How Many Cell Types are There

Edited By Team Careers360 | Updated on Jun 20, 2023 12:12 PM IST

Introduction

The cell is the structural, functional, and biological unit of all known living organisms. We may compare cells to the bricks that are assembled to make buildings. It assembles cells to make the body of every organism. Robert Hooke made the first discovery of cells in 1665 when he noticed that the cork cells were dead cells.

Shape and Size of Cells

Cells can be of different types and sizes. It can be different for different organisms and may also vary from the cell of one organ to the other in the same organism.

Cells are round or elongated in shape, but some cells are long and pointed at both ends (a spindle shape), whereas some are quite long.

It related the shape and size of cells to specific functions that they perform. Sometimes, the cell shape could be more or less fixed and peculiar for a particular type of cell, like nerve cells, which have a typical shape.

Number of Cells in Living Organisms

All organisms are composed of cells. Some cells that can exist as independent organisms are called unicellular organisms, like amoebas.

Multicellular organisms are those that comprise more than one cell, like fungi.

Every multicellular organism comes from a single cell. Cells also divide to produce cells of their kind, and different organs perform their functions like blood cells, nerve cells, etc.

Characteristics of cells

Cells are capable of independent existence, and they can replicate independently.
They contain hereditary information which passes from one generation to another.
Each living cell can perform certain primary functions depending on its location.
Several cells are present depending on the size of an organ or body organization.

Types of cells

Based on the structure, cells are of two types:

Prokaryotic
Eukaryotic

Prokaryotic cells

The cells having nuclear material without a nuclear membrane are termed prokaryotic cells. These are smaller and not very complex in structure.

These are essentially the infoldings of the cell membrane. In prokaryotes, the nuclear region (containing only nucleic acids), called the nucleoid of the cell, may be poorly defined due to the absence of a proper nuclear membrane.

Prokaryotic cells also lack most of the other cytoplasmic organelles present in eukaryotic cells, like those present in bacteria clostridium, blue-green algae, etc.

Eukaryotic cells

The cells, like onion cells and cheek cells, have a well-organized nucleus with a nuclear membrane, termed eukaryotic cells.

These cells are more complex than prokaryotic cells. They separated the nucleus from eukaryotes by a double-layered membrane, and it directs the life process of the cell like the eukaryotic cells are present in protists, fungi, plants and animals, etc.

These cells are more complex than prokaryotic cells. A double-layered membrane separated from the cytoplasm of the nucleus in eukaryotes and directs the life processes of the cell, eukaryotic cells are present in protists, fungi, plants and animals, etc.

All eukaryotic cells are not identical such as plant and animal cells are different having an additional layer, called the cell wall, around the cell membrane.

Difference between Prokaryotic cell and Eukaryotic cell

In the prokaryotic cell, the cell cycle is short by nearly about 20-60 minutes. But the eukaryotic cell cycle is long, about 12-24 hours.
There is no nucleolus in the prokaryotic cell, but one or more nucleoli within the nucleus.
In prokaryotic cells, DNA is circular and lies free in the cytoplasm (no true nucleus), but in the eukaryotic cell, DNA is linear and contained in a nucleus.
In prokaryotic cells, sap vacuoles are lacking, and gas vacuoles may be present, but in the eukaryotic cell, sap vacuoles are commonly present.

Eukaryotic cells are further divided into animal cells and plant cells.

Animal cell

Characteristics of animal cell

It has a thin, flexible and living plasma membrane only.
Plastids are absent.
The cell wall is absent from it.
They have lysosomes.
Animal cells possess centrioles.
It has a nucleus in or near the centre of the cell.
Prominent and highly complex Golgi bodies are present.
Rough Endoplasmic reticulum is absent in animal cells.
They store carbohydrates as glycogen,

Plant cells

Characteristics of plant cells

It has a thick, rigid, dead cell wall beside the plasma membrane in a plant cell.
They pushed its nucleus to one side in the peripheral cytoplasm.
The rough Endoplasmic reticulum is sparse in a plant cell.
The cell wall is present in the plant cell.
They do not have lysosomes.
Plant cells lack centrosomes and centrioles.
Subunits of the Golgi apparatus called dictyosomes are present in plant cells.
They store carbohydrates as starch.