Bacteria and Single Cells
Cells
Now we need to discuss CELLS. You’ve probably heard of cells, and may even know of a few, such as blood cells, nerve cells, or skin cells. What are these things called cells?
Cells are the smallest living things. You’ll be learning a lot about cells in this course. For now, however, I'll introduce you to just a few basic things about them. Cells are extremely tiny organisms that carry out all of the functions of life inside a thin layer of “skin” called (unimaginatively) the CELL MEMBRANE. A good analogy is the thin, flexible skin of a soap bubble.
The cell membrane keep the cell together. Without the membrane, all of the cell’s contents would dissolve into the surroundings. The cell membrane also acts as a filter. It keeps unwanted substances, such as toxins outside of the cell, while allowing useful substances such as nutrients to enter.
Figure 1.11. A single-celled organism called Stentor. The cell membrane of these organisms can extend into a trumpet shape, as on the left, or be retracted into a ball shape, as on the right.
As an example of single cells, and their flexible membranes, consider the Stentors shown in Figure 1.11. Stentors are single cells that live their whole lives as independent beings, roaming ponds and streams and sweeping food into their funnel-shaped mouths. Their cell membranes look somewhat blue in the Figure, and are translucent, enabling you to see the organism's "guts" inside, which look like greenish blobs and swirls.
Because their membranes are flexible, Stentors can change shape, extending into a trumpet to feed, or retracting into a ball for protection. Stentors are some of the largest single-celled organisms on earth, although they only get to be about 2mm long (about the thickness of two dimes).
In case you're wondering why Stentor is italicized, this is a standard convention for scientific names. Every living thing has an official name, called a scientific name or a Latin name. It is the standard name for an
Now we need to discuss CELLS. You’ve probably heard of cells, and may even know of a few, such as blood cells, nerve cells, or skin cells. What are these things called cells?
Cells are the smallest living things. You’ll be learning a lot about cells in this course. For now, however, I'll introduce you to just a few basic things about them. Cells are extremely tiny organisms that carry out all of the functions of life inside a thin layer of “skin” called (unimaginatively) the CELL MEMBRANE. A good analogy is the thin, flexible skin of a soap bubble.
The cell membrane keep the cell together. Without the membrane, all of the cell’s contents would dissolve into the surroundings. The cell membrane also acts as a filter. It keeps unwanted substances, such as toxins outside of the cell, while allowing useful substances such as nutrients to enter.
Figure 1.11. A single-celled organism called Stentor. The cell membrane of these organisms can extend into a trumpet shape, as on the left, or be retracted into a ball shape, as on the right.
As an example of single cells, and their flexible membranes, consider the Stentors shown in Figure 1.11. Stentors are single cells that live their whole lives as independent beings, roaming ponds and streams and sweeping food into their funnel-shaped mouths. Their cell membranes look somewhat blue in the Figure, and are translucent, enabling you to see the organism's "guts" inside, which look like greenish blobs and swirls.
Because their membranes are flexible, Stentors can change shape, extending into a trumpet to feed, or retracting into a ball for protection. Stentors are some of the largest single-celled organisms on earth, although they only get to be about 2mm long (about the thickness of two dimes).
In case you're wondering why Stentor is italicized, this is a standard convention for scientific names. Every living thing has an official name, called a scientific name or a Latin name. It is the standard name for an