Cell

Cell-organelles and Cell-inclusions

Cell-organelles are living sub-cellular structures of the cytoplasm having of the cytoplasm having definite structures and functions and are also known as protoplasmic bodies or organoids.These organelles are the main sites for the various cytoplasmic activities.The cell-organelles are of two types: Some related to the chemical work or metabolism of the cytoplasm, and the others related to the mechanical works.

The organelles related to the chemical work of the cytoplasm are as follows:

1). Mitochondria
2). Plastids (Only in the plant cells)
3). Endoplasmic reticulum
4). Golgi complex
5). Lysosomes
6). Ribosomes
7).Microsomes
8).Microbodies and peroxysomes


Mitochondria

     Mitochondria were first discovered by kolliker(1880 A.D) in the voluntary muscles of insects.Later an Altmann (1890 A.D) made systematic observations and named them as bioplast . The term mitochondria (GK moto=thread;chondrion=granule) was given by C.Benda (1898 A.D).The mitochondria are granular or filamentous cytoplasmic structure also known as "the power house of the cell"as they release energy in the form of ATP during aerobic respiration for the vital activities of cell.

Plastids (Only in the Plant cells)

    The plastids are the double membrane bounded cytoplasmic organelles of the cell of plants and some protozoans such as Euglena.They develop from small bodies called proplastids found in the meristematic regions.They are absent in bacteria, blue green algae, fungi and animals which contain chromatophores instead of plastids.They may be colourless or coloured.One form of plastids can change into another form.For example in tomato the young ovary contains leucoplasts which change into chloroplasts in young fruits and family into Chromoplasts as the fruit ripens.
 The term plastids was given by Haeckel (1866 A.D.) Schimper,(1883 A.D.) divided plastids in two types:
1). Chloroplast
2). Chromoplast

Chloroplast:(GK.chloros=green;plast=living)

      The most common of the plastids are the chloroplasts.They are very important for the plants, because photosynthesis by which complex organic food is manufactured, takes place in them.Chloroplasts were first observed by Antony Von Leeuwenhoek in 1679 A.D.The term chloroplast was given by Schimper (1883 A.D.) These are green plastids possessing green pigment,the chlorophyll.
It is commonly called as "kitchen of plant cell" because food is prepared from CO2 and H2O during photosynthesis.

Chromoplasts:(GK.Chroma=coloured,plast=living) 

     These are coloured plastids which contain varieties of pigments other than green.They are found in coloured parts of plant such as flowers, fruits,etc.These are formed either from the chloroplast by the replacement of chlorophyll with other pigments (e.g.,red pigment lycopin in tomato and chillies) or from the leucoplasts by the development of some pigments (e.g., carotenes in carrot roots).The Chromoplast may also contain anthocyanin a group of colouring matter dissolved in the vascular sap of petals which provides violet, purple, blue, brown and often red colour to the flowers.


           Chloroplasts are also bounded by double layered membrane which encloses matrix or stroma, but there is no lamellae and grana.The Chromoplasts are angular or needle shaped structures.

Types of Plastids

According to their structure, pigments and functions Schimper classified the plastids into following three types.
1.Chloroplast
2.Chromoplasts
3.Leucoplasts

Leucoplasts (GK.Leuco=white,plast=living)

      These are colourless plastids found in embryonic cells,germs cells, meristematic cells,and plant parts which are not receiving lights.They are mainly involved in storage of food materials.According to the nature food storage, leucoplasts are of three types: Amyloplasts(store starch e.g., potatoe tuber , grains of rice, wheat, maize,and millet),Lipoplasts or Elaioplasts(store lipid e.g., seeds of many monocot and dicots)and Proteinoplasts or Aleuronoplasts(store protein e.g., seeds of pulses).

Endoplasmic reticulum

     It is a well developed electron microscopic network of interconnected cisternae, tubes and vesicles present throughout the cytoplasm, especially in the endoplasm of eukaryotes, therefore known as endoplasmic reticulum.ER divides the intra- cellular space into two distinct compartments.Normally,it forms 30-60% membrane system of the cell thus increasing the internal surface 30-40 times as compared to external surface.

      Though ER was first observed by Garnier(1897 A.D) but its ultrastructure was first given by Porter,Claude,and Fullam(1945 A.D).The term "Endoplasmic Reticulum" was given by Porter (1953A.D).



Golgi complex 

       Golgi bodies were first observed by George (1867 A.D), later describe by an Italian Neurologist Camillo Golgi (1898A.D) in nerve cells of barn owl and cat.It is known as Golgi apparatus  or Golgisomes or Lipochondria or Idiosomes or Dalton complex or Baker's body or Dictyosomes .
 
       Golgi body is formed of unconnected units called Dictyosomes (term given by Perroncito,1910 A.D).It is also called "traffic police of the cell."

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