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100 questions in this collection · Page 3 of 10
Question 21 of 100
📘 CLASS XII
Organisms And Populations
Consider the statements regarding different classes of parasites:
I. Lice on humans and ticks on dogs are classic examples of ectoparasites. II. Many marine fish are infested with ectoparasitic copepods. III. Cuscuta is an ectoparasitic plant that has lost its chlorophyll and leaves during evolution and derives nutrition from host plants. IV. The female mosquito is considered an endoparasite because it must feed on human blood for reproduction.
Which of the statements given above are correct?
Statement IV is incorrect because the female mosquito is not considered a parasite, although it requires blood meals for reproduction. Statements I, II, and III are correct examples of ectoparasitism.
Question 22 of 100
📘 CLASS XII
Organisms And Populations
Read the statements about endoparasites and brood parasitism:
I. Endoparasites live inside the host body at sites such as the liver, kidney, lungs, or red blood cells. II. The life cycles of endoparasites are simpler because they are protected inside the host's body. III. Brood parasitism is a phenomenon in birds where the parasitic bird lays eggs in the nest of its host and lets the host incubate them. IV. During evolution, the eggs of parasitic birds have evolved to resemble the host's eggs in size and colour to avoid detection and ejection.
Which of the statements given above are correct?
Statement II is incorrect because endoparasites generally have more complex life cycles due to their high degree of specialization. Statements I, III, and IV are correct.
Question 23 of 100
📘 CLASS XII
Organisms And Populations
Consider the statements regarding commensalism (+, 0):
I. An orchid growing as an epiphyte on a mango branch is an example of commensalism where both organisms benefit. II. Barnacles growing on the back of a whale benefit by getting a free ride and access to food, while the whale is unaffected. III. Cattle egrets forage close to grazing cattle because the moving cattle stir up and flush out insects from the vegetation. IV. Sea anemones with stinging tentacles protect clown fish from predators, while the anemone derives no apparent benefit.
Which of the statements given above are correct?
Statement I is incorrect because in commensalism only one organism benefits while the other is neither harmed nor benefited. Statements II, III, and IV are correct.
Question 24 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements about mutualism:
I. Lichens represent an intimate mutualistic relationship between a fungus and a photosynthesizing alga or cyanobacterium. II. Mycorrhizae are mutualistic associations between fungi and the roots of higher plants, where fungi aid in nutrient absorption. III. Plants pay 'fees' to animal pollinators in the form of pollen and nectar, and to seed dispersers in the form of juicy fruits. IV. To safeguard the system against 'cheaters' (animals stealing nectar without pollinating), plant-animal mutualisms are tightly linked through co-evolution.
Which of the statements given above are correct?
All four statements are correct. Lichens and mycorrhizae are classic examples of mutualism. Plants reward pollinators and seed dispersers with food resources, and these interactions are maintained through tight co-evolution that minimizes cheating.
Question 25 of 100
📘 CLASS XII
Organisms And Populations
Consider the statements about specific co-evolved mutualistic interactions:
I. There is a tight one-to-one relationship between fig trees and pollinator wasps, where a given fig species is pollinated only by its partner wasp species. II. The female wasp uses the fig fruit as an egg-laying site and its larvae feed on some of the developing seeds. III. The Mediterranean orchid Ophrys employs 'sexual deceit' by having a petal that resembles the female bee to attract male bees for pollination. IV. If the female bee's colour pattern changes during evolution, the Ophrys orchid petal does not need to change because male bees are easily fooled.
Which of the statements given above are correct?
Statement IV is incorrect because if the female bee's colour pattern changes, the orchid must also co-evolve to maintain resemblance and ensure successful pollination. Statements I, II, and III are correct.
Question 26 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding the age structure of human populations:
I. A growing population (expanding) is characterized by a very high proportion of pre-reproductive individuals compared to reproductive individuals. II. A stable population shows a bell-shaped pyramid where pre-reproductive and reproductive age groups are almost equal in size. III. A declining population has an urn-shaped pyramid with a low percentage of pre-reproductive individuals. IV. Post-reproductive individuals always constitute the largest percentage of any expanding population.
Which of the statements given above are correct?
Statements I, II, and III are correct. Statement IV is incorrect because an expanding population has a broad base of pre-reproductive individuals, which are much more numerous than post-reproductive individuals.
Question 27 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding the determination of population size and density (N):
I. In any given year, the population of Siberian cranes in the Bharatpur wetlands can be as low as fewer than 10 individuals. II. Chlamydomonas populations in a pond can grow to number in the millions. III. In an area with 200 carrot grass (Parthenium hysterophorus) plants and a single huge banyan tree with a large canopy, biomass or percent cover is a more meaningful measure of population size than total numbers. IV. In a laboratory culture of bacteria in a petri dish, counting total numbers is always the easiest and most practical method to report density.
Which of the statements given above are correct?
Statements I, II, and III are correct. Statement IV is incorrect because counting individual bacteria in a dense culture is impractical; biomass or optical density is generally preferred.
Question 28 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the factors that change population density:
I. Natality (B) and Immigration (I) are the two processes that contribute directly to an increase in population density. II. Mortality (D) and Emigration (E) are the two processes that contribute directly to a decrease in population density. III. If a new habitat is just being colonized, immigration may contribute more significantly to population growth than birth rates. IV. Under normal conditions, immigration and emigration are the most important factors influencing population density.
Which of the statements given above are correct?
Statements I, II, and III are correct. Statement IV is incorrect because under normal conditions natality and mortality are the major factors affecting population density, whereas immigration and emigration become important mainly under special situations such as colonization.
Question 29 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding the parameter r in population growth models:
I. The r value is a very important parameter chosen for assessing the impacts of any biotic or abiotic factor on population growth. II. The intrinsic rate of natural increase (r) for the Norway rat is 0.12, and for the flour beetle it is 0.015. III. In 1981, the r value for the human population in India was 0.0205. IV. The parameter r is mathematically defined as the difference between per capita birth rates (b) and per capita death rates (d).
Which of the statements given above are correct?
Statements I, III, and IV are correct. Statement II is incorrect because the values are reversed: the Norway rat has an r value of 0.015, whereas the flour beetle has an r value of 0.12.
Question 30 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the logistic growth of populations:
I. Verhulst-Pearl Logistic Growth is mathematically expressed by the differential equation: dN/dt = rN[(K - N)/K]. II. A plot of population density (N) in relation to time (t) under resource limitation results in a sigmoid (S-shaped) curve. III. The S-shaped growth curve shows an initial lag phase, followed by phases of acceleration and deceleration, and finally an asymptote. IV. Resources for growth for most animal populations are finite and become limiting sooner or later, making the logistic model more realistic than the exponential model.
Which of the statements given above are correct?
All four statements are correct. Logistic growth is described by the Verhulst-Pearl equation and produces a sigmoid curve that approaches the carrying capacity (K) under limited resources.