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Question

Difficulty: MediumRecognizing Explicit Cause and Effect

Passage:

In temperate marine ecosystems, giant kelp forests play a crucial role by providing food and shelter for a diverse array of species. However, these productive habitats are highly vulnerable to shifts in predator-prey dynamics. Under normal conditions, sea otters feed heavily on herbivorous sea urchins, keeping the urchin population in check. When sea otter populations decline—often due to historical hunting or changes in killer whale feeding habits—the lack of predation allows sea urchin populations to swell dramatically. With their numbers unchecked, the urchins consume kelp holdfasts, the root-like structures anchoring the giant algae to the seafloor, at an unsustainable rate. Consequently, the kelp drifts away, leaving behind a barren rocky expanse known as an 'urchin barren.' This ecological shift not only eliminates the physical structure of the kelp forest but also causes a collapse in the populations of fish and invertebrates that rely on the kelp canopy for protection, illustrating how a disruption in one trophic level can dismantle an entire ecosystem.

According to the passage, the kelp drifts away from the seafloor as a direct result of which of the following events?

  1. A
    The transition of the habitat into a barren rocky expanse.
  2. B
    A sudden increase in the population of sea otters.
  3. Urchins consuming the holdfast structures that anchor the kelp.Answer
  4. D
    Killer whales feeding directly on the root-like structures of the kelp.

Answer

Urchins consuming the holdfast structures that anchor the kelp.
The passage explicitly states that when the urchin population is unchecked, the urchins consume the kelp holdfasts. The author immediately follows this detail with the transition 'Consequently, the kelp drifts away,' which directly establishes that the consumption of the holdfasts by the urchins is the cause of the kelp drifting away.

Step-by-Step Solution

1
Locate the portion of the passage that mentions the kelp drifting away.
The text states: 'Consequently, the kelp drifts away...'
Finding the specific effect mentioned in the question is necessary to trace its cause.
2
Identify the cause linked to this effect by examining the preceding sentence.
The text states that 'urchins consume kelp holdfasts' at an unsustainable rate, followed by the transition word 'Consequently.'
The word 'Consequently' explicitly indicates that the consumption of holdfasts by the urchins is the direct cause of the kelp drifting away.

Key Concept

Recognizing Explicit Cause and Effect
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Topics

Recognizing Explicit Cause and Effect

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