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### Course: Biology archive>Unit 8

Lesson 2: Diffusion and osmosis

# Diffusion - Introduction

Diffusion occurs when particles move from an area of high concentration to low concentration, creating a concentration gradient. This natural, energy-free process occurs due to the random movement of particles, with a higher chance of particles moving from the high concentration side. Over time, this leads to an equilibrium state with equal concentrations on both sides. Created by Sal Khan.

## Want to join the conversation?

• Because everything is probabilistic, doesn’t that mean that it is possible for me to suddenly start choking because all or most of the air molecules moved to the other side of room?
• I think the probability of this happening is infinitely, incomprehensibly small.
• How does water go through the cell membrane?
• Water cannot go through the cell membrane by itself, but there are carrier proteins like aquaporins that can let water to pass through in a process called facilitated diffusion.
• Is passive transport the same as diffusion? If not, what is the difference?
• Diffusion is a type of passive transport.

There are 4 types of passive transport in total: simple diffusion, facilitated diffusion, filtration, and osmosis.
• in one of the explanations of diffusion, it says a "net movement," so what's the meaning of the net movement?
• It is a sum of the particles moving in both directions.

Let set them aside.

You have particles moving from A to B
and from B to A.

Whether does diffusion is from A to or from B to A depends on the net movement.

Let's say 13 particles move from A to B and 11 from B to A.

What is the net movement? :D
• What is higher concentration and lower concentration?
• Higher concentration means that you have more of something on one side and the other side. Lower concentration means you have less of something on one side than an other side. Hope this helps :)
• Are concentration gradients only present in forms of passive transport. If yes, are they present in ALL passive-transport types?
• No! concentration gradients are there, but the real thing that happens is either passive or active transport. In the previous Sal shows us that by applying energy we can prevent molecules by going with the gradient and going against it! And second also No! because there are also Electrical gradients and many more, Passive transport also happens in these!
• What is the difference between osmosis and diffusion? Or is osmosis a kind of diffusion?
• Osmosis is a kind of diffusion. Diffusion is the movement of substances from a high to low concentration, while osmosis is the diffusion of water across a cell membrane that moves from high to low water potential (or, low solute concentration to high solute concentration).
• It is like if you were playing poolball, but all the balls were randomly placed
• Kind of, yes.
(1 vote)
• If there is no gradient, and there is an equal chance that the particles will move either left or right, then how do gradients occur in the first place?