Our Environment (Class 10) — Study Notes

Overview

Our Environment is a high-weightage topic in NSO Class 10, bridging biology, chemistry, and environmental science. It tests your understanding of how living organisms interact with each other and their physical surroundings, forming ecosystems. Questions typically focus on food chains/webs, energy flow, biodegradable vs non-biodegradable waste, ozone layer depletion, and human impact on the environment.

Examiners favor multi-concept questions: for example, linking pesticide use to biomagnification in a food chain, or connecting CFC emissions to ozone depletion. You must recognize the interdependence of biotic (living) and abiotic (non-living) components, understand the flow of energy and matter through trophic levels, and identify sustainable practices. Mastering this topic also prepares you for the Achievers Section, where real-world environmental problems are presented.

Expect 4–6 direct questions plus 1–2 HOTS questions in the Achievers Section. Focus on definitions, cycles, consequences of pollution, and the 3R principle (Reduce, Reuse, Recycle).

Key Concepts

• **Ecosystem**: A self-sustaining functional unit comprising all living organisms (biotic components) and non-living elements (abiotic components like air, water, soil, sunlight) in a given area, interacting through nutrient cycles and energy flow.

• **Food Chain and Food Web**: A food chain is a linear sequence showing who eats whom (grass → grasshopper → frog → snake → hawk). A food web is an interconnected network of multiple food chains, representing realistic feeding relationships in an ecosystem.

• **Trophic Levels**: Organisms occupy different levels based on their position in the food chain. Producers (plants) are the first trophic level; herbivores (primary consumers) are second; carnivores eating herbivores (secondary consumers) are third, and so on. Energy decreases by about 90% at each successive level (10% law).

• **Biodegradable vs Non-Biodegradable Waste**: Biodegradable waste (food scraps, paper, cotton) is decomposed by microorganisms into harmless substances. Non-biodegradable waste (plastics, metals, glass) persists in the environment, causing pollution and harming organisms.

• **Ozone Layer**: A region in the stratosphere (15–30 km altitude) with high ozone (O₃) concentration. It absorbs most of the Sun's harmful UV-B and UV-C radiation, protecting life on Earth from DNA damage, skin cancer, and cataracts.

• **Ozone Depletion**: Caused primarily by chlorofluorocarbons (CFCs) used in refrigerators, air conditioners, and aerosol sprays. Chlorine atoms from CFCs catalytically destroy ozone molecules, thinning the ozone layer, especially over Antarctica (ozone hole).