The nucleus consists of a more compact mass of
protoplasm, separated from the cytoplasm by the nuclear membrane which is also selectively
porous, allowing substances to escape from the nucleus into the
cytoplasm or substances to pass into it. The nucleus controls the cell and all
its activities. Without a nucleus the cell would die.
The nucleus contains many protein-rich threads lying
in nuclear sap. In the ‘resting cell’ the threads are collectively spoken of as
chromatin. These threads or chromosomes are vital to the everyday activities of
the cell and are responsible for determining the hereditary characteristics of
the human body. On the chromosomes in linear arrangement sit the genetic or
hereditary determinants, the genes. The number of chromosomes in
a body cell is constant for a particular species of organism. In man there are
twenty three pairs of forty six chromosomes.
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