Bacteria Protists and Archaea

Bacteria, protists, and archaea belong to the world of microbes-mostly unicellular organisms. Bacteria are prokaryotes, organisms with DNA that is not enclosed within a nucleus, whereas protists are eukaryotes, organisms with a bounded nucleus. Archaea, an ancient life-form recognized only in the late 1970s, are prokaryotes but are different from bacteria. They are the extremists in the bunch, able to survive in the most challenging environmental conditions.

Despite their small size and single-cell structure, bacteria exhibit an amazing range and complexity of characteristics and behaviors. Along with archea, they were the earliest forms of life on the planet. Cyanobacteria, also known as blue-green algae, date back some three billion years and contributed to the formation of Earth’s atmosphere by developing photosynthesis.

Protists are a diverse group that includes protozoans, algae, and lower fungi. They share characteristics with both animals and plants. Protozoans are prevalent in soils and aquatic habitats worldwide, and most maintain symbiotic and even parasitic relationships with other organisms. Algae dominate many aquatic habitats and range dramatically in size-from organisms only millimeters long to strands of the sea up to 200 feet long.

Archaea resemble bacteria under a microscope but are biochemically and genetically different. These are the organisms that live in thermal vents in the deep ocean and even in petroleum deposits underground. But they also thrive in more normal conditions, including with the plankton of the open sea.

WHAT IS VIRUS?

A virus is a microscopic infectious agent that enters animals, plants, or bacteria hosts. A single virus particle, called a virion, is little more than a bundle of genetic material-DNA or RNA- that does not take the form of a cell. Instead, it is encased in a shell called a viral coat, or capsid, made of bits of protein. Some viruses have an additional enclosure around the capsid called an envelope.

Viruses cannot function without their hosts. They cannot synthesize proteins without essential ingredients from their host cells, and they can neither generate nor store energy on their own. In fact, viruses depend on host cells for all their metabolic functions.

Some scientist decline to count viruses among living organisms since they cannot survive on their own and cannot reproduce outside of a host cell. Not usually counted among plants, animals, or prokaryotic bacteria, viruses are instead classified in a group of their own.

What viruses can do, however, is infect, or cause disease. Fortunately, the immune systems of most animal species can fend off infection from many kinds of viruses. Antibiotics cannot cure viral illnesses, but vaccines can prevent them, and many widespread life-threatening viral outbreaks, such as smallpox, have been controlled or eliminated with vaccines.

Source : Newtonsclasses.com