Diffusion and osmosis

[Music] the movement of materials in and out of a living cell involves many processes of these perhaps the most basic and best understood is the physical process of diffusion diffusion depends on the motion of molecules we can get evidence of molecular motion by observing a drop of milk under the microscope fat globules in the milk move back and forth at random they're being bombarded by molecules which themselves move about in a random fashion to show the effect of the random movement of molecules we let some colored gas into a closed container there is a movement of molecules from an area of Greater concentration to an area of lesser concentration this is the process of diffusion after a period of time the gas is diffused evenly throughout the container to show how diffusion is involved in the movement of materials in and out of a living cell will'll represent a cell using this smaller plastic Cube the sides are of an extremely thin plastic which functions as a membrane this membrane has physical properties similar to the membranes that enclose living cells materials which enter or leave a living cell pass through a membrane which surrounds the cell let's see the effect of the membrane on the diffusion of a gas with the cell inside the larger container gas is admitted into the cell at first the gas seems confined within the membrane as time goes on the gas diffuses through the membrane diffusion continues until the concentrations of gas within and without the cell are equal this helps us understand how Gases such as oxygen and carbon dioxide diffuse in and out of living cells all gaseous Exchange in Plants depends on the process of diffusion diffusion also accounts for the exchange of gases in animals oxygen and other gases in the air enter through the rabbit's nose and move into its lungs as the animal breathes inside the lungs the gases move into clusters of air sacs called Alvi in each alveolus oxygen gas is more concentrated than in the surrounding capillary where the blood cells are so oxygen diffuses into the blood in the blood cells carbon dioxide is more concentrated than in the alvus so carbon dioxide diffuses out of the blood cells in much the same manner gas diffuses in and out of other living cells living cells are composed primarily of water and generally exist in Water Solutions immersing the cell model in a container of water helps us simulate the physical conditions encountered by a living cell in the water outside the cell membrane We'll pour some molasses molasses contains glucose one of the simple sugars used by living cells we'll see if molassus Will diffuse through the membrane we'll time the diffusion process at the start the inside of the cell is clear about six hours later some of the Molasses has penetrated the cell membrane after 12 hours the Molasses concentrations outside and inside the cell are nearly equal this membrane is permeable to molasses starch is another material used by living cells we'll pour the starch into the water outside the cell as we did with the Molasses we'll see if the membrane is permeable to starch 6 hours later the starch has diffused throughout the surrounding water but has not permeated the membrane at the end of 12 hours the star still has not penetrated the membrane so this membrane is impermeable to starch a membrane that is permeable to some substances and impermeable to others is called a semi-permeable membrane semi-permeable membranes surround living cells such a membrane is generally permeable to such things as gases water sugars and salts it is generally impermeable to to substances like starches fats and protein this semi-permeable quality of a living cell membrane helps explain why in blood cells gases readily diffuse in and out while large protein molecules stay within the cells in the small intestine large fat molecules must be broken down into smaller glycerin and fatty acid molecules to permeate the m brains of the intestinal wall in plant protoplasm starch must be broken down to sugar to diffuse through the membranes surrounding the cells of the plant all of this movement in and out of cells takes place in water with this plastic sack we'll investigate the diffusion of water through a membrane the egg will provide protein material as found in a cell now the membrane is placed in water see if you can predict what will happen the sack swells inside the sac are water molecules and molecules of protein outside the sac are only molecules of water water then is more concentrated outside than inside side so water diffuses into the sac the diffusion of water through a semi-permeable membrane is called osmosis we can illustrate osmosis in a living cell with the aid of some red blood cells viewed under a microscope the concentration of materials in the water outside the cells is almost the same as inside there is osmotic balance we can upset this balance by adding a drop of distilled water watch what happens to the blood cells now they expand and burst water moving into the cells by osmosis creates osmotic pressure enough to destroy the delicate membranes another example of Osmosis can be shown using plant cells we'll add a salt solution to some algae plants the water molecules outside the cells are less concentrated than inside in this case water diffuses out of the cell causing the membranes to shrink away from the cell walls the protoplasm is crowded into the center ERS of the plant cells as a result of Osmosis using another plant we can demonstrate how osmosis is involved in absorption of water through Roots the plant is being placed into a concentrated salt solution this will reverse the process of osmosis removing water from the plant in time-lapse photography we see the plant wilting we can restore the stiffness to the plant by removing it from the salt solution and placing the roots in fresh water to show that the water diffuses back into the plant we'll use timlapse photography once again osmotic pressure against the cell walls causes a firmness known as turer the maintenance of turer is an important effect of Osmosis osmosis remember is a special case of diffusion diffusion of water through a semi-permeable membrane the diffusion of water the diffusion of glucose the diffusion of gases and other materials helps account for the movement of material materals in and out of living [Music] cells