Plasma Membranes

The plasma membrane is very small. At 7 – 10nm it’s even hard to see exactly what it looks like under an electron microscope. This means that scientists cannot be sure how the membrane functions. However, one theory which is widely accepted is known as the Fluid Mosaic Model.

The Fluid Mosaic Model

The Fluid Mosaic Model maintains that plasma membranes are made from a phospholipid bilayer which contains a number of protein molecules floating inside it. The ‘fluid’ part of the name refers to how certain parts of the membrane are able to move freely. The ‘mosaic’ part refers to how the proteins are laid out. Some proteins are intrinsic or integral which means that they go through the membrane completely. Proteins that are only partly embedded are known as extrinsic or peripheral.

The cell membrane controls what enters and leaves the cell and so is the most important of the cell’s organelles. It’s composed of:

• phospholipids
• proteins
• carbohydrates

Cell Structure

Cells are what make up all living organisms and they have both structural and functional roles. Different cells are designed in specific ways in order to carry out a specific function. However, the biggest difference is between prokaryotic cells, found in bacteria, and eukaryotic cells, found in the other four kingdoms (protoctista, fungi, plants and animals).