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Question Video: Identifying the Incorrect Statement about Auxins in Plants Biology

Which of the following statements about auxins is not true? [A] The primary role of auxins in a plant is to encourage growth by stimulating cell elongation. [B] Indoleacetic acid, IAA, is an example of an auxin. [C] Auxins are not produced by a plant during the summer months. [D] auxins are important in regulating phototropic responses.

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Video Transcript

Which of the following statements about auxins is not true? (A) The primary role of auxins in a plant is to encourage growth by stimulating cell elongation. (B) Indoleacetic acid, IAA, is an example of an auxin. (C) Auxins are not produced by a plant during the summer months. Or (D) auxins are important in regulating phototropic responses.

Auxins are a group of hormones or chemical messengers in plants that play an important role in cell elongation. An example of an auxin is indoleacetic acid, otherwise known as IAA. IAA is mostly produced in the apical or topmost bud, and it’s also produced in very young developing leaves of plants. In these regions, it stimulates and encourages cell elongation, which allows the plant to grow upwards.

As the question is asking us to work out which statement about auxins is not true, we can eliminate both option (B), as we know that IAA is an example of an auxin, and option (A), as we know that IAA can encourage growth by stimulating cell elongation.

Auxins play a role in stimulating directional growth responses. This is the growth of an organism like a plant towards or away from a stimulus in its environment and is otherwise known as a tropism. An example of a tropism is phototropism. The prefix photo- means light, and a phototropic response is the movement towards or away from a light source.

In the shoot of a plant, auxin produced in the shoot tip will diffuse down the stem and accumulate on the shaded side of the shoot. When auxin accumulates in the cells on the shaded side of the shoot, it stimulates cell elongation in those cells. This causes the cells on the shaded side to elongate comparatively more than the cells that are lit by the light source, causing the shoot to bend towards the light source in response to light. This is an example of a phototropic response that’s being regulated by auxin.

Remember, we’re looking for a statement about auxins that’s not true, so we can also eliminate option (D). This is because auxins are important in regulating phototropic responses as we’ve just observed in the shoot. The production of auxin is not seasonal, which means that they’re produced throughout the whole year. Therefore, we can deduce that the incorrect statement is option (C), auxins are not produced by a plant during the summer months, as in fact they’re produced all year round.

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