Video Transcript
The diagram provided shows the
effect of IAA, a type of auxin, on the growth of a plant shoot. What effect does IAA have on the
cells in the shoot? (A) IAA stimulates cell
differentiation. (B) IAA encourages cell
elongation. (C) IAA prevents cell growth. Or (D) IAA helps break down dead
cells in the stem.
Auxins are a group of chemical
messengers called hormones that play a role in stimulating responses in plants. One such response auxins can
control is cell elongation, which can result in directional growth.
The directional growth movements of
an organism like a plant in response to certain stimuli are called tropisms. An example of a tropism controlled
by auxins is called phototropism. And the stimulus it is in response
to is indicated by the prefix photo-, which means light. The diagram provided by the
question shows us phototropism, specifically the growth of a shoot or stem of the
plant in response to a light stimulus approaching from one side.
An example of an auxin, which is
mentioned in the question, is indoleacetic acid, or IAA. IAA is produced by cells in the
shoot tip and diffuses down the stem, accumulating in the cells on the shaded side
of the shoot. IAA stimulates cell elongation in
these shaded cells, causing them to elongate comparatively more than the cells that
are illuminated by the light source. This causes the shoot to bend
toward the direction of the light source in response to light.
Now we have enough information to
answer this question correctly. The effect that IAA has on the
cells of the shoot is (B). IAA encourages cell elongation.
