Answer: <h3>Types of Microorganisms</h3>
<p>All the microorganisms come under kingdom Protoctista (Haeckel &ndash; 1866, a German Zoologist). He included all unicellular microorganisms that are neither plants nor animals under this kingdom Protoctista.</p>
<h4>On the basis of their structure, they are two types:</h4>
<ol>
<li><strong>Eukaryotic (Eu or true nucleus)</strong></li>
<li><strong>Archaea</strong></li>
<li><strong>Bacteria</strong></li>
</ol>
<p><strong>Prokaryotic (pro or primitive nucleus) microorganisms</strong></p>
<ol>
<li><strong>Fungi</strong></li>
<li><strong>Protozoa</strong></li>
</ol>
<h3>Characteristics of microorganisms</h3>
<h4>Bacteria</h4>
<p>&nbsp;</p>
<p>Bacteria are single-celled microbes. The cell structure is simpler than that of other organisms as there are no nucleus or membrane bound organelles. Instead, their control centre containing the genetic information is contained in a single loop of DNA. Some bacteria have an extra circle of genetic material called a plasmid. The plasmid often contains genes that give the</p>
<p>bacterium some advantage over other bacteria. For example, it may contain a gene that makes the bacterium resistant to a certain antibiotic.</p>
<p>Bacteria are classified into 5 groups according to their basic shapes: spherical (cocci), rod (bacilli), spiral (spirilla), comma (vibrios) or corkscrew (spirochaetes). They can exist as single cells, in pairs, chains or clusters.</p>
<p>&nbsp;</p>
<h4>Viruses</h4>
<p>&nbsp;</p>
<p>Viruses are the smallest of all the microbes. They are said to be so small that 500 million rhinoviruses (which cause the common cold) could fit onto the head of a pin. They are unique because they are only alive and able to multiply inside the cells of other living things. The cell they multiply in is called the host cell.</p>
<p>A virus is made up of a core of genetic material, either DNA or RNA, surrounded by a protective coat called a capsid which is made up of protein. Sometimes the capsid is surrounded by an additional spikey coat called the envelope. Viruses are capable of latching onto host cells and getting inside them.</p>
<p>Viruses only exist to make more viruses. The virus particle attaches to the host cell before penetrating it. The virus then uses the host cell&rsquo;s machinery to replicate its own genetic material. Once replication has been completed the virus particles leave the host by either budding or bursting out of the cell (lysis).</p>
<h4>Fungi</h4>
<p>&nbsp;</p>
<p>Fungi can be single celled or very complex multicellular organisms. They are found in just about any habitat but most live on the land, mainly in soil or on plant material rather than in sea or fresh water. A group called the decomposers grow in the soil or on dead plant matter where they play an important role in the cycling of carbon and other elements. Some are parasites of plants causing diseases such as mildews, rusts, scabs or cancer. In crops, fungal diseases can lead to a significant monetary loss for the farmer. A very small number of fungi cause diseases in animals. In humans, these include skin diseases such as athletes&rsquo; foot, ringworm, and thrush.</p>
<p><strong>Types of fungi</strong></p>
<p>Fungi are subdivided on the basis of their life cycles, the presence or structure of their fruiting body and the arrangement of and type of spores (reproductive or distributional cells) they produce.</p>
<p>The three major groups of fungi are:</p>
<p><strong>1. Multicellular filamentous moulds</strong></p>
<p><strong>2. Macroscopic filamentous fungi</strong> that form large fruiting bodies. Sometimes the group is referred to as &lsquo;mushrooms&rsquo;, but the mushroom is just the part of the fungus we see above ground which is also known as the fruiting body.</p>
<p><strong>3. Single-celled microscopic yeasts</strong></p>
<p>&nbsp;</p>
<h4>Protozoa</h4>
<p>&nbsp;</p>
<p>Protozoa are single-celled organisms. They come in many different shapes and sizes ranging from an Amoeba which can change its shape to Paramecium with its fixed shape and complex structure. They live in a wide variety of moist habitats including freshwater, marine environments, and the soil.</p>
<p>Some are parasitic, which means they live in other plants and animals including humans, where they cause disease. Plasmodium, for example, causes malaria. They are motile and can move by:</p>
<p><strong>Cilia </strong>- tiny hair-like structures that cover the outside of the microbe. They beat in a regular continuous pattern like flexible oars.</p>
<p><strong>Flagella</strong> - long thread-like structures that extend from the cell surface. The flagella move in a whip-like motion that produces waves that propel the microbe around.</p>
<p><strong>Amoeboid movement</strong> - the organism moves by sending out pseudopodia, temporary protrusions that fill with cytoplasm that flows from the body of the cell.</p>