Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about coral bleaching. As you know, corals have a symbiotic relationship with tiny algae called zooxanthellae. These algae live inside the coral tissues and provide them with up to 90% of their energy through photosynthesis. When water temperatures rise even slightly above normal, the coral becomes stressed. In response, it expels the algae, which causes the coral to lose its color—hence the term 'bleaching.' But here's a key point: bleaching is not always fatal. If the water cools down quickly, the algae can return, and the coral can recover. However, if the stress persists, the coral will starve and die. Recent studies have shown that some corals are more resilient than others, and researchers are trying to identify the genetic factors that allow certain corals to withstand higher temperatures. This could help in conservation efforts, especially as ocean temperatures continue to rise due to climate change.
❓ 题目 What does the professor say about coral bleaching?
A. It is always a fatal condition for corals.
B. It occurs when corals expel the algae that live inside them.
C. It is caused by a decrease in water temperature.
D. It only affects corals in shallow water.
✅ 正确答案
It occurs when corals expel the algae that live inside them.