Cell membrane facts for kids
The cell membrane is a thin, flexible layer that surrounds the cells of all living things. It's sometimes called the plasma membrane.
Its main job is to separate the inside of a cell from its outside environment. In all cells, the cell membrane keeps the cytoplasm (the jelly-like stuff inside) separate from everything else. Animal cells only have a cell membrane as their outer layer. However, Bacteria, fungi, and plants have a strong cell wall outside their cell membrane. This cell wall gives them extra support and protection.
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Discovering the Cell Membrane
Robert Hooke first saw cells in 1665. His discovery led to the idea of the Cell Theory. Hooke mostly looked at plant cells. Because of this, he thought all cells had a hard cell wall. This idea was a bit misleading. For over 150 years, scientists focused mainly on the cell wall.
As microscopes got better in the 1800s, scientists learned more. They realized that animal cells didn't have cell walls. They also started to understand that a special outer layer existed in all cells. This layer was different from the strong cell wall found in plants.
By the late 1800s, some scientists correctly guessed that cell membranes were important. But many still didn't think they were a vital part of every cell. In 1895, Ernest Overton suggested that cell membranes were made of lipids (fats). This was a big step forward!
It wasn't until the 1900s that the cell membrane's importance was fully understood. In 1925, scientists Gorter and Grendel confirmed that the membrane was "lipid-based." Also in 1925, Hugo Fricke measured how thick these membranes were.
What the Cell Membrane is Made Of
The cell membrane is mostly made of a very thin layer called the phospholipid bilayer. Imagine two layers of tiny molecules called phospholipids. Each phospholipid has a "head" that loves water and a "tail" that hates water.
The water-loving heads face outwards, towards the water inside and outside the cell. The water-hating tails point inwards, away from the water. This arrangement creates a barrier that controls what goes in and out.
Other important parts, like proteins and different types of lipids, are also mixed into the cell membrane. These additions help the cell decide what it takes in or sends out. Some proteins are always stuck in the membrane. These are called integral membrane proteins. Others are only sometimes attached. These are called peripheral membrane proteins.
How the Cell Membrane Works
The cell membrane is "selectively permeable." This means it's picky about what it lets through. It actively regulates (adjusts) what enters and leaves the cell.
Substances can move across the membrane in two main ways:
- Passive movement: This happens without the cell using any energy. Think of a ball rolling downhill.
- Active movement: This requires the cell to use energy. Imagine pushing a ball uphill.
Proteins in the Membrane
Proteins within the cell membrane are super important for its job. These proteins mainly help transport chemicals and information across the membrane.
The membrane has many different proteins. Some proteins on the surface act like gates. They let certain chemicals into the cell and allow others to leave. It's believed that about one-third of all human proteins are membrane proteins!
Some of these proteins are linked to the outside of the cell membrane. For example, the CD59 protein helps identify cells as "self." This stops the immune system from attacking and destroying them.
See also
In Spanish: Membrana plasmática para niños
