Grade 9 - Plant Growth Substances
For Sri Lankan's Overseas

Grade 9 - Plant Growth Substances

Grade 9 - Plant Growth Substances

Plants can be cited as the silent workers on earth and their existence is paramount for the balance of nature, the sustenance of life and terrain. In addition to the natural factors like water, air, minerals and sunlight, chemical substances such as auxins, gibberellins and cytokinins. The chemical compounds that control the growth of plants are commonly known as plant growth substances. It should be noted that only some of the plant growth substances promote plant growth while some hinder it. The substances that promote plant growth can be named as auxins, gibberellins and cytokinins.  


Auxins can be portrayed as a substance that promotes the growth of plants and it is cited as a growth promoting hormone that is typically produced in the tips of plant roots and shoots. This hormone boost the elongation of cells at roots and stems.  As light falls on the plants, auxins tend to diffuse downwards and it increases the pace of new cell growth. Moreover, it speeds up the upward growth of the plant shoots.  IAA or Indole-3acetic acid is the auxin that is found in plants in abundance.  Auxin is stored more in the sides that receives less intensity of light and it tends to shift to the darker side of the plant. This enables the cells to grow longer than those located on the other side of the plant where we can observe a stem tip that is curved towards light.



The above is cited as the phototrophic movement. Auxin is a hormone that acts as a barrier to the growth of the lateral buds. The stem elongation and the growth of fruits in plants are boosted by the hormone called Gibberellins. Cytokinins boost cell division where it improves the growth of leaves, roots, fruits, and flowers and seed germination. This hormone delays plant ageing.  The leaf fall and fruit fall are two natural phenomena that occur in plants. If we observe a naturally fallen leaf stalk, there is a abscission layer that is typically created when the fruits or leaves tend to lose the amount of growth substances in them. We have discussed about the natural growth substances plants. It deserves mentioning that in horticulture and in the case of ornamental plants, artificial growth substances like Cytocell, 2,4 DPA, IAA, IBA and NAA. 







by Mekhala Egodawele

Photo source : Internet