Ecology – Population: NEET MCQs with Answers

Explanation: Pyramid 'B' has a distinctly broader pre-reproductive base than 'A', indicating a very rapidly growing (younger) population, whereas in 'A' the base has narrowed slightly. Since the country adopted measures to curb growth, 'A' must be the more recent pyramid and it shows a slight reduction in the growth rate.

Explanation: The given pyramid is urn-shaped — the pre-reproductive base is narrower than the reproductive middle — which represents a declining population. An expanding population gives a broad-based triangular pyramid and a stable population gives a bell-shaped one. The shape of an age pyramid thus reflects the growth status of the population.

Explanation: Logistic growth occurs under limited resources (A-II) — the population grows fast initially, then slows and levels off at the carrying capacity, giving a sigmoid curve. Exponential (geometric) growth requires unlimited resources (B-I) and gives a J-shaped curve; it is rarely seen in nature. An expanding pyramid is triangular with the largest pre-reproductive class (C-III), whereas a stable (bell-shaped) pyramid has roughly equal pre-reproductive and reproductive classes (D-IV).

Explanation: In the log (exponential) phase both the number of individuals and the rate of growth are at their maximum, since resources are still adequate; growth slows in the stationary phase.

Explanation: Birth rate, death rate, sex ratio and age distribution are attributes possessed by a population but not by an individual. Species interaction takes place between populations and is a community-level feature.

Explanation: Natality is the number of births added to the population per unit time per individual; mortality is the death rate, while immigration and emigration are the entries and exits.

Explanation: A growing population has a triangular age pyramid with a broad base, meaning the pre-reproductive class outnumbers the reproductive class and will soon add heavily to the birth rate.

Explanation: The curve flattens into an asymptote when the population size equals the carrying capacity, because at that point the resources can support no further increase.

Explanation: If N = K, then N/K = 1 and the factor (1 – N/K) becomes zero, so dN/dt = 0 and the population stops growing — the asymptote of the sigmoid curve.

Explanation: Thomas Malthus, in his 'Essay on the Principle of Population' (1798), pointed out that population tends to increase in geometric progression while food supply increases only in arithmetic progression, so that population is ultimately checked by want. This idea deeply influenced Darwin's concept of the struggle for existence. John Stuart Mill wrote 'Principles of Political Economy' and Adam Smith 'The Wealth of Nations'.

Explanation: Competition is most intense between closely related organisms sharing the same niche, because their requirements for food, light, nutrients and space overlap almost completely and these resources are limited. This is the basis of Gause's competitive exclusion principle.

Explanation: Pseudocopulation is a form of floral mimicry in which the flower imitates the appearance, scent or behaviour of a female insect, attracting the male insect to attempt copulation with it. In Ophrys speculum, the male wasp Colpa aurea repeats the act on several flowers and carries pollinia from one flower to another, thereby pollinating the orchid — a relationship beneficial only to the plant.

Explanation: Cuscuta (dodder or amarbel) is a total stem parasite; it is a leafless, chlorophyll-less twiner that produces haustoria to tap water and nutrients from the host phloem. Dischidia is an epiphyte, Opuntia is a xerophyte and Capsella (shepherd's purse) is an ordinary terrestrial mesophyte.

Explanation: Entomophilous flowers are pollinated by insects, and the relationship is mutualistic: the plant uses the insect to ensure cross-pollination, while the insect obtains nectar and pollen as food. Both partners are therefore benefitted, which is the defining criterion of mutualism.

Explanation: When microbes are grown in a closed system (batch culture), the growth curve shows four phases in sequence: (i) lag phase — adjustment with little division; (ii) log or exponential phase — maximum rate of division; (iii) stationary phase — division balanced by death as nutrients deplete and wastes accumulate; and (iv) decline or death phase.