CBSE Class 10 Science Chapter 13 Our Environment — 20 MCQs with Answers

An ecosystem consists of all living organisms (biotic components) and their physical environment (abiotic components) interacting as a unit. Producers (green plants) capture solar energy through photosynthesis; consumers (herbivores, carnivores, omnivores) depend directly or indirectly on producers; decomposers (bacteria, fungi) break down dead organic matter, returning nutrients to the soil. Understanding these roles and their interdependence is foundational. The NCERT defines producers as autotrophs and consumers as heterotrophs. These MCQs test your grasp of definitions, roles, and examples of ecosystem components. Pay attention to keywords like 'autotroph', 'heterotroph', and 'decomposer' — they appear verbatim in board papers.

A food chain is a linear sequence showing who eats whom in an ecosystem, starting with a producer. A food web is a network of interconnected food chains, reflecting the complexity of real ecosystems. Each step in a chain is called a trophic level: producers occupy the first trophic level, herbivores the second, small carnivores the third, and so on. The NCERT emphasises that energy flow in an ecosystem is unidirectional — from sun to producers to consumers — and only about 10 per cent of energy transfers to the next level (the ten-percent law). Consequently, food chains rarely exceed four or five trophic levels. These MCQs test your ability to count trophic levels, distinguish chains from webs, and apply the ten-percent energy rule.

The ten-percent law, first proposed by Raymond Lindeman, states that when energy flows from one trophic level to the next, approximately 10 per cent is stored as biomass in the consumer; the remaining 90 per cent is dissipated as heat during respiration, movement, and other metabolic processes. This principle explains why top carnivores are fewer in number and why pyramids of energy are always upright. NCERT Class 10 Science explicitly mentions this law in Chapter 13, and board exams often ask numerical or reasoning questions based on it. Understanding energy flow also helps explain why ecosystems cannot support unlimited trophic levels. These MCQs require both recall and application of the ten-percent concept.

The ozone layer sits in the stratosphere, approximately 15–35 km above Earth's surface, and absorbs most of the sun's harmful ultraviolet (UV) radiation. Ozone (O₃) is formed when UV rays split oxygen molecules (O₂) into free oxygen atoms, which then combine with other O₂ molecules. However, since the 1980s, scientists observed thinning of this layer — especially over Antarctica — due to chlorofluorocarbons (CFCs) used in refrigerators, air conditioners, and aerosol sprays. When CFCs reach the stratosphere, UV radiation breaks them down, releasing chlorine atoms that catalytically destroy ozone. Increased UV reaching Earth causes skin cancer, cataracts, and harm to phytoplankton. The 1987 Montreal Protocol phased out CFC production globally. NCERT Chapter 13 dedicates a full section to ozone depletion; expect 1–2 MCQs in boards.

Waste materials are classified as biodegradable if they can be broken down by biological processes (decomposers) into simpler, harmless substances. Examples include vegetable peels, paper, cotton cloth, and wood. Non-biodegradable wastes resist decomposition; plastics, glass, metals, and synthetic fibres persist in the environment for years, causing soil and water pollution. NCERT emphasises the environmental impact: plastic bags choke drains, harm aquatic life, and accumulate in landfills. The chapter encourages students to adopt the '3 Rs' — Reduce, Reuse, Recycle — to minimise waste generation. Board exams test this through scenario-based MCQs or assertion-reason questions linking waste type to environmental impact.

Higher-order thinking skills (HOTS) questions and assertion-reason MCQs appeared in CBSE papers from 2020 onward and are now a staple in the competency-based pattern. In assertion-reason format, you are given two statements: Assertion (A) and Reason (R). You must determine if each is true or false independently, then check if R correctly explains A. The four standard options are: (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. Read both statements carefully, verify factual correctness from NCERT, then assess logical linkage. These questions test conceptual depth and are worth 1 mark each but often differentiate top scorers.

Many students confuse trophic level numbering — remember producers are always the first level, not level zero. Another pitfall is mixing up food chain direction; energy flows from producers to consumers, never backwards. In ozone questions, students sometimes write CO₂ instead of CFCs as the cause of depletion; always link CFCs to ozone and CO₂ to global warming. Biodegradable versus non-biodegradable classification errors are common: paper is biodegradable, but laminated or plastic-coated paper is not. In assertion-reason MCQs, students often pick option (a) without checking if the reason truly explains the assertion; verify logical causation, not just factual truth. Lastly, ignoring units in numerical questions — energy in Joules, not kilojoules — can cost marks. Practising past-year CBSE papers and NCERT exemplar questions helps avoid these traps. Mark your mistakes, revisit the relevant NCERT paragraph, and attempt similar questions until the concept is solid.

CBSE Class 10 Science Term-2 papers typically include 16–20 MCQs in Section A, each carrying 1 mark, with no negative marking. Spend no more than 30–40 seconds per MCQ to leave time for longer answers. Read the question stem carefully, underline keywords like 'not', 'except', 'primary', 'mainly', which often flip the expected answer. Eliminate obviously wrong options first; if two options remain, recall NCERT definitions or diagrams to decide. For numerical MCQs, do a quick mental calculation; if your answer does not match any option, recheck the arithmetic. In assertion-reason questions, evaluate each statement independently before judging the explanation link. If completely unsure, make an educated guess — there is no negative marking — but avoid wild guesses that waste mental energy. After finishing the paper, if time permits, revisit marked MCQs and verify your choice against NCERT language. Silly mistakes like misreading '10%' as '1%' or confusing 'producer' with 'consumer' cost easy marks; a final 2-minute scan can catch these. Consistent practice with NCERT-aligned MCQs — such as these 20 questions — builds both speed and accuracy, turning Chapter 13 into a scoring asset in your board exam.

Consistent daily practice with high-quality, NCERT-aligned MCQs is the surest path to scoring full marks in Chapter 13. CBSETUTOR.ai offers an AI-powered tutor available 24×7 that lets you upload a photo of any MCQ or diagram from your textbook, worksheet, or mock test and receive a step-by-step explanation within seconds. Whether you are stuck on why option (B) is wrong in an assertion-reason question or need clarity on trophic level counting, the AI tutor breaks down each concept in simple language. The platform covers all CBSE classes from 6 to 12 at a single subscription of ₹999 per month — no hidden fees, no per-subject charges. Parents appreciate the transparency: one flat fee gives your child unlimited access to Maths, Science, Social Science, and languages, plus the ability to ask follow-up questions until the doubt is fully resolved. A 3-day free trial lets students experience the AI tutor's speed and accuracy before committing. For Class 10 boards, where every mark counts, having an on-demand tutor that never tires and always references NCERT can make the difference between 85 and 95. Integrate 15–20 minutes of MCQ practice on CBSETUTOR.ai into your evening routine, track your weak topics, and watch your confidence soar as exam day approaches.