Cell Membrane and Transport

Liz C, Maddy Z, Livy P, Lauren S, & Melanie Z

The Plasma Membrane

The plasma membrane is an external wall like structure surrounding a cell, creating a boundary for the cytoplasm and regulates the travel of molecules in and out of the cytoplasm. The membrane being made up of lipids and proteins. One layer of the Plasma membrane is called the Phospholipid Bilayer. This is two layers made up of phosphate and lipid molecules, which forms a cell membrane. The first layer is call Hydrophilic, this is the polar heads of phospholipids. The second layer is called Hydrophobic, this is a layer of non-polar heads of phospholipids. These layers can be demonstrated in a fluid mosaic model. This model will show the cholesterol, a compound found in body tissue, Glycolipids and Glycoproteins.

Channel and Carrier proteins are found along, in the Plasma membrane. Channel Proteins are a channel protein which allows molecules across the membrane. While Carrier Proteins are more specific and strict, only allowing selective molecules to travel through the membrane.

Cellular Transport

Concentration Gradient is the gradual decrease in concentration over a distance. The concentration moves from high to low concentration. Look below at the first picture to the right to help you understand concentration gradient better.

Simple Diffusion is the movement of particles from high concentration until equilibrium occurs. Factors that affect the rate of diffusion are temperature, concentration, and pressure. An example of simple diffusion is putting food coloring into water. Look at the picture below in the middle to help you understand simple diffusion better.

Facilitated Diffusion is when certain molecules cross membranes by binding with a carrier protein. Look at the picture below on the left to help you understand facilitated diffusion better.


Osmosis is a process where molecules of a solvent pass through a semipermeable membrane from a less concentrated solution into a more concentrated one. This processes equalizes the solutions on each side. The three solutions are hypotonic, isotonic, and hypertonic.

Active Transport

Active Transport is when material moves against the concentration gradient. The material moves from low to high, requires energy (ATP), and uses carrier proteins to help move the material. An example of active transport would be a potassium pump. Look below at the picture of the potassium pump.

Bulk Transport

Bulk Transport is the movement of molecules into or out of a cell without passing through the cell membrane. This process requires energy because it moves against the concentration gradient (low to high). For molecules to enter a cell they use Endocytosis. These molecules bring food and water into the cell. The function of which these molecules exist the cell is known as Exocytosis. Removing waste and hormones from the cell.