Cytology: Microscopy
Unit Objective I can describe the form and function of prokaryotic and eukaryotic cells and their cellular components.
During this unit, we will describe scientific relationships between structure and function at the cellular and subcellular levels.
We will learn the common features of cells, and the major differences between prokaryotic and eukaryotic cells.
We will also learn that the proper functioning of cell structures is required to maintain homeostasis.
During this unit, then, we will answer the following very important questions:
#1: What are the major differences between prokaryotic and eukaryotic cells?
#2: How do these differences impact the function of each type of cell?
We will continue our study of biology by first focusing on microscopy. To do this, we will learn how to describe how scientists measure objects relate magnification and resolution in using a microscope analyze how light microscopes function compare light and electron microscopes describe a scanning tunneling microscope
Paramecia, which can usually be found in ponds and slow-moving streams, are classic examples of single-celled eukaryotic organisms.
Like all ciliates, these protozoans have more than one nucleus, which may be difficult to see among the many food vacuoles in a paramecium.
Cilia (as we will discover in greater detail later) are eyelash-like appendages covering all surfaces of a ciliate, and rotate forward or backward in unison to move the organism.
Contractile vacuoles, characterized by their central space surrounded by several radiating canals, collect and squeeze excess water out of a cell.
Do you know what type of cells these are? What are the functions of each cell? How is the structure of the cell involved in its function?
Microscopes are instruments that magnify small objects, making them appear larger than their actual size.
In order to fully appreciate the magnifying power of microscopes, we need to brush up on the metric system.
The basic unit of linear distance (length) in the metric system is the meter (m), which is a little bit more than a yard in magnitude.
A kilometer (km) is equivalent to 1 000 meters, about two-thirds of a mile in length. There are 1 000 meters in a kilometer.
A centimeter (cm) is 0.01 meters, about the diameter of a Lincoln penny. There are 100 centimeters in a meter.
A millimeter (mm) is 0.001 meters, about the width of a pencil tip. There are 1 000 millimeters in a meter.
A micrometer (μm) is 0.000 001 meters, about the length of an average bacterial cell.
A nanometer (nm) is 0.000 000 001 meters, about the length of a water molecule.
The International Bureau of Weights and Measures in France provides the standards of the International System of Measurements (the Systéme Internationale, abbreviated SI ).
The Bureau houses the actual measures against which all other measures in the world are calibrated, such as the one-kilogram slug of metal against which all other kilograms are calibrated,
...and the meter-long metal bar against which all other meters the world over are calibrated..
The current SI system was established in 1960.
British philosopher and architect Robert Hooke (1635-1703), in observing specimens of cork using a microscope, was the first scientist to observe what Hooke perceived to be tiny compartments in the cork.
Hooke called these structures cellulae, meaning small rooms, giving birth to the term cell.
Hooke used a light microscope to view cork cells. In a light microscope, light passes through one or more lenses to produce an enlarged image of a specimen.
The effective range of the average light microscope is from 500 mm to 500 nm, powerful enough to magnify blood cells and the very small features on coins.
To observe extremely small specimens, an electron microscope is used An electron microscope forms an image of a specimen using a beam of electrons reflected from the interior of the surface of an organism rather than by using light.
Electron microscopes can magnify in the range of 100 μm to 0.1 nm, powerful enough to magnify objects as small as bacteria.
The magnification of a microscope is the ability of a device to make an object appear larger than its actual size.
The resolution of a microscope is a measure of the clarity of an image produced by a magnifying device. The better the resolution, the clearer the image produced.
Microscopes in high schools across the nation vary in their appearance and function.
The reason that we are able to see the objects that occupy our universe is because each object reflects specific wavelengths of light that can be detected by our eyes.
An apple, for example, absorbs all of the wavelengths of light except for red light, which is why an apple appears red.
A grasshopper absorbs all of the wavelengths of light striking it except for green light, which is why it appears green.
The sky above us appears blue because the molecules in the air that make up our atmosphere absorb all of the wavelengths of light except for blue light.
In magnifying an object, the light waves reflected from an object pass through the ocular and objective lenses of a microscope.
Refraction, the bending of light waves as they pass from one medium to another, results in a magnified image of the specimen.
QUESTION: What is the media through which light waves pass when you use a light microscope?
Using a scanning interferometric apertureless microscope (SIAM), scientists have viewed features approximately four atoms (1 nm) in diameter.
Not only is SIAM technology used for microscopy, it it has shown promise for uses involving the storage of digital information. SIAM has the potential, for example, to store 30 full-length movies on a storage disk the size of a penny.
QUESTION: Would the SIAM likely be more useful in studying the overall structure of a cell, or the structure of biological compounds within the cell?
The SIAM is capable of making molecules visible. It is therefore useful in studying cells on the molecular level; i.e., for studying the structure of certain biological compounds such as proteins.
Other types of microscopes, such as electron microscopes, are used to visualize cells and their organelles. These types of microscopes are useful in understanding the overall structure of the cell.
Dutch spectacle-maker Zacharias Janssen (1585-1632) and his brother Hans, and German-Dutch spectacle-maker Hans Lippershey (1570-1619) constructed the first microscope with the ability to magnify objects from 3X to 10X in the Netherlands in the years between 1590 and 1608.
Dutch microscopist and microbiologist Antonie Philips van Leeuwenhoek (1632-1723) made significant improvements to the microscope, developing lenses with magnifications of up to 300X.
Van Leeuwenhoek produced approximately 400 microscopes during his lifetime, and used them to study a wide variety of specimens such as yeast, muscle tissue, plants, and insects.
German physicist and Nobel laureate Ernst August Friedrich Ruska (1906-1988) and German-American electrical engineer and inventor Reinhold Rudenberg (1883-1961), working independently of one another, invented the transmission electron microscope in 1931.
In 1933, Ruska constructed the first electron microscope more powerful than a light microscope, and was awarded the Nobel Prize in Physics for his achievement.
Electron microscopes (which can magnify specimens up to 200 000X) are used not only in biological research, but in other fields as well.
Earth scientists have used electron microscopes to determine the effects of weathering on the microstructural arrangement of the mineral components of rock, for example, as well as the effect of environmental chemicals on rock formation and stability.
There are several types of microscopes (electron microscopes and others) designed to view very small objects.
A transmission electron microscope (TEM) directs its electron beam at a very thin slice of a specimen stained with metal ions.
Some of the structures in a specimen absorb more electrons than others, and become heavilystained by the metal ions, while those structures that do not as readily absorb electrons are lightly-stained by the metal ions.
Those electrons not absorbed pass through the specimen to a fluorescent screen, forming an image on the screen.
TEMs are most-often used to visualize the internal anatomy of a structure or organism.
A scanning electron microscope (SEM) focuses its electron beam on a specimen coated with a very thin layer of metal.
The electrons that are repelled by the metal bounce off of the specimen onto a fluorescent screen, forming a three-dimensional image of the specimen.
New video and computer technologies that increase the resolution and magnification of microscopes have allowed for the development of devices such as the scanning tunneling microscope (STM).
A scanning tunneling microscope uses a needle-like probe to measure the differences in voltage caused by electrons that leak, or tunnel, from the surface of an object being viewed after an electric current has been applied to the specimen.
The probe glides across the surface of the specimen detecting the leaking electrons. The probe transmits this data to a computer, which maps the tunneling electrons to produce a threedimensional image of the specimen.
Although STMs can be used to view living specimens, they are most-often used to view specimens as small as individual atoms.
QUESTION: What type of microscope would be most useful in studying the general structure of a leaf from a plant?
QUESTION: What type of microscope would be most useful in studying the three-dimensional details of a small organism such as a unicellular protist?
QUESTION: What type of microscope would be most useful in studying the internal structures of a bacterial cell?