Question Bank — Organisms and Populations

Section A — MCQs (1 mark each)

1. Which of the following is not an attribute of a population?
   (a) Birth rate
   (b) Death rate
   (c) Sex ratio
   (d) Body size of an individual

2. In the equation \(N_{t+1} = N_t + [(B + I) – (D + E)]\), which two factors increase population density?
   (a) Mortality and emigration
   (b) Natality and immigration
   (c) Emigration and immigration
   (d) Natality and mortality

3. The shape of an age pyramid that indicates a stable human population is:
   (a) Bell-shaped
   (b) Triangular
   (c) Urn-shaped
   (d) J-shaped

4. Assertion (A): The logistic growth model is considered more realistic than the exponential growth model for most natural populations.
   Reason (R): Resources in any habitat are limited and become limiting sooner or later.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

5. Assertion (A): In Gause’s Competitive Exclusion Principle, two closely related species competing for the same limiting resources cannot coexist indefinitely.
   Reason (R): The competitively inferior species is eventually eliminated.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

6. The interaction in which one species is harmed while the other remains unaffected is called:
   (a) Commensalism
   (b) Amensalism
   (c) Mutualism
   (d) Parasitism

7. Which of the following is an example of commensalism?
   (a) Cuscuta on hedge plants
   (b) Orchid growing as epiphyte on mango branch
   (c) Lice on humans
   (d) Fig and wasp

8. The intrinsic rate of natural increase (r) is used to assess:
   (a) Carrying capacity
   (b) Impact of biotic or abiotic factors on population growth
   (c) Sex ratio
   (d) Age distribution

9. In the logistic growth equation, what does K represent?
   (a) Intrinsic rate of increase
   (b) Carrying capacity
   (c) Initial population density
   (d) Time interval

10. Brood parasitism is observed in:
    (a) Cuckoo and crow
    (b) Fig and wasp
    (c) Lichen
    (d) Mycorrhizae

Section B — Very Short Answer (2 marks each)

1. Define population density. Why is it sometimes expressed as biomass or per cent cover rather than number of individuals?

2. Differentiate between natality and mortality in a population.

3. What is the difference between exponential and logistic growth? Name the type of curve each produces.

4. State Gause’s Competitive Exclusion Principle.

5. Give one example each of ectoparasitism and endoparasitism.

6. What is resource partitioning? How does it help in coexistence of species?

Section C — Short Answer (3 marks each)

1. List any three population attributes that an individual organism does not possess. Explain any one with an example from the chapter.

2. Explain the role of predators in maintaining species diversity in a community with a suitable example.

3. Describe three important defence mechanisms evolved by plants against herbivory.

4. Distinguish between mutualism and commensalism with one example of each.

5. Why do parasites evolve special adaptations such as loss of unnecessary sense organs and high reproductive capacity? Give two examples of such adaptations.

Section D — Long Answer (5 marks each)

1. Describe the logistic population growth curve with the help of a labelled diagram. Write the equation and explain the significance of carrying capacity (K).

2. Explain the various types of interspecific interactions with one example of each. How are they represented using ‘+’, ‘–’ and ‘0’ signs?

3. A population of 100 individuals has an intrinsic rate of natural increase (r) of 0.02. Calculate the population size after 10 years assuming exponential growth. Show the equation and steps. What would happen if resources become limiting?

Section E — Case/Source-Based (4 marks each)

Case 1

In the rocky intertidal communities of the American Pacific Coast, the starfish Pisaster is an important predator. When all starfish were removed from an enclosed area in a field experiment, more than 10 species of invertebrates became extinct within a year due to interspecific competition.

(i) What role do predators play in a community according to this experiment?
(ii) Name the ecological principle illustrated here.
(iii) How does predation help in energy transfer?
(iv) Why are predators considered ‘prudent’ in nature?

Case 2

The Mediterranean orchid Ophrys employs sexual deceit to achieve pollination. One petal resembles the female of a bee species in size, colour and markings. The male bee is attracted, pseudocopulates with the flower and transfers pollen.

(i) What type of interaction exists between the orchid and the bee?
(ii) How does this interaction demonstrate co-evolution?
(iii) Why is this interaction considered mutualistic?
(iv) Name another plant-animal mutualistic relationship mentioned in the chapter.