It only takes one biological cell to create an organism. In fact, there are countless species of single celled organisms, and indeed multi-cellular organisms like ourselves.

A single cell is able to keep itself functional by owning a series of 'miniature machines' known as organelles. The following list looks at some of these organelles and other characteristics typical of a fully functioning cell. The italic links for each lead to an extra description in the dictionary, as do all similar links in the tutorials;

Cells can become specialised to perform a particular function within an organism, usually as part of a larger tissue consisting of many of the same cells working in tandem, for example;

Cells combine their efforts in these tissue types to perform a common cause. The task of the specialised cell will determine in what way it is going to be specialised, because different cells are suited to different purposes, as illustrated in the above list and below example;

Many of these cells contain organelles, though after some cells are specialised, they do not possess particular characteristics as they do not require them to be there. i.e. efficiency is the key, no resources are wasted and the resources available are put to their idyllic optimum.

The cell membrane, otherwise known as the plasma membrane is a semi-permeable structure consisting mainly of phospholipid (fat) molecules and proteins. They are structured in a fluid mosaic model, where a double layer of phospholipid molecules provide a barrier accompanied by proteins.

It is present round the circumference of a cell to acts as a barrier, keeping foreign entities out the cell and its contents (like cytoplasm) firmly inside the cell.

The plasma membrane allows only selected materials to pass in and out of a cell, and is thus known as a selectively permeable membrane. There are a number of methods that allow the exchange of materials in and out the cell possible, mentioned below.

There are three methods in which ions are transported through the cell membrane into the cell,

In cells, sometimes it is required to breakdown more complex molecules into more simple molecules, which can then be 're-built' into what is needed by the body with these new raw materials.

'Pinocytosis' where to contents of a structure (such as bacteria) are drank, essentially by breaking down molecules into a drinkable form.

'Phagocytosis' where contents are 'eaten'. See cell defence for more information in regards to this.

Absorption is the uptake of materials from a cells' external environment. Secretion is the ejection of material.

This page is designed to give you an introductory overview of a single cell. The continuing cell biology tutorial elaborates on the concepts mentioned here, and will give you a fuller understanding of the biological cell at work.

Go here to read the rest:

Biological Cell Introduction - Biology Online