Structure of cell:-
The structure we visualize through electron microscope is known as ultra structure. The cell consists of the main parts such as , the cell membrane, cytoplasm, and nucleus.
Cells vary in their size and shape. Different organisms have different structures. Bacterial cells are spherical, yeast cells are oval, euglena have spindle shape, and amoeba have irregular structure. Size of a cell varies from a few microns to several millimeters.
The cell is covered by a thin membrane is called cell membrane or plasma membrane. Both plant and animal cells consists of cell membrane. The cell membrane allows only certain materials to pass in and out of the cell. Therefore it is known as semi permeable membrane. Cell membrane also maintains the shape of the cell.
Following are the forces which bring about the movement of material in and out of the cell membrane.
Diffusion:– it is a physical process where a random movement of molecules from a region of higher concentration to lower concentration. The difference in the concentration is known as concentration gradient.
Osmosis :- it is a special type of diffusion. It involves the movement of water molecules from the region of higher concentration to a region of lower concentration through a semi permeable membrane.
Cytoplasm :- cytoplasm is gel like material inside the cell membrane. Cytoplasm contains a large amount of water and many chemical substances. The different structures of cells are suspended in the cytoplasm.
The structure inside the cell are called as organelles. These are of two types.
- membranous organelles.
- non membranous organelles.
Membranous organelles: these organelles composed of membrane.
Endoplasmic reticulum:- it is a cytoplasmic structure which provides network inside the cell. It extends from plasma membrane to the nucleus. The rough endoplasmic reticulum contains ribosomes on it’s surface. It helps in transport of substance from one part of the cell to other.
Golgi complex :– it is a bag like organelle having a number of flattened membranous structures placed one above the other. Exact function of golgi complex is unknown, but believed as it involved in secretion of chemicals.