The cells in theses systems vary in shapes and sizes and
have their own specific functions to perform. A cell is made up of membrane,
cytoplasm, lysosmes, nucleus, endoplasmic reticulum, mitochondria and Golgi
complex.
A cell is surrounded by membrane which forms its outer
wall. It is a very thin layer and allows food and oxygen to pass into the cell
and substances made by the cell or waste products to pass out. Membrane
separates cells from one another and gives shape to each cell.
Cytoplasm is a watery, jelly like material which
surrounds the nucleus of the cell. It is living, colorless, translucent and
granulated. All the parts of the cell float in it.
Liposomes are circular tiny packets of digestive
chemicals which can destroy harmful substances or worn out parts of the cell.
They also play an important part in cell division.
Nucleus is a compact body. It is the control centre of a
cell. It contains the chromosomes and DNA of a cell. DNA keeps the cell alive
doing its own special job.
Endoplasmic reticulum is the folded, membrane like
structure in the cytoplasm. Their main function is to transport substances
throughout the cell.
Mitochondria are the cell’s powerhouses. The energy
needed for cellular activities is released here from food and oxygen.
The Golgi complex is the flat arrangement of pockets
where some substances are stored and others are prepared for used outside the
cell.
Different types of cells
Human body has different types of cells. Some
of the smallest cells are in the brain, measuring only 0.005mm. The largest are
the ovum or egg cells with a diameter of 0.2ml. Cells differ in shapes and
sizes. Some of them are round/circle and some are flat. Muscle cells are long
and cylindrical in shape up to 60mm in length.
Tissues and Organs
Despite being independent units, the cells often work
together. The cells performing similar function form a tissue. Every tissue has
its special function to perform.
They are structured differently according to the task they
perform. Muscles, bones and nerves are three different types of tissues.
Life of Cells
Living cells grow and many of them reproduce themselves so
that a body can grow larger and replace the damaged or dead cells. The life
span of some cells is only a few days while some others can live for weeks,
months or years. Bone cells last for about 15-20 years, while white blood cells
only for four months. Skin cells do not live more than 3 weeks. Nerve cells do
not have any reproductive property; therefore, they end with the life itself.
Internal Structure of an Ordinary Cell
Nucleus
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