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Our Environment for Class 10: The Complete CBSE Guide (2026-27)

Our Environment Class 10 forms the ecology foundation of your CBSE Science syllabus, bridging theoretical biology with urgent real-world challenges India faces today—from Bengaluru's waste crisis to Delhi's air quality concerns. This chapter arms you with precise vocabulary (trophic levels, biogeochemical cycles, biotic-abiotic interactions) and quantitative reasoning (ten percent energy law, biological magnification factors) that the board examiners expect in your 2027 paper. Whether you are tackling a 3-mark question on food web construction or a 5-mark analysis of ozone depletion mechanisms, the NCERT framework in Our Environment Class 10 gives you the factual scaffolding. This guide walks you through every concept with worked examples, comparison tables, and the exact question patterns that appeared in 2024 and 2023 board exams.

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Key takeaways

  • ✓Our Environment Class 10 contributes 4-6 marks to the CBSE board exam through one long-answer or two short-answer questions focused on ecosystems and environmental issues
  • ✓The Ten Percent Law states only 10% of energy transfers from one trophic level to the next, explaining why food chains rarely exceed 4-5 levels in natural ecosystems
  • ✓Ozone layer depletion occurs in the stratosphere when CFCs release chlorine atoms that catalytically destroy ozone (O₃) molecules, increasing harmful UV-B radiation reaching Earth
  • ✓Biodegradable wastes like vegetable peels decompose naturally through microbial action within weeks, while non-biodegradable plastics persist for hundreds of years causing environmental harm
  • ✓Food webs provide ecosystem stability because organisms have multiple feeding relationships, so loss of one species does not collapse the entire system unlike simple food chains
  • ✓The 3Rs hierarchy—Reduce first, then Reuse, finally Recycle—represents the most effective strategy for sustainable waste management taught in Our Environment Class 10
  • ✓Biological magnification causes toxin concentration to increase 10-100 times at each trophic level, making top predators most vulnerable to pesticide poisoning even from low environmental doses

What Our Environment Class 10 Covers: NCERT Chapter 15 Breakdown

The NCERT textbook for Our Environment Class 10 spans approximately 12 pages and divides into four major learning objectives. First, students explore ecosystem components—biotic factors (producers, consumers, decomposers) and abiotic factors (sunlight, temperature, soil minerals, water). Second, the chapter details energy flow mechanisms through food chains and food webs, introducing trophic levels and the ten percent law of energy transfer. Third, you study human-induced environmental problems, particularly ozone layer depletion in the stratosphere caused by chlorofluorocarbons used in refrigerants and aerosols. Finally, the chapter addresses waste management strategies, distinguishing biodegradable from non-biodegradable substances and explaining the 3Rs framework. The 2024-25 CBSE blueprint typically allocates 4 marks from Unit V (Natural Resources) to this chapter, often as one long-answer question or two short-answer questions. Past board papers show recurring themes: drawing and labeling a four-organism food chain, explaining why energy decreases along trophic levels, comparing biodegradable versus non-biodegradable waste with three examples each, and describing how CFCs damage the ozone layer with chemical equations. Mastery of Our Environment Class 10 also prepares you for the practicals on vermicomposting and waste segregation that some CBSE schools include in internal assessments.
  • Ecosystem structure: biotic (living organisms) and abiotic (physical-chemical factors) components interacting as functional units
  • Energy flow: unidirectional movement from sun → producers → herbivores → carnivores, with 90% loss at each trophic transfer
  • Ozone depletion: CFCs release chlorine radicals in stratosphere, catalytically breaking O₃ into O₂, reducing UV shield
  • Waste management: biodegradable materials decompose in weeks through bacterial action; non-biodegradable plastics persist 500+ years

Understanding Ecosystems: The Foundation of Our Environment Class 10

An ecosystem is a structural and functional unit where living organisms interact with each other and their physical environment to facilitate energy flow and nutrient cycling. Our Environment Class 10 emphasizes that ecosystems exist at multiple scales—a small pond, a forest, or the entire biosphere. Every ecosystem contains producers (autotrophs like green plants and algae that synthesize food through photosynthesis), consumers (heterotrophs including herbivores, carnivores, and omnivores that depend on other organisms for nutrition), and decomposers (bacteria and fungi that break down dead organic matter into simpler inorganic substances). Abiotic components include solar radiation, temperature, precipitation, soil pH, minerals, and atmospheric gases. The NCERT textbook for Our Environment Class 10 uses a pond ecosystem as a worked example: aquatic plants and phytoplankton serve as producers, small fish and zooplankton as primary consumers, larger fish as secondary consumers, and bacteria as decomposers. Understanding this hierarchy is critical because board exam questions often ask you to identify the trophic level of a given organism or predict ecosystem consequences if one component is removed. For instance, if all decomposers vanished, nutrient recycling would halt, dead matter would accumulate, and soil fertility would plummet, eventually collapsing the entire ecosystem.
  • Producers fix solar energy into chemical bonds (glucose) via photosynthesis: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂
  • Primary consumers (herbivores) obtain energy by eating producers; secondary consumers eat herbivores; tertiary consumers eat secondary consumers
  • Decomposers recycle nutrients: they convert proteins into ammonia, complex carbohydrates into simple sugars, releasing minerals back to soil for plant uptake
  • Abiotic factors regulate population sizes: temperature affects metabolic rates, water availability limits plant growth, soil minerals determine species composition

Food Chains and Food Webs: Energy Pathways in Our Environment Class 10

A food chain is a linear sequence showing the transfer of food energy from producers through successive consumer levels. Our Environment Class 10 teaches that each step in a food chain is called a trophic level—producers occupy the first trophic level, herbivores the second, small carnivores the third, and larger carnivores the fourth. A classic terrestrial food chain from the NCERT textbook is: Grass → Grasshopper → Frog → Snake → Hawk. An aquatic example is: Phytoplankton → Zooplankton → Small fish → Large fish. However, natural ecosystems rarely follow simple linear chains. Instead, multiple food chains interconnect to form a food web, a complex network where organisms feed at multiple trophic levels. For instance, a hawk might eat snakes, frogs, and mice; a frog might eat grasshoppers, beetles, and worms. Food webs provide stability—if one food source declines, organisms can switch to alternatives. The CBSE board exam for Our Environment Class 10 frequently asks students to construct a food web with at least six organisms or to explain why food webs are more realistic than food chains. When drawing, always use arrows pointing from food source to consumer (e.g., Grass → Grasshopper, not the reverse), and ensure your diagram includes at least one organism feeding at two trophic levels to demonstrate web complexity.

The Ten Percent Law: Why Energy Decreases in Our Environment Class 10

The Ten Percent Law, formulated by Raymond Lindeman in 1942, states that only about 10% of the energy available at one trophic level is transferred to the next level; the remaining 90% is lost as heat during respiration, movement, and metabolic processes. Our Environment Class 10 applies this principle to explain why food chains rarely exceed four or five trophic levels. Consider a simple calculation: if a grassland receives 10,000 joules of solar energy, producers (grass) capture roughly 1% (100 J) via photosynthesis. Primary consumers (grasshoppers) obtain 10% of that (10 J), secondary consumers (frogs) get 1 J, and tertiary consumers (snakes) receive just 0.1 J. By the fourth consumer level, energy is insufficient to support a viable population. This energy pyramid has a broad base (many producers) and a narrow apex (few top carnivores). The NCERT textbook for Our Environment Class 10 shows a biomass pyramid where producers have the largest mass, herbivores less, and carnivores least. Board exam questions often present an energy value at the producer level and ask you to calculate energy available to the third trophic level—apply 10% twice (0.1 × 0.1 = 0.01 or 1% of original energy). Understanding energy flow also explains biological magnification: because top predators consume many lower-level organisms to meet energy needs, they accumulate higher concentrations of non-biodegradable toxins.
  • Energy enters ecosystems as sunlight; only 1-2% is captured by photosynthesis due to reflection, wavelength mismatch, and plant inefficiency
  • Each trophic transfer loses 90% as heat (cellular respiration), movement, growth, reproduction, and undigested matter in feces
  • Longer food chains are energetically unsustainable: a fifth trophic level would receive only 0.001% of original solar input
  • Biomass decreases up the pyramid: 1,000 kg of grass supports 100 kg of herbivores, which support 10 kg of carnivores, which support 1 kg of top predators

Biological Magnification: A Critical Concept in Our Environment Class 10

Biological magnification (or biomagnification) is the process by which the concentration of non-biodegradable toxic substances increases progressively at each successive trophic level in a food chain. Our Environment Class 10 uses the example of DDT (dichlorodiphenyltrichloroethane), a pesticide once widely sprayed on crops. When DDT enters water bodies, phytoplankton absorb trace amounts (0.003 ppm). Zooplankton feeding on phytoplankton accumulate higher concentrations (0.04 ppm) because they eat many phytoplankton but cannot metabolize or excrete DDT. Small fish accumulate 0.5 ppm, large fish 2 ppm, and fish-eating birds (like pelicans or eagles) reach 25 ppm—an 8,000-fold increase from the original aquatic concentration. At such levels, DDT interferes with calcium metabolism, causing eggshell thinning and reproductive failure, nearly driving species like the bald eagle to extinction in the 1960s. The CBSE curriculum for Our Environment Class 10 connects this to India's context: mercury from industrial effluents bioaccumulates in fish, posing risks to fishing communities; pesticide residues in food crops can magnify through dairy and meat. Board questions may ask you to explain why top carnivores are most affected by pollutants even when environmental concentrations are low, or to draw a food chain and indicate increasing toxin levels at each step with numerical annotations.

Ozone Layer Depletion: Mechanisms and Consequences in Our Environment Class 10

The ozone layer, a region in the stratosphere 15-30 km above Earth's surface, contains a higher concentration of ozone (O₃) molecules that absorb 97-99% of the sun's harmful ultraviolet-B (UV-B) radiation. Our Environment Class 10 explains that chlorofluorocarbons (CFCs), used in refrigerators, air conditioners, aerosol sprays, and foam-blowing agents, are chemically inert at ground level but drift into the stratosphere over decades. There, intense UV radiation breaks CFC molecules (e.g., CFCl₃), releasing chlorine atoms. A single chlorine atom catalytically destroys thousands of ozone molecules through this cycle: Cl + O₃ → ClO + O₂, then ClO + O → Cl + O₂. The chlorine atom is regenerated and continues breaking down ozone. The NCERT textbook for Our Environment Class 10 highlights the Antarctic ozone hole, discovered in 1985, where ozone concentrations drop by 50% each spring due to polar stratospheric clouds enhancing CFC reactions. Consequences of ozone depletion include increased UV-B reaching Earth, leading to higher rates of skin cancer and cataracts in humans, suppressed immune systems, reduced phytoplankton productivity (disrupting marine food webs), and damage to crops. The 1987 Montreal Protocol phased out CFCs globally; India complied by 2010, switching to hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) as interim replacements, though these also have climate impacts. Board exam questions for Our Environment Class 10 often ask you to write the chemical equations for ozone depletion, name two diseases caused by UV-B exposure, or explain the role of international agreements.
  • Ozone formation: O₂ + UV → O + O, then O + O₂ → O₃; depletion reverses this, reducing the protective layer
  • CFCs persist 50-100 years in atmosphere; even with Montreal Protocol, full ozone recovery expected only by 2060-2070
  • UV-B radiation (280-315 nm wavelength) causes DNA mutations, leading to skin cancers (melanoma, basal cell carcinoma) and eye cataracts in humans
  • Phytoplankton sensitivity: 10% ozone loss causes 5-10% decline in phytoplankton, reducing ocean oxygen production and fish stocks for coastal India

Biodegradable vs Non-Biodegradable Waste: Key Distinction in Our Environment Class 10

Our Environment Class 10 defines biodegradable substances as materials that can be broken down into simpler, harmless products by the biological action of decomposers (bacteria, fungi) within weeks to months. Examples include vegetable peels, fruit waste, paper, cotton cloth, jute bags, wood, and animal dung. These materials undergo decomposition: microorganisms secrete enzymes that digest complex organic polymers (cellulose, proteins, lipids) into monomers (glucose, amino acids, fatty acids), which then enter biogeochemical cycles. In contrast, non-biodegradable substances resist microbial breakdown and persist in the environment for hundreds to thousands of years. Examples are plastics (polyethylene, PVC), synthetic fibers (nylon, polyester), glass, metals (aluminum cans, steel), and certain chemicals (DDT, heavy metals like mercury and lead). The NCERT textbook for Our Environment Class 10 emphasizes that non-biodegradable waste accumulates in landfills, clogs drainage systems (a major problem in Indian cities during monsoons), and harms wildlife—plastic bags choke cattle, marine animals ingest microplastics, and toxic metals leach into groundwater. The 2024 CBSE board exam for Our Environment Class 10 included a 3-mark question asking students to list three biodegradable and three non-biodegradable substances and explain why the latter are environmental hazards. A complete answer mentions persistence (no natural decomposers), bioaccumulation potential, and physical harm to organisms.

Waste Management and the 3Rs: Practical Applications from Our Environment Class 10

Effective waste management is central to Our Environment Class 10, with the NCERT framework prioritizing the 3Rs hierarchy—Reduce, Reuse, Recycle—in that order of importance. Reduce means minimizing waste generation at the source: carry a reusable cloth bag instead of accepting plastic bags, buy products with less packaging, avoid single-use items like plastic straws and disposable cups. Reuse extends product life: refill water bottles, repurpose glass jars for storage, donate old clothes, repair electronics instead of discarding. Recycle converts waste into new materials: paper recycling saves trees (1 ton of recycled paper saves 17 trees), plastic recycling reduces petroleum consumption, metal recycling conserves ores. The CBSE syllabus for Our Environment Class 10 also introduces composting as a method to manage biodegradable kitchen and garden waste. In aerobic composting, organic matter decomposes in the presence of oxygen, producing nutrient-rich humus usable as fertilizer—a practice encouraged by the Swachh Bharat Abhiyan. Vermicomposting uses earthworms (Eisenia fetida) to accelerate decomposition, yielding high-quality compost in 45-60 days. Indian cities like Indore and Ambikapur have achieved high waste segregation rates (above 90% at household level) by implementing door-to-door collection with separate bins for wet (biodegradable) and dry (recyclable/non-biodegradable) waste. Board exam questions for Our Environment Class 10 may ask you to explain each R with two examples, describe the composting process, or suggest how your school can reduce plastic waste (install water dispensers to eliminate plastic bottles, replace disposable plates with steel utensils in canteen, organize recycling drives).
  • Reduce: most impactful—preventing waste generation avoids all downstream disposal problems; e.g., refuse plastic cutlery at restaurants, print double-sided to halve paper use
  • Reuse: extends product lifespan without energy-intensive reprocessing; e.g., glass bottles as drinking containers, old newspapers as packing material, worn-out clothes as cleaning rags
  • Recycle: reprocesses materials into new products but consumes energy (plastic recycling uses 70% less energy than virgin plastic production from petroleum)
  • Composting converts 40-50% of household waste (food scraps, yard trimmings) into valuable soil amendment, reducing landfill load and methane emissions

Harmful Effects of Non-Biodegradable Substances: Real-World Scenarios in Our Environment Class 10

Our Environment Class 10 stresses the long-term ecological and health consequences of non-biodegradable pollutants. Plastic waste is the most visible problem in India—single-use plastics clog urban drainage, causing waterlogging and flooding during monsoons (Chennai 2015, Mumbai 2005 floods partly attributed to plastic-choked drains). Marine pollution from plastics has created the Great Pacific Garbage Patch, a floating mass twice the size of Texas. Microplastics (particles smaller than 5 mm) enter the food chain: plankton ingest them, small fish eat plankton, humans consume fish, leading to potential endocrine disruption from plastic additives like bisphenol A (BPA). Heavy metals are another concern: mercury from coal-fired power plants and chlor-alkali industries bioaccumulates in fish, causing Minamata disease (neurological damage); lead from old paints and batteries causes cognitive impairment in children; cadmium from e-waste damages kidneys. Electronic waste (e-waste) contains over 40 toxic elements—when burned or dumped in landfills, these leach into soil and groundwater. India generates 3.2 million tonnes of e-waste annually (2023 estimate), much of it informally recycled in Delhi, Bengaluru, and Chennai under hazardous conditions. The NCERT textbook for Our Environment Class 10 connects these issues to policy: India banned single-use plastics (items like straws, stirrers, plastic flags) in July 2022; the E-Waste Management Rules 2016 mandate producer responsibility. Board exam questions may ask you to explain two harmful effects of plastic waste with examples or describe how heavy metals biomagnify with a specific pollutant.
  • Plastic ingestion kills an estimated 100,000 marine animals and 1 million seabirds annually worldwide; cattle in Indian cities die from consuming plastic bags mixed with food waste
  • Persistent organic pollutants (POPs) like DDT, PCBs accumulate in fatty tissues, causing reproductive failure, immune suppression, and cancer in top predators including humans
  • Heavy metal toxicity: mercury causes tremors and memory loss; lead reduces IQ and causes anemia; cadmium weakens bones (itai-itai disease in Japan)
  • E-waste hazards: burning circuit boards releases dioxins and furans (carcinogens); acid leaching to recover gold and copper contaminates water with heavy metals

Examining Food Chains: Step-by-Step Construction for Our Environment Class 10 Board Exam

Constructing and interpreting food chains is a high-frequency skill tested in Our Environment Class 10 board exams. Follow this systematic approach: (1) Identify the ecosystem type—terrestrial (forest, grassland, desert) or aquatic (pond, river, ocean)—to choose appropriate organisms. (2) Start with a producer: green plants in terrestrial systems (grass, shrubs, trees), phytoplankton or algae in aquatic systems. (3) Add a primary consumer (herbivore): grasshopper, rabbit, deer, caterpillar for land; zooplankton, snails, small fish for water. (4) Include a secondary consumer (carnivore eating herbivores): frog, small bird, fox for land; small fish, dragonfly nymph for water. (5) Optionally add a tertiary consumer (carnivore eating other carnivores): snake, hawk, owl for land; large fish, kingfisher for water. (6) Draw arrows from food source to consumer—common mistake is reversing arrow direction; the correct convention is Grass → Grasshopper (energy flows to the grasshopper). The CBSE marking scheme for Our Environment Class 10 awards 1 mark for correct organism selection (must belong to the stated ecosystem), 1 mark for proper arrow direction, and 1 mark for labeling trophic levels if asked. A complete 3-mark answer to 'Construct a terrestrial food chain with four organisms' might be: 'Grass (Producer, 1st trophic level) → Grasshopper (Primary consumer, 2nd trophic level) → Frog (Secondary consumer, 3rd trophic level) → Snake (Tertiary consumer, 4th trophic level).' Practice drawing food webs by interconnecting 3-4 such chains with shared organisms to demonstrate realistic feeding relationships.

Important Formulas and Calculations in Our Environment Class 10

While Our Environment Class 10 is largely conceptual, the CBSE board exam occasionally includes numerical problems based on energy transfer. The key formula is derived from the Ten Percent Law: Energy at trophic level (n) = Energy at trophic level (n-1) × 0.10. For example, if producers have 50,000 kJ, primary consumers have 50,000 × 0.10 = 5,000 kJ, secondary consumers have 5,000 × 0.10 = 500 kJ, and tertiary consumers have 500 × 0.10 = 50 kJ. To find energy at any level directly, use: Energy at level (n) = Initial producer energy × (0.10)^(n-1), where n=1 for producers, n=2 for primary consumers, etc. Another calculation involves biomass pyramids: if 1,000 kg of grass supports herbivores, applying 10% efficiency yields 100 kg herbivore biomass, which supports 10 kg carnivore biomass. Biological magnification calculations require multiplying toxin concentration by the number of prey consumed. For instance, if a small fish eats 100 zooplankton each containing 0.01 mg DDT, the fish accumulates 100 × 0.01 = 1 mg DDT (assuming no excretion). If a large fish eats 50 small fish, it accumulates 50 × 1 = 50 mg DDT. Practice these calculations with different starting values—the NCERT textbook for Our Environment Class 10 includes worked examples in the chapter exercises (Questions 6-8 typically involve energy or biomass calculations). Always show units in your board exam answers (joules, kilograms, mg/kg) and write the formula first before substituting numbers to earn full method marks even if the final answer is wrong.
  • Energy transfer efficiency: E₂ = E₁ × 0.10, where E₁ is energy at lower level, E₂ at next higher level (90% lost as heat, respiration, movement)
  • Multi-level energy calculation: If producers = 100,000 J, energy at 3rd trophic level = 100,000 × (0.10)² = 1,000 J
  • Biomass pyramid: Each level supports roughly 10% the biomass of the level below (10,000 kg grass → 1,000 kg herbivores → 100 kg carnivores)
  • Toxin magnification factor: Concentration at level (n) / Concentration at level (1); e.g., if producer has 0.001 ppm toxin and top predator has 10 ppm, magnification = 10,000×

How CBSETUTOR.ai Helps You Master Our Environment Class 10

Our Environment Class 10 combines factual recall (naming ozone-depleting substances, listing biodegradable examples) with higher-order skills (explaining energy flow, analyzing waste management scenarios)—precisely the blend that challenges students. CBSETUTOR.ai offers a 24×7 AI tutor that has ingested the complete NCERT Science textbook for Class 10, including every diagram, worked example, and end-of-chapter question from Chapter 15. When you photograph a tricky food web question from your worksheet or ask 'Why do food chains rarely have more than five trophic levels?', the AI delivers step-by-step explanations rooted in the exact NCERT terminology the CBSE examiners expect. Parents across India use CBSETUTOR.ai at ₹999/month—a single flat rate covering all subjects for Classes 6-12—because it eliminates the need for separate ecology tutors or expensive crash courses. The platform's practice question bank includes previous years' board questions on ozone depletion, 3Rs, and biological magnification, with instant grading and feedback. You can start a 3-day free trial (no credit card required) and experience how interactive AI support transforms passive reading of Our Environment Class 10 notes into active problem-solving, ensuring you can confidently tackle any 4-6 mark question in your 2027 board exam. Whether you struggle with drawing accurate food webs or memorizing the chemical equations for ozone reactions, CBSETUTOR.ai adapts to your pace and learning style, making complex ecological concepts accessible and exam-ready.
  • Instant doubt resolution: upload a photo of any Our Environment Class 10 diagram or question; AI explains within seconds using NCERT-aligned language
  • Exam-focused practice: access 50+ curated board-pattern questions on ecosystems, energy flow, ozone, and waste, with mark-wise breakdown (1-mark, 3-mark, 5-mark)
  • Concept videos and mind maps: visual learners benefit from AI-generated flowcharts (e.g., CFC → Cl → O₃ depletion pathway) and ecosystem diagrams
  • Affordable for all: ₹999/month covers Classes 6-12, all subjects—no hidden fees, cancel anytime, 3-day free trial lets your child test before committing

Common Mistakes Students Make in Our Environment Class 10 Exams

Analyzing past CBSE board answer scripts for Our Environment Class 10 reveals recurring errors that cost students 2-3 marks per question. First, arrow direction in food chains: many students draw Grasshopper → Grass, implying the grasshopper feeds the grass—incorrect; energy flows from grass to grasshopper, so the arrow must point toward the grasshopper. Second, confusing trophic levels with organism types: labeling 'Frog' as the third trophic level is incomplete; you must specify 'Frog (Secondary consumer, 3rd trophic level)' to earn full marks. Third, vague answers on ozone depletion: writing 'CFCs harm ozone' scores 0 marks on a 3-mark question; the examiner expects chemical equations (Cl + O₃ → ClO + O₂), mention of UV radiation breaking CFCs, and consequences (increased UV-B causing skin cancer). Fourth, mixing biodegradable and non-biodegradable examples: listing 'paper' as non-biodegradable or 'plastic' as biodegradable shows conceptual confusion—review the distinction carefully. Fifth, omitting units in numerical answers: if you calculate 500 kJ but write '500', you lose the mark; always append 'kJ' or 'joules'. Sixth, incomplete waste management answers: stating 'use the 3Rs' without explaining each R with specific examples is insufficient. Seventh, ignoring the mark allocation: a 1-mark question needs a one-sentence answer (e.g., 'Producers are organisms that synthesize food via photosynthesis'), whereas a 5-mark question demands detailed steps, examples, and diagrams. Practice with CBSE sample papers for Our Environment Class 10, comparing your answers to the official marking scheme to internalize examiner expectations.
  • Arrow direction error: always draw food chain arrows pointing from food to feeder (Grass → Grasshopper), not reverse
  • Incomplete trophic level labels: 'Grasshopper' alone is insufficient; write 'Grasshopper (Primary consumer / Herbivore, 2nd trophic level)'
  • Vague ozone answers: must include CFCs, chlorine radical mechanism (Cl + O₃ → ClO + O₂), UV-B increase, and at least one health impact (skin cancer, cataracts)
  • Wrong examples: DDT is non-biodegradable (persists for years); fruit peels are biodegradable (decompose in weeks)—do not confuse
  • Forgetting units: write '5,000 kJ' not '5,000'; '0.5 ppm' not '0.5'; examiners deduct 0.5 marks for missing units
  • Generic 3Rs answers: examiners want specific actions—'Reduce: carry reusable bags; Reuse: refill bottles; Recycle: segregate paper and plastic for recycling centers'

Previous Years' Board Questions on Our Environment Class 10

Reviewing past CBSE board papers reveals predictable question patterns for Our Environment Class 10. The 2024 board exam included: (1) 'Construct a terrestrial food chain of four organisms. State the role of decomposers.' (3 marks)—solution requires a labeled chain (Grass → Rabbit → Fox → Eagle) plus one sentence on decomposers recycling nutrients. (2) 'Explain biological magnification with an example.' (3 marks)—model answer describes toxin concentration increase per trophic level, uses DDT in an aquatic food chain (0.003 ppm in phytoplankton → 25 ppm in birds), and states consequences (eggshell thinning, reproductive failure). (3) 'How do CFCs cause ozone depletion? Suggest two steps to protect the ozone layer.' (5 marks)—full answer includes CFC structure (CCl₃F), UV photolysis releasing Cl, catalytic reaction equations (Cl + O₃ → ClO + O₂; ClO + O → Cl + O₂), consequences (increased UV-B, skin cancer, crop damage), and solutions (Montreal Protocol compliance, switch to HFCs/HCFCs, ban aerosols). The 2023 paper asked: (4) 'Differentiate between biodegradable and non-biodegradable substances with three examples each.' (3 marks)—table format earns full marks: biodegradable (vegetable peels, paper, cotton) decompose via microbes in weeks; non-biodegradable (plastic, glass, metals) persist hundreds of years, resist microbial action. (5) 'Why are food chains limited to 3-5 trophic levels?' (2 marks)—answer cites the ten percent law: only 10% energy transfers per level, so by the 4th or 5th level, insufficient energy remains to support viable populations. The 2022 paper included a case study on Swachh Bharat with sub-questions on waste segregation and composting (5 marks total). Practice these question types with strict time limits—allocate 1 minute per mark (3-mark question = 3 minutes)—to simulate exam pressure. The NCERT exercises in Our Environment Class 10 (pages 260-261 in the 2024 edition) mirror board question formats; solve all 13 questions and check answers from the CBSE marking scheme available on cbse.gov.in.

Frequently asked questions

How many marks does Our Environment Class 10 carry in the CBSE board exam, and what question types appear?+
Our Environment Class 10 typically contributes 4-6 marks in the CBSE Science board exam, usually as one 5-mark long-answer question or two short-answer questions (3 marks + 2 marks). Common question types include constructing and labeling food chains or food webs, explaining the ten percent law with numerical examples, differentiating biodegradable from non-biodegradable substances, describing ozone depletion mechanisms with chemical equations, and suggesting waste management strategies using the 3Rs. The 2024 board paper included a 3-mark question on biological magnification and a 5-mark question on ozone layer protection, both directly from NCERT Chapter 15.
My child struggles to remember the difference between food chains and food webs—how can we make this clearer?+
Use a simple visual analogy: a food chain is like a single railway track (one pathway, linear), while a food web is like a railway network (multiple interconnected tracks). Have your child draw a basic food chain (Grass → Rabbit → Fox), then expand it by adding alternate food sources—if the fox also eats birds and snakes, and those animals eat different prey, you have created a food web. Practice by cutting out pictures of organisms from magazines, arranging them on paper, and drawing arrows to show who eats whom. CBSETUTOR.ai offers interactive exercises where students construct food webs digitally and receive instant feedback on arrow direction and organism placement, making the concept stick through repetition.
The ten percent law seems abstract—how do I help my Class 10 student understand why only 10% energy transfers?+
Explain it with a relatable example: when your child eats rice (producer energy), their body uses most calories for daily activities (walking, studying, breathing, maintaining body temperature)—that energy becomes heat and is lost. Only a small portion builds new muscle or tissue that could transfer to the next level if someone ate them (hypothetically). The same applies in ecosystems: a grasshopper uses 90% of the grass energy it eats for hopping, metabolism, and warmth; only 10% becomes grasshopper biomass available to a frog. Draw an energy pyramid with actual numbers (10,000 J at base, 1,000 J at second level, 100 J at third) to visualize the drastic decrease. NCERT Chapter 15 page 255 has a diagram your child should reproduce in their own notes.
What is the easiest way to remember biodegradable versus non-biodegradable substances for the board exam?+
Use this mnemonic: Bio-degradable = Bio (living microbes) can Degrade (break down). If bacteria and fungi can digest it (like food, paper, cotton, wood), it is biodegradable. If microbes cannot digest it (plastic, glass, metal—these need high heat or chemicals to break down), it is non-biodegradable. For the exam, memorize three examples of each: biodegradable (vegetable peels, paper, jute bags) and non-biodegradable (plastic bags, glass bottles, aluminum foil). Write a two-column table in your answer—examiners appreciate organized presentation, and tables often earn full marks even if explanations are brief.
How should my child draw food chain arrows—from predator to prey or prey to predator?+
Always draw arrows from the food source TO the organism eating it, showing the direction energy flows. Correct: Grass → Grasshopper → Frog (energy moves from grass into the grasshopper, then into the frog). Incorrect: Frog → Grasshopper → Grass (this wrongly suggests the frog provides energy to the grasshopper). A helpful trick: the arrowhead points toward the mouth of the eater. Many students lose 1 mark in Our Environment Class 10 questions solely due to reversed arrows, so practice drawing 5-10 food chains with correct arrow direction until it becomes automatic.
Why do we need to learn about ozone depletion in Our Environment Class 10 when India banned CFCs years ago?+
Though India phased out CFCs by 2010 under the Montreal Protocol, CFCs released decades earlier still linger in the stratosphere (atmospheric lifetime 50-100 years), continuing to destroy ozone. Understanding ozone depletion teaches your child how individual chemical compounds (even in small amounts like aerosol sprays) can have global consequences, and how international cooperation (Montreal Protocol) can solve environmental crises—a model for addressing climate change. Board exam questions test this because it exemplifies the link between human activity, chemistry, and ecology. Additionally, newer refrigerants (HFCs) still have climate impacts, so the lesson remains relevant for future policy discussions your child will encounter as a citizen.
Can my child score full marks in Our Environment Class 10 without memorizing chemical equations for ozone depletion?+
No—the CBSE marking scheme explicitly awards 1-2 marks (out of 5) for writing the correct chemical equations: Cl + O₃ → ClO + O₂ and ClO + O → Cl + O₂. Examiners look for these equations to confirm understanding of the catalytic cycle where chlorine is regenerated. Without them, even a well-written descriptive answer will lose marks. Have your child write these equations 10 times daily for a week before the exam. CBSETUTOR.ai includes flashcard drills for such equations, testing recall until your child can write them from memory in under 30 seconds, which is essential during exam time pressure.
What is biological magnification, and why do board exams ask about it in Our Environment Class 10?+
Biological magnification is the increasing concentration of non-degradable toxins (like DDT, mercury) at each successive trophic level in a food chain. For example, if water contains 0.01 ppm DDT, phytoplankton absorb it; small fish eating thousands of phytoplankton accumulate 1 ppm; large fish eating many small fish reach 10 ppm; eagles eating large fish hit 100 ppm—enough to cause eggshell thinning and reproductive failure. Board exams test this because it integrates multiple concepts: food chains, non-biodegradable substances, and real-world pollution consequences. A complete answer requires a labeled food chain, numerical progression of toxin concentration, and stating the ecological impact on top predators. This is a high-scoring 3-5 mark question if answered thoroughly.
How can we practice waste segregation at home to help my child relate to Our Environment Class 10 concepts?+
Set up two bins in your kitchen: one labeled 'Wet/Biodegradable' (vegetable peels, fruit scraps, leftover cooked food, tea leaves) and one 'Dry/Recyclable' (paper, cardboard, plastic bottles, metal cans, glass). Involve your child in sorting waste daily for two weeks before the exam, discussing why each item goes in a particular bin—this hands-on experience cements the biodegradable versus non-biodegradable distinction better than rote memorization. If possible, start a small compost bin for the wet waste and observe decomposition over weeks; take photos to include in internal assessment projects. Many CBSE schools award extra marks for such practical documentation, and it makes exam questions on waste management feel tangible rather than abstract.
My daughter finds ecosystem diagrams confusing—too many arrows and organism names. How can we simplify this for Our Environment Class 10?+
Start with the smallest unit: a three-organism chain (Producer → Primary consumer → Secondary consumer). Have her draw this on paper, then gradually add one organism at a time, asking 'What else could eat the grasshopper besides the frog?' (maybe a bird), 'What else could the frog eat?' (beetles, worms). Each addition creates a new connection, slowly building the web. Use color coding: producers in green, herbivores in yellow, carnivores in red—this visual grouping helps track trophic levels. CBSETUTOR.ai offers interactive drag-and-drop food web builders where students connect organisms digitally, and the AI highlights errors (like connecting two producers), making practice less frustrating than redrawing on paper repeatedly.
Will my son be penalized if he uses different organism examples than the NCERT textbook in Our Environment Class 10 food chains?+
No, CBSE examiners accept any scientifically accurate food chain as long as organisms belong to the correct trophic levels and the stated ecosystem. For example, if the question asks for a forest food chain, writing 'Tree seeds → Squirrel → Hawk → Eagle' is perfectly valid even though NCERT uses 'Grass → Deer → Tiger'. However, avoid mixing ecosystems (do not put 'Phytoplankton → Deer → Lion'—phytoplankton is aquatic, deer/lion are terrestrial). Also, ensure biological accuracy: do not write 'Grass → Snake' (snakes are carnivores, not herbivores). Creativity is fine, but ecological correctness is mandatory. If your son is unsure, sticking to NCERT examples guarantees safety.
How many minutes should my child spend on a 5-mark question about ozone depletion in the Our Environment Class 10 board exam?+
Allocate 5-6 minutes maximum (roughly 1 minute per mark plus 1 minute for planning). In that time, your child should write: (1) definition of ozone layer and its role (1 minute), (2) how CFCs release chlorine and destroy ozone with chemical equations (2 minutes), (3) consequences of ozone depletion—UV-B effects on humans, plants, and marine life (1.5 minutes), (4) preventive measures like Montreal Protocol and CFC alternatives (0.5 minute). Practice timed writing at home: set a stopwatch for 5 minutes and have your child write a full answer, then compare against the CBSE marking scheme. CBSETUTOR.ai tracks response time and provides feedback if answers are too brief or too verbose, training students to hit the optimal length-to-time ratio for maximum marks.

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