By the end of this lesson, you will:
Let's begin by understanding what is cell.
A cell is the fundamental and structural unit of all living organisms. It is the smallest biological, structural, and functional unit of all plants and animals. Therefore, cells are called the ‘building blocks of life’ or the ‘basic units of life’. Organisms made up of a single cell are ‘unicellular’ whereas organisms made up of many cells are ‘multicellular’. Cells perform many different functions within a living organism such as digestion, respiration, reproduction, etc., and keep it alive.
For example, within the human body, a lot of cells give rise to tissue – multiple tissues make up an organ – many organs create an organ system – several organ systems functioning together make up the human body.
The female egg (Ovum) is the largest cell in the human body and the male sperm is the smallest cell in the human body.
Did you know that several hundred years ago there was no knowledge of cells? This is because they were too small for the naked eye. The discovery of the microscope made it possible to observe cells and even study them in detail.
In 1665, Robert Hooke used a microscope to look at a thin slice of cork. He saw tiny little shapes that looked like small rooms with walls around each of them. He named these ‘cellulae’, a Latin word for little rooms.
Later, in 1838 Matthias Schleiden saw that all plants were made of cells. Around the same time, Theodor Schwann saw that all animals were made of cells.
In 1855, Rudolf Virchow determined that all cells came from other cells.
Their discoveries led to the formulation of the “Cell Theory” which states that:
Today, the Modern Cell Theory includes more ideas:
The Cell Theory is one of the basic principles of biology. It is the underlying main belief on which other ideas are based. Plants, animals, and all living things are made up of one or more cells. Cells cannot just happen - they come from other cells. Cells need energy to carry out their life processes. All cells are made up of almost the same chemicals. Cells pass on their traits during cell division.
In 1665, Robert Hooke published Micrographia, a book filled with drawings and descriptions of the organisms he viewed under the recently invented microscope. The invention of the microscope led to the discovery of the cell by Hooke.
Invented in 1590 by a Dutch optician named Zacharias Janssen, the compound (or light) microscope gives students and scientists a close-up view of tiny structures like cells and bacteria. The microscopes we use today are far more complex than those used in the 1600s and 1800s.
There are two primary types of modern microscopes used: light microscopes and electron microscopes. Electron microscopes provide higher magnification, higher resolution, and more detail than light microscopes. However, a light microscope is required to study living cells as the method used to prepare the specimen for viewing with an electron microscope kills the specimen.
1. The Eyepiece Lens - The eyepiece contains the ocular lens, which the user looks through to see the magnified specimen. The ocular lens has a magnification that can range from 5x to 30x, but 10x or 15x is the most common setting.
2. The Eyepiece Tube - The eyepiece tube connects the eyepiece and ocular lens to the objective lenses located near the microscope stage.
3. The Microscope Arm - The microscope arm connects the eyepiece tube to the base. This is the part you should hold when transporting a microscope.
4. The Microscope Base - The base provides stability and support for the microscope when it is upright. The base also typically holds the illuminator or light source.
5. The Microscope Illuminator - Microscopes require a light source for viewing. This can come in the form of a built-in, low-voltage illuminator light, or a mirror that reflects an external light source like sunlight.
6. Stage and Stage Clips - The stage is a platform for the slides, which hold the specimen. The stage typically has a staged clip on either side to hold the slide firmly in place. Some microscopes have a mechanical stage, with adjustment knobs that allow for more precise positioning of slides.
7. Aperture - This is a hole in the microscope stage, through which the transmitted light from the source reaches the stage.
8. The Revolving Nosepiece - The nosepiece contains objective lenses. Microscope users can rotate this part to switch between the objective lenses and adjust the magnification power.
9. The Objective Lenses - The objective lenses combine with the eyepiece lens to increase magnification levels. Microscopes generally feature three or four objective lenses, with magnification levels ranging from 4x to 100x.
10. The Rack Stop - The rack stop prevents users from moving the objective lenses too close to the slide, which could damage or destroy the slide and specimen.
11. Condenser Lens and Diaphragm - The condenser lens works with the diaphragm to focus the intensity of the light source onto the slide containing the specimen. These parts are located under the microscope stage.
