Listen to part of a lecture in a biology class. Professor: Today we're going to discuss a fascinating adaptation in desert plants called 'crassulacean acid metabolism,' or CAM photosynthesis. Unlike most plants, which open their stomata during the day to take in carbon dioxide, CAM plants, like cacti and succulents, open their stomata at night. This is a clever strategy for survival in arid environments. During the night, when temperatures are cooler and humidity is higher, they open their stomata and absorb CO2. This CO2 is then stored as malic acid in the vacuoles of the cells. During the day, the stomata remain closed to prevent water loss through transpiration. The stored malic acid is then broken down to release CO2, which is used in the Calvin cycle to produce sugars. This allows CAM plants to photosynthesize during the day without opening their stomata, thereby conserving precious water. However, this adaptation comes at a cost: CAM plants grow more slowly than typical plants because they have to store and process CO2 in this two-step process. So, while they are highly efficient in water use, they are less efficient in terms of growth rate.
❓ Câu hỏi What is the main advantage of CAM photosynthesis for desert plants?
A. It allows plants to grow faster than typical plants.
B. It enables plants to keep their stomata open during the day.
C. It minimizes water loss by opening stomata only at night.
D. It increases the absorption of sunlight during the day.
✅ Đáp án đúng
It minimizes water loss by opening stomata only at night.
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
