Organisms and Populations Mock Test – Class 12 Biology

1. In a removal experiment, species P declines when species Q is removed, and species Q also declines when species P is removed. Which interaction is most consistent with this reciprocal dependence?

2. A host population evolves a defence that sharply reduces parasite attachment. Later, parasite variants that overcome this defence become common. Which additional observation would most strongly demonstrate reciprocal co-evolution rather than only one-sided parasite adaptation?

3. Reference values report for the Norway rat and for the flour beetle under the stated conditions. Based only on these values, which conclusion is justified?

4. Directly observing and counting every tiger in a large forest is difficult. A census may therefore estimate tiger abundance using

5. Examine the interaction outcomes below.

Which sequence correctly identifies the corresponding sign patterns?

6. Two populations are observed for the same duration. Population X loses of its individuals, while population Y loses of its individuals. Which statement is supported by these data?

7. Population P has when alone and when species Q is present. Population Q has alone and in the presence of P. Which sign pattern best represents the measured interaction?

8. A pesticide kills most susceptible insects in a population, whereas individuals carrying a heritable resistance trait survive and reproduce disproportionately. After many generations, resistance is much more common. At what level is the evolutionary change recognised?

9. Assertion: Evidence for competitive exclusion is often clearer in controlled laboratory studies than in natural communities.
Reason: Natural communities may contain additional ecological factors that complicate the outcome of competition.

10. Two populations have the same intrinsic rate , but population P has individuals whereas population Q has . Under exponential growth, how do their instantaneous absolute rates of increase compare?

11. Under exponential conditions, a population begins at and has . Which expression gives its expected density after ?

12. A host population begins with . Before parasitic infection, , , and . Infection raises deaths to and reduces births to , while migration remains unchanged. What is after infection?

13. A plant population has per-capita birth rate and death rate . Loss of a pollinator reduces to , while a newly abundant parasite raises to . How does the intrinsic rate change?

14. Populations P and Q begin with the same density . Under constant exponential conditions, P doubles every and Q doubles every . What is the ratio after ?

15. An age-pyramid display separates males on one side and females on the other. In both sexes, the pre-reproductive band is much narrower than the reproductive band, while the post-reproductive band is also substantial. Which interpretation is most appropriate?

16. A population is initially far below the supportable level of its habitat and shows rapid increase. As density rises, competition for finite resources becomes stronger and growth begins to slow. Which transition has occurred?

17. A pollinator obtains nectar from a flower but transfers pollen only when it contacts a particular reproductive structure. A mutation allows the animal to reach nectar without making that contact. Which consequence is most likely?

18. A long-established population is monitored under ordinary conditions, whereas another population is just colonising a previously unoccupied habitat. Which comparison is most consistent with population-demographic principles?

19. Three populations have the following age compositions.

If other demographic conditions remain broadly comparable, which interpretation is most appropriate?

20. Population P has and , whereas Population Q has and . Which comparison is correct under the simple exponential framework?

21. Acacia and cactus reduce herbivore damage partly through thorns. In this context, thorns are best classified as

22. Two populations are monitored over the same interval.

Which conclusion follows from the data?

23. A biological-control predator reduces pest density but then becomes extremely efficient and nearly eliminates its prey. If the predator depends strongly on that prey, what secondary consequence is most plausible?

24. Host P and Host Q are closely related, but a parasite successfully establishes only on P. Which explanation is most consistent with host specificity?

25. Calotropis contains poisonous cardiac glycosides. If a herbivore population evolves greater tolerance to these compounds, which changed outcome is most reasonable?

26. In an interspecific interaction, one population benefits while the second population is harmed. Which conclusion can be made from the sign pattern alone?

27. In a mycorrhizal association, the fungus improves mineral acquisition by plant roots and receives carbohydrates from the plant. If the plant stops supplying carbohydrates while continuing to receive mineral benefits, which description is most accurate?

28. Two populations of the same species have the same and the same , but Habitat P has while Habitat Q has . Which population has the greater instantaneous logistic growth rate?

29. Species P lives on species Q and gains physical support. Detailed measurements show no resource extraction and no measurable effect on the growth or reproduction of Q. This evidence supports

30. Food remains apparently abundant in an experimental habitat, yet the feeding efficiency of species P falls sharply whenever species Q is present because Q disrupts access to feeding sites. This is best interpreted as

31. Species P and Q appear to use the same broad food category, but detailed observations show that P feeds primarily at dawn and Q primarily at night. Both persist for many generations. Which mechanism best explains the coexistence?

32. A bacterial culture originates through asexual division from a small number of cells and contains thousands of genetically similar individuals occupying the same culture vessel. Which statement best explains why it is still treated as a population?

33. A population is observed near , and its curve is almost horizontal. Which additional observation would be fully compatible with this state?

34. A student claims that a group can be called a population only if its members reproduce sexually and can interbreed. The most appropriate correction is that

35. Which statement best describes the usual relative importance of demographic processes in an established population and during colonisation of a new habitat?

36. An experiment produces the following observations:

The pattern most strongly supports

37. Which sequence best matches the characteristic progression of logistic growth?

38. Population P gains individuals during an interval mainly because births exceed deaths, while Population Q gains individuals mainly because immigration exceeds emigration. Which conclusion is most accurate?

39. Which statement about is incorrect?

40. A barnacle population benefits from living on whales. Suppose new evidence shows that whales carrying barnacles also gain a substantial feeding advantage from the association. How should the interaction be reinterpreted?

41. An inferior competitor occupies only the upper part of a rocky shore while a superior competitor is present. After the superior competitor is removed, the inferior species expands downward. However, it still fails to occupy an even lower region where physical conditions are unsuitable. Which conclusion is most precise?

42. A plant population has . Loss of an effective pollinator reduces births from to , while a parasite simultaneously raises deaths from to . Immigration is and emigration is . What is the revised ?

43. Assertion: A predator that is extremely efficient at exploiting its prey may ultimately reduce its own long-term persistence.
Reason: Severe prey depletion can remove the predator's food base and subsequently cause predator numbers to decline.

44. In the same type of field study, Chathamalus expands into a lower zone after Balanus is removed but still fails to occupy an even lower region. Which inference is most careful?

45. A graph plots against for a population under resource limitation. The curve is initially shallow, becomes steep, then gradually flattens near a horizontal line labelled . What does the flattening portion indicate?

46. Consider the following changes:
I. A predator is removed from a prey population.
II. A superior competitor is removed from an inferior competitor's habitat.
III. A specialised pollinator disappears from a plant population.
Which set of predictions is most appropriate?

47. A researcher compares two apparently stable populations. Population P has low natality and low mortality, while Population Q has high natality and high mortality of equal magnitude. Both maintain approximately constant . Which conclusion is most accurate?

48. A fish population in a large lake cannot be counted completely. Researchers place identical traps using the same sampling effort during successive surveys. Which observation can serve as a useful relative index of population density?

49. The intrinsic rate of natural increase is useful in population ecology primarily because it

50. Consider the following changes to ecological associations:
I. An orchid begins extracting nutrients from the mango tree on which it grows.
II. A sea anemone is discovered to gain food consistently from its associated clownfish.
III. A nectar visitor takes rewards but stops transferring pollen.
Which sequence of classification changes is most appropriate?