The use of plastics has led to a number of environment-related problems. For this, which one of the following statements is correct?
- (a)They are non-biodegradable.
- (b)They do not get released into water and food.
- (c)They do not have any biochemical synthesis activity.
- (d)They are harmless to humans.
Correct — A, They are non-biodegradable. Biodegradation is the breakdown of organic matter by micro-organisms such as bacteria and fungi, and it works only where microbes have enzymes that fit the material's chemical bonds. Common plastics are long synthetic polymers with carbon backbones and linkages that no soil or marine microbe has evolved to attack, so the material is not consumed — it is only broken into ever smaller fragments. That is the root of every environment-related problem the stem refers to: a discarded plastic bottle persists on the order of a century in the marine environment, against roughly a year for a wool glove. The other three options either state the reverse of what plastics do or say nothing about why they cause harm.
- (b)They do not get released into water and food. — The opposite is true, and it is one of the reasons plastics are a public-health concern — fragments and additives do find their way into water and into the food chain as microplastics.
- (c)They do not have any biochemical synthesis activity. — This is not the reason plastics damage the environment, and as a blanket claim it is not even accurate — polyhydroxyalkanoates such as PHBV are polyesters made by micro-organisms through bacterial fermentation, and they are biodegradable.
- (d)They are harmless to humans. — Contradicts the stem itself. If plastics were harmless there would be no environment-related problem to explain, and the concern over additives and microplastic ingestion says otherwise.
Biodegradation is the breakdown of organic matter by micro-organisms. A material biodegrades when microbes possess enzymes capable of cutting its bonds and using the fragments for energy. Natural polymers such as wool, cotton and paper are readily attacked. Conventional plastics — polyethylene, polypropylene, polystyrene, PET — have carbon backbones with linkages microbes have not evolved to handle, so they persist. Weathering, sunlight and abrasion still fragment them, which converts a visible litter problem into an invisible microplastic one.
Read this stem carefully: it does not ask what is true of plastics in general, it asks which statement explains the environment-related problems. That framing kills option (c) even before its accuracy is examined, because a lack of 'biochemical synthesis activity' names no harm. Options (b) and (d) are both simply the reverse of the known position. Indicative degradation times from the same literature are worth carrying as ranges rather than constants — about a year for a wool glove, about a century for a plastic bottle, around two centuries for an aluminium can, and effectively indefinitely for glass. Note also what non-biodegradability is not: glass and aluminium are also non-biodegradable, yet they are far less troublesome, because they are chemically inert and are recycled at high rates. It is the combination of persistence, fragmentation and low recovery that makes plastic the harder problem.
- Biodegradation is the breakdown of organic matter by micro-organisms such as bacteria and fungi.
- Conventional plastics have carbon backbones with bonds that microbes have not evolved to attack, so they fragment rather than decompose.
- Indicative marine degradation times: a wool glove about a year, a plastic bottle about a hundred years, glass essentially indefinite.
- Not every polymer is persistent — PHBV and other polyhydroxyalkanoates are microbially produced polyesters and are biodegradable.
- Equating non-biodegradable with harmful; glass and aluminium are also non-biodegradable but pose a much smaller problem.
- Assuming all plastics are synthetic and persistent — some polyesters are made by bacteria and do break down.
- Answering a 'why is this a problem' stem with a statement that is true but explains no harm.
Asked as a single-correct item on the property of plastics that causes environmental damage, and in later papers as a direct 'why do plastics not degrade easily' stem.
Consider the following statements: Statement-I: Many chewing gums found in the market are considered a source of environmental pollution. Statement-II: Many chewing gums contain plastic as gum base. Which one of the following is correct in respect of the above statements?
- (a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
- (b) Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I
- (c) Statement-I is correct, but Statement-II is incorrect
- (d) Statement-I is incorrect, but Statement-II is correct
Answer(a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
Same logic in a different disguise, and from the same exam year. UPSC asks you to accept that the plastic content of a gum base is what makes it a pollutant — precisely the reasoning this CDS item wants, that the persistence of the polymer is the cause of the harm.
- practice — not a real PYQ
Which one of the following materials is biodegradable?
- (a)A woollen glove
- (b)A polythene bag
- (c)An aluminium can
- (d)A glass bottle
Answer(a) A woollen glove — wool is a protein fibre that bacteria and fungi can metabolise; the other three are non-biodegradable.
- practice — not a real PYQ
Microplastics in the environment are best described as
- (a)plastics that have been fully decomposed by bacteria
- (b)small fragments produced as larger plastic items break up
- (c)a class of biodegradable polyesters
- (d)plastics manufactured for medical use only
Answer(b) small fragments produced as larger plastic items break up — fragmentation, not decomposition, is what weathering achieves.