Question

What are 5 Examples of prokaryotic cells?

Answer 1

Prokaryotic cells are the cells which lack the membrane bound cell organelles and do not possess a well-defined nucleus. Bacteria are the sole members of kingdom Monera and Monera is a kingdom of prokaryotic cells. Therefore, the kingdom Monera is also known as prokaryota. Being the earliest forms of life, bacteria can survive under all kinds of habitats like hot springs, dry deserts, below icebergs, ocean bottoms, dust particles, inside and outside the body of other organisms. The air we breathe in contains thousands of bacteria in their spore stage. And even a teaspoon full of soil contains more bacteria than the human population in India.

Complete explanation:
They are divided into two major groups of bacteria: archaebacteria (ancient bacteria) and eubacteria (true bacteria). Group eubacteria is further divided into two types: bacteria and cyanobacteria. Some other groups of monerans are rickettsiae, actinomycetes and mycoplasma.
Archaebacteria: These are special bacteria since they live in mostly harsh habitats such as extreme salty (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens). Presence of a different type of cell wall structure is responsible for their survival in extreme conditions. Methanogens are present in the gut of animals such as cows and buffaloes which are known as ruminants. They are responsible for the production of methane (biogas) from the dung of ruminant animals.
Eubacteria: They are known as true bacteria and there are thousands of eubacteria present. They are characterized by the presence of a rigid cell wall and a flagellum, if motile. The blue green algae also referred to as Cyanobacteria have chlorophyll similar to green plants and are photosynthetic autotrophs. They are colonial or filamentous, unicellular, freshwater/marine or terrestrial algae. Their colonies are generally surrounded with gelatinous sheath. Cyanobacteria form blooms in polluted water bodies and some of these can fix atmospheric nitrogen in specialized cells called heterocysts. e.g., Nostoc and Anabaena. Chemosynthetic autotrophic bacteria oxidize various inorganic substances such as nitrates, nitrites and ammonia and produce ATP with the released energy. They play a great role in recycling nutrients like phosphorus, iron, sulphur, and nitrogen. Most abundant in nature are the heterotrophic bacteria. Majority of these are decomposers and have a significant impact on human affairs. They help in production of curd from milk, production of antibiotics, fixing nitrogen in legume roots, etc. Some of them being pathogenic in nature cause damage to humans, crops, farm animals and pets causing diseases like cholera, tetanus, typhoid, citrus canker, etc.
Mycoplasma: They are known as PPLO (Pleuropneumonia like organisms). Theycompletely lack a cell wall. They can survive without oxygen and are the smallest living cells known to occur on Earth. Many of these organisms are pathogenic in animals and plants.
Actinomycetes: These are mycelial bacteria which form radiating colonies in culture. That’s why they are known as ray fungi. Their cell wall contains mycolic acid. Most of them are saprotrophic, a few are pathogenic in plants and animals. Fragmentation is quite common in these while other modes of reproduction include conidia, sporangiospores and arthrospores.
Rickettsiae: these are a diverse collection of obligately intracellular Gram-negative bacteria found in ticks, lice, mites, fleas, mammals and chiggers. They are pathogenic in nature and cause infections that disseminate in the blood to many organs.

Note:
Based on their shapes bacteria are grouped under four categories: the spherical coccus (cocci), the rod-shaped bacillus (bacilli), the comma-shaped Vibrio and the Spirillum (spirilla). Some of them are autotrophic. They may be chemosynthetic autotrophic or photosynthetic autotrophic but the vast majority of bacteria are heterotrophs. Reproduction in bacteria is mainly through fission but sometimes under unfavorable conditions, they produce spores. They also reproduce through a type of sexual reproduction by adopting a primitive type of DNA transfer from one bacterium to another.