Questions & explanations
1. Decomposers play a crucial role in the detritus food chain primarily by:
- A. Consuming live plants and animals
- B. Converting dead organic matter into inorganic nutrients
- C. Fixing atmospheric nitrogen into usable forms
- D. Producing oxygen through photosynthesis
Answer: B. Converting dead organic matter into inorganic nutrients
Decomposers (e.g., bacteria and fungi) break down dead organic matter, releasing nutrients like carbon, nitrogen, and phosphorus back into the environment for reuse by producers.
2. Why are food webs considered more stable than simple food chains in an ecosystem?
- A. Food webs have fewer trophic levels, reducing energy loss.
- B. Food webs provide alternative feeding pathways, buffering against species loss.
- C. Food webs rely on a single producer species, increasing efficiency.
- D. Food webs eliminate competition among consumers.
Answer: B. Food webs provide alternative feeding pathways, buffering against species loss.
In a food web, multiple interconnected food chains offer alternative routes for energy flow, so if one species declines, others can compensate, enhancing stability.
3. According to the ten percent law, if producers have 10,000 J of energy, how much energy is available to secondary consumers?
- A. 10 J
- B. 100 J
- C. 1,000 J
- D. 10,000 J
Answer: B. 100 J
Only 10% of energy is transferred to the next trophic level. From producers (10,000 J) to primary consumers: 1,000 J; from primary to secondary consumers: 100 J.
4. Which of the following correctly distinguishes a grazing food chain from a detritus food chain?
- A. Grazing food chain begins with dead organic matter; detritus food chain begins with living plants.
- B. Grazing food chain begins with living plants; detritus food chain begins with dead organic matter.
- C. Both begin with living plants but differ in consumer types.
- D. Both begin with dead organic matter but differ in decomposer activity.
Answer: B. Grazing food chain begins with living plants; detritus food chain begins with dead organic matter.
Grazing food chains start with autotrophs (living plants), while detritus food chains start with dead organic matter (detritus) and involve decomposers.
5. What does 'standing crop' refer to in an ecosystem?
- A. The total biomass of living organisms at a given time
- B. The annual net primary productivity of an ecosystem
- C. The amount of energy fixed by producers per unit time
- D. The total dead organic matter present in the soil
Answer: A. The total biomass of living organisms at a given time
Standing crop is the biomass (or energy content) of living organisms present in an ecosystem at a particular moment, often expressed per unit area.
6. Which statement best describes energy flow in an ecosystem?
- A. Energy flows in a cyclic manner, being reused by organisms.
- B. Energy flows unidirectionally from producers to consumers and eventually dissipates as heat.
- C. Energy flows bidirectionally between trophic levels.
- D. Energy is recycled through decomposers back to producers.
Answer: B. Energy flows unidirectionally from producers to consumers and eventually dissipates as heat.
Energy transfer in ecosystems is one-way; it enters as sunlight, passes through trophic levels, and is lost as heat at each step, not recycled.
7. In a grassland ecosystem, which group represents the primary consumers?
- A. Grasshoppers feeding on grass
- B. Grass producing food via photosynthesis
- C. Frogs eating grasshoppers
- D. Fungi decomposing dead grass
Answer: A. Grasshoppers feeding on grass
Primary consumers are herbivores that directly feed on producers (plants). Grasshoppers eating grass are primary consumers.
8. What is the ultimate source of energy for nearly all ecosystems on Earth?
- A. Geothermal heat
- B. Solar radiation
- C. Chemical energy from deep-sea vents
- D. Nuclear energy from Earth's core
Answer: B. Solar radiation
The Sun is the primary energy source for most ecosystems, driving photosynthesis in producers and sustaining the food web.