TEAS - 2.5
Microorganisms and their roles
Microorganisms, or microbes, are too small to see without magnification. The pages group them as bacteria, viruses, protozoans, fungi, and animals. Many reproduce quickly and form large populations that can be studied in a laboratory, but their small size requires special techniques and equipment such as microscopes. The pages separately note that viruses are not living things and that parasitic worms can be visible to the naked eye.
Microorganisms benefit living systems by producing oxygen, decomposing organic material, providing nutrients for plants, and maintaining human health. Some are pathogenic and cause disease in plants or humans. Microbes are characterized by their cellular components, morphology (size and shape), means of locomotion, and reproduction.
Term | Description |
Free-living microbes | Obtain what they need from their surrounding environment. |
Parasite | Lives in or on a larger organism and obtains most of its sustenance from that organism. Its actions can damage the host through infection and disease. |
Host | The larger organism in or on whose body a parasite lives. |
Pathogen | An infectious agent; a disease-causing microbe. |
Main groups and disease examples
Term | Description |
Bacteria | Unicellular prokaryotes that lack a nucleus. Cell-wall structure is an important classification feature. Examples of illnesses include tuberculosis, meningitis, and food poisoning. Not all bacteria are pathogenic; harmless bacteria may support essential bodily functions. |
Viruses | Noncellular entities with a DNA or RNA core surrounded by a protein coat. They invade and multiply inside healthy prokaryotic or eukaryotic cells. Examples include influenza, measles, mumps, HIV, and COVID-19. |
Protozoans / protists | Unicellular eukaryotes. They feed on other cells and are traditionally divided by locomotion. The pages describe their extensive numbers, biomass, and diversity. Disease examples include dysentery, malaria, and sleeping sickness (African trypanosomiasis). |
Fungi | Include mushrooms, molds, and yeast; all are eukaryotic and have a true nucleus. They absorb organic nutrients as decomposers, live symbiotically with plants, or have harmful parasitic relationships with hosts. The pages associate fungi with asthma, athlete’s foot, ringworm, lung infections, and bloodstream infections. |
Animals: helminths | Parasitic worms are large enough to see without magnification and can inhabit many body areas. Flatworms such as tapeworms can live in the intestines. Roundworms can live in the gastrointestinal tract and lymphatic system. |
Infectious versus noninfectious disease
A disease is a condition that impairs the normal functioning of cells, tissues, and organs. The pages distinguish two categories:
Term | Description |
Infectious / communicable disease | Described in these pages as disease that spreads from one person to another and is caused by pathogenic microorganisms, including bacteria, protozoans, and viruses. Examples: cholera, chickenpox, and COVID-19. |
Noninfectious disease | Does not spread directly from one person to another. The pages describe causes other than pathogens, including age, nutritional deficiency, gender, and lifestyle. Examples: diabetes, cancer, and asthma. |
How infectious diseases spread
Term | Description |
Direct contact | Contact with a sick individual, including skin-to-skin contact and sexual contact, can transmit disease to a new host. |
Common surfaces | Touching shared surfaces can transmit disease. |
Body fluids | Contact with fluids such as blood or saliva can spread infectious disease. |
Droplets | Coughing or sneezing releases droplets. These remain in the air for a short time and may land on another person’s skin or be inhaled into the lungs. |
Airborne particles | Some infectious agents travel through the air as small particles for longer periods. Healthy people can inhale them and become ill. |
Microscopes: lenses and resolution
Microscopes are important microbiology tools and are essential in medicine for cellular discoveries. The pages describe a simple microscope associated with Anton van Leeuwenhoek: a tube, magnifying lens, and stage used to observe microbes and circulating blood cells. They also describe Robert Hooke’s use of a compound microscope in 1665.
A compound microscope uses two lens sets for magnification: the ocular lens next to the eye and the objective lens next to the specimen or object. Microscopes can be classified by the physical principles used to produce an image, including light and electron microscopes.
Resolution depends inversely on the wavelength of illumination. The pages give an electron wavelength of 0.5 nanometers and a light wavelength about 1,000 times larger (approximately 0.5 micrometers). The shorter electron wavelength allows smaller structures to be resolved.
Light and electron microscopes
Term | Description |
Light microscopes | Depend on a light source. The six types listed are bright-field, dark-field, phase contrast, fluorescence, confocal scanning laser microscopy (CSLM), and differential interference contrast (DIC). |
Electron microscopes | Use electrons instead of light. They form an image from a beam of high-speed electrons with a wavelike pattern. Magnification can reach 150,000 times the specimen’s size, with greater resolution than light microscopes. |
Electron microscope limitation | Must operate in a vacuum, which prevents studying live cells. |
Electron microscope types | Transmission electron microscope (TEM) and scanning electron microscope (SEM). |