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Cells vary in size. With few exceptions, individual cells cannot be seen with the naked eye, so scientists use microscopes (micro = “small”; scope = “to look at”) to study them. A microscope is an instrument that magnifies an object. Most photographs of cells are taken with a microscope, and these images can also be called micrographs. Light Microscopes To give you a sense of cell size, a typical human red blood cell is about eight millionths of a meter or eight micrometers (abbreviated as eight μm) in diameter; the head of a pin of is about two thousandths of a meter (two mm) in diameter. That means about 250 red blood cells could fit on the head of a
pin. Electron Microscopes In contrast to light microscopes, electron microscopes (Figure 1b) use a beam of electrons instead of a beam of light. Not only does this allow for higher magnification and, thus, more detail (Figure 2), it also provides higher resolving power. The method used to prepare the specimen for viewing with an electron microscope kills the
specimen. Electrons have short wavelengths (shorter than photons) that move best in a vacuum, so living cells cannot be viewed with an electron microscope. For another perspective on cell size, try the HowBig interactive at this site. Cell Theory The microscopes we use today are far more complex than those used in the 1600s by Antony van Leeuwenhoek, a Dutch shopkeeper who had great skill in crafting lenses. Despite the
limitations of his now-ancient lenses, van Leeuwenhoek observed the movements of protista (a type of single-celled organism) and sperm, which he collectively termed “animalcules.” Occupation Spotlight: CytotechnologistFigure 3. These uterine cervix cells, viewed through a light microscope, were obtained from a Pap smear. Normal cells are on the left. The cells on the right are infected with human papillomavirus (HPV). Notice that the infected cells are larger; also, two of these cells each have two nuclei instead of one, the normal number. (credit: modification of work by Ed Uthman, MD; scale-bar data from Matt Russell) Have you ever heard of a medical test called a Pap smear (shown in Figure 3)? In this test, a doctor takes a small sample of cells from the uterine cervix of a patient and sends it to a medical lab
where a cytotechnologist stains the cells and examines them for any changes that could indicate cervical cancer or a microbial infection. Section SummaryA cell is the smallest unit of life. Most cells are so tiny that they cannot be seen with the naked eye. Therefore, scientists use microscopes to study cells. Electron microscopes provide higher magnification, higher resolution, and more detail than light microscopes. The unified cell theory states that all organisms are composed of one or more cells, the cell is the basic unit of life, and new cells arise from existing cells. Licenses and AttributionsWhen you move the slide to the right in what direction does the image move?9. The proper way to use a microscope is to look through the eyepiece with both eyes open to help avoid eye strain. Remember, everything is upside down and backwards. When you move the slide to the right, the image goes to the left!
When you move the slide to the left on the stage what direction does the image appear to move?A specimen that is right-side up and facing right on the microscope slide will appear upside-down and facing left when viewed through a microscope, and vice versa. Similarly, if the slide is moved left while looking through the microscope, it will appear to move right, and if moved down, it will seem to move up.
What happens when you move a microscope slide to the right?Answer and Explanation: If you move your slide to the right, the specimen moves to the left as you are viewing it microscopically. This occurs due to the use of the mirror in the microscope that makes it appear to move in the opposite direction.
What moves the slide left and right on a microscope?The stage clamp holds the microscope slide in place. Below the stage is a set of knobs called the STAGE ADJUSTMENT KNOBS. The top (larger) stage adjustment knob moves the stage vertically (towards you and away from you). The bottom (smaller) stage adjustment knob moves the stage horizontally (left/ right).
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