Plants are living things, just like you and me, and like us they have needs to survive. The require food, water, nutrients and light.
Since they can’t get up and walk to a water source, food source or light source, they have developed methods to attain these resources.
Tropism is a growth in response to a stimulus.
Plants grow towards light, water, nutrients and sometimes against gravity.
Tropism can be Positive or negative.
Positive tropism – is growth towards the stimulus.
Negative tropism – is growth away from the stimulus.
If we place a plant on the windowsill, it will bend towards the light.
It doesn't move towards the light, but grows towards the light.
This is an example of Phototropism. Growth towards a light source is an example of Positive phototropism.
If you look at seeds grow, you’ll see the roots growing down and the stem growing up.
This is an example of geotropism.
The roots show positive geotropism, as they grow with gravity downward.
Stems show negative geotropism, because they grow up against gravity.
If we cover the tip of the plant however, the plant doesn’t seem to respond to light stimulus.
If we look at the video to the left, we see how the plant continues to grow straight when covered but towards the light when not.
Auxin is the plant hormone released from the tip, down the plant. Telling one side to grow faster than the other, so it bends towards the light.
The cells on one side will elongate faster than the other side. Causing it to bend in one direction.