A CELL-AND ITS ORGANELLES

Every living organism is made up of small  basic  units called 'cell'. A cell is called as a basic structural and functional unit of an organism. The cells are the building blocks of a body. The size of a cell is very very small starting from 0.5 microns to 1 micron . The smallest cell is a bacterial cell which is 0.5 micron whereas the biggest cell is an ostrich egg cell which is 18cm×17cm.

 Every cell has its own particular structures called organelles which are very very important because each carry out their own specific function.

A typical cell consists of the following organelles:

NUCLEUS: The central dark black color spot present in the cell is called nucleus.  It is also called as "CONTROL ROOM OF THE CELL". It has all genetic material which can be either DNA or RNA . This genetic material is responsible for passing the characters from parents to children. The nucleus is also involved in cell division.

CYTOPLASM: The fluid present inside the cell which holds all the cell organelles in it is called cytoplasm.

Before it was thought to be the essence of life hence it was named as 'protoplasm' meaning ' life fluid' but when the nucleus was discovered and it was found that the new life originates from the nucleus and cytoplasm is only the fluid content of  cell ,then the name protoplasm was changed to 'cytoplasm 'meaning  " cell fluid".

CELL MEMBRANE: The outer covering of a cell is called cell membrane or plasma membrane. It gives shape and size to the cell and encloses and protects cytoplasm.  It is made up of lipids and proteins . It selectively allows the exchange of substances across it hence it is called as " selectively permeable membrane.

MITOCHONDRIA: The minute black dots found scattered in cytoplasm are the mitochondria. They are also called as " power houses of the cell" because they are involved in providing the energy needed through cellular respiration. They are very small about 0.5 nano metres about 100 to 150 times s aller than the nucleus.Around 150 to 200 mitochondria are found in every cell. They are double layered structures whose outer layer is smooth but inner layer is folded inwards into finger like projections called ' cristae' and the space in between the cristae' is called ' matrix'.

ENDOPLASMIC RETICULUM: The membranous structures found in the cytoplasm are called ENDOPLASMIC RETICULUM. They create passages in the  to transport substances across the cell. Some membranes have black granules ( called ribosomes) on their surface hence called as " ROUGH ENDOPLASMIC RETICULUM"(RER)  whereas some membranes do not have granules on them hence they are called as "SMOOTH ENDOPLASMIC RETICULUM" (SER).The RER  helps in making or synthesis of proteins and SER helps in making of lipids . The SER of liver cells also helps in detoxification of poisons and drugs.

GOLGI BODIES: The membranous structures with the vesicles at their ends are called Golgi bodies or Golgi apparatus . They were first discovered by Camellio Golgi in 1898 . They are the packaging units of the cell. All the substances are packed and sealed here before transferring to endoplasmic reticulum.

LYSOSOMES:  Tiny structures found in the cells are lysosomes which has digestive enzymes in them . When any substance has to be be destroyed,they are sent to lysosomes,then the lysosomes burst to release their enzymes . These enzymes then digest those harmful substances or sometimes the whole cell hence they are also called as "SUICIDAL BAGS OF THE CELL"

RIBOSOMES: The black granules found either on the surface of reticulum or scattered freely in cell are called ribosomes. They can be free on bound on reticulum. They are the sites of protein synthesis.

PLASTIDS : These are the special organelles present only in plant cells to carry out photosynthesis. These are of three types. Chloroplasts, green plastids ,containing green color pigment called chlorophyll. Leucoplast, the colourless plastids and the Chromoplasts, the coloured plastids .

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VACOULES:  The large empty spaces present in the cells to store food and fluids are called vacoules. They also remove unwanted substances from the cells. Plant cells have bigger vacoules compared to animal cells . In some plant cells they occupy almostvthe entire cell.