55 Replies to “Osmosis | Membranes and transport | Biology | Khan Academy”

  1. I found this a little bit tedious. For the information I was trying to learn, the presentation went about too long and redundant almost telling a story to small kids. Not something i would want to see if I'm pressed for time and at the level of my inquiry (Graduate school). Maybe, just clear and concise terms and going direct to the point. But still thankful for the video to educate people.I still will continue to use your channel πŸ™‚

  2. Water model have moved beyond "molecules bouncing of each other" and "water molecules that (supposedly while flying by Na+) MIGHT stick to Na+". Why is this "billiard ball" model still taught?

  3. This didn't explain hydrostatic or osmotic pressure to me at all which is the part I'm having trouble understanding. Osmosis by itself isn't that much of a hard concept to understand.

  4. MY MAN KHAN! although you give lessons for free and shit 2 million subscribes and views getting you MULLA and you be hustling and horsing around the city with your eyes closed doing wheelie on yo Harley Davidson. keep it up.

  5. osmosis happens because the higher the concentration of solute the more ordered the solution is (lower entropy).This allows water molecules to diffuse more freely like a gas through the solution with less resistance- many water molecules are bound to solute molecules by van der waals forces and ionic forces and hydrogen bonds, so low pressure pathways are created for diffusing water molecules.
    There is a good article here on wikipedia about osmosis:

  6. What is exactly meant by the net movement of water molecules in osmosis?
    Water molecules pass in both directions randomly not down a concentration gradient as well, so is the net movement the movement of water molecules that do move down a concentration gradient?

  7. I have doubts about the mechanical blocking argument. The big molecules (of the high solute concentration) would equally block input and output which would balance out it's presence.

    I was happy to hear the charge argument, that made more sense to me.

    What about capillary action? Is it not possible that the water flows to the high solute concentration caused by adhesion towards the solute molecules? Or even initially adhesion towards the cell membrane, and after that greater adhesion to the high solute molecules?

    Last but not least, from Tesla's perspective: think of the universe in terms of vibration. Does vibration have a say in this story whatsoever?

  8. hi i got a little bit confuse but may u answer he some of the questions? All about osmosis
    this is what i understand from this video , inside the molecule have sugar (salute).So the water outside the cell will go into the molecule so the water outside the molecule and inside the molecule become the same.
    Am I right?
    pls answer me, I am going to have a exam.pls thx

  9. In general these are great videos, however, you are mistaken in the forces producing osmosis. First, water molecules are not randomly moving in the same way that the solute particles are. The polarity of water dictates that there will be hydrogen bonds formed between adjacent molecules. In the liquid form, the water molecules "line up nose to tail". A such, it is not the random movement of individual molecules that dictates the probability of crossing from one side to the other. In addition, the solute molecules do not "get in the way" preventing water from moving toward the membrane on the hypertonic side.
    The force causing diffusion of solutes is the repulsion of solute by other solute molecules increasing the probability that solute will collide and be "pushed" from the hypertonic side to the hypotonic side. As water molecules do not repel each other, the same force is not present for osmosis as diffusion.
    The forces causing osmosis are not from the water molecules, but from the solute. Solute molecules will be surrounded by water molecules which are hydrogen-bonded in a "shell" around the solute. The solute, along with the shell, are moving with Brownian motion, but can't cross the membrane, so there is a high probability that solute will concentrate at the membrane (they are moving randomly in 3 dimensions, but prevented from progressing across the membrane, so they concentrate there. This relatively high concentration of solute results in repulsion of solute, along with the shell of water, away from the membrane. The movement of solute and shell of water away from the membrane exerts inertia on other water molecule, and the solute, the shell of bound water, and the water molecules in the same general area all move away from the membrane. This creates a small area where water is absent on the hypertonic side of the membrane. As water on the hypotonic side can cross the membrane, water molecules are drawn across the membrane to fill the vacant space. In a simple form, diffusion is a "pushing" force produced by solute molecules repelling other solute molecules. Osmosis is a "pulling" force produced by solute molecules moving away from the membrane.

  10. But salman what about they molecules that are gonna enter, aren't they gonna get attracted to the water molecule that's close to the entrance pores

  11. Can i ask you something Khan ? The table salt or the sodium chloride ( NaCl ) is neutral because when sodium ion ( Na- ) bonds with chloride ion ( Cl+ ) it becomes neutral because the positive charge cancels the negative charge then how are the water molecules attracted to the salt the salt is neutral how come it will attract ??????????

    Please answer πŸ˜ŠπŸ˜€

  12. Is probability of molecules passing through really the explanation of the mechanism of osmosis? He kept saying it was just a theory, so what's the actual scientific reason for it?

  13. This is a fantastic explanation! Before I never understood why, in osmosis, there is a flow from an area of lower solute concentration to one of higher solute concentration, but it makes so much sense!

  14. You can demonstrate osmosis at home using Umibudo (sea grapes.) The umibudo are packed in super-salty water, which makes them shrivel by osmosis. When you rehydrate them in fresh water, you can see them swell up as the water rushes in by osmosis. Osmosis before your eyes!

  15. is it also the case that, on the side of the higher water concentration, then a higher proportion of the molecules which hit the semi-permeable membrane are molecules which can pass through it (so water), so this side has a higher rate of molecule interactions which could cause the molecule to pass through and therefore on average more molecules will pass through, causing net movement from high water concentration to low concentration?

  16. Im from India
    And you're the reason that I'm capable to complete my graduation…
    Thanks a lot…..
    Thanks khan academy

  17. This video helped me a lot in my exams ,thanks a lot Khan academy for publishing this video and .I love your teaching style

  18. When it is not like a door, how does it stop what it doesn't allow to pass? I mean, if the entrances are like a permanently open gate?

  19. Hi. Most of industrial RO membrane pore size is around 0.0001-0.001mcm. As you know the dimension of water molecule is around 0.275nm. How can water pass through the RO membrane?

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