CUET UG Biology Booster Test 2-Ecosystem Stability and Function

Ecological stability implies a community's ability to maintain a steady state over time despite environmental fluctuations. A community with minimal year-to-year variation in biomass production is more stable, whereas high fluctuations reflect an unstable, unpredictable system.

A hallmark of a stable community is its "biotic resistance" or ability to resist invasions by alien (exoti C) species. Being vulnerable to weeds indicates a lack of stability, making Option A the correct choice for the "EXCEPT" criteria.

Tilman's outdoor experiments established that plots with higher species richness (high diversity) show less year-to-year variation in biomass and higher overall productivity. Conversely, low richness leads to unstable, highly variable production.

Tilman's experiments demonstrate that increased species richness leads to higher productivity and ecosystem stability. Translating this to agriculture, increasing crop variety (polyculture) promotes both stability and yield.

According to Ehrlich's hypothesis, the removal of rivets (species) starts slowly (3); initially, the plane seems safe (2). As more rivets are lost, the structure weakens significantly (1) until a critical threshold is crossed, leading to total collapse (4).

In the Rivet Popper hypothesis, "popping a rivet" refers to the loss or extinction of a species, not the creation of new species (speciation). Thus, this analogy is incorrect.

This analogy implies that some species (like those on the wings) are critical for major ecosystem functions. Their extinction is far more consequential to ecosystem stability than the loss of less significant species (like those on the seats).

Ehrlich's analogy suggests that an ecosystem has a buffer of "minor" species; losing them may not trigger an immediate collapse (I). However, losing key functional species (wing rivets) immediately threatens the system's structural integrity (II).

The history of life, including the five massive extinction episodes that occurred before humans appeared, is documented through the examination of fossil records across geological strata.

Geological history records exactly five mass extinction episodes occurring over the roughly 3-billion-year period between the diversification of life and the emergence of humans.

The background extinction rate refers to the natural rate at which species become extinct in the absence of major catastrophic events. According to NCERT, this rate was approximately one species per year before significant human influence. Ecologists warn that because of habitat destruction, overexploitation, pollution, invasive species, and climate change, the current extinction rate is about 100 to 1,000 times higher than the background rate. Therefore, the estimated current extinction rate becomes 100–1,000 species per year. Option C correctly reflects the estimate given in NCERT. Options A and B greatly underestimate the increase. Option D exaggerates the estimate beyond what NCERT mentions.

The previous five mass extinctions and the current Sixth Extinction all involve the disappearance of a large number of species. Therefore, large-scale loss of species is not unique to the present extinction. The distinguishing features of the Sixth Extinction include: It is primarily caused by human activities. It is occurring at an exceptionally rapid rate. Scientists warn that nearly half of existing species could disappear within about a century. Thus, Option D is the correct answer because it describes a feature common to all mass extinctions rather than a distinguishing characteristic.

According to NCERT, biodiversity loss leads to several ecological consequences: Plant production declines due to reduced ecosystem efficiency. Ecosystems show lower resistance to environmental disturbances such as drought. Pest and disease cycles become more variable, making ecosystems less stable. Thus: 1 → ii 2 → iii 3 → i Hence, Option A is correct.

NCERT explains that ecosystems with high biodiversity are generally more stable and resistant to environmental disturbances. When biodiversity declines, ecosystems become less capable of coping with stresses such as drought, floods, or disease outbreaks. Therefore, an ecosystem with reduced biodiversity will show lower resistance when exposed to drought. Option A accurately reflects this concept. The other options contradict ecological principles described in NCERT.

The narrowly utilitarian argument emphasizes the direct economic value humans obtain from biodiversity. Examples include food, medicines, fuel, fibre, timber, resins, perfumes, and industrial products. Resins, perfumes, firewood, and fibre are all directly harvested products. However, intrinsic spiritual value is an intangible benefit and belongs to the broadly utilitarian or ethical perspective, not the narrowly utilitarian one. Therefore, only statements I and II are correct.

Bioprospecting refers to the systematic exploration of biological resources for commercially valuable genetic and biochemical compounds. A country must first possess rich biodiversity, which provides diverse organisms and genes. Scientists then explore this molecular and genetic diversity through bioprospecting to identify useful compounds. These discoveries can lead to medicines, industrial products, and other commercially valuable resources, resulting in substantial economic benefits. Thus, the logical sequence is: 2 → Nations endowed with rich biodiversity 1 → Exploration of molecular and genetic diversity 3 → Economic benefits from natural products Therefore, Option B is correct.

NCERT emphasizes the broadly utilitarian value of biodiversity by illustrating the enormous value of oxygen released by forests. Instead of calculating oxygen production directly, the textbook asks readers to imagine the enormous cost if humans had to purchase an equivalent quantity of oxygen in the form of hospital oxygen cylinders. This comparison helps appreciate the invaluable ecological services provided freely by forests. Therefore, Option D is correct. Option A relates to afforestation, not oxygen valuation. Option B is unrelated to the NCERT example. Option C concerns carbon trading rather than oxygen production.

Broadly utilitarian arguments emphasize the indirect ecological and aesthetic benefits humans receive from biodiversity, such as oxygen production, climate regulation, pollination, beautiful landscapes, bird songs, and flowering plants. Timber, however, is a directly harvested economic product, making it an example of the narrowly utilitarian argument rather than an intangible ecological benefit. Thus, Option C is the correct answer.

The ethical argument for biodiversity conservation states that every species has an intrinsic value, regardless of whether humans currently derive any economic benefit from it. Since all living organisms are products of millions of years of evolution, humans have no moral right to drive them to extinction simply because they appear economically unimportant. Therefore, Option C is correct.

NCERT states that humans share Earth with millions of plant, animal, and microbial species and have an ethical responsibility to protect this biological heritage. Passing biodiversity to future generations "in good order" means conserving ecosystems and ensuring the survival and well-being of all species rather than exploiting them for immediate gains. Thus, Option A correctly reflects the ethical argument for biodiversity conservation.