Why do living things have cells?

Why do living things have cells? Good question. I begin with three introductory remarks.

1) A cell is a building block of living things, surrounded by a membrane, which serves as a boundary. Cells were first named such by Robert Hooke, who saw a resemblance between cork tissue he looked at in a microscope (see here for picture), and the cells in a monastery. The cell theory is the idea that all living things are made of cells, and that these cells came from other cells, which existed before them. The cell theory dates to the 18oos.

2) Strictly speaking, not all living things do have cells. Most bacteria, and some other organisms, are made of only one cell, not cells.

3) What is meant by "Why"? Good question. There are several meanings, and several possible answers. One of the meanings is "What is the cause?" One answer is that I have cells because my parents did. Another meaning, and answer, would be that "Organisms have cells because God designed living organisms in this way, or because pre-organisms which had cell-like structures were selected over pre-organisms that didn't." There are theories about the origin of cells from non-living things by evolutionary processes. As would be expected, even if this is the way things came about, there is little or no hard evidence for this. It is possible that God used evolutionary processes to bring about His design for living things.

Another meaning is "What is the function of cells?" As interesting as are the other meanings of "Why?", this is the meaning I am using in this musing. Another way to put it is "What good does the possession of cells do living things?"

I have dealt previously with another basic biological question, namely "Why is there sex?"

OK, why? The answer seems to be that cells allow for specialization. Cells, tiny units, more or less self-sufficient, can have many different functions in the same organism. Most likely, the cell arrangement, wherein discrete units exist, somewhat disconnected from the other units, makes the extreme specialization necessary for our existence possible in a way that having one part of a seamlessly connected whole perform a specialized function could not.

And cells are specialized. For example, some skin cells seem to mostly be there just to act as a barrier between the organism and what's outside of it. Antibody-producing cells seem to manufacture only one particular antibody, helping to fight off only one type of invader each. Neurons (nerve cells) don't produce eye pigment, or secrete digestive enzymes, or carry Oxygen. They transmit messages, sometimes over long distances.

Each of these cells is part of one single organism. Each of these cells (except the antibody-producing cells, where there is some variation) has the same genetic information. But different parts of the genetic information are expressed in each different type of cell.

I'm made up of trillions of cells, and trillions more of my cells have died since my conception. I'm glad for all of them. Here's a web page, from the Howard Hughes Medical Institute, answering the same question that I have.

Thanks for reading. I hope to post on being thankful for cell division in a day or two. To see another post on scientifically oriented gratitude, go here.

*   *   *   *   *

August 5, 2013. Upon looking at this post after a few years, I decided to add something: There's another way in which having cells helps organisms. It is related to something called the surface to volume ratio. What is that? Suppose you compare three pieces of jello -- each one containing the same amount of jello, in other words, the same volume. Further, for simplicity, suppose that the jello forms a cube, 4 units of length on a side. Inches, centimeters, pick your unit. OK. What's the surface area of such a piece of jello? It has six sides, and each side is 4 x 4 units squared in area. So, the total surface is 6 x 4 x 4 = 96 units squared. Now, lets take the second piece of jello. This time, we'll imagine that it is sliced across, such that there's a top half, and a bottom half. Then, we slice it again, twice, down from the top, at right angles, so that the piece of jello is now made of eight smaller cubes, each 2 x 2 x 2 units, four on top, four on the bottom. The volume remains the same. What's happened to the surface? The total surface is now the total of the surface of 8 cubes, each with 6 sides, each side 2 x 2, so that the total surface is 8 x 6 x 2 x 2, and the total surface is now 192 units squared.

Then, imagine that the third piece of jello is cut so that there are four layers of 16 small cubes, 1 unit on the side. The total surface will be 4 x 16 x 6 x 1 x 1 = 384 square units. The surface to volume ratio increases, as the object is divided into smaller subunits.

What's the point? The point is that, as a volume is divided into smaller and smaller subunits, the volume acquires more and more surface area. This is true whether the subunits are cubes, spheres, or of some other shape. If the volume is a living organism, that organism would have more surface, to absorb external material (such as Oxygen or water) and, also more surface area to expel unwanted wastes, if divided into cells.

As aside - I once saw a nestful of baby killdeers fall off a two-story building. Their parents had raised them from eggs on the roof. After a brief period of recovery, they ran off, unfazed. If I had fallen off, I wouldn't have been unfazed. An elephant would have likely have been more seriously injured. Why? At least partly because a small bird has more surface per volume than I do, hence, more air resistance. An elephant, or a whale, has even less external surface per volume.

Thanks for reading.