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).

• **Biomagnification**: Progressive accumulation of non-biodegradable toxic substances (pesticides like DDT, heavy metals like mercury) in organisms at successive trophic levels. Top predators accumulate the highest concentrations, suffering severe health effects.

• **Waste Management**: Involves reducing waste generation, reusing materials, recycling (paper, plastic, metal, glass), composting organic waste, and safe disposal. Landfills and incineration should be minimized; sanitary landfills with proper lining prevent groundwater contamination.

Formulas / Key Facts

• **10% Law**: Only ~10% of energy is transferred from one trophic level to the next; the remaining 90% is lost as heat during respiration and metabolic processes.
• **Ozone Formation**: O₂ + UV light → O + O; then O + O₂ → O₃. Ozone is both formed and broken down by UV radiation in a natural balance.
• **Ozone Destruction by CFCs**: CFCl₃ (UV) → CFCl₂ + Cl; then Cl + O₃ → ClO + O₂; ClO + O → Cl + O₂. One Cl atom can destroy 100,000 ozone molecules.
• **Montreal Protocol (1987)**: International treaty to phase out ozone-depleting substances (CFCs, halons). By 2010, CFC production was largely eliminated globally.
• **Biodegradable materials**: Paper, cotton, jute, wood, food waste, animal waste, natural rubber.
• **Non-biodegradable materials**: Plastics, synthetic fibers (nylon, polyester), glass, metals, e-waste, pesticides like DDT.
• **Primary Producers**: Always plants and some bacteria (cyanobacteria). They fix solar energy via photosynthesis.
• **Decomposers**: Bacteria and fungi that break down dead organic matter, recycling nutrients back into the soil.

Worked Examples

**Example 1: Energy Flow in Food Chain** In a pond ecosystem, plants capture 10,000 J of solar energy. If a food chain exists as: Plants → Small fish → Large fish → Human, how much energy is available to humans?

**Solution**: Apply the 10% law at each trophic level.

• Energy in plants (producers) = 10,000 J
• Energy in small fish (primary consumers) = 10% of 10,000 = 1,000 J
• Energy in large fish (secondary consumers) = 10% of 1,000 = 100 J
• Energy available to humans (tertiary consumers) = 10% of 100 = **10 J**

Only 0.1% of the original energy reaches the top consumer.

**Example 2: Identifying Biodegradable Waste** Classify the following as biodegradable (B) or non-biodegradable (N): plastic bag, banana peel, aluminum can, cotton cloth, glass bottle, dead leaves.

**Solution**:

• Plastic bag: **N** (takes hundreds of years to decompose)
• Banana peel: **B** (decomposes in weeks)
• Aluminum can: **N** (metal; does not decompose naturally)
• Cotton cloth: **B** (natural fiber; microbes can break it down)
• Glass bottle: **N** (chemically inert; persists indefinitely)
• Dead leaves: **B** (organic matter; decomposed by fungi and bacteria)

**Example 3: Ozone Hole and UV Radiation** If the ozone layer over a region is depleted by 40%, what is the likely consequence?

**Solution**: Ozone absorbs UV-B radiation. A 40% depletion means significantly more UV-B reaches Earth's surface. Consequences:

• Increased skin cancer and cataracts in humans
• Damage to phytoplankton (aquatic food chain disruption)
• Reduced crop yields and plant growth

This scenario matches observations over Antarctica during spring (ozone hole).

Common Mistakes

• **Confusing food chain with food web**: A food chain is a single path; a food web is multiple interconnected chains. Exam questions may show a diagram and ask you to count chains within a web — trace each path separately from producer to top consumer.

• **Thinking energy increases up the food chain**: Wrong. Energy **decreases** by ~90% at each level due to respiration, heat loss, and incomplete consumption. Top predators receive the least energy, which is why large carnivores are rare.

• **Mixing up ozone (O₃) at ground level vs stratosphere**: Ground-level ozone is a pollutant causing respiratory problems; stratospheric ozone is protective. CFCs harm the stratospheric ozone layer, not ground ozone.

• **Assuming all plastics are identical**: Some plastics are recyclable (PET, HDPE); others are not. Biodegradable plastics (like PLA from cornstarch) do exist but are rare. Standard plastics (polythene bags) are non-biodegradable.

• **Forgetting decomposers in nutrient cycling**: Students often omit bacteria and fungi when drawing ecosystems. Decomposers are essential — they convert dead matter into nutrients that producers reuse, closing the nutrient loop.

Quick Reference

• **10% Law**: Only 10% energy transfers to next trophic level; 90% lost as heat.
• **Ozone depletion culprits**: CFCs (refrigerants, aerosols) release Cl atoms that destroy O₃.
• **Biodegradable**: Naturally decomposed by microbes (food, paper, cotton).
• **Non-biodegradable**: Persists in environment (plastics, metals, glass).
• **Biomagnification**: Toxins accumulate and concentrate at higher trophic levels.
• **3R Principle**: Reduce consumption, Reuse items, Recycle materials.