What are cell membranes and what do they do? Do plant cells have them, or do they just contain cell walls? This lesson answers those questions through an investigation into cell membranes, then you can test your knowledge with a short quiz.
What Is a Cell Membrane?
All living things are made from cells. Plant cells are somewhat unique because unlike animal cells, plant cells contain both a cell wall and cell membrane. Animal cells only have the cell membrane. The cell membrane is a semi-permeable covering surrounding the outside of the cell. Plant cell membranes are found on the outside of the cell cytoplasm and just inside the cell wall.
So, the answer to the question, ‘Do plant cells have a cell membrane?’, is ‘Yes!’
Cell Membrane Function
Now, what do plant cell membranes actually do? Well, our initial definition said that cell membranes are semi-permeable, and that they surround the cell. This information hints at two primary functions of plant cell membranes. First, the membrane retains the cell’s cytoplasm and interior parts, and second, it allows specific substances to pass through it, while prohibiting others from doing so.The first of these functions is fairly obvious. Just like a water balloon holds water inside, the cell membrane holds all cellular components inside. No big surprise there.
The membrane, along with the cell wall beside it, keeps the cell together. So rather than focus on the obvious function, let’s look at the second job: controlling entry and exit from the cell. By controlling what gets into and out of the cell, the membrane is functioning as a regulatory structure.
An example of something the plant cell membrane regulates is the release of enzymes. Enzymes are molecules that speed up chemical reactions. One such enzyme belongs to the pitcher plant. These plants are carnivorous and eat insects.
The plant cell membrane inside pitcher plants will release enzymes to aid in digestion. Inversely, plant cell membranes can also prevent material from entering the cell. For example, harmful bacteria cannot simply invade the plant cell’s interior because the membrane will not allow it to cross.
Controlling Entry and Exit
To understand how plant cell membranes control the material entering and exiting the cell, we must first understand what the membrane is made of. For that, let’s look at the cell membrane up close:
In a cross section of a cell membrane, we can see the green proteins embedded in the membrane.
Proteins are structures within the cell membrane that regulate entry to and exit from from the cell. Proteins are like doorways into the cell. Different molecules will use different doorways, or proteins, to cross the membrane.
Other molecules will be denied entry because there is no doorway for them. It is because of these proteins that the plant cell membrane is capable of performing its second function: regulating entry and exit from the cell.
Plant cells, such as those within trees, bushes, grasses, and other plants, do contain cell membranes. These plant cell membranes are semi-permeable and located between the cell’s interior and outer cell wall. The membrane performs two vital functions. First, it creates the outer boundary of the cell and, in conjunction with the cell wall, holds the cell together.
And, second, it controls entry to and exit from the cell. The plant cell membrane is capable of performing this second task because of proteins embedded within it. Proteins are the structures inside the cell membrane through which material passes. An example of something that proteins help regulate is the release of enzymes.
Enzymes are molecules that speed up chemical reactions.