Are micro organisms good or bad? Give reason. If you could make your own cell, a new one, what cell organelles will it have? *
Answers
Answer:
However, the majority of the microbes are harmless and actually help to maintain our health. The microbes of the skin, mouth, and nose fight against bad bacteria that want to enter the body to cause disease. These good bacteria act like guards that keep away the harmful bacteria that make us sick.
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Explanation:
The first step in infection is for the pathogen to colonize the host. Most parts of the human body are well-protected from the environment by a thick and fairly tough covering of skin. The protective boundaries in some other human tissues (eyes, nasal passages and respiratory tract, mouth and digestive tract, urinary tract, and female genital tract) are less robust. For example, in the lungs and small intestine where oxygen and nutrients, respectively, are absorbed from the environment, the barrier is just a single monolayer of epithelial cells.
Skin and many other barrier epithelial surfaces are usually densely populated by normal flora. Some bacterial and fungal pathogens also colonize these surfaces and attempt to outcompete the normal flora, but most of them (as well as all viruses) avoid such competition by crossing these barriers to gain access to unoccupied niches within the host.
Wounds in barrier epithelia, including the skin, allow pathogens direct access to the interior of the host. This avenue of entry requires little in the way of specialization on the part of the pathogen. Indeed, many members of the normal flora can cause serious illness if they enter through such wounds. Anaerobic bacteria of the genus Bacteroides, for example, are carried as harmless flora at very high density in the large intestine, but they can cause life-threatening peritonitis if they enter the peritoneal cavity through a perforation in the intestine caused by trauma, surgery, or infection in the intestinal wall. Staphylococcus from the skin and nose, or Streptococcus from the throat and mouth, are also responsible for many serious infections resulting from breaches in epithelial barrier..
Several bacteria that replicate in the host cell cytosol (rather than in membrane-enclosed compartments) have adopted a remarkable mechanism for moving, which depends on actin polymerization. These bacteria, including Listeria monocytogenes, Shigella flexneri, and Rickettsia rickettsii (which causes Rocky Mountain spotted fever) induce the nucleation and assembly of host cell actin filaments at one pole of the bacterium. The growing filaments generate substantial force and push the bacteria through the cytoplasm at rates up to 1 μm/sec. New filaments form at the rear of each bacterium and are left behind like a rocket trail as the bacterium advances, depolymerizing again within a minute or so as they encounter depolymerizing factors in the cytosol. When a moving bacterium reaches the plasma membrane, it continues to move outward, inducing the formation of a long, thin protrusion with the bacterium at its tip. This projection is often engulfed by a neighboring cell, allowing the bacterium to enter the neighbor's cytoplasm without exposure to the extracellular environment, thereby avoiding recognition by antibodies produced by the host's adaptive immune system (Figure 25-33).