1. Energy flow in an ecosystem is:
Correct Answer: a) Unidirectional
Explanation: Energy flows through an ecosystem in one direction - from the sun to producers (plants), then to consumers (herbivores, carnivores), and finally to decomposers. Unlike nutrients, energy is not recycled but is lost as heat at each trophic level according to the Second Law of Thermodynamics.
2. A food chain starts with:
Correct Answer: c) Producers
Explanation: All food chains begin with autotrophic producers (green plants, algae, or photosynthetic bacteria) that convert solar energy into chemical energy through photosynthesis. These form the foundation of every ecosystem's energy flow as they are the only organisms capable of producing food from inorganic substances.
3. In a food web, if the population of snakes decreases, what happens to the grass population?
Correct Answer: a) Increases
Explanation: This demonstrates trophic cascade: Fewer snakes → More herbivores (like rabbits) survive → Increased herbivory → Reduced grass population. The snake acts as a top-down control on the ecosystem. Such predator-prey dynamics are crucial for maintaining ecological balance.
4. Ecological pyramids are based on:
Correct Answer: a) Number, biomass, and energy
Explanation: Ecological pyramids graphically represent three parameters at different trophic levels: (1) Pyramid of Numbers (individual count), (2) Pyramid of Biomass (dry weight), and (3) Pyramid of Energy (productivity). Each provides unique insights into ecosystem structure and function.
5. Which pyramid is always upright?
Correct Answer: c) Pyramid of energy
Explanation: Energy pyramids must always be upright because energy decreases at each trophic level (10% Law). Only ~10% of energy is transferred between levels, with ~90% lost as metabolic heat. This universal energy loss pattern makes energy pyramids the most consistent ecological representation.
6. Autotrophs in an ecosystem are:
Correct Answer: a) Green plants
Explanation: Autotrophs (producers) are organisms that synthesize their own food from inorganic substances using sunlight (photoautotrophs like plants) or chemical energy (chemoautotrophs). They form the base of all food chains and are essential for energy input into ecosystems.
7. Photosynthesis uses:
Correct Answer: d) All the above
Explanation: The photosynthesis equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Chlorophyll pigments absorb sunlight, which splits water molecules. The hydrogen from water combines with CO₂ to form glucose, while oxygen is released as a byproduct.
8. Primary consumers (herbivores) include:
Correct Answer: a) Rabbit
Explanation: Primary consumers occupy the second trophic level, feeding directly on producers. Examples include: (1) Grazers (rabbits, deer), (2) Browsers (giraffes), (3) Granivores (seed-eating birds), and (4) Nectarivores (butterflies). They convert plant biomass into animal biomass.
9. The 10% energy transfer rule implies:
Correct Answer: c) Both a and b
Explanation: Lindeman's 10% Law states that only ~10% of energy is transferred between trophic levels because: (1) ~90% is lost as metabolic heat during respiration, (2) Not all biomass is consumed, and (3) Not all consumed biomass is assimilated. This limits food chain length to typically 3-5 levels.
10. Ecological pyramids were devised by:
Correct Answer: d) Charles Elton
Explanation: British ecologist Charles Elton introduced ecological pyramids in his 1927 book "Animal Ecology." His pyramid concept illustrated the decreasing numbers, biomass, and energy at successive trophic levels, forming the basis for modern understanding of ecosystem energy flow.