Organisms and Populations: Class 12 Important Questions with Answers

Practice set: test yourself

Try every question before looking at the answers below. 64 or more out of 80 means you are ready for the board.

C. Very short answer (1 mark each)

1. What does r stand for?
2. Give r for the flour beetle.
3. Name the shape of a declining age pyramid.
4. How are tigers counted in reserves?
5. Which moth story shows biological control?
6. Name the starfish predator studied.
7. Who showed resource partitioning in warblers?
8. Name the two intermediate hosts of the liver fluke.
9. Name a plant ectoparasite.
10. Give an example of commensalism in the sea.

D. Short answer I (2 marks each)

1. Calculate the death rate: 4 of 40 fruitflies die in a week.
2. When is per cent cover better than numbers?
3. Write the equations for exponential and logistic growth.
4. What is competitive release?
5. Why are predators 'prudent'?
6. How does the Monarch butterfly escape predators?
7. Give two adaptations of parasites.
8. Why is the fig–wasp relation a mutualism?

Rough work

E. Short answer II (3 marks each)

1. Explain three roles of predators with examples.
2. Describe the logistic growth curve and its equation.
3. State Gause's principle and explain resource partitioning.
4. Explain brood parasitism with an example.
5. Explain sexual deceit in Ophrys and co-evolution.
6. Describe three types of age pyramids.

F. Long answer (5 marks each)

1. Describe the exponential and logistic growth models with graphs and equations. Which is more realistic and why?
2. Explain predation, competition, parasitism, commensalism and mutualism with one example each.

G. HOTS (higher-order thinking)

1. Why did natural selection not produce totally harmless parasites?
2. Why are herbivores and plants more affected by competition than carnivores?
3. Why do invasive species spread fast?
4. When does immigration matter more than births?

20 MCQs

1. An attribute of a population, not an individual:
   (a) death (b) age (c) birth rate (d) sex
2. Density decreases by
   (a) emigration (b) natality (c) immigration (d) births
3. A broad-based age pyramid shows a
   (a) declining (b) extinct population (c) stable (d) expanding
4. dN/dt = rN describes
   (a) logistic (b) exponential growth (c) decline (d) steady state
5. r for the Norway rat is
   (a) 0.12 (b) 0.015 (c) 0.0205 (d) 1.5
6. K stands for
   (a) growth rate (b) density (c) birth rate (d) carrying capacity
7. Logistic growth gives a
   (a) sigmoid curve (b) J curve (c) straight line (d) U curve
8. Rats: births 280, deaths 200, immigrants 40, emigrants 50. Net increase:
   (a) 80 (b) 10 (c) 70 (d) 90
9. Prickly pear in Australia was controlled by a
   (a) beetle (b) virus (c) fungus (d) moth
10. Calotropis defends by
    (a) thorns (b) cardiac glycosides (c) camouflage (d) hairs
11. Flamingoes and fishes compete for
    (a) space (b) light (c) zooplankton (d) mates
12. The Abingdon tortoise became extinct due to
    (a) competition with goats (b) predation (c) disease (d) hunting
13. Connell's study involved
    (a) warblers (b) barnacles (c) starfish (d) wasps
14. Resource partitioning in warblers was shown by
    (a) Gause (b) Connell (c) MacArthur (d) Darwin
15. An ectoparasite of humans:
    (a) liver fluke (b) tapeworm (c) Plasmodium (d) lice
16. Cuckoo and crow show
    (a) brood parasitism (b) mutualism (c) commensalism (d) competition
17. Clownfish and sea anemone show
    (a) commensalism (b) mutualism (c) predation (d) amensalism
18. Mycorrhiza is an example of
    (a) parasitism (b) commensalism (c) competition (d) mutualism
19. Ophrys male bee behaviour is
    (a) predation (b) pseudocopulation (c) nectar robbing (d) oviposition
20. Interaction (−, 0) is
    (a) commensalism (b) mutualism (c) amensalism (d) parasitism

1 (c) · 2 (a) · 3 (d) · 4 (b) · 5 (b) · 6 (d) · 7 (a) · 8 (c) · 9 (d) · 10 (b) · 11 (c) · 12 (a) · 13 (b) · 14 (c) · 15 (d) · 16 (a) · 17 (a) · 18 (d) · 19 (b) · 20 (c)

Assertion–Reason (6)

(a) Both true, R explains A. (b) Both true, R does not explain A. (c) A true, R false. (d) A false, R true.

1. A: Logistic growth is more realistic. R: Resources become limiting sooner or later.
2. A: Cattle never browse Calotropis. R: It makes poisonous cardiac glycosides.
3. A: The Monarch butterfly is distasteful to birds. R: It makes the chemical in its own body from birth.
4. A: Chthamalus spreads when Balanus is removed. R: This is competitive release.
5. A: Predators always drive prey to extinction. R: Predators transfer energy to higher trophic levels.
6. A: Fig species are pollinated only by their partner wasp. R: The wasp uses the fruit for egg-laying and seeds for its larvae.

Key: 1 (a) · 2 (a) · 3 (c) · 4 (a) · 5 (d) · 6 (a)

Answers to the practice set