Are the plants colour sensitive?

By Upali Salpadoru
Prior to working out the details of the project Nelly grasped it with the help of this diagram. Can they distinguish a colour and grow towards that? The results of this experiment may even help NASA who are trying to grow plants in space vehicles bound to distant worlds.
It is a well known fact that the plants grow towards light. This sensitivity is exhibited in many ways. The sunflowers follow the sun from dawn to dusk. For what purpose? No body seems to know. Lotus flowers open in the morning and close as the sun sets. The compound leaves of the legume family close at night. It is generally believed that this is an adaptation to reduce the loss of water. But even when there is a plentiful supply of water they continue this exercise.
Plants need light for the vital function of ‘photosynthesis’. (Making of food by combining carbon dioxide and water using light energy) This can be performed only by the green matter called Chlorophyll. These are generally the leaves and the young shoots. What about the other growing parts that lack chlorophyll, such as the roots? Do they grow towards light(Positive) or away from light (Negative) or remain unconcerned (Neutral).
Lights have colours. Sunlight is supposed to be white. (not at sun rise or sun set) The human eye is capable of differentiating six to seven colours. [ROY Grows Blue Violets… Red,Orange,Yellow,Green,Blue and Violet] Some animals are believed to see ultra violet and infra red too. How many colours can the plants detect? What are these colours? What experiments can we devise and carry out in order to solve this problem? Lack of which colour will make some leaves fold?
To find the Favourite colour of seedlings.
When baby shoots and the roots are coming out of the seeds they are called seedlings. Ali wanted to find out which colour will attract the baby shoots and the roots. He took a light proof circular box and fixed three LEDs on the sides. LEDs have been chosen as they need very low current. They were connected to a battery as shown here. The blue circle shows the negative wire while the positive is shown by the red circle. Three seedlings, may be mustard, green gram or any other were placed in the centre. They could be horizontally placed on moist paper. The box has to be covered from above. Lights have to be switched on only after the roots and shoots have come out.
To find the colour that will accelerate plant growth.
Ali and Nelly planned this experiment using the stored up Wesak lanterns (buckets). These are weather resistant and allow only certain colours to pass through. By placing the cover over a few stones it is possible to allow some ventilation. It was a long term experiment that had to be done in the garden.
They selected a few plants of the same kind and size in their garden. Two plants are shown in the diagram.
Each one is covered with water proof coloured paper.
The first plant receives only red light while the other one gets only blue light. The wire which is used to hang the lantern is cut in the middle and used to tie the lantern to pegs in the ground. Some stones or sticks may be kept at the base to permit ventilation. It is very important to attend to the needs of the plants. The soil must supply air, water and the mineral salts. All plants must receive the same amount of sunlight. They must be protected from insects etc.
The number of similar experiments that could be done will depend only on your ingenuity. If you do these experiments, and maintain reports your teachers will help you to prepare them for publication in the school magazine, or you may even send them to us.









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