grow in certain directions, not haphazardly. So controlled movements can be either slow or fast. If fast responses to stimuli are to be made, information transfer must happen very quickly. For this, the medium of transmission must be able to move rapidly.
Fill a conical flask with water. Cover the neck of the flask with a wire mesh. Keep two or three freshly germinated bean seeds on the wire mesh. Take a cardboard box which is open from one side.
Keep the flask in the box in such a manner that the open side of the box faces light coming from a window (Fig. . ). After two or three days, you will notice that the shoots bend towards light and roots away from light.
Now turn the flask so that the shoots are away from light and the roots towards light. Leave it undisturbed in this condition for a few days. Have the old parts of the shoot and root changed direction? Are there differences in the direction of the new growth?
What can we conclude from this activity? Response of the plant to the direction of light Figure . Figure . Figure .
Figure . Figure . Plant showing geotropism Electrical impulses are an excellent means for this. But there are limitations to the use of electrical impulses.
Firstly, they will reach only those cells that are connected by nervous tissue, not each and every cell in the animal body. Secondly, once an electrical impulse is generated in a cell and transmitted, the cell will take some time to reset its mechanisms before it can generate and transmit a new impulse. In other words, cells cannot continually create and transmit electrical impulses. It is thus no wonder that most multicellular organisms use another means of communication between cells, namely, chemical communication.
If, instead of generating an electrical impulse, stimulated cells release a chemical compound, this compound would diffuse all around the original cell. If other cells around have the means to detect this compound using special molecules on their surfaces, then they would be able to recognise information,