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.