Question

What is a cell?

Answer 1

Robert Hooke in the year $1665$ examined a thin slice of cork and while doing his observations he saw that cork resembled the structure of a honeycomb consisting of many little small compartments. Robert Hooke called these compartments (boxes) as cells. Cell is a Latin word. It means ‘a little room’. He did his observations through a self-designed microscope. This was the very first time in the history of science that someone has observed that living things appear to consist of separate units and today in the world of biology these units are known to be cells.

Complete answer:
Cell is the basic structural and functional unit of all living organisms. Each cell has the capacity to perform basic functions that are characteristics of all living forms.
A cell has the capacity to replicate itself hence it is known as the building block of life. Each and every cell contains a fluid called cytoplasm. Cytoplasm is enclosed by a membrane called plasma membrane or cell membrane. Inside cytoplasm there are certain specific components in it which are known as cell organelles. Each cell organelle performs special functions, such as making new material in the cell, clearing up waste material from the cell and so on. Because of these organelles, a cell is able to live and perform all its functions. All the cells have the same organelles, no matter what their function is or what organisms they are found in.
It is known that a single cell may constitute a whole organism like in amoeba, Chlamydomonas, paramecium and bacteria. These organisms are known as unicellular organisms. On the other side there are many cells grouped together in a single body performing different functions in it and forming various body parts in a multicellular organism such as fungi, plants and animals. Some organisms have cells of different kinds and the shape and size of cells are related to the specific function they perform. Some cells change shape like amoeba and some are peculiar for their particular type like nerve cells.
Based on the structure of the cell, there are two types of cells:
Prokaryotic cells
Eukaryotic cells
A typical cell is made up of following: outer cell membrane, cell wall in plants, inside nucleus which is separated by a well nuclear membrane in the eukaryotic cell, nucleus and cell membrane separated by a fluid called cytoplasm and various cell organelles which are responsible for performing certain specific functions to carry out life’s processes. These are: endoplasmic reticulum, plastids in plant cells, Golgi apparatus, lysosomes, mitochondria, vacuoles.

Note:
Cells were also observed under compound microscope with higher magnification by Anton Van Leeuwenhoek who concluded that the cells are alive, they possess motility and cells were named animalcules. Robert Brown in $1883$ provided the first insight to cell structure. He described the presence of nucleus present in the cells of orchids. Various functions of cell are as follows:
It provides support and structure.
It facilitates growth mitosis.
It allows transport of various substances.
Energy production.
It aids in reproduction.