in this video we're going to talk about diffusion specifically the factors that affect the rate of diffusion but first what is diffusion what would you say diffusion is how would you define it diffusion is the movement of material from a region of high concentration to a region of low concentration so let's say that the top part is the outside part of the cell and the bottom part is the inside part of the cell oxygen is a small nonpolar gas that can easily diffuse across this semi-permeable membrane which is made up of phospholipids so oxygen is going to flow from a region of high concentration through this membrane to a region of low concentration so that is an example of diffusion it's the movement of material from a region of high concentration to a region of low concentration and down its concentration gradient but now what are some factors that affect the rate of diffusion one factor is the difference in the concentration of o2 outside and inside the cell so the triangle means change the difference between those two concentrations as that difference increases the rate of diffusion will increase so the magnitude of the concentration gradient is proportional to the rate of diffusion another factor that affects diffusion is temperature at higher temperatures gas particles can diffuse into or out of the cell membrane and so as we increase its temperature the rate of diffusion of oxygen into the cell will increase as well at higher temperatures gas molecules have more kinetic energy which means they're moving faster and at higher speeds they can diffuse across the cell membrane at a higher rate so that's why temperature and diffusion rate are directly related now the next thing we need to talk about is the mass of the particle as the molar mass of the gas increases the rate of diffusion will decrease so these two they're inversely related let's compare oxygen and carbon dioxide in the case of co2 the concentration of co2 inside the cell is higher than the concentration of co2 outside the cell so this gas is going to flow in this direction now the molar mass of oxygen gas is 32 grams per mole and you could check this in the periodic table each oxygen atom has a molar mass of 16 grams per mole carbon dioxide has a molar mass of 44 grams per mole so looking at the two numbers which gas has a higher rate of diffusion assuming if everything else is equal let's say the temperature is the same the constant excuse me the concentration gradient is the same just analyzing the molar mass which gas will diffuse at a higher rate now as we said before as the molar mass increases the rate of diffusion decreases this is because heavy molecules tend to move more slowly whereas the lighter molecules tend to move at a higher speed because carbon dioxide is heavier than o2 it's going to diffuse across the membrane at a slower rate oxygen being the lighter gas it's going to move at higher speeds and so therefore it will diffuse across the membrane at a higher rate so heavy gas molecules that have high molar masses tend to move more slowly their speed is lower and because the speed is lower the rate at which they will travel across the membrane will be lower as well the speed of a particle and the rate of diffusion are directly related the next factor that influences the rate of diffusion is surface area as the surface area of the cellular membrane increases the rate of diffusion will increase because there's more area in which the gas particles can flow through so here's a visual representation the first object has less area than the second object and so less gas particles will be able to flow through the first object but for the second one because it has a greater surface area more gas particles can flow through it and so this one will have a higher rate of diffusion because it has more surface area the next factor has to do with the thickness of the membrane so let's say this is membrane 1 and let's say this is membrane 2. the first membrane is thicker and so it's going to take a longer time for oxygen to flow through it the second one is smaller so oxygen will be able to flow through quicker on that one so as the thickness of the membrane increases the distance in which these gas particles have to travel increases and thus the rate of diffusion decreases so the rate of diffusion is inversely related to the distance traveled which is proportional to the thickness of the membrane so as you increase the thickness of the membrane the rate of diffusion decreases so those are some factors that affect the rate of diffusion of gas particles and other particles that are flowing through the cellular membrane