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Listen to an Academic Talk Test #090
Listen to an Academic Talk
1. What is the talk mainly about?
A) How plants use hormones to grow
B) The different parts of a plant cell
C) How plants react directionally to stimuli
D) The process of photosynthesis in leaves
2. According to the lecturer, what role does the hormone auxin play in phototropism?
A) It absorbs sunlight for the plant.
B) It causes cells on the shaded side to lengthen.
C) It helps the plant's roots grow deeper.
D) It makes the entire plant grow faster.
3. What can be inferred about a seed that is planted upside down?
A) It will not be able to sprout at all.
B) Its stem will grow downward while its roots grow upward.
C) Its stem and roots will eventually grow in the correct directions.
D) It will develop much more slowly than a normal seed.
4. Why does the lecturer discuss both phototropism and gravitropism?
A) To show that all tropisms are a response to light
B) To argue that one tropism is more important than the other
C) To provide examples of different plant growth responses
D) To explain why plants need both sunlight and water
Lecturer: Plants might seem passive, but they are constantly responding to their environment in very active ways. One of the main ways they do this is through tropisms, which are directional growth movements in response to an external stimulus.
The most famous example is phototropism—growth towards light. You've all seen a houseplant bend towards a window. This happens because a hormone called auxin builds up on the shaded side of the stem. This causes the cells on the dark side to grow longer than the cells on the light side, which makes the stem bend toward the light source.
Another key tropism is gravitropism, the response to gravity. A plant's roots show positive gravitropism, meaning they grow downward, into the soil, anchoring the plant and seeking water. The stem, however, shows negative gravitropism by growing upward, against gravity, to reach the sunlight.
These tropisms are not random; they are crucial survival mechanisms that help plants optimize access to essential resources.
The most famous example is phototropism—growth towards light. You've all seen a houseplant bend towards a window. This happens because a hormone called auxin builds up on the shaded side of the stem. This causes the cells on the dark side to grow longer than the cells on the light side, which makes the stem bend toward the light source.
Another key tropism is gravitropism, the response to gravity. A plant's roots show positive gravitropism, meaning they grow downward, into the soil, anchoring the plant and seeking water. The stem, however, shows negative gravitropism by growing upward, against gravity, to reach the sunlight.
These tropisms are not random; they are crucial survival mechanisms that help plants optimize access to essential resources.
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