Teacher's Corner

What are Microbes?

The smallest form of life on Earth is the microbe. Although microbes have existed for millions of years, their presence was not detected until the seventeenth century. It was in 1683 that Dutch merchant Anton van Leeuwenhoek, who made microscopes as a hobby, detected "wee animalcules" in scrapings from his teeth. It took scientists another 200 years to establish the relationship between microbes and disease.

Although some microbes are deadly, most are harmless, and some are extremely beneficial. These microscopic organisms can be found virtually anywhere - in air, water, plants, animals, and humans.

A microbe is any living organism that spends its life at a size to tiny to be seen with the naked eye. Microbes include bacteria and cyanobacteria, protists, some fungi, and even some very tiny animals that are too small to be seen without the aid of a microscope. Viruses and the recently discovered prions are also considered microbes.

The word microbe is short for microorganism, which means small organism. Grouped by physical and behavioral characteristics, microbes fall into the following major categories:

Viruses are the smallest and simplest microbes. They are simply a ball of genes wrapped in a shell that is about a millionth of an inch across. No one knows how long they have been on Earth or how they evolved. They reproduce by injecting their genes into a cell to produce thousands of new viruses.

Bacteria are much larger than viruses, being about 125,000th of an inch long. If a virus were human sized, a bacterium would be as big as the Statue of Liberty. These one celled bodies either make their own food through chemical processes or feed on live hosts or dead matter. Bacteria have existed on Earth for more than 3.5 billion years. Kingdom Monera contains bacteria and blue green bacteria.

Fungi are decomposers in nature. They break down matter into nutrients and minerals that plants and animals reuse. Of all the 100,000 known species of fungi, familiar examples include mushrooms, yeast, mold, and mildew.

What is a Prokaryote?

Prokaryotes are cells without a nucleus. The genetic material is a single, circular DNA and is contained in the cytoplasm. Prokaryotic cells may have photosynthetic pigments, such as is found in cyanobacteria. Some prokaryotic cells have external whip-like flagella for locomotion or hair-like pili for adhesion. Prokaryotic cells come in multiple shapes: cocci (round), bacilli (rods), and spirilla (helical). They do not engulf solids, nor do they have centrioles or asters. There are prokaryotes that have a cell wall made of peptidoglycan.

What is a Eukaryote?

These are cells with a nucleus, which is where the genetic material is surrounded by a membrane much like the cellular membrane. Eukaryotic cells are found in humans and other multi-cellular organisms like plants, animals, algae, and protists. They have both a cellular membrane and a nuclear membrane that is linear and complexed with proteins that help it "pack" and is involved in regulation.

Eukaryotes are composed of both plant and animal cells. Plants vary from animal cells in that they have large vacuoles, a cell wall, chloroplasts, and lack lysosomes, centrioles, pseudopods, and flagella. Animal cells do not have the chloroplasts and may or may not have cilis, pseudopods, or flagella.

Bacteria and Antibiotics

The cell wall is the target for antibiotics, as well as for carbohydrates that our immune system uses to detect infection. A major threat to mankind is the antobiotic-resistant strains of bacteria which have been created by overuse of antibiotics.

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