BASIC STRUCTURE OF A CELL

Every cell has three important structures . The nucleus, cytoplasm and cell membrane.

THE NUCLEUS : The dark circular spot present inside the cell is called nucleus. It controks all the functions of cell hence it is called " control room of cell". It has genetic material either DNA or RNA which helps in passing the characters from parents to offsprings. The nucleus also plays a major role in cell division.

The membrane covering the nucleus is caller nuclear membrane. The fluid present inside the nucleus is called nucleoplasm.

Based on the presence or absence of nucleus ,the cells can be of two types: 

PROKARYOTIC CELL: 

The cells which do not have membrane bound nucleus are called prokaryotic cells Such organisms are called prokaryotes . Ex: Bacteria, cyanobacteria , blue green algae etc.

EUKARYOTIC CELLS: 

The cells which has membrane bound nucleus are called eukaryotic cells . Such organisms are called eukaryotes . Ex: All higher plants and animals. Few exceptions are RBC's in infants and Phloem tube cells in plants.

THE CELL MEMBRANE: It is also called as plasma membrane.The outer covering of any cell is called cell membrane. It is made of lipids and proteins . It gives the shape and size to the cell and encloses and protects the cytoplasm . The animal cell has only one outer layer ,cell membrane but the plant cell has an additional layer over the cell membrane called cell wall. The cell wall is tough and fibrous layer and is made of cellulose . It gives protection to the cell and exerts an inward pressure called turgor pressure to balance the outward pressure exerted by the cell sap because of this the plant cell is able to withstand the extreme weather  changes in its surroundings.

The cell membrane or plasma membrane also helps in selective passage of substances accross the cell ,hence it is also called as selectively permeable membrane.

THE CYTOPLASM:  The jelly like fluid present inside the cell surrounding the nucleus is called cytoplasm. It acts like a floating medium which holds all cell organelles in it. Before it was thought that new life arises because of cytoplasm hence it was called as protoplasm which means life fluid' but when it was discovered that new life originates due to the nucleus and cytoplasm is just a fluid in the cell ,then it was renamed as cytoplasm which means cell fluid.