Chapter 13 · Question 8

Distinguish between biodegradable and non-biodegradable substances. Give examples of each. Why is the increasing proportion of non-biodegradable waste a serious environmental concern?

Answer Revealed

Direct Answer:

Biodegradable substances are those that can be broken down by biological processes — through the action of bacteria, fungi, and other decomposers — into simpler, harmless substances that return to the soil. Examples: vegetable peels, paper, cotton cloth, food waste, fallen leaves, wood, animal dung. Non-biodegradable substances are those that cannot be broken down by biological processes and persist in the environment for decades or centuries. Examples: plastics (polythene, PVC), glass, metals, pesticides (DDT), electronic waste. The increasing proportion of non-biodegradable waste is dangerous because these materials accumulate in the environment, cannot be recycled by natural processes, may harm organisms (animals ingest plastics), and can release toxic substances — or enter the food chain via biological magnification.

Simple Explanation

Biodegradable waste is nature-friendly — things like vegetable peels, paper, and cotton clothes rot away naturally thanks to bacteria and fungi. Non-biodegradable waste — plastic bags, glass bottles, metal cans — just sits there for hundreds of years. The problem is that we are making more and more of the stuff nature cannot handle. Plastic chokes animals, leaches chemicals into soil, and never really goes away — it just breaks into smaller pieces called microplastics.

Exam-Ready Structure

The classification of waste into biodegradable and non-biodegradable categories is central to understanding the waste management crisis, and is covered in NCERT Class 10 Chapter 13 under Section 13.2.2. 1. Biodegradable substances: (a) Substances that are broken down by biological processes — specifically by the action of bacteria, fungi, and other saprophytes (decomposers). (b) The concept of enzyme specificity is important here: specific enzymes produced by decomposers can break down specific natural organic substances. Humans cannot digest coal because we lack the specific enzymes for it. Similarly, decomposers have particular enzymes that act only on natural organic matter. (c) Examples: spoilt food, vegetable peels, used tea leaves, waste paper, cotton and jute cloth, wood, fallen leaves, animal dung, fruit peels, grass, leather. (d) Activity 13.5 demonstrates this: students bury household waste and observe at 15-day intervals. Materials that change form and structure over time are biodegradable; those that remain unchanged are non-biodegradable. 2. Non-biodegradable substances: (a) Substances that cannot be broken down by biological processes. (b) They may be chemically inert and persist in the environment for a long time under ambient, normal conditions. (c) Even when physical processes like heat and pressure act on them, they still persist for long durations. (d) Examples: plastic (polythene bags, PVC, PET bottles), glass, metals (tin cans, aluminium foil), synthetic fibres (nylon, polyester), pesticides (DDT), electronic waste (circuit boards, batteries), ceramic materials. 3. Environmental concern — increasing proportion of non-biodegradable waste: (a) Accumulation: Non-biodegradable waste does not disappear — it builds up in the environment, leading to littering, heaps of garbage, and pollution of land and water bodies. (b) Harm to organisms: Animals may ingest plastic or become entangled in it; marine life is severely affected by plastic pollution in oceans. (c) Toxicity: Some non-biodegradable materials release hazardous chemicals as they slowly degrade under physical conditions. (d) Biological magnification: Non-biodegradable pesticides and industrial chemicals enter food chains and accumulate at higher trophic levels, as discussed in the biological magnification concept. (e) Land and water pollution: Non-biodegradable waste contaminates soil and groundwater. 4. Lifestyle changes: NCERT notes that improvements in lifestyle, increased use of disposable items, and changes in packaging have all increased the proportion of non-biodegradable waste in municipal solid waste.

Key Points

Biodegradable: broken down by biological processes (bacteria, fungi); examples — vegetable peels, paper, cotton cloth, wood, animal dung
Non-biodegradable: NOT broken down by biological processes; persist in the environment; examples — plastics, glass, metals, pesticides, e-waste
Enzyme specificity determines biodegradability — decomposers have enzymes only for natural organic substances
Non-biodegradable waste accumulates, harms organisms, releases toxins, and enters food chains
Lifestyle changes, disposable items, and new packaging materials have increased the proportion of non-biodegradable waste

Common Mistakes

Claiming that heat and sunlight 'biodegrade' plastics — physical breakdown into smaller pieces is not biodegradation; the material still persists chemically
Assuming all natural materials are biodegradable — some natural materials like certain rocks take geological time to break down, but the term specifically refers to biological decomposition

Distinguish between biodegradable and non-biodegradable substances. Give examples of each. Why is the increasing proportion of non-biodegradable waste a serious environmental concern?