Concentration of a chemical in a solution refers to how many of the chemical's molecules are sitting in a small volume of the solution. Concentration could be measured in molecules per liter, although molecules are so small compared to a liter that we usually use different units just like we wouldn't want to measure the distance between the earth and the sun in inches. A gradient is a measurement of how much something changes as you move from one region to another.
So a concentration gradient is a measurement of how the concentration of something changes from one place to another. Let's give a few examples. If we picture each individual molecule as a little blue dot, a constant concentration of molecules no gradient would look like the picture below:.
A solution, essentially, has two major components, the solvent the dissolving component, e. In biochemistry, concentration pertains to the amount of a sub-component of a solution, e.
Gradient, in turn, is a term that in general refers to the progressive increase or decrease of a variable with respect to distance. In this regard, a concentration gradient would be the outcome when the amounts of solutes between two solutions are different. In biology , a concentration gradient results from the unequal distribution of particles, e.
This imbalance of solutes between the two solutions drives solutes to move from a highly dense area to a lesser dense area. This movement is an attempt to establish equilibrium and to eliminate the imbalance of solute concentrations between the two solutions.
Synonym: density gradient. In biological systems, there are two major transport phenomena: passive transport and active transport. In passive transport, particles e. This means that the particles move from areas of high concentrations to areas of low concentrations.
Because of the passive movement of particles no chemical energy is spent as it takes place. Examples of passive transport are simple diffusion, facilitated diffusion, filtration, and osmosis. Conversely, active transport is the transport of particles against the concentration gradient. This means that the particles are moved to an area of low concentration to an area of high concentration.
Because of this, chemical energy is spent to move the particles to an area that is already saturated or dense with similar particles. Simple diffusion is a type of passive transport that does not require the aid of transport proteins. Since the movement is downhill , i. A neutral net movement of particles will be reached when the concentration gradient is gone. That means that the equilibrium between the two areas is reached. The amount of particles or solutes in one area is similar to that of the other area.
In facilitated diffusion, the process needs a transport protein. Similar to simple diffusion, it is driven by a concentration gradient and equilibrium is attained when there is no longer a net movement of molecules between the two areas. In many cases, though, the concentration gradient is not enough factor in passive transport. For example, the presence of two different solutions on the external surface of the cell would have two different degrees in saturation and solubility.
For instance, small lipophilic molecules and nonpolar gas molecules could diffuse more readily through the lipid bilayer of the cell membrane than polar molecules, including water. One of the molecules that require a transport protein to move down the concentration gradient across a biological membrane is water.
Osmosis is similar to diffusion as both of them are characterized by a downhill movement. The difference lies though in the particle that moves. In diffusion, it is about the movement of solutes. In osmosis, it is about the movement of the solvent, i. Video transcript - In the first video where we introduced the idea of diffusion and concentration gradients, we had a container with only one type of particle in it, we had these purple particles.
And in our starting scenario we had a higher concentration of the purple particles on the left-hand side than we had on the right-hand side. And so if we looked at its concentration gradient, so the concentration gradient went from high concentration on the left to low concentration on the right.
And we saw what happened. Since you have more of these particles here and they're all bouncing around in different directions randomly, you have a higher probability of things moving from the left to the right than from the right to the left. You will have things move from the right to the left, but you're going to have more things, so you'll have a higher probability of things, moving from left to right.
And so if you let some time pass, then they become more uniformly spread across a container. They have moved down their concentration gradient to make things more uniform. Now, what's interesting about this diagram is I've introduced a second particle, these big yellow particles.
And we see that their concentration gradient is going in the other direction. So we have a low concentration, in fact we have no, on the left-hand, we have none of the yellow particles on the left-hand side, and we have a high concentration on the right-hand side. So their concentration gradient goes from right to left. And the whole point of this video is to show that each particle moves down its unique concentration gradient, assuming that it's not blocked in some way, it's going to move down its unique concentration gradient irrespective of what the other particles are going to do, for the most part.
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