The term microbe refers to microscopic organisms, which include bacteria, fungi, protoctista and viruses. Microbes cannot be seen within the naked eye.

Bacteria
Bacteria are unicellular, which means they have one cell. They are found almost everywhere and can reproduce very quickly with binary fission. They can survive in very hash conditions. Most live in or on their food. Many bacteria are harmless or even usefull to the human body but some can cause diseases.

Viruses
Viruses are not living organisms. The only characteristic of life that they display is reproduction, but this is only carried out inside a host cell. This means that they cannot reproduce unless they replicate within a host cell. Viral infections can occur in all types of living organisms. For example, influenza, human papilomavirus (HPV). A general virus structure is that they have a DNA in the middle or centre, a protein coat which is outside of the DNA and then an envelope on the outside. Zoonotic viruses, for example coronavirus, can jump between animal to animal and species to species.

Fungi
Some fungi are unicellular, which means they have one cell, for example, yeast. Some are multicellular, which means they have multiple cells, for example, mushrooms. Fungi feed extracellularly (outside their cells) by releaasing dygestive enzymes onto their food. This is called saprophytic nutrition and fungi are saphrophitus. Other fungi are useful, for example, yeast. Yeast is used to make bread and beer, and penicilllium produces the antibiotic Penicillin.

Protoctista
Protoctista are simple organisms. They are organisms that are cannot be classified as animals, plants or fungi. Some of them resemble animal cells and take in and digest solid food, for example, amoeba. Other protoctista possess chloroplast and photosynthesize like plants, for example, seaweeds and single-celled algae such as Euglena or Chlorella. Some protoctista can cause diseases such as malaria (caused bby Plasmodium) and dysentery (caused by Amoeba). Protists are simple eukaryotic organisms that are neither plants nor animals or fungi. Protists are unicellular in nature but can also be found as a colony of cells. Most protists live in water, damp terrestrial environments or even as parasites.

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Bacteria:

• Single-celled microorganisms

• Prokaryotic cells without a nucleus

• Diverse shapes and sizes

• Play important roles in ecosystems

• Some bacteria cause diseases

Viruses:

• Non-living infectious agents

• Consist of genetic material and protein coat

• Require a host cell to replicate

• Cause various diseases in humans, animals, and plants

• Not classified as living organisms

Fungi:

• Eukaryotic organisms

• Obtain nutrients by absorbing organic matter

• Reproduce through spores

• Include mushrooms, yeasts, and molds

• Play roles in decomposition and nutrient cycling

Protoctista:

• Diverse group of eukaryotic microorganisms

• Single-celled or multicellular

• Include algae, protozoa, and slime molds

• Occupy various habitats, including aquatic environments

• Important in food chains and oxygen production

Spontaneous Generation