CELL

WHAT ARE CELLS?

 

It is very interesting to know that cell are the fundamental unit of life, all the functions are carried out by the cell, they are not visible through naked eyes. Cell is a Latin word for 'a little room'.

OK, so who discovered cell?

 There were many people who were involved in the study and discovery of cell:

Image of a cell

• ROBERT HOOKE,1665 - was the first one that saw the structure of a honeycomb consisting of many compartments inside of a cork (bark of tree) though a self designed primitive microscope and he called these boxes cell.

• LEEUWENHOEK,1674 - with his improved microscope discovered free living cells in the pond water for the very first time.
• ROBERT BROWN,1831 - discovered nucleus of the cell.
• PURKINJI,1839 - coined the term 'protoplasm' for the fluid substance of the cell.
• SCHLEIDEN ANS SCHAWNN,1839 - explained all the plants and animals are composed of cells and cells are the basic unit of life.
• VIRCHOW,1856 - expanded the theory by suggesting that all cells arise from pre -existing cell.

There are hundred type of cells present in a human body, but few of them are most common and important ones:

• Smooth muscle cells - Muscle cells form muscle tissues, which enables all bodily movement.
• Blood cells - It transports oxygen throughout the body, fight against infection and helps in clotting of blood if got any infections, and also helps in clotting by forming a mesh like structure. Blood cells are produced by bone marrow. There are mainly three types of blood cells RED BLOOD CELLS, WHITE BLOOD CELLS, PLATELETS.
• Nerve cells - They send signals between brain, spinal cord and other body organs via nerve impulse.
• Fat cells - They are also called adipocytes, containing droplets of stored fats that can be used for energy.
• Ovum - They are also called female gametes, are not motile in nature and comparatively large in size. 
• Sperm - They are also called male gametes, and are motile in nature, they fertilizes the ovum to form a new individual.
• Stem cells  - It have the ability to build organs or tissues from a unspecialized cells. 

  

  Stem cells building up new cells

Cells are surrounded by cell wall and then plasma membrane which is a semi permeable membrane and animal cells are only surrounded by only plasma membrane.

CELL WALL-  It is a rigid outer covering which lies outside of that of the plasma membrane and is mainly made up of cellulose. This is totally permeable membrane.

YOU ALL MUST BE THINKING WHY IS CELL WALL PROVIDED ONLY TO THE PLANT CELL?

HERE'S THE ANSWER.

• It provides structural strength to the plants due to cellulose.
• Because of their walls, such cells can withstand much greater changes  in the surrounding medium than animal cells(such as osmosis).

So, what's exactly inside of a cell?

• CELL ORGANELLES
• NUCLEUS
• cytoplasm

There are many types of cell organelles present inside of a cell like GOLGI APPARATUS, MITOCHONDRIA, ENDOPLASMIC RETICULUM (ROUGH), ENDOPLASMIC RETICULUM (SMOOTH), PLASTIDS, VACUOLES, RIBOSOMES etc.  but to deal with genes, chromosomes, protein formation and all the stuff related with genetics we need to know about RIBOSOMES and NUCLEUS.

TO begin with Genetics, we first need to know how are the cells divided.

They are divided in 2 ways:

• MITOSIS - Division of a cell into two halves with same number of chromosomes.
• MEIOSIS - Division of a cell into four cells containing half the original number of chromosomes.