Do All Cells Have a Cell Membrane?

Instructor: Megan Gilbert

Megan has a master's degree in nursing and is a board certified Women's Health Nurse Practitioner. Her area of clinical focus is the impact of infectious disease on pregnancy. She has experience teaching college allied health classes. She is also a certified EMT and holds a certificate of added qualification in electronic fetal monitoring.

This lesson explores whether all cells have a membrane and includes an introduction to the cell membrane. Additionally, it touches on some specialized cell membranes present in the body.

The Beauty of Nature

When sitting at a microscope watching the beautiful moving blobs that are cells dance around on the slide before you, it is natural to start to contemplate their design. Cells, the most basic unit of life, can exist on their own (as in the case of bacteria) or as part of a complex organism (like a human), and can be seen individually when viewed through a microscope. As you stare at the beautiful movement in the microscope, you may begin to wonder which characteristics all cells share and which characteristics are unique between cells. Cell membranes would be one example of a shared characteristic.

Microscopic view of a reproducing malaria plasmodia in a sea of red blood cells with crystal violet staining present in order to clarify cell outline. What do the different types of cells in this picture all have in common?
microscope

While cells are made of many components, one of the most basic is the cell membrane, which separates the inside of the cell from the outside of the cell.

All cells have a cell membrane, although there are slight variations. Some cells also have cell walls. While these cell walls provide additional protection and support, they do not replace the function of the cell membrane.

The Cell Membrane

A cell membrane works to keep the inside of the cell and the outside of the cell separate. You can think of it as the skin of the cell. The cell membrane is selectively permeable. This means that only certain substances or molecules are allowed to move through the membrane. Substances that the cell needs will be allowed to enter, and substances that are no longer needed or are potentially harmful will be excreted from the cell through the membrane.

Additional functions of the cell membrane include:

  1. Cell signaling - allows the cell to send messages to other cells
  2. Cell adhesion - allows the cell to connect to other cells or to other structures
  3. Cell structure - attachment point for other key pieces of the cell, such as the cell wall or cytoskeleton

Variations in Cell Membranes

Several types of cells have unique cell membranes. While they are still cell membranes, they have different names because they have unique adaptations.

The cell membrane in muscle cells (myocytes) is called a sarcolemma. The sarcolemma can help send and receive conduction signals from other muscles.

The cell membrane in an egg cell (oocyte) is called an oolemma or the zona pellucida. It helps protect the oocyte and allows fertilization by a single sperm cell (while preventing multiple sperm cells from entering the cell).

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