Simple Diffusion

Concentration Gradients

We would be in a physical classroom together. I would walk into class with some luscious and juicy type of citrus fruit. You know I’m a fan of blood oranges and tangerines Coming times. I like the citrus fruits. I would start to open up my juicy citrus fruit. I would ask students to raise their hand when they finally smell the juicy citrus fruit. What I’ve done by opening up my juicy citrus fruit is I’ve created a concentration gradientA difference in the concentration of a substance across a space.. Cool the scent moleculesGroups of atoms bonded together. released from my tangerine are very concentrated around me. Without any help, the molecules will move from where I am located. This is an area of high concentration. They will move to the outer reaches of the classroom. Those areas are low concentration. It is these two areas with a difference in concentration that are a concentration gradient. All concentration gradients want to become homogeneously mixed. When you die, you will decompose. The molecules that make you will become homogeneously mixed with this earth and this universe. Your molecules will move from where they are in high concentration in your body. They will spread to areas where they are in low concentration, which are the outer edges of the universe. I think on a big scale sometimes. Go bigger go home

Diffusion

What’s more important to us than luscious juicy tangerines Or is the verb diffusionPassive movement of molecules from areas of high to low concentration.. A concentration gradient is two areas with a difference in concentration. But diffusion is the movementA fundamental property of life involving motion of the body or its parts. of citrus molecules. They move from an area of high concentration to an area of low concentration. If I put a drop of ink into a glass of waterThe universal solvent essential for life., it will spread. After an hour, there will be a homogeneous mixture. No energyThe capacity to do work or cause change. is required. Molecules move from an area of high concentration to an area of low concentration naturally. Diffusion requires no energy. It is a passive movement. It reflects the will of the universe to make a homogeneous mixture. It is the will of the universe to create homogeneous mixtures from all gradients. And it is this rule that your body uses to move molecules.

Simple Diffusion

Simple diffusion is Movement from an area of high concentration to an area of low concentration. So this term would fit the example of my juicy tangerine. When we think about the cellsThe basic structural and functional units of life. in our body, simple diffusionThe passive movement of molecules across a membrane without the use of transport proteins. involves molecules fitting between the phospholipids. These molecules fit into the phospholipid bilayer. Only very small molecules can do this. The tales of the phospholipids create a nonpolar area of the cell membrane. Only nonpolar molecules can make the journey. Small nonpolar molecules like oxygen and carbon dioxide are capable of simple diffusion. In factA statement based on direct observation that is repeatedly confirmed., if I were to stand here with my mouthThe opening of the digestive tract where food enters and mastication begins. open, oxygen would diffuse into me. Carbon dioxide would diffuse out without any help. However that rate of diffusion would not be fast enough to keep me alive.  If I were, say, a jellyfish, I could just jiggle around the ocean. Diffusion of gases would happen without lungs or even gills.

Simple Diffusion

You can determine the direction of simple diffusion by figuring out where a molecule is in high concentration. You can also do this by identifying where the molecule is in low concentration. But there are other things that affect this process of simple diffusion. Let’s revisit the example of the ink drop in a glass of water. There are two actions I could take. These actions would speed up the process that makes a homogeneous mixture. I could stir the water adding kinetic energyEnergy of motion. to the system and increasing the rate of diffusion. I could also heat the water adding kinetic energy to the system and increasing the rate of diffusion. So how quickly the molecules move down that gradient can also be called the time to equilibrium. This is how long it takes a solutionA homogeneous mixture of two or more substances. to make a homogeneous mixture. Time frame depends on the distance of the gradient. If I were in a larger classroom, it would take longer for the student in the back corner. It would take time for them to smell my tangerine. This time frame depends on the size of the molecule. Smaller molecules move more quickly. This time frame depends on temperature. As we know from the example, heating our glass of water with the ink droplet demonstrates that increasing temperature reduces the time to equilibrium. There is also something called the steepness of the gradient. This is the relative difference between the area of high concentration and the area of low concentration. If the concentrations are very different, it will take a long time. All of the molecules need to move to make a homogeneous mixture. If the concentrations are relatively similar it will not take a long time until we create the homogenous mixture. The last thing that affects the time it takes to take a gradient to a homogeneous mixture is electrical forces. Unfortunately there are chemical gradients but there are also electrical gradients. Keep this in mind because when we hit the chapter about muscles it will come into play