Cell Theory-Human Cells

cell structure

I love Biryani. I love my body. You ask what’s the connection? As rice makes up a biryani, cells make up our body! The bodies of all the organisms are made up of very small entities called the cell.

The cell is capable of autonomous existence. As.As we all know, the body of all living beings is made up of cells which carry out certain elementary functions. Therefore, a cell is called as the “Basic structural and functional units of living organisms”.

  • Robert Hooke (1665): He was an English researcher who witnessed honeycomb-like dead cells in a thin portion of cork underneath a microscope. He created the word ‘cell ‘, which stands for a small room or box.
  • Anton Von Leeuwenhoek (1667): He first observed and described a living cell.
  • Matthias J Schleiden (1838): He was a German botanist who established by his studies in different plant cells and Theodore Schwann(1839), was an English zoologist established by his studies on different animal cells framed ’cell theory’.


Cell theory was framed by M J Schleiden (1838) and Theodore Schwann (1839). The key values of cell theory are

  • All existing organisms are generated out of cells and products of cells.
  • All cells arise from prevailing cells from the process of cell partition.
  • The body of living organisms is created of one or more cells.

Living Beings show variety in cell number, shape and size

Creation of the electron microscope and staining procedures aided scientists to study the comprehensive configuration of cell. The count of cells varies from a solitary cell to several cells in an being. The creatures composed of a lone cell are known as unicellular organisms. These are capable of independent survival. The individual cell has all the utilities of reproduction, respiration, excretion, and digestion growth. Thus, they are appropriately called a cellular organisms Eg: Paramecium,Amoeba, Euglena, etc.

Staining Technique: It is a method of using dyes like Haematoxylin, Methylene blue, Eosin, Fast green, Saffranine to colour the parts of cells.

The creatures made up of multiple cells are entitled multicellular organisms. The cells in these creatures,vary in their form and size depending on their function. The cells are spherical, oval, polyhedral, discoidal, spindle-shaped, cylindrical in shape. The shape of the cells varies with the functions they perform. Eg:

Parenchyma cells – Polyhedral cells that accomplish storage function.

Sclerenchyma cells – Spindle-shaped cells that are responsible for the mechanical sustenance.

White blood cells – Amoeboid cells that protect the body from pathogens.

Nerve cells – Long and branched that conduct nervous system impulses

Muscle cells – cylindrical orspindle-shaped cells concerned with the movement of body parts

The dimensions of the cell vary from few micrometres (µm) to few centimetres (cm). The size of bacteria differs from 0.1 to 0.5 µm. The minutest cell PPLO (Pleuro pneumonia-like creature) is around 0.1 µ in diameter. The biggest cell is an ostrich egg that has dimensions of 170 to 180 mm in diameter. Some Sclerenchyma fibres can be up to 60 cm in length.Although, the normalize of the cell varies from 0.5 to 10 µm in diameter.

Practise This Question

if a function f(x) is discontinuous in the interval (a,b) then baf(x)dx never exists.