An introduction to cells, including the history of their discovery and the development of cell theory.
Close your eyes and picture a brick wall. What is the basic building block of that wall? A single brick, of course. Like a brick wall, your body is composed of basic building blocks, and the building blocks of your body are cells.
Fortunately, your cells are way more interesting than bricks. (Just as you, undoubtedly, are much more interesting than a brick wall!) Bricks are generally square-shaped, like all other bricks, while cells can have many shapes—round, square, spindle-shaped, and star-like. Bricks generally stay put, while many types of cells will happily migrate from one place to another. And if you slice a brick in half, you just find more brick, while if you slice a cell in half—which is a good trick, given how tiny they are—you’ll find an intricate and beautiful array of specialized structures that help the cell perform its function. Yes, cells are building blocks, but they’re the most amazing building blocks in the world!
Cells perform a huge number of different roles within your body. For example, epithelial cells protect the outside surface of the body as part of the skin and cover the organs and body cavities within. Bone cells build up bones to provide support for the body. Cells of the immune system fight invading bacteria. Blood and blood cells carry nutrients and oxygen throughout the body while removing carbon dioxide. Each of these cell types plays a vital role in the growth, development, and day-to-day maintenance of the body.
In spite of their enormous variety, however, cells from all organisms—even ones as diverse as humans, onions, and bacteria, shown from left to right in the pictures below—share certain fundamental characteristics. We’ll explore these more in the articles to come. Here, we’ll take a quick peek at cell theory and at how cells were first discovered.
It may seem obvious now that we, and other living things, are made up of cells. Prior to the 1600s, however, it wasn’t obvious at all, for the simple reason that no one had ever seen a cell up close and personal. To distinguish individual cells in a piece of tissue or individual bacteria in a sample of liquid required the development of relatively high-powered microscopes, instruments used for magnifying objects otherwise too small to be seen. For more on how microscopes are used in biology today, check out the article on microscopy.
The first person to observe cells as microscopic structures was the British scientist Robert Hooke. In fact, he was the person who gave cells their name. In his book Micrographia, he used the term cell to refer to the box-like structures he saw when he looked at dead cork tissue through a simple microscope
. He chose cell as the name because these boxes reminded him of the cells of a monastery, the simple rooms in which monks slept .
The cells that Hooke observed, however, were in dead tissue, and were in fact cell walls left behind after the death of the real cells. The first person to observe living, moving cells was Anton van Leeuwenhoek, a Dutch shopkeeper and crafter of lenses. In the 1670s, inspired by Hooke’s book, he began to build his own, more powerful microscopes
. With these, he was able to observe living single-celled organisms—such as bacteria—and sperm cells, which he collectively called animalcules.
Despite the discovery that cells existed, it took quite some time for scientists to realize that they weren’t just an odd fringe case, but rather, the essential building blocks of all plants, animals, and other living things. In fact, it wasn’t until the 1830s that botanist Matthias Schleiden and zoologist Theodor Schwann put forth a revolutionary idea: all the different parts of plants and animals are made up of cells, and that cells can be produced from other cells
German scientist Rudolf Virchow later added to this theory by stating that all cells must come from other cells—not just that some cells could, under the right circumstances, be formed this way
. However, he appears to have actually stolen this idea from Polish scientist Robert Remak .
The ideas of all these early thinkers are summarized in modern cell theory, which states:
- All living things are composed of one or more cells.
- The cell is the basic unit of life.
- New cells arise from pre-existing cells.
That’s all fine and dandy, but it may leave you wondering: if all cells come from cells, where did that first cell come from? We’ll return to that head-scratcher in later articles, when we look at the origins of life.
Want to join the conversation?
- What is the main function of a typical cell in the human body?(18 votes)
- Cellular biology is a pretty in depth field, but cells basically break down sugars into usable energy, they regulate growth through cellular division, and synthesize different proteins to perform a variety of essential biological functions depending on what type of cell it is.(34 votes)
- in the second paragraph, when you cut a cell in half, what do you see, and are any cells the same?(13 votes)
- When cut a cell in half you will see a cell membrane, cell wall (in some cells), cytoplasm- the jelly-like substance in the cell, mitochondria- the energy supplier to the cell, the nucleus- which is the brain of the cell which tells the cell what it should become for example a blood cell or nerve cell. There are other components in the cell but this is as simple as I can remember.(26 votes)
- how many cells is an egg made of?(5 votes)
- When you say that, do you mean it in an "embryonic egg, inside of the womb" context or an egg that has been laid?(6 votes)
- Does number of the cells in our body always remain the same ?(5 votes)
- Not really: cells continuously die and split so that they keep getting destroyed but the body replaces them too. Also, children have fewer cells than adults (adults are larger and therefore need more cells).(13 votes)
- Is it actually possible to cut a cell in half (as mentioned in the second introductory paragraph)? If so, how? If not, how do scientists know what the inside of a cell looks like?(7 votes)
- Are cells in the human body more reliant on other cells than unicellular organisms?(4 votes)
- We are looking at it on a different scale.
An unicellular organism does not even have 'other cells to be reliant on' since it is unicellular. In a unicellular organism, interacting with other cells would mean intra- or inter-species interactions.
In those terms, the answer is yes.(6 votes)
- What is a cell made up of?(4 votes)
- A cell has three main parts: the cell membrane, the nucleus, and the cytoplasm. The cell membrane surrounds the cell and controls the substances that go into and out of the cell. The nucleus is a structure inside the cell that contains the nucleolus and most of the cell's DNA. It is also where most RNA is made.(6 votes)
- how would that first cell survive?(3 votes)
- Most likely because of the lack of competition. If you were the only organism alive, with lots of resources around you, why wouldn't you be able to survive?(5 votes)
- are cells made out of cells(2 votes)
- Lol that's not possible! Cells are instead made out of various biomolecules and cell organelles, which are made out of various other molecules bonded together.(6 votes)