Phases of Growth of Plants
There are three phases of growth – meristematic, elongation and maturation. We can understand this better by looking at a seed. We already know that the tips of roots and shoots exhibit continuous growth and hence are meristematic. The cells in this region are rich in protoplasm and have large nuclei. The cells next to this region represent the elongation growth phase. In this region, there is the formation of new cell walls, vacuoles etc. The region next to the elongation phase represents the maturation phase in which the cells attain their maximal size.
The number of cells in organisms increases in a number of ways. The increased growth per unit time is termed as the growth rate. This can be expressed mathematically. There are two types of growth rates – Arithmetic and Geometric.
In arithmetic growth rate, out of the two daughter cells produced by the mitotic division of a cell, only one daughter cell continues to divide while the other differentiates and matures.
The following curve represents arithmetic growth phase:
In the case of the geometrical growth phase, the initial growth is slow and it increases rapidly thereafter at an exponential rate. In this, both the daughter cells retain their ability to divide. The following curve represents geometric growth phase:
Conditions for growth
Some of the elements essential for the growth of plants are oxygen, water, and nutrients. Water enters the cells and causes turgidity. This results in enlargement of the cell. Water also provides medium for activities of enzymes. The metabolic energy required for various activities is obtained from oxygen and sometimes nutrients. Optimum temperature, light, and gravity are also required for the proper growth and development of the plant.
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