Biodegradable and non-biodegradable

ICSE calls these biodegradable and non-biodegradable wastes. Bacteria and other decomposers break waste down with enzymes. Each enzyme works on certain substances only, so many man-made materials are left whole.

• Biodegradable: vegetable peels, used tea leaves, paper, leaves, grass, cow dung.
• Non-biodegradable: plastics, glass, Styrofoam, metal cans, and pesticides such as DDT. They last a long time, and some harm living things.

Biomedical waste is a separate idea. It is waste from hospitals, clinics and laboratories, such as used syringes. It is named for where it comes from, not for whether it rots.

A small example

Bury a day's waste from home in a pit, under at least 15 cm of soil. Keep it moist and look every 15 days. Peels and leftover food change form. Plastic packets stay the same.

Where marks go

CBSE's 2026-27 sample paper has no question on this. In a choice question, the marking scheme gives the mark only for the right option. If a question asks which group is not biodegradable, every item in that group has to fit.

In ICSE, the 2024 Biology paper asked for the odd one out among leaves, Styrofoam, grass and cow dung. The answer was Styrofoam. CISCE's report on the 2024 ICSE Biology paper names "cow dung" as a wrong choice. Its report on the 2025 paper says some answers mixed up biomedical and biodegradable waste, and did not score.

About the author

Deepti Sardana

Founder Member & Academic Lead

An IIT alumna (M.Sc., M.Phil.) with over 25 years in teaching, child psychology and learning assessment. As Academic Lead at EduBrahma, she leads the method TRUtesting uses to find where and why a child loses marks.

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