Welcome to week 16 of Science Friday. I apologize for my absence last week. I had unexpected issues with my laptop and sent it for repairs. Looking over all my postings for SciFri, I have noticed a large emphasis on physics. While I would not say that this emphasis is disproportionate, since physics is indeed the base of the science pyramid, I do think I should give some attention to equally fascinating aspects of the world around us. Today, we will explore the miraculous world the biological cell. The biological cell’s existence answers the following question: what is the most fundamental constituent of life? While physicists are not sure if quarks and leptons are the most fundamental constituents of all matter, biologists have recognized the cell as the fundamental unit of life for decades. From the work of many dedicated scientists, we have the cell theory, which describes all cells—from bacteria to the cells of our immune system—in a few bullet points. All life is made of one or more cells The cell is the fundamental unit of structural and functional organization for life All cells come from preexisting cells An individual cell, while containing complex machinery, does not seem capable of forming complex systems as we see around us. Let’s describe generalized cell. Cells that make up animals and plants are known as [i]eukaryotes[/i]. Certain single-celled organisms are also eukaryotic. Eukaryotes are cells that dedicate different chemical reactions to different internal compartments of the cell. For example, the mitochondria of eukaryotes transform the energy of sugars into biology’s energy currency, ATP (adenosine triphosphate). The nucleus serves as the container for life’s most important molecule, DNA (deoxyribose nucleic acid). Ribosomes function to synthesize polypeptide chains, more commonly referred to as proteins. In essence, each structure has a specific biochemical task to continuously execute. Along with eukaryotes, there are also [i]prokaryotic[/i] cells. Examples of prokaryotes are many of the bacteria in the world around us (both harmful and helpful). Prokaryotes are significantly smaller than eukaryotes (in perspective, the size of a mitochondrion in eukaryotes is the size of a prokaryotic cell). Prokaryotes do not have specialized internal structures to execute specific biochemical tasks like eukaryotes. Furthermore, they contain only one circular strand of DNA (chromosome) that is in the cytoplasm, which is the cellular fluid inside a cell (there are no nuclei in prokaryotes). There is another classification (Archaea), but I will skip them here for brevity’s sake. You can think of Archaea as the extremophiles of the biosphere; these cells reside in extremely high temperature and salinity environments. While this framework is a nice concise way to describe all cells, it also underplays the sheer spectacle. Let’s approach their description a slightly different way. The human body is an immensely complex system of tissues, organs, and systems. Not only do we have the basic structural and physiological mechanisms to survive, we also have the capacity to understand our place in a larger universe and ask questions as profound as “Where did we come from?” Yet, we are nothing more than the sum of [i]trillions[/i] of cells. Some may say that this reductionist assessment of humans is an awful way to describe us. They fear that the meaning of love, anger, and passion is entirely lost when we say we are nothing more than the sum of many cells. On the contrary, I find this quite inspiring. Just think about it: every decision we make, every bond we form, and every question we pose is the culmination of trillions of cells executing their normal physiological functions. This sum of cells is what determined that gravity is the curvature of spacetime. This sum of cells is what invented integral and differential calculus. This sum of cells is what produced beautiful works of art that address the human condition. This sum of cells is us in every way imaginable. We are a consortium of cells. This realization is not only humbling, it is quite awe-inspiring. It is what attracts me to the biological sciences in general, and I hope I have been able to transfer some of that awe to you today. Thanks for reading! Stay tuned for more Science Fridays to come.