IndexBacteriaVirusFungiProtozoaA microorganism is a living organism and can only be seen through a microscope. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay BacteriaBacterial cells are prokaryotic cells (single-celled organisms). Bacterial cells have a variety of different organelles including a single circular strand of DNA, plasmids (small loops of DNA), a cytoplasm, a cell membrane, and a cell wall. Furthermore, being a single-celled organism, bacteria often have other adaptations such as a flagellum (a tail for movement) or particular shapes. Bacterial cells are found almost everywhere. Some are pathogens (disease-causing bacteria). Pathogenic bacteria release harmful toxins into the body. Others, however, are completely harmless (the so-called flora) and perform the necessary function in the organism. An example of non-pathogenic bacteria in the human body are the 300-500 different types of bacteria found in the intestine. This helps both the digestive system and the immune system. For example, there is Bacteroides fragilis which is always present in the intestine. In terms of bacterial reproduction, they reproduce through binary fusion. This process involves the splitting of the bacteria in two. These then divide again to make four. This process then repeats creating a cycle. In order for bacteria to grow, they must have the optimal temperature and PH, along with nutrients, water and sometimes oxygen. In terms of temperature, the ideal temperature depends on the type of bacteria but, for optimal growth, the bacteria must be warm. At 0 – 5°C bacteria tend to grow more slowly while at -18°C bacteria become dormant (inactive). Additionally, most bacteria grow best at neutral pH, but some thrive in particularly acidic or alkaline conditions. Oxygen is necessary only for aerobic bacteria. An example of an opportunistic infection is tuberculosis (TB), a pathogenic disease caused by bacteria. This condition affects the lungs and is caused by tuberculosis Mycobacterium. Through inhalation of contaminated droplets from an infected person, tuberculosis spreads. There are a variety of signs and symptoms that tend to develop slowly. These include a cough that lasts more than 3 weeks and may bring up phlegm and blood, pyrexia (increased body temperature), weight loss, night sweats, and swollen lymph nodes. Typically, in healthy people, the body's defense system kills the bacteria and, as a result, no symptoms occur. However, in case of active tuberculosis, antibiotics are used for 6 months and hospital treatment is sometimes required. It can almost always be treated. Finally, there is also a BCG vaccine which is administered to at-risk areas and vulnerable groups such as health and social care workers. VirusesViruses, the smallest of all microorganisms, duplicate by attaching themselves to a host cell and penetrating it. The virus then tells the cell to make copies. At some point, the cell will explode, causing the virus to enter new host cells and reproduce. This can happen within a few hours. Each time the virus reproduces, the DNA is slightly altered, making it, over time, unrecognizable to the organism. This is why the human body can catch a common cold more than once and vaccines can become ineffective. All viruses are simple organisms that contain a strand of genetic material and a protein coat. To grow, microorganisms must have water along with mineral elements and gases, such as oxygen. Microorganisms also need the correct conditions and, in terms of.