# Organization of Natural Systems Worksheet ## Section A: Multiple Choice Questions
Q1: Which of the following levels of biological organization includes both biotic and abiotic components? (a) Population (b) Community (c) Ecosystem (d) Organism
Solution:
Ans: (c) Explanation: An ecosystem is the only level of organization that includes both biotic factors (living organisms) and abiotic factors (non-living components like water, soil, and temperature). A population includes only one species in an area, a community includes multiple species but only living things, and an organism is an individual living thing.
Q2: In a food chain, organisms that produce their own food through photosynthesis are called: (a) Primary consumers (b) Decomposers (c) Secondary consumers (d) Producers
Solution:
Ans: (d) Explanation:Producers (also called autotrophs) make their own food through photosynthesis. Primary consumers are herbivores that eat producers, secondary consumers eat primary consumers, and decomposers break down dead organic matter.
Q3: Which term describes all the individuals of the same species living in a specific area at the same time? (a) Community (b) Population (c) Biosphere (d) Niche
Solution:
Ans: (b) Explanation: A population consists of all members of the same species living in a defined area at the same time. A community includes different species, the biosphere encompasses all life on Earth, and a niche is the role an organism plays in its environment.
Q4: What percentage of energy is typically transferred from one trophic level to the next in an energy pyramid? (a) 50% (b) 25% (c) 10% (d) 1%
Solution:
Ans: (c) Explanation: According to the 10% rule, approximately 10% of the energy from one trophic level is transferred to the next level. The remaining 90% is lost as heat through metabolic processes, movement, and other life functions. This explains why food chains typically have only 4-5 levels.
Q5: Which of the following represents the correct hierarchical sequence of biological organization from smallest to largest? (a) Organism → Population → Community → Ecosystem → Biosphere (b) Population → Organism → Community → Ecosystem → Biosphere (c) Community → Population → Organism → Ecosystem → Biosphere (d) Organism → Community → Population → Biosphere → Ecosystem
Solution:
Ans: (a) Explanation: The correct hierarchical sequence from smallest to largest is: Organism (individual living thing) → Population (same species in an area) → Community (different species in an area) → Ecosystem (community plus abiotic factors) → Biosphere (all life on Earth).
Q6: In a symbiotic relationship where one organism benefits and the other is harmed, the relationship is called: (a) Mutualism (b) Commensalism (c) Parasitism (d) Competition
Solution:
Ans: (c) Explanation:Parasitism is a symbiotic relationship where one organism (the parasite) benefits while the other (the host) is harmed. In mutualism, both organisms benefit; in commensalism, one benefits and the other is unaffected; and competition is not a symbiotic relationship but rather a struggle for resources.
Q7: Which biogeochemical cycle does NOT have a significant atmospheric component? (a) Carbon cycle (b) Nitrogen cycle (c) Water cycle (d) Phosphorus cycle
Solution:
Ans: (d) Explanation: The phosphorus cycle lacks a significant atmospheric component because phosphorus does not form volatile compounds that enter the atmosphere. It cycles primarily through rocks, soil, water, and organisms. The carbon, nitrogen, and water cycles all have important atmospheric phases.
Q8: Organisms that obtain energy by consuming dead organic matter are classified as: (a) Herbivores (b) Carnivores (c) Producers (d) Decomposers
Solution:
Ans: (d) Explanation:Decomposers (such as bacteria and fungi) break down dead organic matter and recycle nutrients back into the ecosystem. Herbivores eat plants, carnivores eat animals, and producers make their own food through photosynthesis.
## Section B: Fill in the Blanks Q9: The specific role that an organism plays in its environment, including its habitat and interactions with other organisms, is called its __________.
Solution:
Ans: niche Explanation: An organism's niche describes its functional role in the ecosystem, including what it eats, what eats it, its habitat requirements, and its behaviors. It is often described as the organism's "profession" in the ecosystem.
Q10: A network of interconnected food chains showing the feeding relationships in an ecosystem is called a food __________.
Solution:
Ans: web Explanation: A food web represents the complex, interconnected feeding relationships in an ecosystem, showing that most organisms eat and are eaten by multiple species. This is more realistic than a simple linear food chain.
Q11: The total mass of living organic matter in a given area or trophic level is called __________.
Solution:
Ans: biomass Explanation:Biomass represents the total dry mass of all living organisms in a specific area or at a specific trophic level. It decreases at higher trophic levels due to energy loss, which can be visualized in a biomass pyramid.
Q12: The layer of Earth where all life exists, including land, water, and atmosphere, is called the __________.
Solution:
Ans: biosphere Explanation: The biosphere is the global ecological system that includes all living organisms and their relationships with the lithosphere (land), hydrosphere (water), and atmosphere (air). It represents the highest level of biological organization.
Q13: Organisms that can convert atmospheric nitrogen into forms usable by plants are called nitrogen-__________ bacteria.
Solution:
Ans: fixing Explanation:Nitrogen-fixing bacteria (such as Rhizobium) convert atmospheric nitrogen gas (\(N_2\)) into ammonia (\(NH_3\)) or ammonium (\(NH_4^+\)), which plants can use. This is a critical step in the nitrogen cycle.
Q14: In an energy pyramid, the organisms at the base are the __________, which have the greatest biomass and energy.
Solution:
Ans: producers Explanation:Producers form the base of the energy pyramid and have the greatest total energy and biomass because they capture energy directly from the sun through photosynthesis. Each successive trophic level has less energy available.
## Section C: Word Problems Q15: In a grassland ecosystem, grass contains 10,000 kilocalories of energy. If a grasshopper (primary consumer) eats the grass, approximately how much energy will be available to a bird (secondary consumer) that eats the grasshopper? Show your calculation.
Solution:
Ans: Energy available to grasshopper = \(10,000 \times 0.10 = 1,000\) kcal Energy available to bird = \(1,000 \times 0.10 = 100\) kcal Final Answer: 100 kilocalories
Q16: A forest community contains 500 oak trees, 300 maple trees, 200 deer, 150 rabbits, 50 foxes, and 25 hawks. How many populations are present in this community? Explain your reasoning.
Solution:
Ans: Populations present: 1. Oak trees 2. Maple trees 3. Deer 4. Rabbits 5. Foxes 6. Hawks Each different species represents one population. Final Answer: 6 populations
Q17: In a marine ecosystem, the producers have a total biomass of 8,000 kg. Based on the typical biomass transfer between trophic levels, calculate the approximate biomass of the tertiary consumers (third-level carnivores) in this ecosystem.
Solution:
Ans: Biomass of primary consumers = \(8,000 \times 0.10 = 800\) kg Biomass of secondary consumers = \(800 \times 0.10 = 80\) kg Biomass of tertiary consumers = \(80 \times 0.10 = 8\) kg Final Answer: 8 kg
Q18: A scientist studying a pond ecosystem identifies the following organisms: algae, water fleas, small fish, large fish, and bacteria. Construct a food chain with four trophic levels from these organisms, identifying each organism's trophic level.
Solution:
Ans: Trophic Level 1 (Producers): Algae Trophic Level 2 (Primary Consumers): Water fleas Trophic Level 3 (Secondary Consumers): Small fish Trophic Level 4 (Tertiary Consumers): Large fish (Note: Bacteria function as decomposers) Final Answer: Algae → Water fleas → Small fish → Large fish
Q19: In a temperate forest ecosystem, there are 1,000 kg of plant material (producers), 100 kg of herbivores, 10 kg of carnivores, and 1 kg of top carnivores. If a disease killed 50% of the herbivore population, predict what would happen to the producer and carnivore populations. Explain your reasoning using ecological principles.
Solution:
Ans: Producers: Would initially increase because fewer herbivores are consuming them. Carnivores: Would decrease because there is less food (herbivores) available for them. This demonstrates the interdependence of trophic levels and how disruptions cascade through the ecosystem. Final Answer: Producers would increase; carnivores would decrease
Q20: A biology student is studying the nitrogen cycle in a farm field. She notes that farmers often plant legumes (like clover) to improve soil nitrogen. If the legume plants contain nitrogen-fixing bacteria in their root nodules that convert 50 kg of atmospheric nitrogen into usable forms each growing season, and the plants are then plowed back into the soil where decomposers release 80% of the nitrogen for use by other plants, how much nitrogen becomes available for the next crop?
Solution:
Ans: Nitrogen fixed by bacteria = 50 kg Nitrogen released by decomposers = \(50 \times 0.80 = 40\) kg This represents the nitrogen made available through nitrogen fixation and decomposition in the nitrogen cycle. Final Answer: 40 kg of nitrogen
The document Worksheet (with Solutions): Organization of Natural Systems is a part of the Grade 9 Course High School Biology.
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