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Question Video: Describing the Tropisms Displayed by Plant Shoots Biology

Which of the following is correct about plant shoots? [A] Plant shoots are positively phototropic and negatively gravitropic. [B] Plant shoots are negatively phototropic and positively gravitropic. [C] Plant shoots are negatively hydrotropic and positively gravitropic. [D] Plant shoots do not display any major tropisms.

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Video Transcript

Which of the following is correct about plant shoots? (A) Plant shoots are positively phototropic and negatively gravitropic. (B) Plant shoots are negatively phototropic and positively gravitropic. (C) Plant shoots are negatively hydrotropic and positively gravitropic. Or (D) plant shoots do not display any major tropisms.

The answer options in this question provide us with different examples of tropisms that can be carried out by plants. A tropism is the response of an organism like a plant to grow toward or away from a stimulus. Remember, a stimulus is any detectable change in an organism’s internal or external environment that can trigger an effect in that organism. A tropism can either be positive or negative. While a positive tropism is the response of an organism to grow toward a stimulus, a negative tropism is the response of an organism to grow away from a stimulus.

Let’s take a look at plant shoots and the different tropisms they can display. Plant shoots and leaves contain the majority of the photosynthesizing cells in a plant. Photosynthesis is the process by which plants use light and inorganic materials to make their own food. As this process requires light, which is usually provided by the Sun, plant shoots tend to grow toward the direction where most sunlight is available. This is an example of a tropism, specifically termed phototropism, as the prefix photo- means light. As the plant shoot is growing toward the light stimulus, it is a positive tropism.

Learning this information allows us to eliminate answer option (B) that states that plant shoots are negatively phototropic, which we now know is incorrect. We can also rule out answer option (D), as we know that the plant shoots do show at least one major tropism, and this option suggests otherwise.

A gravitropic response is the movement of an organism in response to a different stimulus, gravity. As the roots of the plants tend to grow downward toward the pull of gravity to access more water and minerals deeper in the soil, they can be described as positively gravitropic. However, this question concerns the plant shoots, not the plant roots. As plant shoots are usually observed to grow upward against the pull of gravity, plant shoots are actually negatively gravitropic. This means we can eliminate answer option (C), suggesting that the shoots are positively gravitropic, which we now know is incorrect.

This leaves answer option (A), which appropriately describes two tropisms that are often displayed by plant shoots. Plant shoots are positively phototropic and negatively gravitropic.

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