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Growth and Development

   

   

  • Growth and Development

    Growth may be regarded as the permanent and irreversible increase in size of an organism. It involves a permanent increase in such measurable aspects as length, weight, width and so on.

    Development on the other hand is the gradual change in form and complexity of an organism in the course of its life. It involves modifications of cells formed during cell division into different shapes to form specialized tissues.
    Many changes that occur during development of an organism are not measurable.

    Germination

    Germination is the process through which a seed develops into a seedling. For the process to occur water is absorbed through the micropyle in a process called imbibition causing the seed to swell. The water taken up is used to dissolve and break down the stored food in the cotyledon into soluble food substance, which is then taken to the growing regions of the plumule and radicle.

    A seed embryo germinates into a seedling with a radicle developing into a root as the plumule develops into a shoot. The radicle increases in size forming roots which may assume different shapes i.e. Specialized roots. The plumule develops into the shoot system which differentiates into stems, branches, leaves and flowers.

    There are 2 types of germination

    Epigeal germination
    Hypogeal germination.


    Epigeal germination

    If all the necessary conditions for germinations are present, the radicle emerges first, grows out through the micropyle down into the soil as a primary root and other roots arise from it. The part of the embryo between the cotyledon and the radicle is called hypocotyl. The hypocotyl curves and pushes upwards protecting the delicate shoot tip, then straightens and elongates carrying the cotyledons above the soil level. This type of germination is called epigeal germination.

    Hypogeal Germination

    If all conditions are availed, the radicle emerges first, along its protective covering called coleorrhiza. The radicle grows down and develops some root-hairs behind its tip. Other adventitious roots arise from the base of stems producing a fibrous root system. The part of the embryo between embryo and cotyledon is called epicotyl. The epicotyl elongates above the soil and allows the plumule to grow out of its sheath (the coleoptiles) to form the 1st foliage leaves and start manufacturing food. The cotyledons remain below the ground but the stored food is broken down and transported to the growing region making it shrink and reduce in size. The cotyledon then withers away. This type of germination is known as hypogeal germination.

     

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