Listen to part of a lecture in a biology class. Professor: Today we're going to talk about a fascinating adaptation in desert plants, specifically the role of CAM photosynthesis. Unlike typical plants that open their stomata during the day to take in carbon dioxide, CAM plants, such as cacti and succulents, open their stomata at night. This reduces water loss because nighttime temperatures are cooler and humidity is higher. During the night, they take in CO2 and store it as malic acid in their vacuoles. Then, during the day, when the stomata are closed, the malic acid is broken down to release CO2 for the Calvin cycle, which drives sugar production. This separation of carbon fixation and the Calvin cycle over time is key to their survival. Now, a common misconception is that CAM photosynthesis is rare. In fact, it is estimated that about 10% of plant species use CAM, and it has evolved independently many times. So, what's the main advantage of CAM?
❓ Question What is the main advantage of CAM photosynthesis mentioned by the professor?
A. It allows plants to absorb more sunlight during the day.
B. It reduces water loss by keeping stomata closed during the day.
C. It enables plants to grow faster than C3 plants.
D. It eliminates the need for carbon dioxide intake entirely.
✅ Correct Answer
It reduces water loss by keeping stomata closed during the day.
TOEFL Listening Tips
Skim the questions first to predict the content
Watch for signal words in lectures and conversations (however, actually, in fact)
For main idea questions, focus on the beginning; for detail questions, focus on examples and data
For attitude questions, pay attention to the speaker's tone and word choice
Take notes on keywords; don't try to write down every word
