The ninth and final basic property of cells that Karp provides us with is that:
Though the exact mechanism by which cells arose is yet unknown to biologists, science-based potential explanations have been proposed for decades. It is thought that the precursor to cells was some sort of precellular life form. And the precursor to that precellular life form is thought to be nonliving organic materials present in the primordial seas (Karp 2013).
Though it is difficult to say exactly where cells came from, it is much easier to talk about their evolution. Information about the evolution of cells is obtained by studying organisms that exist today. Though different cells found in different parts of the body differ substantially in a number of ways, such as cells of the human intestinal tract and cells that line that same tract, these cells often have a lot in common. These cells may share a common genetic code, a plasma membrane, and ribosomes (Karp 2013).
Modern biologists have deduced that all of the organisms on Earth today originally came from a single, common ancestral cell that lived over three billion years ago. This cell is known as the last universal common ancestor because it gave rise to and connects all of the living organisms on the earth today. Evolution, such as that of the last universal common ancestor over billions of years, continues to occur. That being said, the basic properties of cells that we discussed (nine in total) are subject to said evolution, and can be modified over time. Not only that, but there are perhaps a multitude of organisms that don’t actually exist yet, but will in the future, that will evolve to have a number of properties characteristic of their own cells (Karp 2013).
Karp’s eighth basic property of cells is that:
Cells, despite their size, are more durable than we think. Because of this, in recent years, the term robust has been used to describe cells. Cells endure throughout dangerous fluctuations in composition and behavior. Feedback circuits are activated when fluctuations occur, allowing the cell to return to its appropriate state. Previously, I mentioned that cells are highly complex as well as organized. Well, for this state to be maintained, the cell requires both energy and constant regulation. When cells break down, the importance of a cell’s regulatory mechanisms becomes evidence. When a cell fails to correct a mistake during the duplication of its DNA, a debilitating mutation may be the result, or in another case, the cell’s growth-control safeguards may break down, converting the cell into a cancer cell, which has the ability to destroy the whole organism (Karp 2013).
Though the current knowledge on self-regulation of cells seems impressive, there is a lot more to be discovered. In 1891, a German embryologist, Hans Driesch, discovered that he could completely separate the first two or four cells of a sea urchin embryo. He also observed that each of the isolated cells would continue to develop into a completely normal embryo (under regular circumstances). At the time, this was intriguing. That the isolated cell could regulate its own activities and then form an entire embryo, that it could recognize the absence of its neighbors, that it could redirect the entire course of the cell’s development, and that merely a portion of an embryo could have a sense of the whole all were rather remarkable things. At yet, even today we are unable to answer these questions definitively (Karp 2013).
In biology, many processes can be described using a series of ordered steps. In the cell, nucleic acids hold the information for “product design,” (such as in the assembly-line construction of an automobile). Proteins are like the construction workers. The presence of nucleic acids and proteins makes the study of the living cell worlds different from the nonliving cell. What makes a cell’s processes much different from the assembly-line construction of a car is that each step occurs spontaneously, and not with the benefit of conscious direction. Each spontaneous event must trigger the next step automatically. Cellular activities of different types thus require unique tools and machinery, all of which are highly complex, and all of which have only been obtained over the course of history through natural selection and biological evolution (Karp 2013).
Karp tells us that the seventh basic property of cells is that:
Cells, like the organisms they make up, respond to environmental stimuli. Some of the ways in which certain types of cells do this are obvious: single-celled protists may move away from objects in their path, or move toward sources of nutrients. Some cells, such as those within multicellular plants and animals, might not have such obvious responses to environmental stimuli. Receptors cover most cells, and receptors interact with substances in the environment (environmental stimuli) in highly specific ways. Receptors on cells are involved in a number of different pathways, being that cells can possess receptors to hormones, growth factors, extracellular materials, and even to substances existing on the surfaces of other cells. Receptors provide pathways through which external stimuli are able to evoke a particular response in target cells. In response to specific stimuli, cells may alter their metabolic activities by moving from one place to another, or even commit suicide (which you may have learned about in other biology courses, termed apoptosis) (Karp 2013).
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