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Sub-Topic 3: Growth
Meaning of Growth
Growth is defined as an irreversible increase in size and mass due to formation of new protoplasm in the cell. Whenever the anabolic processes proceed at a faster rate than the catabolic process, there will be a supply of new substances to cause growth.
The three distinct processes that contribute to growth are cell division, cell enlargement and cell differentiation. In cell division, the nucleus and then the cytoplasm of the parent cell divide to form two daughter cells, then into four and so on bringing about an increase in the number of cells.
The daughter cells then increase in mass and size (i.e. enlarge) and eventually develop into a special type of cell (i.e. differentiate) by changing its shape and structure to carry out a particular function. The kind of cell it becomes depends on its position in the body of the organism. It may develop into a nerve cell in the brain, a muscle cell in the heart or a ciliated lining cell in the trachea.
Root Tip Showing Apical Meristem
This lengthwise section of the tip of a plant root shows the apical meristem, which, with its rapidly dividing cells, is responsible for primary growth. Apical meristem can also be found at the tips of stems.
Basis of Growth
Cell division (mitosis) is the basis for growth in all multicelluar organisms. Mitosis is the cell division which occurs in the body cell (somatic cells) during which a parent cell divides to produce two daughter cells having the same number of chromosomes as itself.
Mitosis does not occur in all the cells of growing region of the organisms e.g. the root tips or shoot apices and cambium that undergo mitosis. These growing regions are described as meristems.
Cell division by mitosis occurs in four successive phases of continuous sequence namely prophase, metaphase, anaphase and telophase. Between the end of one mitosis and the commencement of a new mitotic division is a period described as interphase or pre-mitotic phase.
Interphase is not a resting time, but a period during which the young daughter cells accumulate and synthesize new body materials, thus preparing itself for the next division.
Diagram showing the growth of embryo
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