Set 10: Central Ideas (Intermediate)
Explanation
PASSAGE
The following text is from a scientific article about marine biology. Dinoflagellates are single-celled organisms common in marine environments. Some species, such as *Noctiluca scintillans*, are capable of bioluminescence, producing bright flashes of blue light when disturbed by waves or predators. This light is produced by a chemical reaction involving a molecule called luciferin and an enzyme called luciferase. While visually stunning to humans, this bioluminescence serves a defensive purpose: the sudden flash startles predators, allowing the plankton to escape, or it acts as a "burglar alarm," illuminating the predator and making it visible to its own predators.
Which choice best states the main idea of the text?
Detailed Explanation
Choice B is the best answer. The text describes the bioluminescence of Noctiluca scintillans and explicitly states its function: 'While visually stunning to humans, this bioluminescence serves a defensive purpose.' It further explains how: by startling predators or exposing them to larger threats (the 'burglar alarm' effect). This directly supports the idea that the light is a defensive mechanism.
Choice D is incorrect because the text mentions 'disturbed by waves or predators' but never mentions attracting mates.
Choice C is incorrect because the text only says these chemicals are involved in the light reaction, not that they are the only chemicals in the organism.
Choice A is incorrect because the text explicitly provides a use for the light (defense), confirming it is not useless.
Key Evidence:
• "bioluminescence serves a defensive purpose"
• "sudden flash startles predators"
Why others are wrong: D (Unsupported - text discusses defense, not mating), C (Too extreme - text limits discussion to the light reaction), A (Contradicts text - text explains the specific utility of the light).
🎯 Keep Practicing!
Master all sections for your best SAT score