Listen to part of a lecture in a biology class. Professor: Today, we’re going to discuss a fascinating adaptation in desert plants. Unlike most plants, which open their stomata during the day to take in carbon dioxide, many desert plants, such as cacti and succulents, use a process called CAM photosynthesis. CAM stands for crassulacean acid metabolism, named after the Crassulaceae family where it was first discovered. At night, these plants open their stomata to absorb carbon dioxide, and it is stored as malic acid in vacuoles. During the day, the stomata remain closed to prevent water loss, but the stored carbon dioxide is released for photosynthesis. This allows them to survive in extremely arid conditions. However, CAM comes with a trade-off: it is less efficient than regular C3 photosynthesis, so these plants grow more slowly. Also, if water is plentiful, some CAM plants can switch back to C3. This flexibility is key to their survival.
❓ คำถาม What is the main advantage of CAM photosynthesis for desert plants?
A. A. It allows plants to grow faster than C3 plants.
B. B. It prevents water loss by keeping stomata closed during the day.
C. C. It enables plants to absorb more carbon dioxide during the day.
D. D. It helps plants store water in their vacuoles.
✅ คำตอบที่ถูกต้อง
B. It prevents 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