage of plastic bags. (b) Paddy fields require a large amount of water. The pesticides and chemical fertilizers used are washed down into the soil or waterbodies. How do these chemicals reach our bodies? What is this phenomenon known as?

CBSE 2026 · Set 31/5/2 · 1 mark

Which of the following is a non-biodegradable pollutant ?

  • Paper
  • DDT
  • Wood
  • Vegetable peel

CBSE 2026 · Set 31/5/2 · 1 mark

The reasons for excessive generation of wastes are : (i) Use and throw policy. (ii) Increased availability of packaged food. (iii) Increased construction wastes. (iv) Non-sorting of dry and wet wastes. Which of the following options are correct ?

  • (i), (iii) and (iv)
  • (i), (ii) and (iii)
  • (i), (ii), (iii) and (iv)
  • (ii), (iii) and (iv)

CBSE 2026 · Set 31/5/2 · 3 marks

(a) Mention any one harmful effect of using plastic bags on the environment. Suggest better alternatives to the usage of plastic bags. (b) Paddy fields require a large amount of water. The pesticides and chemical fertilizers used are washed down into the soil or waterbodies. How do these chemicals reach our bodies ? What is this phenomenon known as ?

CBSE 2026 · Set 31/5/3 · 1 mark

An ecosystem contains maximum number of:

  • Producers
  • Herbivores
  • Carnivores
  • Omnivores

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Class 10 Science Formula Sheet

Every formula and chemical equation from the 10 chapters on one page, checked against the NCERT textbook and the CBSE 2026-27 syllabus. Free PDF download.

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Class 10 Science Previous Year Questions, Chapter-wise

All 875 CBSE board questions from 2022–2026, sorted by chapter and question type. Free PDF download.

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