Video Transcript
In high concentrations, what effect do auxins have on cells in the root? (A) Auxins inhibit cell elongation and growth in the root. (B) Auxins stimulate cell elongation and growth in the root. Or (C) auxins have no effect on the growth of root cells.
Auxins are a group of chemical messengers called hormones that control cell
elongation in plants, among their many other functions. Auxins are capable of stimulating a change in normal plant cell growth. And whether that is increasing or decreasing the rate of elongation depends on where
in the plant they are acting and their concentration.
To answer this question, we need to work out the effect that these hormones have on
cells in the root. Auxins are usually produced in and released from cells in the tip of plant roots and
shoots, as these are often the areas of the plant where most cell elongation, and
therefore growth, is required. From there, auxins can diffuse to the rest of the plant from cell to cell.
In plant shoots, auxins tend to accumulate in cells that are not directly exposed to
light. A high concentration of auxins in the shoot causes the cells in these shaded regions
to elongate comparatively more than those in the illuminated regions. This causes the shoot of the plant to curve toward light, allowing the photosynthetic
cells in the shoot and any leaves attached to it to capture more light for
photosynthesis.
The roots of plants rarely contain photosynthetic cells as they function to burrow
deep into soil where little light is available to absorb water and minerals instead
of capturing light. To accommodate this function, a high concentration of auxins results in the opposite
effect in the roots to in the shoots, inhibiting cell elongation and causing the
roots to turn away from a source of light, which usually results in them growing
downward, deeper into soil.
It is important to note that as most roots are already found under soil where little
light is available, the distribution of auxins in the roots are usually strongly
influenced by other stimuli, such as the downward pull of gravity and even the
presence of water in soil. This can help the roots to grow toward areas where more water is available, usually
deeper in soil, even in the absence of a light stimulus.
Using the information we have learned, we can deduce that the correct answer to this
question is (A). In high concentrations, auxins inhibit cell elongation and growth in the root.
