CBSE Class 10 Science 2022 · Paper 31/2/1 · Question 7(b)

(a) Garbage is the waste material - things we no longer need and throw away - produced by our daily activities in homes, schools, offices, markets and industries, for example vegetable peels, leftover food, waste paper, packaging, plastic bags and broken glass. It is classified into two classes: biodegradable wastes, which are broken down by biological processes (by bacteria and other saprophytes), such as vegetable peels and paper; and non-biodegradable wastes, which are not broken down in this way and persist for a long time, such as plastics and glass. (b) It means that each enzyme acts on a particular substance, so a specific enzyme is needed to break down each substance and no single enzyme can break down everything. For example, salivary amylase breaks down starch but not proteins. That is why we get no energy by eating coal, and why many human-made materials, such as plastics, are not broken down by decomposers - no enzyme of theirs acts on them - so they are non-biodegradable.