201. Assertion: Not every introduced species becomes invasive.
Reason: A species becomes invasive only when it establishes, spreads, and causes ecological harm in the new region.
ⓐ. Assertion is false, but Reason is true.
ⓑ. Both Assertion and Reason are false.
ⓒ. Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
ⓓ. Assertion is true, but Reason is false.
Correct Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
Explanation: Introduction alone is not enough to classify a species as invasive. Many introduced species fail to establish, remain limited, or do not significantly harm native communities. A species is called invasive when it successfully spreads and negatively affects indigenous organisms or ecosystem functioning. The reason therefore explains why all introduced species are not equally dangerous.
202. Which option correctly matches an organism with the type of biodiversity threat it represents?
ⓐ. Nile perch — alien species invasion
ⓑ. Passenger pigeon — alien species invasion
ⓒ. Parthenium — co-extinction
ⓓ. Dodo — habitat fragmentation
Correct Answer: Nile perch — alien species invasion
Explanation: Nile perch is a classic example of alien-species invasion because it was introduced and then harmed native fish diversity. Passenger pigeon and dodo are extinction examples, while Parthenium is an invasive weed rather than a co-extinction case. This distinction matters because the examples represent different causes of biodiversity loss. Accurate mapping helps separate invasion from extinction and co-extinction.
203. Why can invasive species be especially dangerous in a new habitat?
ⓐ. They always convert into endemic species after introduction.
ⓑ. They never face any ecological interactions in the new region.
ⓒ. They can affect only domesticated organisms and not wild ones.
ⓓ. Native species may not be adapted to the new competitor, predator, or weed.
Correct Answer: Native species may not be adapted to the new competitor, predator, or weed.
Explanation: Native species in an ecosystem often evolved without exposure to the newly introduced organism. Because of this, they may lack effective defenses or competitive responses against the invader. The alien species may then spread rapidly and disrupt existing ecological relationships. This mismatch is one reason invasive species can have severe effects.
204. Fill in the blank in the most accurate way:
Alien species invasion differs from co-extinction because invasion involves the impact of a(n) ______ species on native organisms.
ⓐ. extinct
ⓑ. introduced
ⓒ. overharvested
ⓓ. fragmented
Correct Answer: introduced
Explanation: Alien invasion begins with the arrival of a species from outside its natural range. The ecological problem develops when that introduced species establishes itself and harms native organisms. Co-extinction, in contrast, occurs when one species disappears because another species on which it depends is lost. The word “introduced” captures the defining feature of invasion most accurately.
205. Co-extinction refers to the disappearance of
ⓐ. a dependent species after extinction of the species it relies on
ⓑ. two unrelated species because of the same seasonal change
ⓒ. all species in a habitat after fragmentation
ⓓ. native species after the introduction of an alien predator
Correct Answer: a dependent species after extinction of the species it relies on
Explanation: Co-extinction occurs when species are so closely linked that loss of one leads to loss of the other. The dependence may involve parasitism, pollination, dispersal, or some other obligatory relationship. This makes co-extinction different from habitat loss or invasion, where the immediate cause is different. The idea highlights how biodiversity is interconnected rather than made of isolated species.
206. Which example best illustrates co-extinction?
ⓐ. A forest divided into patches by road construction
ⓑ. A fish population declining due to overharvesting
ⓒ. A host fish becoming extinct and its host-specific parasite disappearing with it
ⓓ. A native grassland being invaded by an introduced weed
Correct Answer: A host fish becoming extinct and its host-specific parasite disappearing with it
Explanation: The defining feature of co-extinction is biological dependence between the two species. If the parasite cannot survive without its host, loss of the host directly causes the parasite’s extinction as well. This is different from direct killing, habitat destruction, or biological invasion. The relationship between the two organisms is the key clue.
207. A flowering plant disappears from a region, and its highly specialized pollinator also vanishes soon after. This is best described as
ⓐ. habitat fragmentation
ⓑ. over-exploitation
ⓒ. alien species invasion
ⓓ. co-extinction
Correct Answer: co-extinction
Explanation: A coevolved plant-pollinator pair can become so tightly linked that one cannot persist without the other. If the plant disappears and the pollinator depends strongly on it, the pollinator may also vanish. This is a classic example of extinction spreading through biological association. It shows why species interactions are crucial for conservation.
208. Which statement best distinguishes co-extinction from alien species invasion?
ⓐ. Co-extinction occurs only in aquatic habitats, while invasion occurs only on land.
ⓑ. Co-extinction results from loss of a dependent biological partner, whereas invasion results from harmful introduced species.
ⓒ. Co-extinction affects only plants, whereas invasion affects only animals.
ⓓ. Co-extinction always follows over-exploitation, whereas invasion always follows habitat loss.
Correct Answer: Co-extinction results from loss of a dependent biological partner, whereas invasion results from harmful introduced species.
Explanation: Co-extinction is driven by dependency between species, such as host-parasite or plant-pollinator relationships. Alien invasion, in contrast, begins when a non-native species is introduced and causes ecological harm. Both reduce biodiversity, but the mechanism is different in each case. Identifying the direct cause helps separate the two clearly.
209. Which of the following is not an example of co-extinction?
ⓐ. Water hyacinth spreading rapidly and suppressing native aquatic plants
ⓑ. A pollinator disappearing after the extinction of its specialized host plant
ⓒ. A parasite being lost after extinction of its host species
ⓓ. A dependent mutualist vanishing when its obligate partner is removed
Correct Answer: Water hyacinth spreading rapidly and suppressing native aquatic plants
Explanation: Water hyacinth is an invasive alien plant, so this case belongs to alien species invasion rather than co-extinction. The other options all involve one species disappearing because another essential partner has been lost. Co-extinction always involves some form of obligatory dependence. Invasion instead involves an introduced species harming natives.
210. Why can co-extinction make biodiversity loss more severe than it first appears?
ⓐ. It affects only extinct species and not living communities.
ⓑ. It always reverses naturally after a short time.
ⓒ. It is limited to microorganisms and parasites.
ⓓ. The extinction of one species can trigger further loss in associated species.
Correct Answer: The extinction of one species can trigger further loss in associated species.
Explanation: Co-extinction shows that one extinction event may not remain isolated. If several other species depend on the lost one, they may also decline or disappear. This creates a chain of secondary losses that enlarges the total damage. Biodiversity decline is therefore often more connected and far-reaching than it looks at first.
211. Assertion: Co-extinction demonstrates that species in ecosystems are often biologically interdependent.
Reason: The extinction of one species can cause extinction of another species that relies on it obligatorily.
ⓐ. Assertion is false, but Reason is true.
ⓑ. Both Assertion and Reason are false.
ⓒ. Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
ⓓ. Assertion is true, but Reason is false.
Correct Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
Explanation: Co-extinction is possible only because many species are linked through strong ecological or evolutionary relationships. When one obligatory partner disappears, the dependent one may also be lost. This directly shows that ecosystems function through networks of dependence. The reason therefore explains the assertion accurately.
212. A host-specific louse vanishes after the extinction of the bird species on which it lived. The immediate cause of the louse’s loss is
ⓐ. habitat fragmentation
ⓑ. loss of its obligatory host
ⓒ. excessive exploitation by humans
ⓓ. competition with an invasive weed
Correct Answer: loss of its obligatory host
Explanation: The louse depended directly on that bird for survival, so extinction of the host removed the conditions needed for the louse’s existence. This is a textbook pattern of co-extinction. The cause is not overuse, invasion, or habitat splitting in the immediate sense. The dependency itself is the deciding factor.
213. Which set correctly lists the three broad reasons commonly given for conserving biodiversity?
ⓐ. Narrowly utilitarian, broadly utilitarian, and ethical
ⓑ. Ecological, geological, and historical
ⓒ. Genetic, species, and ecosystem
ⓓ. In situ, ex situ, and cultural
Correct Answer: Narrowly utilitarian, broadly utilitarian, and ethical
Explanation: The reasons for conserving biodiversity are commonly grouped into three broad categories. Narrowly utilitarian reasons focus on direct uses, broadly utilitarian reasons emphasize ecosystem services and indirect benefits, and ethical reasons stress intrinsic value. These categories are different from levels of biodiversity or conservation methods. Keeping them distinct helps organize the logic of conservation.
214. Conserving biodiversity because it provides food, fibre, fuel, and medicines is mainly a
ⓐ. cultural argument
ⓑ. geological argument
ⓒ. narrowly utilitarian argument
ⓓ. aesthetic argument only
Correct Answer: narrowly utilitarian argument
Explanation: Narrowly utilitarian value refers to direct economic or practical benefits derived from living organisms. These include food, firewood, fibre, construction material, industrial products, and medicines. The emphasis is on resources humans use in a clear and immediate way. This makes it different from indirect ecosystem services or ethical duty.
215. Which statement best represents the ethical argument for biodiversity conservation?
ⓐ. Species should be conserved only when they are commercially profitable.
ⓑ. Biodiversity is important mainly because it increases tourism income.
ⓒ. Species are valuable only when they support crop production.
ⓓ. Each species has intrinsic value, and humans have a duty to protect it.
Correct Answer: Each species has intrinsic value, and humans have a duty to protect it.
Explanation: The ethical argument does not depend on immediate human benefit. It holds that living species deserve respect and protection simply because they exist as part of the natural world. This view also includes responsibility toward future generations. The focus is moral obligation rather than direct economic gain.
216. Protecting biodiversity because ecosystems provide services such as pollination and atmospheric oxygen balance is mainly a
ⓐ. genetic argument
ⓑ. broadly utilitarian argument
ⓒ. narrowly utilitarian argument
ⓓ. taxonomic argument
Correct Answer: broadly utilitarian argument
Explanation: Broadly utilitarian value includes indirect benefits that ecosystems provide to human society. Pollination, oxygen generation, nutrient cycling, climate moderation, and other ecological services fall into this category. These benefits are not always harvested as direct products, but they are essential for human survival and economy. This makes the argument broader than simple resource extraction.
217. Which statement best distinguishes a narrowly utilitarian reason for conserving biodiversity from a broadly utilitarian one?
ⓐ. Narrowly utilitarian reasons deal with indirect ecosystem services, whereas broadly utilitarian reasons deal with moral duty.
ⓑ. Narrowly utilitarian reasons focus on direct human use, whereas broadly utilitarian reasons include indirect ecosystem services.
ⓒ. Narrowly utilitarian reasons apply only to wild animals, whereas broadly utilitarian reasons apply only to plants.
ⓓ. Narrowly utilitarian reasons concern species richness, whereas broadly utilitarian reasons concern genetic diversity.
Correct Answer: Narrowly utilitarian reasons focus on direct human use, whereas broadly utilitarian reasons include indirect ecosystem services.
Explanation: The difference lies in the kind of benefit being considered. Narrowly utilitarian value refers to direct products such as food, fuel, fibre, and medicines obtained from living organisms. Broadly utilitarian value includes larger ecological services such as pollination, oxygen balance, and other ecosystem functions that support life indirectly. Both are important, but they operate at different levels of benefit.
218. Which of the following is the best example of a narrowly utilitarian value of biodiversity?
ⓐ. Medicinal compounds obtained from plants
ⓑ. Moral duty toward future generations
ⓒ. Resistance of ecosystems to environmental perturbation
ⓓ. Intrinsic worth of every species
Correct Answer: Medicinal compounds obtained from plants
Explanation: Direct use of biological resources for human benefit is the core of the narrowly utilitarian argument. Medicines derived from plants are a clear example because they provide immediate practical value. This differs from ecosystem services, which are indirect, and from ethical reasoning, which does not depend on economic use. The example therefore belongs squarely in the narrowly utilitarian category.
219. More than 25% of currently marketed drugs are derived from
ⓐ. fungi
ⓑ. algae
ⓒ. animals
ⓓ. plants
Correct Answer: plants
Explanation: A significant proportion of modern marketed drugs comes from plant sources. This shows that biodiversity has direct practical value in medicine and health care. The importance of plants is not limited to food or wood alone. Their chemical diversity also makes them valuable sources of therapeutic compounds.
220. About how many plant species contribute to traditional medicines?
ⓐ. About 2,500
ⓑ. About 25,000
ⓒ. About 2.5 lakh
ⓓ. About 25
Correct Answer: About 25,000
Explanation: Traditional medicine draws on a very large range of plant species. The figure of about 25,000 plant species shows how strongly human health has depended on biodiversity across cultures and time. This is a direct-use argument for conservation. It also suggests that loss of plant diversity may mean loss of future medicinal opportunities.
