Competency-Based Question Bank: Organisms and Populations

Section A: Competency-Based Multiple Choice Questions (Application & Analysis)

1. Analyze the Age Pyramid: A population of rabbits in a forest has an age pyramid with a very broad base that tapers sharply towards the top. What does this indicate about the future of this rabbit population? a) It is declining rapidly. b) It is stable and will not change. c) It is expanding and the population size will increase. d) The post-reproductive individuals are dominating. Answer: c) It is expanding and the population size will increase. Explanation: A broad base indicates a very large number of pre-reproductive individuals (young). As they mature, they will enter the reproductive phase, leading to a population boom.

2. Evaluate the Interaction: In a dense forest, a large banyan tree provides support for an orchid to grow on its branches. The orchid gets better access to sunlight, but the banyan tree is neither harmed nor benefited. This interaction is an example of: a) Mutualism b) Parasitism c) Commensalism d) Amensalism Answer: c) Commensalism Explanation: Commensalism is a (+,0) interaction. The orchid (Commensal) benefits from the physical support, while the tree (Host) is unaffected.

3. Predict the Growth: A bacteria culture is growing in a flask with unlimited nutrients. If the intrinsic rate of natural increase (r) remains constant, the growth curve obtained will be: a) S-shaped (Sigmoid) b) J-shaped (Exponential) c) Straight line d) Bell-shaped Answer: b) J-shaped (Exponential) Explanation: When resources are unlimited, populations exhibit exponential growth described by the equation dN/dt = rN, which plots as a J-shaped curve.

4. Assertion (A): The prickly pear cactus introduced into Australia in the 1920s caused havoc by spreading rapidly. Reason (R): The cactus had no natural predators in the new environment to check its population growth. 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. Answer: a) Both A and R are true and R is the correct explanation of A. Explanation: Invasive species often spread uncontrollably because the natural herbivores or pathogens that limit them in their native habitat are absent in the new environment.

5. Calculate: In a pond, there were 20 lotus plants last year and through reproduction, 8 new plants were added. The birth rate (per lotus per year) is: a) 0.8 b) 0.2 c) 0.4 d) 0.04 Answer: c) 0.4 Explanation: Birth rate = Number of births / Initial population. $8 / 20 = 0.4$ offspring per lotus per year.

6. Competitive Exclusion: Two species of birds feed on the same type of seeds. According to Gause's Competitive Exclusion Principle, what is the most likely long-term outcome if resources are limited? a) They will hybridize to form a new species. b) Both species will coexist indefinitely by sharing resources. c) One species will outcompete and eliminate the other. d) Both species will increase their population size. Answer: c) One species will outcompete and eliminate the other. Explanation: Gause's principle states that two species competing for the same limiting resource cannot coexist indefinitely; the inferior competitor will be eliminated.

7. Resource Partitioning: To avoid the outcome in Question 6, species often evolve mechanisms like "Resource Partitioning". Which of the following is an example of this? a) Fighting physically for the same territory. b) One species feeding at dawn and the other at dusk. c) One species eating the other. d) Both species migrating to a new area. Answer: b) One species feeding at dawn and the other at dusk. Explanation: Temporal resource partitioning involves using the same resource at different times to avoid direct competition.

8. Adaptation Analysis: Kangaroo rats in North American deserts can survive without drinking water. How do they achieve this? a) They absorb water from the air through their skin. b) They rely entirely on metabolic water produced during fat oxidation. c) They store water in a hump like camels. d) They only come out when it rains. Answer: b) They rely entirely on metabolic water produced during fat oxidation. Explanation: They obtain water as a byproduct of internal fat oxidation and have highly concentrated urine to minimize water loss.

9. Identify the Strategy: An organism invests all its energy into a single, massive reproductive effort (breeding once) and then dies. This strategy is called Semelparity. Which of the following is an example? a) Humans b) Birds c) Bamboo / Pacific Salmon d) Elephants Answer: c) Bamboo / Pacific Salmon Explanation: Bamboo species flower once in their lifetime (after 50-100 years) and die. Pacific Salmon also spawn once and die.

10. Logistic Growth: In the logistic growth equation $dN/dt = rN((K-N)/K)$, what does 'K' represent? a) The initial population size. b) The rate of reproduction. c) The carrying capacity of the environment. d) The mortality rate. Answer: c) The carrying capacity of the environment. Explanation: 'K' is the maximum population size that the environment can sustain indefinitely with available resources.

11. Ecological Niche: Which statement best describes an "ecological niche"? a) The physical place where an organism lives. b) The functional role and status of an organism in its community. c) The collection of all species in an area. d) The climate of a region. Answer: b) The functional role and status of an organism in its community. Explanation: A niche includes not just the habitat (address) but also the organism's "profession" (what it eats, who eats it, how it interacts).

12. Parasitism vs Predation: Why is a female mosquito not considered a parasite, even though it needs human blood? a) It kills the human. b) It lives permanently on the human body. c) It needs blood only for reproduction (egg development), not for its own survival/food. d) It is smaller than the host. Answer: c) It needs blood only for reproduction... Explanation: A true parasite derives its nutrition/energy from the host for survival. The mosquito feeds on nectar for energy; blood is specifically a protein source for egg maturation.

13. Population Attribute: Which of the following is an attribute of a population but not of an individual? a) Birth b) Death c) Sex Ratio d) Sex Answer: c) Sex Ratio Explanation: An individual is either male or female (Sex). Only a group (population) can have a "Ratio" of males to females. Similarly, Birth Rate/Death Rate are population attributes.

14. Amensalism: The interaction between Penicillium mold and Staphylococcus bacteria is an example of Amensalism because: a) Both benefit. b) The mold kills the bacteria, but the mold is unaffected. c) The bacteria eat the mold. d) The mold lives inside the bacteria. Answer: b) The mold kills the bacteria, but the mold is unaffected. Explanation: Amensalism is a (-, 0) interaction. Penicillin antibiotic kills bacteria (-), but the mold doesn't derive benefit from killing them (0).

15. Verhulst-Pearl Logic: Why is the logistic growth model considered more realistic than the exponential model for most natural populations? a) Because resources are rarely unlimited in nature. b) Because predators do not exist in nature. c) Because 'r' is always zero in nature. d) Because diseases kill organisms before they reproduce. Answer: a) Because resources are rarely unlimited in nature. Explanation: No population can grow infinitely; eventually, food or space becomes limiting, leading to environmental resistance and a carrying capacity (K).

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Section B: Case-Study & Source-Based Questions

Case Study 1: The Barnacle War

In the rocky intertidal zone of Scotland, two species of barnacles, Balanus and Chthamalus, compete for space. Joseph Connell observed that Balanus dominates the deeper zone, while Chthamalus is restricted to the upper zone. When he removed Balanus experimentally, Chthamalus colonized the deeper zone successfully.

16. Analyze: What does this experiment demonstrate about the relationship between these two species? a) They are in a mutualistic relationship. b) Balanus is competitively superior to Chthamalus in the deeper zone. c) Chthamalus prefers the upper zone and cannot survive deep water. d) They do not compete at all. Answer: b) Balanus is competitively superior to Chthamalus in the deeper zone. Explanation: Since Chthamalus could grow deep when Balanus was gone, it proves it was excluded by competition, not by inability to survive there.

17. Concept: The fact that Chthamalus could live in the deeper zone but doesn't because of Balanus illustrates the difference between: a) Predator and Prey. b) Fundamental Niche and Realized Niche. c) Immigration and Emigration. d) Parasitism and Commensalism. Answer: b) Fundamental Niche and Realized Niche. Explanation: Fundamental Niche = Where it can live. Realized Niche = Where it actually lives due to competition.

18. Prediction: If Chthamalus evolves a stronger shell that Balanus cannot crush, what might happen to their distribution? a) Chthamalus might reclaim some of the deeper zone (Niche expansion). b) Balanus will go extinct immediately. c) Both will migrate to the open ocean. d) No change. Answer: a) Chthamalus might reclaim some of the deeper zone (Niche expansion). Explanation: This is "Competitive Release". If the competitive pressure is removed or countered, the species expands into its full potential range.

Case Study 2: The Co-evolution of Figs and Wasps

Fig trees and wasp species show a tight one-to-one relationship. A specific fig species can only be pollinated by its partner wasp species. The wasp lays eggs in the fig fruit, and the larvae feed on some of the seeds.

19. Identify: What type of interaction is this? a) Parasitism (Wasp eats seeds). b) Commensalism (Wasp gets home, fig unaffected). c) Mutualism (Both benefit: Pollination & Food/Shelter). d) Competition. Answer: c) Mutualism Explanation: It is an obligate mutualism (+/+). The plant gets pollinated, and the wasp gets a safe nursery and food for larvae.

20. Cheating: Sometimes, a wasp lays eggs but does not pollinate the flower. What term is used for such an individual? a) Mutualist b) Commensal c) Cheater d) Predator Answer: c) Cheater Explanation: In mutualism, an individual that takes the benefit without paying the cost (service) is called a "cheater".

21. Evolutionary Consequence: If the fig species goes extinct, what will happen to its specific pollinator wasp? a) It will adapt to pollinate oak trees. b) It will become a predator. c) It will also go extinct (Co-extinction). d) It will survive on other fruits. Answer: c) It will also go extinct (Co-extinction). Explanation: Because the relationship is specific and obligate ("one-to-one"), the wasp cannot survive or reproduce without its specific partner.

Case Study 3: Population Regulation in a Lake

A lake has a carrying capacity (K) for 1000 fish. Currently, there are 500 fish. The intrinsic rate of increase (r) is 0.1.

22. Calculate: Using the logistic growth formula, what is the rate of population growth ($dN/dt$) at this moment? Formula: $dN/dt = rN ((K-N)/K)$ a) 50 b) 25 c) 100 d) 10 Answer: b) 25 Explanation: $dN/dt = 0.1 \times 500 \times ((1000 - 500) / 1000)$ $dN/dt = 50 \times (500/1000)$ $dN/dt = 50 \times 0.5 = 25$.

23. Analyze: When the population reaches 1000 fish (N=K), what will be the growth rate? a) Maximum (rN) b) Zero c) Negative d) 0.1 Answer: b) Zero Explanation: If N = K, then (K-N) = 0. The whole term becomes zero. The population stops growing.

24. Reasoning: Which factor is likely a "Density-dependent" factor regulating this fish population as it approaches K? a) A sudden flood (Natural disaster). b) A drop in temperature. c) Competition for food and oxygen. d) Sunlight intensity. Answer: c) Competition for food and oxygen. Explanation: Density-dependent factors (competition, disease, waste) become stronger as the population size increases. Floods/Temperature are Density-independent.

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Section C: Creating, Designing & Critical Thinking

25. Designing an Investigation: You suspect that allelopathy (Amensalism) is occurring in a field where Walnut trees are growing (no grass grows under them).

• Hypothesis: The Walnut tree roots secrete a chemical that inhibits grass growth.
• Experiment: Design a simple pot experiment with controls to test this. Answer:
• Hypothesis: Walnut soil contains an inhibitory toxin (Juglone).
• Experiment Design:
  • Group A (Test): Plant grass seeds in soil taken from directly under the Walnut tree.
  • Group B (Control): Plant grass seeds in neutral garden soil from a distance away.
  • Group C (Leachate): Plant seeds in neutral soil but water them with water that has soaked Walnut leaves/roots.
• Prediction: If grass grows in B but dies/stunts in A and C, the hypothesis of chemical inhibition is supported.

26. Scenario Analysis (Invasive Species): Scenario: The Water Hyacinth (Eichhornia) was introduced to India for its beautiful flowers. It has now clogged waterways and killed native fish.

• Analysis: Why did this alien species become invasive?
• Impact: How does it kill the fish? Answer:
• Analysis: It became invasive because it propagates vegetatively at a phenomenal rate and, crucially, it has no natural enemies (herbivores) in India to check its growth.
• Impact: It forms a dense mat on the surface, blocking sunlight and air exchange. As the older plants rot, decomposers use up all the dissolved oxygen, causing the fish to suffocate (Eutrophication).

27. Creating a Model: Draw a graph showing Population Growth over time.

• Curve A: Exponential (J-shaped).
• Curve B: Logistic (S-shaped).
• Task: Label the Lag phase, Log phase, Deceleration phase, and Carrying Capacity (K). Mark the point where environmental resistance begins to act significantly on Curve B. Answer: (Visual description)
• X-axis: Time (t). Y-axis: Population Density (N).
• Curve A (J): Starts low, rises slowly, then shoots up vertically.
• Curve B (S): Starts low (Lag), rises steeply (Log), then the slope flattens out (Deceleration) until it becomes horizontal at level K.
• Resistance: The point where Curve B diverges from Curve A (bends away) marks the onset of environmental resistance.

28. Ethical/Practical Debate: Topic: "To save the Endangered Tiger, we should remove all other predators (like Leopards) from the sanctuary."

• Critique: Evaluate this strategy using the concept of the Food Web and Interference Competition. Why might this backfire? Answer:
• Critique: While this might reduce Interference Competition (direct fighting), it disrupts the food web.
• Backfire: Leopards often prey on smaller animals or different species than tigers (Resource Partitioning). Removing them might cause an explosion of mesopredators (like dogs/cats) or certain herbivores, destabilizing the ecosystem balance. Also, biodiversity conservation aims to save the system, not just one species.

29. Formulating a Strategy: You are managing a fishery. You want to harvest fish for maximum profit without crashing the population.

• Question: At what population size relative to Carrying Capacity (K) is the growth rate ($dN/dt$) maximum? (Hint: Look at the logistic curve slope).
• Strategy: Should you harvest when N is low, high (near K), or medium (K/2)? Explain why. Answer:
• Maximum Growth: Occurs at N = K/2 (half the carrying capacity). This is the inflection point of the sigmoid curve where the slope is steepest.
• Strategy: Harvest to keep the population near K/2. At this level, the population is reproducing at its fastest rate (Maximum Sustainable Yield), allowing for the quickest replenishment of harvested fish. At K, growth is near zero. At low N, there aren't enough breeders.

30. Adaptation Design: Design a hypothetical organism adapted to live in a Deep Sea Hydrothermal Vent (High pressure, high temp, no light).

• Features: Describe its energy source, body structure, and sensory organs. Answer:
• Name: Thermo-Crab.
• Energy Source: Chemosynthesis. It hosts symbiotic bacteria in its gut that convert Hydrogen Sulfide ($H_2S$) from the vent into sugar (since there is no sunlight for photosynthesis).
• Body Structure: Highly compact, fluid-filled body with no air cavities (to resist crushing pressure); enzymes resistant to denaturation at 100°C (Thermostable).
• Sensory: No eyes (useless in dark); highly developed Chemical Sensors (antennae) to detect sulfur plumes and food.