Photostropism
Phototropis is one of the many trophic movements in plants.
In other words, it is a growth movement in response to an external stimulus. In this case,
the stimulus is light. Other stimulus ncludes grabity and water. Due to the theme of this
section, we shall firmly adhere to how light can cause movements in certain plant parts.
When phototropism takes place, shoots grow towards a light
source when light is emitted to absorb maximum light for photosynthesis to take place.
This is known as positive phototropism. Other plant parts such as the
leaves will also orientate themselves to receive maximum sunlight.
However, in another case, not all plants parts respond in
the same way to light. For instance, roots will move away from a light source. This is
thus, known as negative phototropism.
Let's now take a look at how the shoot respond to light.
Consider the following growth movement by a shoot :
When the side of the shoot tipis exposed to light, one side
will turn towards the light . Why is that so? There is the presence of a growth hormone
called auxin in the plant shoots. Its concentration is higher on one side
of the shoot when it is exposes to light. Thus, in other words, the part of the shoot that
is shaded from the light will develop a lower level of auxin.
As such, when auxin level increases on one side of the
shoot the cells on the shaded side will grow and elongate faster than the cells on the
shoot tip being exposed to light. Thus, we observe that the shoot bends towards light.
Isn't it amazing how plants can respond cleverly to light?
