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100 questions in this collection · Page 8 of 10
Question 71 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding the introduction of the prickly pear cactus in Australia:
I. The prickly pear cactus was introduced into Australia in the early 1920s. II. It quickly became an invasive weed, spreading over millions of hectares of rangeland. III. The invasive cactus was successfully controlled by introducing a cactus-feeding beetle from its native habitat. IV. This control method is an example of biological control utilizing natural predator-prey regulation.
Which of the statements given above are correct?
Statements I, II, and IV are correct. The prickly pear cactus became a serious invasive weed in Australia and was successfully controlled by introducing a cactus-feeding moth as a biological control agent. Statement III is incorrect because the biological control agent was a moth, not a beetle.
Question 72 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the ecological role of predators:
I. Predators reduce the intensity of competition among competing prey species. II. The removal of a dominant predator can lead to a decrease in species diversity in a community. III. In the American Pacific Coast intertidal zone, the starfish Pisaster is a keystone predator. IV. The extinction of more than 10 invertebrate species following Pisaster removal was caused by direct predation by other carnivores.
Which of the statements given above are correct?
Statements I, II, and III are correct. Pisaster is a keystone predator that maintains community diversity by preventing competitive exclusion. Statement IV is incorrect because the loss of species resulted from increased interspecific competition rather than direct predation by other carnivores.
Question 73 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding the intrinsic rate of natural increase (r):
I. The parameter r is calculated as the per capita birth rate minus the per capita death rate (r = b - d) under non-limiting conditions. II. A higher r value indicates a lower reproductive potential for the population under natural conditions. III. The r value of a species can change depending on environmental conditions and habitat quality. IV. The r value of the flour beetle (0.12) is higher than that of the Norway rat (0.015).
Which of the statements given above are correct?
Statements I, III, and IV are correct. The intrinsic rate of natural increase is given by r = b − d, varies with environmental conditions, and is higher in the flour beetle (0.12) than in the Norway rat (0.015). Statement II is incorrect because a higher r value indicates greater reproductive potential.
Question 74 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the general patterns of competition:
I. Herbivores and plants are generally more adversely affected by competition than carnivores. II. Two closely related species can co-exist indefinitely even if they compete for the exact same limiting resource. III. Resource partitioning is an evolutionary mechanism that allows competing species to co-exist. IV. Carnivores are highly sensitive to competition because their food resource is always extremely uniform and stable.
Which of the statements given above are correct?
Statements I and III are correct. Herbivores and plants are generally more affected by competition, and resource partitioning promotes coexistence. Statement II is incorrect because Gause's Competitive Exclusion Principle states that species competing for the same limiting resource cannot coexist indefinitely. Statement IV is incorrect because carnivores are generally less affected by competition and their food resources are not uniformly stable.
Question 75 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding co-evolutionary safeguards in mutualism:
I. Mutualistic interactions are vulnerable to cheaters, organisms that exploit rewards without providing services. II. Nectar thieves are animals that consume nectar from flowers without performing pollination. III. To minimize exploitation by cheaters, mutualistic plant-animal interactions are tightly linked through co-evolution. IV. The evolution of a flower's structural traits is often tightly coupled with the sensory or morphological traits of its specific pollinator to prevent cheating.
Which of the statements given above are correct?
All four statements are correct. Mutualistic interactions are susceptible to cheaters such as nectar thieves, and co-evolution between interacting species helps maintain the stability of these associations by favoring effective partners.
Question 76 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the trade-offs in life history strategies:
I. Organisms that produce a large number of offspring must always produce small-sized offspring due to energy allotment constraints. II. Producing a small number of large-sized offspring is typically associated with higher survival rates of individual offspring. III. Birds and mammals have evolved to produce large numbers of small-sized offspring to maximize their Darwinian fitness. IV. Oysters and pelagic fishes produce a small number of large-sized offspring to minimize larval predation in open water.
Which of the statements given above are correct?
Statements I and II are correct. Organisms face an energy allocation trade-off between offspring number and offspring size. Birds and mammals generally produce fewer, larger offspring, whereas oysters and pelagic fishes produce numerous small offspring. Therefore, statements III and IV are incorrect.
Question 77 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements comparing exponential and logistic growth models mathematically:
I. In the exponential model, population growth rate (dN/dt) is unrestricted and increases continuously with population size (N). II. In the logistic model, when population density (N) equals the carrying capacity (K), the population growth rate (dN/dt) is at its maximum. III. The logistic equation contains a built-in feedback factor, (K-N)/K, which reduces the per capita growth rate as density increases. IV. At very high densities where N exceeds K, the term (K-N)/K becomes negative, causing the population size to decrease.
Which of the statements given above are correct?
Statements I, III, and IV are correct. When N = K, the term (K-N)/K becomes zero and population growth stops. Hence, statement II is incorrect.
Question 78 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the intrinsic rate of natural increase (r):
I. A population with a high birth rate and a low death rate will exhibit a high positive r value. II. The intrinsic rate of natural increase is a constant property of a species and cannot change with environmental variables. III. The value of r for the human population of India was reported as 0.0205 in 1981. IV. In the integral equation Nt = N0ert, e is the base of natural logarithms.
Which of the statements given above are correct?
Statements I, III, and IV are correct. The intrinsic rate of natural increase varies with environmental conditions that influence birth and death rates. Therefore, statement II is incorrect.
Question 79 of 100
📘 CLASS XII
Organisms And Populations
Read the following statements regarding competitive release and experimental evidence:
I. Competitive release occurs when a species restricted to a small area expands its range dramatically once its competitor is removed. II. It provides strong indirect evidence that competition is a major factor shaping community structure in nature. III. Connell's experiments showed that the smaller barnacle Chathamalus underwent competitive release when the larger barnacle Balanus was removed. IV. Competitive release can only occur in terrestrial environments and is never observed in aquatic or marine ecosystems.
Which of the statements given above are correct?
Statements I, II, and III are correct. Connell demonstrated competitive release in marine barnacles. Statement IV is incorrect because competitive release occurs in terrestrial, freshwater, and marine ecosystems.
Question 80 of 100
📘 CLASS XII
Organisms And Populations
Consider the following statements regarding the stability of population density (N):
I. No population in nature remains completely static; density fluctuates constantly due to changing seasons and resource availability. II. A population that is heavily dependent on seasonal resources will show sharp crashes and rapid booms. III. Immigration (I) and Emigration (E) are completely insignificant in determining the density of animal populations under any ecological circumstance. IV. The formula Nt+1 = Nt + [(B + I) - (D + E)] demonstrates that even small shifts in migration can alter population trends.
Which of the statements given above are correct?
Statements I, II, and IV are correct. Immigration and emigration may become highly important under certain ecological situations such as migration or colonization. Therefore, statement III is incorrect.