Osmosis and Water Potential (Updated)

Published by Darron Toy on


Captions are on! Click CC at bottom right to turn off. You can stay up to date with us on Twitter (@AmoebaSisters) and Facebook! When we were kids, growing up in West Texas,
our winters would be cold but rarely experienced snow. But we did have ice, which resulted in the
roads being salted. As the salt mixes in and dissolves into water
on the road, this can lead to a lower freezing point which can help prevent the roads from
icing over. And while this is great for making the roads
more safe, it wasn’t so great for the plants that lived right along the roadside. It often caused them to die. Now winter can be hard for many plant species,
but I’m talking about this salt affecting even some hardy plant life. This issue with salt and plants isn’t limited
to winter. During hurricanes near the coast, salty ocean
water can be dumped in large quantities into soil. While the effect may not be instant, this
can eventually actually kill plants- including trees- that had originally survived the hurricane. Why? Do plants just dislike salt that much? Well it’s actually related to this awesome
term: osmosis. When you are talking about osmosis, you are
talking about the movement of water thru a semi-permeable membrane, like a cell membrane. Water molecules are so small that they can
travel through the cell membrane unassisted, or they can travel in larger quantities through
protein channels like aquaporins. The movement of water molecules traveling
across a cell membrane is passive transport, which means, it does not require energy. In osmosis, water molecules travel from areas
of a high concentration (of water molecules) to a low concentration (of water molecules). But there’s another way to think about water
movement in osmosis. A low water concentration likely means there
is a greater solute concentration. Solutes are substances— like salt or sugar—that
can be dissolved within a solvent—-like water. Water has the tendency to move to areas where
there is a higher solute concentration, which would mean less water concentration. So if you want to easily figure out where
the water will travel—-look to the side where there is a greater solute concentration. Unless we bring in another variable, like
pressure, water will generally have a net movement to the area of higher solute concentration. So let’s bring out a U-tube! Ha, U-tube. That’s funny. There’s a semi-permeable membrane in the
middle of it. Let’s assume that it is similar to a cell
membrane in that water molecules can squeeze through it—the molecules are quite small—but
salt can’t. Salt molecules are too large. Right now, there is just water in this U-tube. The water levels on side A and side B are
equal. That doesn’t mean that the water molecules
aren’t moving—water molecules like to move—but the net movement across the two
sides is zero. That means, the overall change in the direction
of movement is zero. Now let’s imagine on side B, you dump a
huge amount of salt there. Remember, the salt molecules are too large
to pass thru this semi-permeable membrane. So which direction will the water initially
move towards—A or B? Think about what we mentioned with osmosis. The answer is B! Side B has a higher solute concentration than
side A. Water moves to areas of higher solute concentration, which is also the area of lower
water concentration. The water level on side B will be higher in
the U-tube. You can almost think of the water as trying
to equalize the concentrations—diluting side B. Once equilibrium is reached, the net
movement of water across the two sides will be zero but remember that water still likes
to move and movement still occurs. Here’s some vocabulary to add in here—we
call side B hypertonic. This means higher solute concentration! But we can’t just say something is hypertonic
without comparing it to something else. We say Side B is hypertonic to side A because
it has a higher solute concentration than side A. In osmosis, water moves to the hypertonic
side. We say side A is hypotonic (hypo rhymes with
low which helps me remember low solute concentration) when compared to side B. Let’s get a little more real life now instead
of just the U-tube. As you know, water is important for your body
and many processes that occur in the body. When someone gets an IV in a hospital—it
may look like the fluid in the IV is just pure water. But it is certainly not pure water. That would be a disaster because of osmosis—let’s
explain. Let’s say hypothetically pure water was
in an IV. Now an IV tube typically runs through a vein,
so that you have access to your blood stream. Really useful for running medication through. Blood actually consists of many different
types of components and red blood cells are a great example. So what do you think has a higher solute concentration? The hypothetical pure water in this IV tube? Or the red blood cells? Well cells are not empty vessels—they contain
solutes. The pure water that hypothetically is running
through this IV tube has no solutes. So where does the water go? It goes to the areas of higher solute concentration—inside
the cells. The cells are hypertonic compared to the pure
water in the IV tube because the cells have a greater solute concentration. The cells would swell and possibly burst! Exploding red blood cells are not good. If a person needs fluids, they typically will
receive a solution that is isotonic to their blood plasma. Isotonic means equal concentration so you
won’t have any swelling or shrinking red blood cells. Or let’s talk about the aquarium. I have always wanted a saltwater fish tank,
ever since I was a little kid. But I’ve only had freshwater tanks. So far. I did often question when I was a kid, why
is it that a saltwater fish can’t be in my freshwater tank? Well let me explain one reason why this would
be dangerous to a saltwater fish and how it relates to osmosis. First ask—where is there a higher solute
concentration? In the saltwater fish cells? Or in the freshwater that the fish would be
placed in? Definitely in the saltwater fish cells. So where would the water go? It goes to the area where there is a higher
solute concentration—-the hypertonic side—-so it goes into the cells of that poor saltwater
fish. If not rescued, it could die. Now one thing to clarify: saltwater fish and
freshwater fish are not necessarily isotonic their surroundings. But they have special adaptations that allow
them to live in their environment and usually cannot make a major switch from a saltwater
environment to freshwater. Now—not all fish have this problem. There are some fish that have amazing adaptations
to switch between fresh and salt water, and they have to deal with this osmosis problem. Salmon for example. I think if I could pick to be a fish, I’d
be a salmon. No question. Osmosis explains how many kinds of plants
get their water. Sure, many plants have roots. But how does the water get in the roots? When it rains, the soil becomes saturated
with water. The root hair cells generally have a higher
concentration of solutes within them than the solute concentration in the saturated
soil. The water travels into the root cells as the
root hair cells are hypertonic compared to the hypotonic soil. By the way, you may wonder—well, why don’t
those root hair cells burst with all that water? That brings us to our next osmosis topic and
why plant cells walls are amazing! So let’s bring in another variable that
can influence osmosis: pressure potential. This is when it’s very useful to understand
how one can calculate water potential. Water potential considers both solute potential AND pressure potential. In osmosis, water travels to areas of lower
water potential. So the formula is water potential=pressure
potential + solute potential. Adding solute actually causes the solute potential
to have a negative value and the overall water potential to lower. Water will travel to areas of lower water
potential. But exerting pressure can raise the pressure
potential, a positive value, therefore raising the total water potential. Let’s give a quick example. In the popular water potential in potato cores
lab—all kinds of neat variations of this lab procedure exist online—you can calculate
the water potential in potato cores using the water potential formula. When a potato core is first put into distilled
water—that’s pure water—the potato core cells starts to gain water. You’d expect that. The water is moving towards the higher solute concentration. Thanks to their higher solute concentration, they have a lower solute potential. That mean a lower total water potential than
the surroundings and water travels to areas of lower water potential. But over time as the potato core cells gain
water, the water that has entered exerts pressure against the plant cell walls from inside the
plant cells. Therefore raising the overall water potential in the potato core cells. We want to point out that this turgor pressure
that results in plant cells, thanks to osmosis and plant cell walls, is critical for overall
plant structure and the ability of plants to grow upright and not wilt. Turgor pressure is definitely something to
explore. In summary, where would living organisms be
without osmosis? After all, it involves movement of one of
our very valuable resources: water. Well, that’s it for the Amoeba Sisters and
we remind you to stay curious.


100 Comments

Amoeba Sisters · January 2, 2019 at 10:28 pm

We like to pin clarifications & corrections at the top of our videos! We are so appreciative of feedback we receive as it helps us continue to improve. In this video, we say the word "molecules" several times. Chemically speaking—the term "molecule" may be ok when referring to water but not salt as we did in 2:54. Salt is formed by ionic bonds [not molecular (covalent) bonds like you would see in water]. We also notice in the comments that people have questions about the diagram at 5:34. Many textbooks, in our experience, focus on the solution the cell is placed in only. Our diagram at 5:34 actually labels both the cell (as either hypertonic or hypotonic) AND the solution (as either hypertonic or hypotonic). If assuming no added pressure, look for the area that is hypertonic. It may be the cell that is hypertonic or it may be the solution that is hypertonic. But as the diagram shows, the hypertonic area (assuming no pressure) is where the net movement of water will go. We try to include addressing the cell as well as its surrounding solution, because Pinky noticed her students otherwise tended to memorize terms corresponding to swelling or shrinking, which turned out to hurt understanding. Hope that helps! 🙂

SpaceElkks · January 8, 2019 at 4:10 am

So over time if you place fresh water in a saltwater tank(not all at once, but over the time of days), the cells in the fish will adapt to less salt and over time will be able to live in fresh water, right?

Avery Huie · January 8, 2019 at 5:54 pm

I didn’t like this video

V Rand · January 8, 2019 at 8:05 pm

Did anyone notice that at 1 min 30 second the arrow which is supposed to be high water concentration is actually showing high solute concentration. There is a boo boo there.

Little Dreamer · January 9, 2019 at 5:12 pm

Love yo soooo much U R amazing!!!!!!!! 💖 💖 💖 💖 💖

Ivyy Nicolee · January 10, 2019 at 2:25 am

Bio is killing me 😢

Sophia Strobl · January 12, 2019 at 12:15 am

I hate it when teachers make us watch amoeba sisters

Nyck · January 14, 2019 at 7:53 pm

Incredible video.
Fun fact, my teacher was the one who recommended your channel to my class.
Good job on making this insane quality and easy to understand videos.

Anne Zhu · January 16, 2019 at 1:35 am

Why does water move from areas of high water potential to low water potential?

Peter Gaardsholt · January 17, 2019 at 3:44 pm

god job

Anja R · January 17, 2019 at 9:25 pm

My hs biology teacher emailed me the link to one of your videos… I think ever since that day I've SEEN every video, LIKED every video and subscribed. You two remind me of my sister and I 😉 I think that's why our hs science teacher recommended you <3 STAY CURIOUS!

Ben Manley · January 21, 2019 at 5:55 pm

very useful, thanks!

Julian Cheun · January 22, 2019 at 6:27 am

love your videos

Duhnuh Mae · January 22, 2019 at 10:02 am

Thankss

ZeldaSonicFan2004 · January 24, 2019 at 5:58 am

When I think of Osmosis, I think of Osmosis Jones. BTW, nice video!

Aniket Meena · February 1, 2019 at 8:47 pm

One thing in my bucket list is to find out who you are 😂🍻
I totally love your videos and I am a Fan of your unique style of teaching !
I love your voice too ❤

grace h. · February 5, 2019 at 4:00 am

shout out to my bio teacher lmao

Sheynna Weber · February 5, 2019 at 10:56 pm

THANK YOU SO MUCH

The winner of all aspects · February 8, 2019 at 6:26 pm

Thank you so much

Nique H · February 11, 2019 at 5:17 am

I just want to say I am a Biochemistry student who is currently a ICU nurse and your videos are awesome! I have been looking for a channel that can dumb things down to my level lol! This is not an insult! I hope that much is understood! Thank you sooo much!

Lysistrata Wieland · February 11, 2019 at 4:41 pm

I like every video

朱持永 · February 12, 2019 at 3:17 am

哇有中文

Science Fox · February 15, 2019 at 10:47 am

Cool Awesome videos

Ayaat Wadi · February 17, 2019 at 12:29 am

That’s so weird in Britain you call Aquaporins channel proteins.

Gerald Gomez · February 17, 2019 at 9:55 pm

Ok I’m a little confused. At 5:26 you say the red blood cells are “hypertonic” and would swell and burst. But at 5:36 you show that the red blood cells are “hypotonic” and they swell. So do they swell in hypertonic or hypotonic solutions?

GabrielKnightz · February 21, 2019 at 12:06 pm

Help me understand, if liquids move from a lower to higher solute concentration , how does Brining work in cooking?
shouldn't all the water in the (let's say) chicken be drawn out?
Please, i would appreciate it if someone could explain the mechanics of it to me.
Amoeba Sister?
Thanks.

Isti Fed · February 22, 2019 at 11:27 am

Absolute gold. I study for medical exams and I got confused by the term osmosis. I love when something is explained so simply that even a kid could understand. Thanks!

melikesgames · February 23, 2019 at 3:29 am

Very enjoyable learning experience! You should be a highly paid teacher/artist. 😀

Julia Skachkov · February 25, 2019 at 4:28 pm

Ur not funny

sunny le fabulous · February 26, 2019 at 2:49 am

god bless this channel

Erin Barthel · February 26, 2019 at 7:17 pm

umm i was forced to watch this

Will TS · March 1, 2019 at 10:19 am

actually die

Madde - Chan · March 4, 2019 at 11:32 pm

just taking notes my edit will be my notes

I am Tomahawk · March 6, 2019 at 3:48 am

Clear explanations and great examples!

I am Tomahawk · March 6, 2019 at 3:50 am

A fun way to demonstrate osmosis at home is with Umibudo (sea grapes.) Umibudo is packed in super salty water, which makes them shrivel up (by osmosis.) When you rehydrate them in fresh water, you can see them swell up as the water rushes in by osmosis! Osmosis right before your eyes!

Kaylen Vee · March 7, 2019 at 11:53 am

Your artwork reminds me of this card game about exploding cats…

Eric M Earle · March 8, 2019 at 5:10 am

really really good. finally made sense – concept clarified by whole video, really for me around minute 9

Nathan Zhou · March 8, 2019 at 10:13 pm

I would be a bull shark rather than a salmon.

cash cosgrove · March 10, 2019 at 8:16 pm

this video is so good if you are strugeling in class when learning about difusion or osmosis watch this vid i have my test tomorrow and it just saved me a load of time for studying

David Bowerman · March 13, 2019 at 5:24 pm

being forced to do things is great

Nicholas Smith · March 15, 2019 at 4:01 pm

I love the Amoeba sisters

Arki Maine · March 19, 2019 at 3:20 am

Does this apply to oil and water in the process of osmosis?

Nozakai · March 19, 2019 at 11:19 am

Can you do a video on Hypertonic and Hypotonic solutions?

Trans Cutie Anonymous · March 27, 2019 at 11:56 pm

I’m so confused.

Mel · March 30, 2019 at 6:08 am

You are better than my Barron's….

Nobody Iknow · April 1, 2019 at 5:33 am

jeez love you guys! interesting and well explained

Playagame LP · April 1, 2019 at 9:29 pm

What a great video.

Isabella H · April 3, 2019 at 1:08 am

Thank you for teaching me something my teacher attempted but failed at teaching us in the span of 40 minutes in a 10 minute video.😫

Oludae Byrd · April 10, 2019 at 1:48 pm

4:31 I JUST CAN'T STOP LAUGHING🤣🤣🤣

Oludae Byrd · April 10, 2019 at 1:52 pm

7:31 KAWAII AM I RIGHT?!!?!?!?!?!?

Yusra Rehan · April 12, 2019 at 4:26 pm

Can't understand the water potential and solute potential part… ☹️

Suani Avila · April 14, 2019 at 5:31 pm

just three more seconds

Suani Avila · April 14, 2019 at 5:32 pm

1:10 doesn't being polar effect this though

Maroti Telang · April 27, 2019 at 5:42 pm

Please pronounceate properly. I hope you dont fell bad

Froot ӏ օ օ թs · April 29, 2019 at 1:29 pm

My teacher is forcing me to watch this I decided to just go on Snapchat and play this in the background so she thought I was on it sksksksksksksks #edgytingz

Rarw rarw rarw Xd EDGE RArw

ClapwarE Gaming · May 6, 2019 at 10:34 pm

Now im confused, hypotonic and hypertonic here and in the book provided by our school is literally the OPPOSITE, but as usual ill stick with the book

rachel pu · May 6, 2019 at 10:55 pm

hey, i've been watching your videos for a long time and they really REALLY help me with biology. I have an EOC in three days and decided to just study with your videos. however, on 5:34, i found something. i don't know if it's just me or i'm looking at the diagram wrong, but aren't hypotonic cells the swelling cells? in the diagram, the swelling cells are labeled as hypertonic instead of hypotonic. the same with the shrinking cells–they are labeled as hypotonic instead of hypertonic. if this isn't a mistake, could somebody explain to me why this is the case i would gladly appreciate it

Sarah Son · May 8, 2019 at 1:05 am

You are science Ling Lings
Ling ling 40 hrs… Oh and there's a tumbleweed snowman at 0:11. Tee Hee Hee

Subodh B · May 12, 2019 at 12:14 pm

Good video .My teacher just showed as this video in the class today.

Adi Arenas · May 14, 2019 at 4:00 pm

I totally wish you were my biology teacher! You explain something meant to be complicated so simply and make it so easy to understand. Thank you!! 🙏🏻❤️

ZRDattck · May 18, 2019 at 7:36 pm

Now when hypertonic and hypotonic are the side A and B does it have anything to do with club soda (Tonic Water)?

LISHA CHUNDU · May 21, 2019 at 1:05 am

I love these videos they really helped me study for my exams.You rock Amoeba Sisters!

Katherinne Roman · June 13, 2019 at 11:20 am

im an artist taking a summer bio course and this really helped alot

Shraddha Menon · June 18, 2019 at 7:39 am

What about the water we drink? Does it not get inside our red blood cells?

meghna sankhla · July 20, 2019 at 6:42 am

😀

Kalei Kathleen · July 24, 2019 at 11:32 pm

Ha! U-tube!

Milly Shell · August 1, 2019 at 12:32 pm

amoeba sister coming in clutch as usual

Jessica Matz · August 12, 2019 at 11:15 am

what if salt was dumped on both sides ?wold the water go crazy?

Jake ebrado Ebrado · August 18, 2019 at 3:16 pm

I didnt understand at 5:28 wherein it is labeled as hypertonic which SWELLS, but in the diagram, it SHRINKS

Roshni Pethekar · August 19, 2019 at 2:01 pm

Mam can you speak slow from which we can understand

Lucas Burkemper · August 22, 2019 at 2:52 am

pcds kids wya

Zod IV · August 29, 2019 at 7:39 pm

Oh my GOSHHHHHHHHH THANK YOU SO MUCH.I almost cried when you explained this so clearly.

Irshia haque · September 2, 2019 at 8:43 pm

thanks to you guys, I can now understand SOME sort of biology… I've always been bad at memorizing, and the teachers at our school aren't that good with making us UNDERSTAND rather than telling us to memorize them.
anyways, its 3 am here, and I'm studying biology for my exam tomorrow. wish me luck! 😀 <3

Thabata Lizeth Gónzalez Garibay · September 4, 2019 at 9:24 pm

always savin my life

Syd · September 5, 2019 at 4:29 am

This made things so much easier to understand , thank you!

Katherine Reyes · September 11, 2019 at 12:32 am

You could talk about 1topic for just almost 10min and its easy to understand
out proctor is teaching this for almost 3hours and we still find it hard

GELAI Official · September 11, 2019 at 8:42 am

Salt water affects plants because salt water has high concentration of solute. So, when the salt water comes in to contact with plants, the tendency of the water inside the cell goes out making it shrinks and dried out.

Helena · September 12, 2019 at 3:22 pm

I learnt more from this than at school thank you I really needed this because im going over the gcse topics x

I CY · September 16, 2019 at 10:49 pm

Nobody cares

ET Potcast · September 18, 2019 at 3:42 am

👍

Thomas Smith · September 18, 2019 at 8:50 am

Amazing Video. Thanks Heaps

Angel Ibarra · September 20, 2019 at 6:54 pm

I like the amoeba sisters like my step sis😈

Desyre Jc · September 20, 2019 at 6:55 pm

Science is fun if you know what I mean😏

Aiman Dhiloon · September 21, 2019 at 6:51 pm

Not even lying, this is the BEST video to watch

Andrix · September 21, 2019 at 7:22 pm

Funny and well explained – many thanks!

Allegra Salaine · September 22, 2019 at 5:00 am

love this channel so much!

Magui C.M. · September 22, 2019 at 2:53 pm

i love this channel

猫龙 · September 23, 2019 at 6:53 am

Learn a lot thanks

angelica fajardo · September 24, 2019 at 4:59 am

Am i the only one who laughed at the U-Tube pun?

Nathan Vasquez · September 24, 2019 at 3:32 pm

wow so cool

JSJ Angling · October 2, 2019 at 1:56 am

The Amoeba Sisters are my teachers

Palak Singh · October 2, 2019 at 3:00 am

Cleared all my doubts thank you very much❤❤❤

He Pengfan · October 2, 2019 at 9:14 am

Now I can finally pass science in piece

Hannah Buenker · October 2, 2019 at 11:27 pm

Thank you Amoeba sisters for helping me pass my science classes!! You're the best!! 🙂

Peter Le · October 3, 2019 at 3:49 am

Wear your seat belt kids.

N • G · October 6, 2019 at 2:18 pm

YOU ARE AMAZING !!!

Alexandar Bezanovski · October 8, 2019 at 12:41 am

My college class made this so much more complicated than it needed to be. You guys do such a great job at explaining!!! I've been watching your videos since high school and you never disappoint amoeba sisters!

Livingitamanda · October 8, 2019 at 10:18 pm

3:53 me when i hear a new vocab word at 5 yrs old 🤣

Brock kocian · October 9, 2019 at 2:40 am

Great video super helpful, love little funny pictures.

Auri Clydd · October 9, 2019 at 4:34 am

I was failing bio till I started watching ur vids thx

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