UGC NET Questions (Paper – 1)

Biomagnification describes how substances that are not readily metabolised, such as DDT or methylmercury, become more concentrated as they move up food chains. Predators at higher trophic levels accumulate contaminants from many prey organisms,leading to high internal concentrations. The stem referencing increases at successive trophic levels corresponds directly to biomagnification.

Option A:
Bioaccumulation focuses on the build up of a substance in a single organism over time,not on changes across trophic levels. While related,it does not capture the chain wide amplification described in the question.

Option B:
Biomagnification shows why top predators, including humans, can experience toxic effects even when environmental concentrations are low. Because the stem emphasises increases from level to level in the food chain,this process is the appropriate answer.

Option C:
Biotransformation refers to the chemical modification of substances by organisms,often through metabolic processes. It can sometimes reduce toxicity and does not necessarily result in increased concentrations. Therefore it is not the right option.

Option D:
Biofertilisation involves using microorganisms or organic materials to enhance soil fertility. It has nothing to do with pollutants increasing through food chains,so it cannot fit the blank.

Biomagnification occurs when chemicals that are persistent and fat-soluble accumulate in organisms and become more concentrated at higher trophic levels. Predators eat many prey items, each containing stored pollutants, leading to a build-up in their bodies over time. Substances such as DDT and methylmercury are well-known examples that biomagnify. The definition referring to progressive increase in concentration at successive trophic levels therefore correctly describes this process.

Option A:
Option A is incorrect because biomagnification is about pollutant concentration, not species richness. The number of species in a food chain is a separate ecological attribute.

Option B:
Option B is incorrect even though energy does diminish at higher trophic levels due to inefficiencies. That phenomenon relates to ecological pyramids and energy flow, not to the accumulation of contaminants.

Option C:
Option C is correct as it highlights both the persistence of certain chemicals and their tendency to move up the food chain. This explains why top predators, including humans, can face health risks even when environmental concentrations appear low.

Option D:
Option D is incorrect; microbial multiplication in sewage plants is part of biological treatment and waste breakdown. It does not involve the stepwise concentration of pollutants at different trophic levels.

Bioaccumulation occurs when a substance such as a heavy metal or persistent organic pollutant is taken up by an organism faster than it can be eliminated. Over time,its concentration in tissues increases,even if environmental levels remain low. The stem clearly describes this gradual build up,so bioaccumulation is the correct term.

Option A:
Bioaccumulation focuses on processes within an individual organism,highlighting uptake,storage and slow elimination. It helps explain why organisms can carry high internal loads of contaminants despite low external exposures. This explanation matches the description in the question.

Option B:
Biomagnification refers to increasing concentrations of a substance at successive trophic levels in a food chain. While it depends on bioaccumulation in organisms,it is a broader community level phenomenon,not the individual process emphasised in the stem.

Option C:
Biodegradation is the breakdown of substances by microorganisms into simpler compounds,often reducing toxicity. It is essentially the opposite of accumulation and therefore cannot fill the blank.

Option D:
Bioindicators are species or communities whose presence or condition reflects environmental quality. They may themselves accumulate pollutants,but the term describes their indicative role rather than the chemical accumulation process.

Biomagnification occurs when persistent pollutants that are not easily broken down accumulate as they move up food chains. Small organisms take up low concentrations from water, but predators eat many contaminated prey. At each trophic level, the pollutant concentration in tissues becomes higher. The highest levels are often found in top predators, such as fish-eating birds, which is exactly what the correct statement describes.

Option A:
Option A is incorrect because water usually contains relatively low concentrations of DDT compared to living organisms. It is in organisms, not in the water itself, that concentrations tend to build up.

Option B:
Option B is incorrect since saying concentrations decrease at higher trophic levels reverses the observed pattern. That would imply biodilution, not biomagnification.

Option C:
Option C is correct because it shows increasing concentration from plankton to fish and then birds. This pattern explains why eggshell thinning was observed in birds exposed to DDT through aquatic food chains.

Option D:
Option D is incorrect because DDT is known for its persistence and slow breakdown. Its ability to enter and stay in organisms is the reason biomagnification occurs.

Biomagnification occurs when persistent, fat-soluble pollutants accumulate at higher levels in a food chain. Small organisms like plankton take up low concentrations from water, but predators eat many contaminated prey. At each trophic level, the pollutant becomes more concentrated in body tissues, so top predators show the highest levels. The classic example is DDT accumulation from plankton to fish to fish-eating birds.

Option A:
Option A is incorrect because water generally has lower concentration than organisms; pollutants move into and concentrate within living tissues.

Option B:
Option B is incorrect; biomagnification means increasing, not decreasing, concentrations at higher trophic levels.

Option C:
Option C is correct as it describes rising concentration from lower to higher levels, matching observed patterns for DDT and similar pesticides.

Option D:
Option D is incorrect because DDT is persistent and not completely degraded before entering food chains, which is why biomagnification occurs.