Video Transcript
Where in a plant are the highest
concentrations of auxins found? (A) In the tip of the stem. (B) In the pollen of the
flowers. (C) In the wall of the xylem. Or (D) in the guard cells of the
stomata.
To answer this question, we need to
work out where the highest concentration of auxins are found in a typical plant. Auxins are a group of chemical
messengers called hormones that can control cell elongation in plants, among their
many other functions. The majority of auxins are produced
and released from cells found at the tip of plant stems and roots. From there, auxins diffuse to the
rest of the plant from cell to cell. The action of auxins in plant stems
is especially important for various reasons. For example, the stems and any
leaves that may be attached to them usually contain the majority of a plant’s
photosynthesizing cells.
Remember, photosynthesis is the
process by which plants use light energy, carbon dioxide, and water to synthesize
sugars like glucose, providing the plant with a food source. As this process requires light, it
is imperative that the stems of a plant are able to grow in the appropriate
direction to respond to a light stimulus. This is achieved with the help of
auxins, which accumulate on the shaded side of the stem when the light source is
arriving from one side, stimulating those cells to elongate comparatively more than
those on the illuminated side of the stem. This results in the stem bending
toward the light source.
This directional growth movement of
the plant stem in response to light is called phototropism. And it helps to expose the
photosynthesizing cells to more light. As phototropism is controlled by
auxins, high concentrations of auxins must be continually produced in the tip of the
plant stem to allow these directional growth movements in response to light. This means that the correct answer
to this question is (A). The highest concentrations of
auxins are found in the tip of the stem.
