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Listen to an Academic Talk Test #040
Listen to an Academic Talk
1. What is the lecture mainly about?
A) How plants respond to the environment through growth
B) The role of hormones in plant reproduction
C) The process of photosynthesis in different plants
D) How plants compete with each other for resources
2. According to the professor, what causes a plant stem to bend toward light?
A) Cells on the sunny side grow faster.
B) A growth hormone gathers on the shaded side.
C) The plant is seeking warmth from the sun.
D) Water pressure changes within the stem.
3. What can be inferred about a plant placed in a dark room with a single light from above?
A) Its roots will grow toward the light.
B) Its stem will grow straight up.
C) It will not be able to perform gravitropism.
D) It will stop producing the hormone auxin.
4. Why does the professor discuss both stems and roots?
A) To show that different parts of a plant can have opposite responses
B) To argue that root growth is more important than stem growth
C) To explain that both parts grow toward light
D) To demonstrate that gravity affects stems more than roots
Professor: We tend to think of plants as motionless, but they are constantly responding to their environment through growth. These directional growth movements are called tropisms. Perhaps the most familiar example is phototropism—the tendency for a plant to grow toward a light source. This happens because a plant hormone called auxin accumulates on the shaded side of the stem. This concentration of auxin causes the cells on the dark side to grow longer than the cells on the sunny side, which effectively bends the stem toward the light. Another important tropism is gravitropism, which is growth in response to gravity. A plant's stems show negative gravitropism, meaning they grow upwards, away from the pull of gravity. The roots, however, show positive gravitropism, growing downwards into the soil. These responses are not accidents; they are critical survival mechanisms that ensure a plant can access light for photosynthesis and its roots can find water and anchor it securely.
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