Download Viewing Cells Microscopes are used to magnify cells. The number of

Viewing Cells
Microscopes are used to magnify cells.
The number of living things in your environment that you cannot see is much greater than the number
that you can see. Many of the things that you cannot see are only one cell I size. To see most cells, you need to
use a microscope. Trying to see separate cells in a leaf is like trying to see individual photos in a photo mosaic
picture that in on the wall across the room. As you walk toward the wall, it becomes easier to see the individual
photos. When you get right up to the wall, you can see details of each small photo. A microscope has one or
more lenses that enlarge the image of an object as though you are walking closer to it. Seen through these
lenses, the leaf appears much closer to you, and you can see the individual cells that carry on life processes.
Early Microscopes
In the late 1500s, the first microscope was made by a Dutch maker of reading glasses. He put two
magnifying glasses in a tube and got an image that was larger than the image that was made by either lens
alone. In the mid 1600s, Antonie van Leeuwenhoek, a Dutch fabric merchant, made a simple microscope with a
tiny glass bead for a lens. With it, he reported seeing things in pond water that no one had ever imagined. His
microscope could magnify up the image of an object 270 times larger than its actual size. Today you would say
his lens has a power of 270x. Early compound microscopes were crude by today’s standards. The lenses would
make an image larger, but it was not always sharp or clear.
Modern Microscopes
Scientists use a variety of microscopes to study organisms, cells, and cell parts that are too small to be
seen with the human eye. Depending on how many lenses a microscope contains, it is called simple or
compound. A simple microscope is similar to a magnifying lens. It has only one lens. A microscope’s lens
makes an enlarged image of an object and directs light toward your eye. The change in apparent size produced
by a microscope is called magnification. Microscopes vary in powers of magnification.
The compound light microscope has two sets of lenses – eyepiece lenses and objective lenses. The
eyepiece lenses are mounted in one or two tube-like structures. Images of objects viewed through two eye
pieces, or stereomicroscopes, are three-dimensional. Images of objects viewed through one eyepiece are not.
Compound light microscopes usually have two to four movable objective lenses. The posers of the eyepiece
and objective lenses determine the total magnifications of a microscope. If the eyepiece lens has a power of 10x
and the objective lens has a power of 43x, then the total magnification is 430x (10x times 43x).
The microscope led to the discovery of cells.
In the 1660s, Robert Hooke began using microscopes to look at all sorts of materials. He was the name
who gave the cell its name. While looking at a sample of cork, a layer of bark taken from an oak tree, he saw a
group of similarly shaped compartments that looked to him like empty rooms, or cells. In the 1830s, Matthias
Schleiden used a microscope to study plants and concluded that all plants are made of cells. Theodor Schwann,
after observing different animal cells, concluded that all animals are made up of cells. Eventually, they
combined their ideas and became convinced that all living things are made of cells. Several years later, Rudolf
Virchow hypothesized that cells divide to form new cells. Virchow proposed that every cell came from a cell
that already existed. His observations and conclusions and those of others have come to be known as the cell
theory.
The cell theory is important to the study of biology.
The observations and evidence gathered over a longtime by any scientists are summarized in the three
concepts of the cell theory: every living thing is made of one or more cells, cells carry out the functions needed
to support life, and cells come only from other living cells. The importance of the cell theory is indicated by the
word theory. A scientific theory is a widely accepted explanation of things observed in nature. A theory must
be supported by evidence, including experimental evidence and observations. A theory proves its value when it
explains new discoveries and observations. Theories are important for a number of reasons. Certainly they
satisfy scientists’ desire to understand the natural world, and they serve as foundations for further research and
study. Theories can also lead to research that has some practical benefit for society.
Louis Pasteur
The work of the French scientist Louis Pasteur shows how an understanding of cell theory can have
practical uses. Pasteur lived in the 1800s, when there was no mechanical refrigeration in homes. People were
used to having foods spoil and milk go sour. During this time, many people died from diseases such as typhoid
fever, tuberculosis, and diphtheria. Pasteur’s work showed that microscopic organisms were involved both in
the spoilage of food and in disease. Pasteur observed that milk that turned sour contained large numbers of tiny
single-celled organisms called bacteria. He developed a process, now known as pasteurization, in which heat is
used to kill bacteria.
Bacteria and Spontaneous Generation
Using a microscope to study air, water, and soil, Pasteur found microorganisms everywhere. He found
bacteria in the blood of animals, including people who were sick. Pasteur referred to the microorganisms as
“germs.” He realized that an understanding of germs might help prevent disease. Pasteur’s work led to the first
animal vaccinations for cholera and anthrax and to treatment for rabies in humans.
At the times that Pasteur was doing his research, there were scientists who thought that bacteria grew
from nonliving materials in a process known as spontaneous generation. Pasteur conducted a now-famous
series of experiments that disproved spontaneous generation and confirmed the cell theory. He showed that
cells come only from other cells. Two flasks are filled with a bacteria filled broth and then boiled to kill the
bacteria. Then, one flask was kept sealed and the other flask left open to expose the contents to the air.
Bacteria only grew in the flask that was exposed to air.