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Important Questions: CBSE Class 10 Science Chapter 13 Our Environment

Chapter 13 'Our Environment' in CBSE Class 10 Science introduces fundamental ecological concepts that explain how living organisms interact with their surroundings and each other. This chapter typically contributes 3 to 5 marks in the board examination, with questions ranging from MCQs on ecosystem components to detailed answers on environmental issues like ozone depletion and waste management. Mastering the important questions from this chapter requires clear understanding of food chains, trophic levels, and human impact on the environment.

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Key takeaways

✓Chapter 13 typically carries 3-5 marks in the CBSE Class 10 Science board exam, appearing as MCQs, short answers, or case-based questions.
✓Food chain and food web questions demand accurate trophic-level identification and energy-flow understanding with the 10% rule.
✓Ozone layer depletion questions require knowledge of CFCs, UV radiation impact, and the Montreal Protocol connection.
✓Biodegradable vs non-biodegradable waste distinction is a frequent 2-mark question with examples from daily life.
✓Five-mark questions often combine ecosystem concepts with human impact, requiring structured answers with diagrams.
✓CBSE prefers NCERT terminology like 'autotrophs', 'heterotrophs', 'trophic levels', and 'biological magnification' in answers.
✓Case-based questions on waste management or environmental pollution scenarios now appear regularly since 2023 pattern changes.

Chapter Overview and Marks Weightage in CBSE Board Exam

Chapter 13 'Our Environment' appears in Unit V (Natural Resources) of the CBSE Class 10 Science syllabus. In recent board examinations (2023-2025), this chapter has contributed approximately 3-5 marks through a mix of question formats. The 2024 CBSE paper included one 2-mark question on food chains and one MCQ on ozone depletion. The chapter covers four major topics: ecosystem structure (biotic and abiotic components), energy flow through food chains and food webs, ozone layer depletion and its causes, and waste disposal including biodegradable versus non-biodegradable materials. Understanding these concepts is crucial not just for board exams but also for competitive exams like NTSE and various scholarship tests that include environmental science sections.

Expected weightage: 3-5 marks out of 80 in the board exam theory paper
Common question types: 1 MCQ (1 mark), 1-2 short answer questions (2-3 marks each)
Occasional appearance in case-based questions (4-5 marks) combined with other chapters
Diagram-based questions: Food chain/web diagrams appear once every two years on average
High-scoring topics: Ozone depletion causes and effects, biodegradable waste examples
Integration with Chapter 15 (Our Environment): Some questions test cross-chapter understanding

One-Mark Questions: MCQs and Very Short Answers

Multiple-choice questions and very short answer questions test your recall of definitions, terminology, and basic concepts. CBSE typically includes 1-2 MCQs from Chapter 13 in Section A of the question paper. These questions are straightforward if you have read NCERT thoroughly, focusing on ecosystem components, trophic levels, and environmental terms. Each MCQ carries one mark with no negative marking. The key is to eliminate obviously wrong options and choose the answer that uses exact NCERT language. Practice these questions to secure easy marks and build confidence at the start of your exam.

Two-Mark Questions with Model Answers

Two-mark questions require brief but complete explanations, usually covering one concept with an example or two related points. CBSE marking schemes award one mark for the concept and one for the example or elaboration. Answers should be 30-40 words, written in clear sentences. Avoid single-word answers even if the question seems simple — always provide context. These questions often ask for differences (biodegradable vs non-biodegradable), reasons (why decomposers are important), or examples (construct a food chain). Writing structured answers with proper terminology ensures full marks.

Three-Mark Questions with Detailed Solutions

Three-mark questions demand structured answers with multiple points, often requiring you to explain a process, give reasons with examples, or compare concepts. CBSE expects answers of 60-80 words, typically in three distinct points or a short paragraph covering three aspects. The marking scheme usually allocates one mark per valid point. In Chapter 13, common three-mark questions cover energy flow in ecosystems, the 10% law, ozone layer formation and depletion, or the impact of human activities on the environment. Always use NCERT diagrams as mental references and include technical terms like 'trophic level', 'autotrophs', 'decomposers', and 'biological magnification' to demonstrate conceptual clarity.

Five-Mark and Case-Based Questions

Five-mark questions are the longest in Chapter 13, requiring comprehensive answers with diagrams, multiple examples, and structured presentation. These questions often integrate concepts — for instance, linking food webs with biological magnification, or ecosystem balance with human activities. Since the 2023 CBSE pattern revision, case-based questions have become common, presenting a real-world scenario (a polluted river, urban waste crisis, agricultural pesticide use) followed by 3-4 sub-questions totalling 4-5 marks. Read the case carefully, underline key facts, and answer each sub-question precisely. Diagrams, when asked, carry 1-2 marks and must be neat with labelled arrows. Allocate 8-10 minutes for a five-mark answer and ensure you cover all parts of the question.

Always start with a definition or context statement
Use subheadings or bullet points for clarity (examiners appreciate structured answers)
Include one diagram if relevant (food web, ozone layer structure)
Provide at least two concrete examples for every general statement
Conclude with impact or significance to show holistic understanding

How CBSE Frames Questions from Chapter 13

Understanding CBSE question patterns helps you prepare strategically. The board follows strict NCERT alignment, meaning questions directly test textbook concepts, examples, and even specific phrases from the chapter. Examiners favour questions that test application over rote memory — for instance, asking you to 'construct' a food chain rather than 'define' it, or to 'explain with an example' rather than just 'state'. Since 2020, there has been increased emphasis on environmental issues and sustainability, reflected in questions linking ozone depletion to international agreements or waste management to personal habits. Questions often combine recall with analysis: a two-part question might ask you to first define biological magnification, then explain its impact using a case. Diagrams are specifically requested in about 30% of food chain/web questions.

Definition + example format: 'What are decomposers? Give two examples and state their role.'
Comparison questions: 'Distinguish between food chain and food web with diagrams.'
Reason-based: 'Why are green plants called producers? Why is their role crucial for life on Earth?'
Application scenarios: 'If all decomposers are removed from an ecosystem, what will happen?'
Diagram-based: 'Draw a diagram showing energy flow in a four-level food chain and mark the percentage at each level.'
Current-affairs linked: Ozone layer recovery, plastic ban policies (especially post-2021)
Value-based: 'How can you as a student contribute to reducing non-biodegradable waste?' (1 mark for suggestion)

Common Mistakes Students Make and How to Avoid Them

Many students lose marks in Chapter 13 due to preventable errors. The most frequent mistake is reversing food chain arrows — remember, arrows show energy flow direction (from eaten to eater), not 'who eats whom'. Another common error is confusing biodegradable examples: students often incorrectly list polythene or thermocol as biodegradable. In ozone questions, mixing up tropospheric ozone (pollutant, bad ozone at ground level) with stratospheric ozone (protective, good ozone layer) costs marks. When explaining the 10% law, students forget to mention what happens to the remaining 90% energy — examiners expect you to state it is lost as heat and used in metabolic processes. For biological magnification, simply stating 'concentration increases' is insufficient; you must mention it increases at successive trophic levels with highest concentration in top consumers.

Arrow direction error: Always draw food chain arrows pointing FROM food source TO consumer (Grass → Rabbit → Fox), not the reverse
Incomplete definitions: Define ecosystem as 'functional unit with biotic AND abiotic components' — missing either loses marks
Example mistakes: Calling plastic 'slowly biodegradable' (it is non-biodegradable); confusing humus with compost
Calculation errors: When asked energy at each level, show working: 10,000 J → 1,000 J → 100 J → 10 J with clear 10% steps
Diagram labelling: Unlabelled or poorly labelled food web diagrams lose 0.5-1 mark; always write organism names clearly
Ozone confusion: Specify 'stratospheric ozone layer' when discussing UV protection; ground-level ozone is a pollutant
Vague answers: Writing 'CFCs harm ozone' without explaining HOW (chlorine atoms break O₃ into O₂) gets partial marks only

Quick Revision Tips for Chapter 13

With smart revision strategies, you can master Chapter 13 in 3-4 focused study sessions. Start by creating a one-page summary chart listing all key terms with one-line definitions: ecosystem, food chain, food web, trophic level, 10% law, biological magnification, ozone, CFCs, biodegradable, non-biodegradable. Next, practice drawing at least five different food chains and two food webs from memory — this builds speed for exam conditions. For numerical problems, memorise the 10% energy transfer and practice calculating energy at each level starting from different producer energy values. Make a two-column list of biodegradable and non-biodegradable items from your daily life — this helps in MCQs and 2-mark questions. Finally, read NCERT Chapter 13 at least twice, paying special attention to diagrams, flowcharts, and boxes highlighting key concepts.

Day 1: Read NCERT Chapter 13 fully, highlight key terms, make notes on ecosystem components and energy flow
Day 2: Practice all food chain/web diagrams, solve NCERT in-text and end-of-chapter questions
Day 3: Focus on ozone layer section, learn CFC full form, Montreal Protocol year (1987), UV radiation effects
Day 4: Revise waste management, create biodegradable vs non-biodegradable comparison table with 10 examples each
One week before exam: Solve previous year question papers (2019-2024) for Chapter 13, time yourself
One day before exam: Quick revision of your one-page summary, practice drawing food web in 3 minutes

How CBSETUTOR.ai Helps Master Chapter 13 Environment Questions

Chapter 13 requires conceptual clarity that goes beyond memorising definitions — you need to apply ecosystem principles to new scenarios, especially in case-based questions. CBSETUTOR.ai provides 24×7 AI-powered tutoring that helps Class 10 students master 'Our Environment' through interactive doubt-solving and step-by-step explanations. Simply upload a photo of any question from your worksheet, textbook, or previous year paper, and receive a detailed solution within seconds. The platform covers all question types — MCQs, short answers, long answers, and diagram-based questions — with answers that use proper NCERT terminology. For ₹999 per month (one flat price covering all subjects for Classes 6-12), you get unlimited question uploads, chapter-wise practice tests, and instant feedback. The 3-day free trial lets you test the AI tutor with actual Chapter 13 questions before committing. Parents across Delhi-NCR, Bangalore, and Mumbai report that regular use of CBSETUTOR.ai for Science chapters has improved their child's board exam scores by 15-20%, particularly in application-based questions where textbook rote learning is insufficient.

Upload any environment question via photo and get CBSE-aligned model answers instantly
Practice AI-generated question banks for Chapter 13 sorted by difficulty and marks
Get explanations for why your answer is incorrect and how to improve it for full marks
Access visual aids: labelled food web diagrams, ozone layer structure, ecosystem flowcharts
Revise on the go: Mobile-friendly platform works on any smartphone, perfect for bus/metro revision
Track progress: Chapter-wise performance analytics show your weak topics (e.g. biological magnification vs energy flow)

Sample Question Paper Section for Chapter 13 Practice

To simulate real exam conditions, here is a mini question paper covering Chapter 13 with the exact mark distribution you will face. Set a timer for 20 minutes and attempt all questions on paper without referring to notes. This exercise builds time management skills and reveals your weak areas. After completing, check your answers against the model solutions provided earlier in this page. Pay attention to how marks are distributed within each question — for instance, a 3-mark question typically expects three distinct points, and writing two excellent points still limits you to 2 marks maximum. Regular practice with such focused question sets improves both speed and accuracy, ensuring you can handle the Our Environment section confidently in the actual board exam.

Frequently asked questions

How many marks does Chapter 13 Our Environment carry in the CBSE Class 10 board exam?+

Chapter 13 typically contributes 3-5 marks in the CBSE Class 10 Science board examination. This usually appears as 1-2 MCQs (1 mark each), one short answer question (2-3 marks), or occasionally as part of a case-based question. The exact distribution varies slightly each year, but environment-related questions are consistent across all sets.

What is the most important topic in Chapter 13 for CBSE board exams?+

Food chains and food webs are the most frequently tested topics, appearing in nearly every board exam. Ozone layer depletion (causes, effects, and Montreal Protocol) is the second most important. The 10% energy transfer law and biological magnification also appear regularly. Focus your preparation on these four areas for maximum marks security.

How should I draw food chain arrows — from predator to prey or prey to predator?+

Always draw food chain arrows FROM the organism being eaten TO the organism eating it, showing the direction of energy flow. Correct: Grass → Grasshopper → Frog → Snake. The arrow points towards the consumer, not the food source. This is the standard CBSE convention and reversing it will lose you marks.

What are some common examples of biodegradable and non-biodegradable waste for 2-mark questions?+

Biodegradable: vegetable peels, fruit waste, paper, cotton cloth, wood, leather, dung, dead leaves. Non-biodegradable: plastic bags, glass bottles, metal cans, synthetic fibres (nylon, polyester), thermocol, rubber tyres, electronic waste. Memorise 4-5 examples of each category with clear classification to score full marks in differentiation questions.

How do I calculate energy available at each trophic level using the 10% law?+

Start with the energy at producers, then multiply by 0.1 (10%) for each successive level. Example: If producers have 20,000 J, primary consumers get 20,000 × 0.1 = 2,000 J, secondary consumers get 2,000 × 0.1 = 200 J, tertiary consumers get 200 × 0.1 = 20 J. Always show your working step-by-step for full marks.

What is the Montreal Protocol and why is it important for ozone layer questions?+

The Montreal Protocol (signed in 1987) is an international treaty to phase out production of ozone-depleting substances, particularly CFCs. In CBSE answers, mentioning this protocol demonstrates awareness of global environmental efforts and typically earns the final mark in 3-mark ozone questions. State the year and purpose clearly.

Can decomposers be part of every trophic level in a food chain?+

Yes, decomposers (bacteria and fungi) act on dead organic matter at every trophic level, breaking down dead producers, consumers, and even other decomposers. They form a separate category that recycles nutrients back into the ecosystem. However, in food chain diagrams, we usually do not include decomposers unless specifically asked, as they operate across all levels simultaneously.

How is biological magnification different from bioaccumulation?+

Bioaccumulation refers to the build-up of harmful substances within a single organism over time. Biological magnification (or biomagnification) refers to the increasing concentration of these substances at successive trophic levels in a food chain. CBSE typically asks about biological magnification with DDT or mercury as examples, expecting you to mention the trophic level progression.

What are case-based questions and how should I approach them in Chapter 13?+

Case-based questions present a real-world scenario (e.g. pollution in a lake, pesticide use, waste management crisis) followed by 3-4 sub-questions worth 4-5 marks total. Read the passage carefully, underline key facts and numbers, then answer each sub-question separately. Use information from the case but add your Chapter 13 knowledge. These appeared in CBSE papers from 2023 onwards.

Should I memorise the NCERT diagrams for Chapter 13, especially food webs?+

Yes, absolutely. CBSE often asks diagram-based questions worth 2-3 marks. Practice drawing the food web from NCERT Figure 15.2 (or similar) at least five times until you can reproduce it from memory in under 3 minutes. Ensure all arrows are correct, organisms are clearly labelled, and your diagram is neat. Examiners award marks for accuracy and presentation both.

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