Substances will move through the membrane by diffusion. This is the random spreading out of particles until they are even. For example, when you put your instant coffee in boiling water, the coffee particles spread out and fill the entire mug, this is diffusion. A second way that substances can move through the cell membrane is by osmosis. This is a special type of diffusion where water moves from a high to a low concentration through a 'partially permeable membrane', or a membrane specially shaped to only allow water molecules through. To learn about Osmosis in more detail visit Osmosis
A final way that substances can be moved through a membrane is active transport. This is where important substances are moved by the membrane. This process requires energy.
Active transport is the mediated process of moving molecules and other substances across membranes. Active transport differs from passive transport in that it utilizes chemical energy in the form of adenosine triphosphate, or ATP, to move molecules against the concentration gradient — from an area of lower concentration to an area of higher concentration. There are two types of active transport:
Primary Active Transport
Primary active transport directly utilizes chemical energy to move molecules through a membrane. The sodium-potassium pump, present in almost all animal cells, is an example of the use of primary active transport. It expends ATP energy to move sodium ions out of the cell and replace them with potassium ions. This exchange leaves the interior of the cell more positively charged than the cell’s exterior. This means the sodium-potassium pump must overcome not only a concentration gradient but also an electrochemical gradient as well. Secondary Active Transport
In secondary active transport, molecules are moved through a membrane as the direct result of the diffusion of another substance. The sodium-calcium exchanger, or antiporter, uses the normal diffusion of sodium ions into the cell to power the transport of calcium out of the cell (and across a higher concentration gradient). In another example, the glucose symporter uses the normal diffusion of sodium ions into the cell to piggyback the transport of glucose into the cell as well.
Diffusion and OsmosisDiffusion - the process by which molecules spread from areas of high concentratiion, to areas of low concentration. When the molecules are even throughout a space - it is called EQUILIBRIUMConcentration gradient - a difference between concentrations in a space. OSMOSISWatch this animation of water molecules moving across a selectively permeable membrane. Water molecules are the small blue shapes, and the solute is the green.The solute is more concentrated on the right side to start with, which causes molecules to move across the membrane toward the left until equilibrium is reached.Start Animation| | Selectively Permeable - membranes that allow some things through, the cell membrane is selectively permeable, water and oxygen move freely across the cell's membrane, by diffusionOsmosis - the diffusion of water (across a membrane)Water will move in the direction where there is a high concentration of solute (and hence a lower concentration of water.A simple rule to remember is:Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This is also why you get thirsty after eating something salty.Type of Solutions | If the concentration of solute (salt) is equal on both sides, the water will move back in forth but it won't have any result on the overall amount of water on either side."ISO" means the same| | The word "HYPO" means less, in this case there are less solute (salt) molecules outside the cell, since salt sucks, water will move into the cell.The cell will gain water and grow larger. In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell...