Reproductive rate is affected by changes in temperature, nutrition, and pH. Reproduction: Binary fission is the usual method of reproduction, but some bacteria exchange genetic material with members of the same species or different species. They range in size from less than 0.5 to 1.0 μm in diameter to 10 to 20 μm in length for some of the spirilla. Size: On average, bacilli measure about 1 μm in diameter by 4 μm in length. Spiral bacteria are rigid (spirilla), flexible (spirochetes), or curved (vibrios). Rod-shaped bacteria are called bacilli, more oval ones are called coccobacilli, and those forming a chain are called streptobacilli. Spherical or ovoid bacteria occur as single cells (micrococci) or in pairs (diplococci), clusters (staphylococci), chains (streptococci), or cubical groups (sarcinae). Shape: There are three principal forms of bacteria. Bacteria that cause disease are called pathogens.īacterial (-ăl), adj. Millions of nonpathogenic bacteria live on human skin and mucous membranes these are called normal flora. Bacteria synthesize DNA, RNA, and proteins, and they can reproduce independently but may need a host to provide food and a favorable environment. Some bacteria produce a polysaccharide or polypeptide capsule, which inhibits phagocytosis by white blood cells. The cytoplasm is surrounded by a rigid cell wall composed of carbohydrates and other chemicals that provide the basis for the Gram stain. bacteria Ī one-celled organism without a true nucleus or cell organelles, belonging to the kingdom Procaryotae (Monera). To hear audio pronunciation of this topic, purchase a subscription or log in.
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