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In your body, there are trillions of cells that help you do everything.
Each of these tiny cells has an even tinier cell membrane surrounding it. These parts of the cell are responsible for deciding what goes in and out of their cell.
This is a very important job, and the cell membrane is made up of lots of complex parts that make sure everything goes smoothly. Learn more about these incredible features with our 12 amazing facts about cell membranes.
If you are interested in learning more about cells, making models of cells is a great way to expand your understanding. Many important scientific breakthroughs were also discovered when scientists developed models of their ideas and figured out what works. Have a go at making your own cell with our guide to making a plant cell model. Or, if you just want to learn more about how science works, you can check out our collection of exciting online science classes and events.
What Is The Cell Membrane?
The cell membrane is an important part of all cells. Here's Why:
1) The cell membrane, also known as the plasma membrane, is a thin layer that separates the inside of the cell from the outside. Lots of things happen in our cells, including functions that we need to survive, so it is important that the right things are inside the cell when they need to be.
2) In order for the cell membrane to do its job properly, it needs to be semipermeable. This is a fancy word which basically means that the membrane allows some materials to pass through it, whilst others cannot. This is a really important function of the cell membrane as it means the cell membrane can regulate what goes in and out of the cell.
3) In animals and humans, the cell membrane is the only layer between the cell and the outside. However, other living things like plants and bacteria also have a cell wall, which goes around the cell membrane to offer extra protection.
How Is A Cell Membrane Structured?
The structure of a cell membrane allows it to do many of its necessary functions.
4) The structure of the cell membrane is what makes it semipermeable. The structure of the plasma membrane is a phospholipid bilayer. A phospholipid is a lipid (a type of fat) made out of a phosphate head and two fatty acid tails. It looks a little like a weird jellyfish.
5) The membrane of a cell is made up of two layers of lots of phospholipids lined up next to each other, with the phosphate heads pointing in opposite directions. The phosphate heads are on the outside of the membrane because they are 'hydrophilic', which means they love water. The fatty acid tails are on the inside of the membrane because they are 'hydrophobic', which means they fear water. There's lots of water on either side of the membrane, which is why the phospholipids line up the way they do.
6) The structure of a cell membrane can be seen using a fluid mosaic model. The fluid mosaic model shows how the phospholipid bilayer makes up most of a cell membrane. There are also proteins and cholesterols in cell membranes, which help to let materials pass through the membrane when they need to.
7) There are many different types of proteins that can be found in cells. Integral proteins, also known as channel proteins or transport proteins, can go from one side of the cell's membrane to the other and allows ions and other molecules to pass through. Other proteins in the membrane include peripheral proteins, which help to control the properties of the membrane.
8) Some molecules, which are very important for the function of the cell, can pass through the membrane easily, such as oxygen and carbon dioxide. However, when there is a molecule that needs to enter or leave the cell at a specific rate, it has to pass through the proteins in the membrane. This rate is called the rate of diffusion and is one of the ways the cell membrane controls what goes on in the cell.
How Does The Cell Membrane Change?
The ever-shifting structure of the cell membrane helps it to do some pretty cool things.
9) Animal cells divide through a process known as mitosis. This is when the DNA of a cell separates and the cell splits in two. In doing so, a new membrane forms between the two new cells. This is called cytokinesis and occurs when the cytoplasm forms a cleavage furrow in the middle of the old cell, separating it into two new 'daughter' cells.
10) Sometimes a cell will need to bring larger molecules from outside to inside the cell. To do this, an interesting process called endocytosis occurs. In endocytosis, part of the cell membrane forms around the molecule, encasing it in a membranous structure called a vesicle.
11) The vesicle then detaches from the rest of the membrane and enters the cell, where it will take the molecule where it needs to go. Because the membrane is made up of phospholipid molecules, it can replace the vesicle easily. It acts a bit like a liquid; if you have a bucket of water and you scoop a cup of the water out of the bucket, the rest of the water molecules replace the area you scooped up. This is similar to how plasma membranes work.
12) The opposite process can also occur. This is known as exocytosis. This happens when molecules need to leave the cell. Vesicles made of the phospholipid bilayer will carry the molecules towards the membrane. When the vesicle reaches the membrane, it fuses with the lipid bilayer and pushes the molecule outside the cell.
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