Organisms and Populations Mock Test – Class 12 Biology

1. Cuscuta is classified as a parasitic plant because it

2. A parasite normally follows the sequence: snail → fish → definitive host. A control programme removes most fish but leaves snail populations unchanged. Which effect is most direct?

3. An orchid initially grows on a mango tree without extracting nutrients and is classified as a commensal. Later, specialised structures are discovered that penetrate the mango tissues and obtain nutrients while reducing mango growth. How should the interaction now be classified?

4. A Monarch caterpillar feeds on a poisonous plant and later develops into a highly distasteful adult butterfly. Which changed condition would most directly weaken this defence mechanism?

5. A brood-parasitic bird lays a well-mimicked egg in a host nest, but the host abandons the nest before incubation begins because of an unrelated disturbance. What is the most direct consequence for the brood parasite?

6. Reference examples list intrinsic rates of natural increase as approximately for the Norway rat, for the flour beetle and for the Indian human population in . Which ordering correctly compares the cited values without treating them as present-day demographic measurements?

7. A host population evolves a defence that reduces infection by a particular parasite. Several generations later, parasite variants capable of overcoming this defence become more common. This sequence is most consistent with

8. In another fig population, wasps continue obtaining oviposition sites and larval food, but a change in their behaviour causes almost complete failure of pollen transfer. What has happened to the reciprocal balance of the association?

9. Two populations are observed for the same interval.

Ignoring migration, which conclusion is correct?

10. Two populations have the same current density but different age distributions.

If other demographic influences remain comparable, which prediction is most reasonable?

11. Two forest patches contain teak trees of the same species but are separated geographically and experience different local conditions. For a field study, the most biologically useful approach is to

12. In an experiment, species P and Q are grown alone and together. Both show lower reproductive success when together. When P is removed, Q improves; when Q is removed, P also improves. Which interaction is most strongly supported?

13. Which comparison correctly distinguishes the orchid-mango association from mycorrhiza?

14. A female mosquito takes a blood meal from a mammal. Which claim is not justified merely from this observation?

15. Consider four interactions.

Which classification is correct?

16. A population begins with . During the interval, , , and an unknown number emigrate. The final population is . What is ?

17. Two plant populations experience similar herbivore abundance. Population P has numerous thorns but no strong chemical deterrent; Population Q has no thorns but produces a compound that inhibits herbivore digestion. Herbivores spend less time beginning a feeding bout on P but show reduced growth after feeding on Q. Which interpretation is most appropriate?

18. A population has when its habitat has . A severe environmental change suddenly lowers carrying capacity to , while population density remains immediately after the change. According to the logistic relation, what is the immediate tendency?

19. A population follows logistic growth with and . A habitat improvement raises to while remains initially. What happens immediately to the density-dependent factor ?

20. Population P and Population Q are both growing exponentially. Their instantaneous absolute increases are equal, but and . Which relationship between their intrinsic rates is required?

21. 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?

22. 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?

23. A parasite normally requires the sequence definitive host → intermediate host P → intermediate host Q → definitive host. A control measure prevents transmission from P to Q but does not affect the parasite within P. Which result is most directly expected?

24. A researcher records the number of individuals of one deer species living in a defined forest area and studies how their abundance changes over several years. The principal ecological level being investigated is the

25. A population remains close to for several years because immigration offsets mortality. During the same period, the pre-reproductive fraction falls steadily and the post-reproductive fraction rises. Which conclusion is most defensible?

26. Examine the demographic events below.

Which assignment is correct?

27. In a fruit-fly population of individuals, individuals die during . The death rate for that interval is

28. A predator population is removed from a community. Its prey population increases sharply and subsequently suppresses several competing species. Which chain best accounts for the final decline in community diversity?

29. A host parasite lives inside red blood cells, whereas another parasite lives attached to the external surface of a marine fish. Which classification is correct?

30. A researcher wants to determine whether a tiger population has increased between two years using pug marks and faecal pellets. Which design gives the strongest relative comparison?

31. A population has , and . Immigration adds individuals and emigration removes during the same interval. Which statement correctly separates the exponential and demographic-balance descriptions?

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 brood-parasitic bird uses two host populations. Host P rejects eggs mainly when their colour differs from its own eggs, whereas host Q rejects eggs mainly when their size differs. A parasite variant matches host egg colour well but still produces noticeably larger eggs. Where should this variant have the greater acceptance success?

34. A prey population has in a habitat with . Predator abundance increases and lowers prey density to , but the predator remains present. Which statement best describes the resulting ecological situation?

35. A lichen association is experimentally separated into its fungal and photosynthetic partners. The fungal partner shows a sharp decline in carbohydrate availability, while the photosynthetic partner loses the protected structural environment normally provided by the fungus. Which inference is strongest?

36. Use the arrangement described below. The bottom band of an age pyramid is pre-reproductive, the middle band is reproductive and the top band is post-reproductive. All three bands have broadly comparable widths, with no unusually broad base or sharply narrowed young group. Which interpretation is most appropriate?

37. A population follows

If , which relationship follows directly?

38. Four species pairs are observed experimentally.

Which sequence of interaction signs is correct?

39. Nearly of insects are described as phytophagous. Which statement best connects this observation to plant defence?

40. Which description most closely represents an ecological population?

41. A female mosquito takes a blood meal required for reproduction. Using the ecological classification boundary for parasitism, it should

42. A plant loses most of its mycorrhizal fungal partners while soil mineral availability remains low. Which effect is most directly expected?

43. Consider the following groups:
I. Rats of one species living in an abandoned building
II. Teak trees of one species within a forest tract
III. Bacteria of one species growing on a culture plate
IV. All plants, animals and microorganisms within a lake
Which set contains only ecological populations?

44. A parasite reduces host growth but does not noticeably change host mortality. A predator preferentially captures smaller, slower hosts. After parasite prevalence rises, predation on infected hosts also increases. Which statement best integrates the interaction?

45. A community contains competitor P, competitor Q, predator R and mutualistic pollinator S. Removing Q allows P to expand. Removing R then causes P's herbivorous prey to increase. Finally, loss of S reduces recruitment of a flowering plant population. Which statement best illustrates the general lesson from these manipulations?

46. Population density of a herbivore increases after several years of unusually high food availability, then falls sharply after a severe winter. Which conclusion is best supported?

47. Two organisms show the sign pattern . Which additional observation would best distinguish predation from parasitism?

48. 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?

49. 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

50. A species begins colonising a previously unoccupied habitat. Which sequence is most biologically plausible during the early establishment of the population?