Q1. [4] medium exam-ready
Read the following and answer the questions that follow:
A class was asked to bury two sets of waste materials in the school garden: Set A contained vegetable peels, leftover food and dried leaves; Set B contained plastic wrappers, an old polythene bag and an empty medicine strip. After 30 days, they dug up both sets. Set A had largely decomposed and was mixed into the soil, while Set B remained almost unchanged.
(i) What term describes the materials in Set A? What organisms are mainly responsible for their breakdown? [1]
(ii) Give a reason why the materials in Set B remained unchanged after 30 days. [1]
(iii) Describe two harmful effects that materials like those in Set B can have on the environment if left unmanaged. [2]
Generated by claude-sonnet-4-6 · 2026-06-26 01:00 · grounding rag
Model Answer
(i) The materials in Set A are called biodegradable substances. They are mainly broken down by microorganisms (bacteria and fungi/saprophytes) present in the soil.
(ii) The materials in Set B are non-biodegradable. Bacteria and other saprophytes do not possess the specific enzymes needed to break down human-made materials like plastic and polythene, so they remained unchanged.
(iii) Two harmful effects of non-biodegradable materials:
- They persist in the environment for a very long time, accumulating in soil and water bodies, disrupting the ecosystem.
- They may harm living organisms in the ecosystem — for example, through biological magnification if toxic substances enter food chains.
Source: Chapter 13, Section 13.2.2 — Managing the Garbage we Produce
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Explanation
- (i) The key term "biodegradable" and the agents (bacteria/fungi/saprophytes) are both needed for the 1 mark.
- (ii) The reason must refer to the absence of specific enzymes in microorganisms — this is exactly what the textbook states. Just saying "plastic doesn't decompose" is too vague.
- (iii) The textbook states non-biodegradable substances either "persist in the environment for a long time" or "harm the various members of the ecosystem." Mention both distinct effects. Biological magnification is a valid second point from the same chapter.