Video Transcript
Which of the following is a correct
function of auxins in a plant? (A) Inhibiting plant growth in
summer months, (B) increasing the lignification of plant cells, (C) preventing
pathogen entry, or (D) stimulation of cell elongation in the stem.
Auxins are a group of chemical
messengers called hormones that have many different functions. To answer this question, we need to
investigate some of the key functions of auxins in plants, so let’s dive right
in.
Auxins are produced in the tips of
plant roots and stems and can diffuse throughout the rest of the plant from cell to
cell to cause their various effects. For example, auxins produced in the
cells at the tip of the stem diffuse downward to the cells below. A high concentration of auxins in
these cells triggers a series of events that stimulates cell elongation, and
therefore the growth of the stem.
If a light source arrives from
directly above the stem, auxins diffuse down the stem equally and results in
symmetrical cell elongation on all sides of the stem. This causes the stem to grow
directly upward toward the light source coming from above. If the light source arrives from
one side, auxins accumulate in the cells on the shaded side of the stem, causing
these cells to elongate comparatively more than those on the illuminated side. This asymmetrical cell elongation
causes the stem to bend in the direction of light.
The directional growth movement of
the stem in response to light is called phototropism. Phototropism helps to expose the
plants photosynthesizing cells, the majority of which are found in the stem and any
leaves that might be attached to it, to more light so that they can carry out
photosynthesis more efficiently to produce their own food. We’ve found the correct answer to
this question, (D). A function of auxins in a plant is
stimulation of cell elongation in the stem.
