The electron microscope was first created in 1933 and magnified up to a million times. First electron microscope was a transmission. It used electrons to recreate an image. Scanning electron microscope developed later, it uses a beam of particles to scan across specimen to recreate image of its surface. They are used for the viewing of biological and inorganic species. Electron microscope has higher resolution than light microscope allowing higher magnification. Light microscope has limited magnification as there is a physical limit imposed by photons. The stereomicroscope has low level of magnification, but gives 3-D view. Electron microscopes give a view of structures that would not normally be visible by optical microscopy. Bonus to light microscopes is that it is possible to view living cells, in the electron microscope the specimen must be dry so it is not possible to observe the living. Anti-body viruses were first observed by electron microscope in 1941. Electron tomography has demonstrated the structure of viruses. Had discovers with cell ultrastructure’s and individual atoms have been observed. It has viewed nerve and muscle cells and various pollen has been observed.
The compound light microscope or optical microscope is a piece of technology that uses light and magnifying lenses to observe small objects which cannot be seen by the naked eye. The ingenious theory behind light and magnification combined; forms a complex enhancement of specimen identification/observation. Light microscopes enable more opportunities for knowledge in biology, research, and material science. The light microscope can magnify up to a whopping 1,500 times! Therefore the specimen has to be small enough for light to pass through it and it displays a 2D view of the specimen. The compound light microscope is able to have one eyepiece (monocular) or two eyepieces (binocular) to look through.
Light microscopes were used to discover a very important specimen. They were used to discover cells such as blood cells. The stereo microscope is known as the optical microscope. It has low magnification. It reflects light off the specimen, it has two separate optical paths and is used to study solid specimens. The primary use for the stereomicroscope is looking at large and solid surfaces or specimens. The microscope allows for detailed work such as microsurgery, watch making and circuit board manufacturing.
When Robert Hooke published his book Micrographia in 1665 it became a best seller. Hooke had made one of the first microscopes. With it, he observed many types of living things and made accurate drawings of what he saw, as his detailed picture of the flea shows (Figure 1.4). Hooke’s most famous achievement, as far as science was concerned, was his diagram of very thin slices of cork (Figure 1.5). He was surprised to see that, under the microscope, the cork looked like a piece of honeycomb. He described the ‘holes’ and their boundaries in the ‘honeycomb’ as cells because they reminded him of the rooms in a monastery. Hooke had discovered plant cells.
Although some called Micrographia ‘the most ingenious book ever’, others ridiculed Hooke for spending so much time and money on ‘trifling pursuits’. Thankfully for us, and for the whole science of microbiology, which developed from this discovery of cells, Hooke ignored the taunts and kept experimenting with microscopes. It was because of Hooke’s important contribution to microbiology that other scientists went on to develop a further understanding of cells.
Cell theory describes the main ideas about the importance of cells and their role in living things. It was first proposed in 1839 by two German biologists, Theodor Schwann and Matthias Schleiden. In 1858, Rudolf Virchow concluded the final part of the classic cell theory. The combined cell theory included the following three principles: all organisms are composed of one or more cells
cells are the basic unit of life and structure
new cells are created from existing cells.
Any living thing that has more than one cell is referred to as multicellular, but there are many living things, such as bacteria, that consist of only one cell! These are called single-celled or unicellular organisms. Micro-organisms are often referred to as microbes. You probably know people who wear glasses to help them read. The glass or plastic lenses magnify the size of the text. In the same way, microscopes magnify the size of the object placed under them. The first microscopes were very basic. However, over time their magnifying ability has improved. Scientists can now look at images that have been magnified thousands of times using various systems of lenses. This makes it possible to study the structure of cells. The stereomicroscope is used for viewing larger objects, such as insects (Figure 1.15). It can magnify up to 200 times and shows a three-dimensional view of small things. The compound light microscope (Figure 1.16) is used to observe thin slices of specimens, such as blood cells. It can magnify up to 1500 times. Its view is flat—that is, two dimensional.
The specimen must be thin enough to allow light to pass through it. The stereomicroscope has two eyepieces to look through, whereas the compound light microscope can have one or two eyepieces. The word monocular is used to describe a microscope with one eyepiece (mono = one). Microscopes with two lenses are called binocular (bi = two). The compound light microscope uses the effect of two lenses (one in the eyepieces and one further down the column called the objective lens) combined with light to give a greater magnification. It can be used to observe much smaller things than those seen under a stereomicroscope. To look at cells clearly through a compound light microscope, very thin layers of a sample must be used. The light has to be able to get through or all you will see is a dark shadow—a bit like a leadlight window. Most cells are clear in colour, so a stain, like iodine, is used to help make them more visible by providing contrast.
Although light microscopes, like the compound light microscope and stereomicroscope, had served scientists well for more than 300 years, the explosion of new technology in the 20th century led to the invention of more complex microscopes, such as electron microscopes. An electron microscope uses electrons (tiny negatively charged particles) to create images. The first electron microscope, the transmission electron microscope (TEM), was invented in 1933 to help study the structure of metals. The scanning electron microscope (SEM), developed later, uses a beam of electrons to scan across a specimen and to recreate the image, showing details of its surface.
Electron microscopes can magnify up to a million times! Using this technology, many more details of the cell that were formerly invisible to scientists are now beginning to be understood. The development of the synchrotron is one of the biggest changes to microscopes. Synchrotrons are ‘microscopes’ that are about the size of a football field and cost a fortune to build. The synchrotron provides even more magnification than an electron microscope and can ‘see’ down to the level of the molecules (particles) that make up substances. There are currently forty-three synchrotrons across the world. Australia’s synchrotron opened in 2007 and is located near Monash University, in Melbourne. There are many beneficial applications of synchrotron science. For example, researchers can use the synchrotron to invent ways to tackle diseases, make plants more productive and metals more resilient.