A cell membrane is kind of like the guard that watches over the cell. It is a thin layer that surrounds the cell’s organelles and cytoplasm, and it ensures that only approved materials can enter and exit the cell.
Keeping the cell healthy is the main job of the cell membrane and to allow materials in and out it has small openings or doorways.
This ability is called being “permeable” and it lets those materials leave that are supposed to (such as waste), approved materials enter when they are supposed to (such as food); and it blocks anything that could be toxic to the health of the cell.
The cell membrane is often compared to a kind of “plastic bag” that has small holes and surrounds the cell.
Most of the structure of the membrane is made up of phospholipids, which make of the “bag”, and proteins that are found inside and outside of the holes to assist in moving materials in an out of the cell.
Sometimes called the “plasma membrane”, it’s so small (10 mm thick), that it can barely be seen using a transmission electronic microscope. Although both animal-like cells and plant-like cells have cell membranes, each type is different.
Animal cell membranes differ from plant cell membranes because they have a harder membrane due containing a substance called cholesterol.
Unlike plant cell membranes, animal cell membranes have a single outside membrane that accomplishes all of the functions.
Plant-like cells have a cell wall as the first layer of protection and the structure of this wall is very rigid.
The membrane as a secondary protection area and it’s found inside the cell wall. Since plant cell membranes have the sturdy wall, they don’t need the cholesterol that animal cell membranes use.
The plant cell membrane is a lot softer than animal cell membranes.
Since the membrane is a kind of two-dimension flow, scientists refer to cell membranes as “fluid mosaic”. This is mainly because of the job that they do.
The plasma membrane is made up of the same materials that surround the organelles on the inside of the cell. Different species have different cell and membrane sizes, depending upon the purpose of the cell.
The term “membrane transportation” is a scientific name for the molecules that are allowed to enter and leave using the membrane access. There are two types of transportation:
Passive transport, which is the allowance of molecules to flow across the membrane from an area where they have a high population to one that has a low population.
This is also called the process of “diffusion” and we can see this happen to our fingers and toes when we are in the water for a long time. Diffusion is what lets water in and makes our fingers and toes wrinkly.
Active transport is the exact opposite, moving molecules from a low concentration to a higher one.
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