<h2>The Cell Theory</h2>
<p id="fs-id1456208">The microscopes we use today are far more complex than those used in the 1600s by Antony van Leeuwenhoek, a Dutch shopkeeper who had great skill in crafting lenses. Despite the limitations of his now-ancient lenses, van Leeuwenhoek observed the movements of protista (a type of single-celled organism) and sperm (<a href="#attachment_95634">see image below</a>), which he collectively termed “animalcules.”</p>
<div class="wp-caption alignnone" id="attachment_95634" style="width: 800px"><a href="https://data.ulearngo.com/assets/c6f1203b-4078-443d-92d4-e6f8b6ee26b5"><img alt="sperm-cells" class="size-full wp-image-95634" height="600" src="https://data.ulearngo.com/assets/c6f1203b-4078-443d-92d4-e6f8b6ee26b5" width="800"/></a><p class="wp-caption-text">Human sperm stained for semen quality testing in the clinical laboratory. Image Attribution: <a href="https://commons.wikimedia.org/wiki/File:Sperm_stained.JPG">Sperm stained.jpg</a> by "Bobjgalindo"/Wikimedia Commons (<a href="https://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA 4.0</a>)</p></div>
<p id="fs-id1283231">In a 1665 publication called <em data-effect="italics">Micrographia</em>, experimental scientist Robert Hooke coined the term “cell” for the box-like structures he observed when viewing cork tissue through a lens. In the 1670s, van Leeuwenhoek discovered bacteria and protozoa. Later advances in lenses, microscope construction, and staining techniques enabled other scientists to see some components inside cells.</p>
<p id="fs-id2182808">By the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann were studying <a data-lesson="complex-tissue-structure" data-subject="biology" data-tutorial="introducing-animal-diversity" href="https://app.ulearngo.com/biology/introducing-animal-diversity/complex-tissue-structure">tissues</a> and proposed the <strong>unified cell theory</strong>, which states that:</p>
<ul>
<li>all <a data-lesson="principles-of-biology" data-subject="biology" data-tutorial="biology-foundations" href="https://app.ulearngo.com/biology/biology-foundations/principles-of-biology">living things</a> are composed of one or more cells,</li>
<li>the cell is the basic unit of life, and</li>
<li>new cells arise from existing cells.</li>
</ul>
<p>Rudolf Virchow later made important contributions to this theory.</p>
<h2>Cytotechnology</h2>
<p id="fs-id1848543">Have you ever heard of a medical test called a Pap smear (<a href="#attachment_95636">see image below</a>)? In this test, a doctor takes a small sample of cells from the uterine cervix of a patient and sends it to a medical lab where a cytotechnologist stains the cells and examines them for any changes that could indicate cervical <a data-lesson="cancer" data-subject="biology" data-tutorial="introducing-the-cell" href="https://app.ulearngo.com/biology/introducing-the-cell/cancer">cancer</a> or a microbial infection.</p>
<div class="wp-caption alignnone" id="attachment_95636" style="width: 544px"><a href="https://data.ulearngo.com/assets/4f3616b4-b772-484c-8f1c-f24c47b1ed25"><img alt="uterine-cervix-cells" class="size-full wp-image-95636" height="347" src="https://data.ulearngo.com/assets/4f3616b4-b772-484c-8f1c-f24c47b1ed25" width="544"/></a><p class="wp-caption-text">These uterine cervix cells, viewed through a light microscope, were obtained from a Pap smear. Normal cells are on the left. Human papillomavirus (HPV) have infected the cells on the right. Notice that the infected cells are larger; also, two of these cells each have two nuclei instead of one, the normal number. Image Attribution: modification of work by Ed Uthman, MD; scale-bar data from Matt Russell</p></div>
<p id="fs-id1194585">Cytotechnologists (cyto- = “cell”) are professionals who study cells via microscopic examinations and other laboratory tests. As a result of their training, they are able to determine which cellular changes are within normal limits and which are abnormal. Their focus is not limited to cervical cells. In addition, they study cellular specimens that come from all organs. When they notice abnormalities, they consult a pathologist, who is a medical doctor who can make a clinical diagnosis.</p>
<p id="fs-id1348294">Cytotechnologists play a vital role in saving people’s lives. When they discover abnormalities early, a patient’s treatment can begin sooner, which usually increases the chances of a successful outcome.</p>

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Cell Theory

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Cell Theory

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