Plastics do not decompose when buried in soil, even though many food materials do. Why are bacteria and other…

Question

Plastics do not decompose when buried in soil, even though many food materials do. Why are bacteria and other decomposers unable to break down plastic?

Accepted Answer

## Model Answer Bacteria and decomposers break down substances using **specific enzymes**. Just as enzymes in our body are specific to particular substances, no natural enzyme exists that can break down the chemical structure of plastics (human-made materials). Since plastics lack a matching biological enzyme, they cannot be decomposed by bacteria or other saprophytes, making them **non-biodegradable**. *Source: Chapter 13, Section 13.2.2 – Managing the Garbage we Produce* --- ## Explanation - The key concept here is **enzyme specificity** — examiners want this term used explicitly. - Mention that plastic is a **human-made (synthetic) material**, for which no corresponding enzyme exists in nature. - Avoid vague answers like "bacteria can't digest plastic" without explaining *why* (enzyme specificity is the reason). - Two marks = two clear points: (1) enzymes are specific, (2) no enzyme exists for plastic → non-biodegradable.

Science (086) — AI-generated practice question