Answers and bookmarks are saved in this browser, across visits. They do not sync to your account.
100 questions in this collection · Page 6 of 10
Question 51 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the population growth equation Nt+1 = Nt + [(B + I) - (D + E)]:
I. The population density will increase if (B + I) is greater than (D + E). II. Under normal conditions, immigration (I) and emigration (E) are the primary drivers of population growth. III. If a new habitat is being colonized, immigration (I) may contribute more significantly to population growth than birth rates (B). IV. The population density remains completely stable at Nt+1 = Nt only when both I and E are equal to zero, regardless of birth and death rates.
Which of the statements given above are correct?
Statement I is correct because population density increases when births plus immigration exceed deaths plus emigration. Statement III is correct because immigration can dominate population growth during colonization of a new habitat. Statement II is incorrect because under normal conditions births and deaths are the major determinants of population size. Statement IV is incorrect because stability occurs whenever B + I = D + E; immigration and emigration need not both be zero.
Question 52 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding the defensive adaptations of the weed Calotropis:
I. Calotropis is an invasive weed that grows widely in abandoned agricultural fields and dry habitats. II. The plant produces highly poisonous cardiac glycosides as a chemical defense mechanism. III. Cattle and goats avoid browsing on Calotropis due to its extreme physical thorns. IV. The chemical defenses of Calotropis affect the heart rate and digestive systems of animals that attempt to eat it.
Which of the statements given above are correct?
Statements I, II, and IV are correct. Calotropis produces poisonous cardiac glycosides that deter herbivores. Statement III is incorrect because the plant relies on chemical rather than thorn-based defense.
Question 53 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the mutualistic association between fig trees and wasps:
I. A given fig species can be pollinated by many different species of wasps, depending on the season. II. The female wasp uses the fig fruit as an oviposition site and the developing seeds nourish its larvae. III. The wasp pollinates the fig inflorescence while searching for suitable egg-laying sites. IV. In return for pollination, the fig tree provides some developing seeds as food for the wasp larvae.
Which of the statements given above are correct?
Statements II, III, and IV are correct. Statement I is incorrect because there is a highly specific one-to-one relationship between a fig species and its pollinating wasp species.
Question 54 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding the mathematical parameters of the Verhulst-Pearl logistic growth equation:
I. The term r represents the intrinsic rate of natural increase. II. The term K represents the carrying capacity of the environment. III. The expression (K − N)/K represents the fraction of carrying capacity still available for population growth and functions as environmental resistance. IV. When N is extremely small compared to K, the value of (K − N)/K approaches 1 and growth is approximately exponential.
Which of the statements given above are correct?
All statements are correct. In the logistic equation, r is the intrinsic rate of natural increase, K is the carrying capacity, (K − N)/K represents environmental resistance, and when N is much smaller than K the equation approximates exponential growth.
Question 55 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the pollination mechanism in the Mediterranean orchid Ophrys:
I. The orchid employs sexual deceit to get pollinated by a specific species of bee. II. One petal of the flower resembles the female bee in size, colour and markings. III. The male bee attempts pseudocopulation with the flower after mistaking it for a female. IV. During pseudocopulation, pollen adheres to the male bee and is transferred to another flower during subsequent visits.
Which of the statements given above are correct?
All four statements are correct. Ophrys orchids achieve pollination through sexual deceit by mimicking female bees, resulting in pseudocopulation and pollen transfer.
Question 56 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding the mutualistic association known as Mycorrhiza:
I. Mycorrhiza represents a mutualistic association between fungi and the roots of higher plants. II. The fungal hyphae absorb essential mineral nutrients, especially phosphorus, from the soil and deliver them to the plant. III. In return, the host plant provides the fungus with carbohydrates and shelter. IV. Plants with mycorrhizal associations show enhanced resistance to root-borne pathogens and increased tolerance to salinity and drought.
Which of the statements given above are correct?
All statements are correct. Mycorrhiza is a classic mutualistic association in which fungi enhance nutrient uptake and stress tolerance, while plants provide carbohydrates to the fungus.
Question 57 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the ecological pressures of herbivory:
I. Herbivores are essentially predators of plants. II. Unlike animal prey, plants cannot run away from their predators, forcing them to evolve diverse morphological and chemical defenses. III. Phytophagous insects feed on plant sap and other tissues, accounting for nearly 25% of all known insect species. IV. Herbivory only reduces plant biomass but has zero impact on the reproductive fitness or survival rate of plant populations.
Which of the statements given above are correct?
Statements I, II, and III are correct. Herbivores are considered plant predators, plants have evolved morphological and chemical defenses because they cannot escape herbivores, and nearly 25% of insects are phytophagous. Statement IV is incorrect because herbivory can significantly reduce plant survival and reproductive fitness.
Question 58 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding Darwinian fitness and life history traits:
I. Organisms under ecological pressure evolve toward maximizing their reproductive fitness (high r value) in their respective habitats. II. Reproductive strategies are fixed at the species level and are completely unaffected by the physical or biotic factors of the habitat. III. Some organisms maximize fitness by producing a small number of large-sized offspring with high parental care. IV. Other organisms maximize fitness by producing huge numbers of small-sized offspring with minimal parental care.
Which of the statements given above are correct?
Statements I, III, and IV are correct. Organisms evolve life history strategies that maximize reproductive fitness according to environmental conditions. Statement II is incorrect because reproductive strategies evolve in response to both biotic and abiotic pressures.
Question 59 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding methods for estimating population density (N):
I. Absolute population size can sometimes be determined without counting every single individual in the area. II. For a very large or fast-moving population, relative density (e.g., number of fish caught per trap) is a practical and sufficient metric. III. The total count of bacterial colonies in a culture plate is the only acceptable method to study bacterial growth kinetics. IV. Tiger reserves use indirect census methods, estimating population size based on pug marks and fecal pellets.
Which of the statements given above are correct?
Statements I, II, and IV are correct. Ecologists frequently use relative density and indirect estimation methods instead of absolute counts. Statement III is incorrect because bacterial growth can also be estimated using biomass, turbidity, optical density and other indirect methods.
Question 60 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding the rocky intertidal sea coasts of Scotland:
I. The intertidal zone is dominated by two species of barnacles: Balanus and Chathamalus. II. The larger barnacle Balanus is restricted to the upper intertidal zone because it cannot tolerate deep water. III. The smaller barnacle Chathamalus occupies the upper intertidal zone because it is competitively excluded from the lower zone by Balanus. IV. Connell's field experiments demonstrated that removing Balanus allows Chathamalus to expand its distribution downward.
Which of the statements given above are correct?
Statements I, III, and IV are correct. Connell demonstrated that Balanus is competitively superior and excludes Chathamalus from the lower intertidal zone. Statement II is incorrect because Balanus naturally occupies the lower intertidal region.