6. cell organelles- Endoplasmic reticulam

 

It  is      discovered   with    R.porter,   Albert   claude  and  Ernenest  of  F. Fullam in  the year  1945. It  is divided  into  Rough endoplamic reticulam  and   Smooth   endoplasmic   reticulam.  Generally in      resting cells  it  is   limited   and   in  growing  cells  it   is  unlimited.  cells surrounding  an  embryo   have large  endoplamic  reticulam   which one   is  helpful  for  its    nutrition.  If   it   is  associated  with   ribosomes,   an  cell  organelle  it  is  called  rough  endoplamic reticulam    and  the  endoplamic reticulam  with  absence of  ribosomes is  called   as  smooth   endoplamic reticulam.  It  is   a sac  like  structure having  folds.  It  gives  skeletal framework to  the cell.  The  smooth  endoplamic  reticulam  helps  in  the synthesis  of lipids  and glycogen  breakdown.  During cell division, the  endoplamic  membrane  disappear    and   form a   new nuclear  membrane.

5. cell organelles: Mitochondria

In  the  cytoplasm  there are  found minute  thread like, rod shaped  structure  called  Mitochondria  they are also called as the power  house of  cells. It presents in Eukaryotic cells. Liver cells and muscle cells may contain hundreds and thousands of mitochondria.

STRUCTURE OF MITOCHONDRIA:

Mitochondria ranges from 0.2µ to 2.0µ in diameter. It has  double membrane. The outer mitochondrial membrane which encloses the entire organelle, it can associate with  Endoplasmic reticulam. Next one is inner membrane that one is  extended into many plate like structure called Cristae. It extends into inner matrix of  mitochondrion. The inner membrane  is permeable to oxygen, carbon- di- oxide  and water. The space between outer and inner membrane space  is called  inter membrane  space. Each part of  mitochondria has its own set of enzymes. The mitochondria is the respiratory organelles of cells, here  carbohydrates and fats are completely  oxidized into carbon-di-oxide and  water. The energy used during in this oxidation is used for the synthesis of ATP. When this bond ATP is converted into ADP large quantities of energy is released. That energy is used for various types of cellular work. So Mitochondria produces energy for the normal activity of cells. when it fails to work cells will not work because of lack of energy and there is no normal activities of cells of  plants, animals and human beings. when they work  irregularly, which leads  damage to cells of brain, head, skeletal  muscles and respiratory system in humans.  Thus, mitochondria is the power house of cells.

4. Cell organelles: Plastids

     In  the cytoplasm there  are  a number of  small rounded or ellipsoid bodies called plastids. Plastids are found in Plants.  They  have special pigments called Chlorophyll. They have the capacity to  synthesise substances like starch and protein. 

A.   CHLOROPLASTS:

    Plant  chloroplasts are large sac like organelles about  5 to 10µm long having three membrane namely inner outer and thylakoid membrane. Thylakoid membrane forms a  network of flattened disc called thylakoids which are frequently arranged in stacks called grana. They are inter connected  by a tubular structure called stroma lamellae. A thylakoid has a flattened  disc shape structure inside it has  empty space called  thyllacoidel  space or lumen. DNA  and several types or RNA have been discovered  in association with chloroplasts. In the presence of sunlight  the chloroplasts produce carbohydrates from carbon-di-oxide  from the atmosphere.

B.   CHROMOPLAST:

    In the petals of many flowers which are coloured yellow or red. Here there are plastids have the capacity for developing and retaining pigments called Xanthophyll and carotin. They are irregular in  shape and are called chromoplasts.

3. LEUCOPLASTS:

     In  underground plant parts like the stem and roots are found certain  colourless plastids called leucoplasts. They have the capacity for forming starch from soluble sugers. These three plastids are inter connected and capable of getting converted into another. The  chloroplasts get converted into leucoplasts  in the absence of light. Leucoplasts become chloroplast when exposed to sunlight.