Water Potential
Summary
TLDRThis video script delves into the concept of water potential, crucial for understanding osmosis. It explains how water moves into or out of cells based on factors like solute concentration and pressure potential. The script uses visuals to illustrate the differences between hypotonic, isotonic, and hypertonic solutions, and how these affect cell behavior. It also covers the mathematical model of water potential, including the formula for calculating solute potential, emphasizing the importance of understanding how solutes decrease water's ability to move.
Takeaways
- π Water potential, symbolized by the Greek letter Psi (Ξ¨), is a measure of the tendency of water to move into or out of a system based on several factors.
- π¬ The cell membrane's structure, with phospholipids and proteins, plays a crucial role in water movement, especially through aquaporins which facilitate diffusion.
- π‘ Tonicity (hypotonic, isotonic, hypertonic) describes the concentration of dissolved materials or water relative to a cell, affecting osmosis and water movement.
- π§ Hypotonic solutions have a higher concentration of water outside the cell, leading to water influx and potential cell swelling.
- π In hypertonic solutions, the cell loses water to the surrounding solution, causing the cell to shrivel, a process known as plasmolysis in plant cells.
- π§ͺ Isotonic solutions have equal concentrations of water inside and outside the cell, resulting in no net movement of water.
- π The change in mass (Ξ mass) of a system can be predicted based on the concentration of solutes and the principles of osmosis.
- π± Water potential is modeled mathematically to describe the movement of water in and out of cells, considering factors like pressure and solute potential.
- π Solute potential is always negative, as the presence of solutes in water decreases the water's potential to move, thus lowering the overall water potential.
- π‘ Pressure potential comes from the rigid cell wall in plant cells, increasing as the cell takes on water and exerts pressure against the wall.
- βοΈ The solute potential can be calculated using an equation that considers the number of particles a solute dissociates into, the molar concentration, a pressure constant, and temperature in Kelvin.
Q & A
What is the Greek letter symbolized by 'Ξ¨' used to represent in the context of the video?
-In the context of the video, 'Ξ¨' (Psi) is used to represent water potential, which describes how water moves into or out of a system based on certain factors.
What are the two main components of a phospholipid molecule found in the cell membrane?
-The two main components of a phospholipid molecule are a negatively charged head made of a phosphate molecule or ion, and neutral or uncharged tails which are fatty acids attached to a glycerol molecule.
How do the properties of the phospholipid bilayer contribute to the structure of the cell membrane?
-The amphiphilic nature of phospholipids, with hydrophilic heads and hydrophobic tails, causes them to orient themselves into a bilayer, with the heads facing the aqueous environment and the tails facing inward, thus forming the cell membrane structure.
What is the role of aquaporins in the cell membrane?
-Aquaporins are integral proteins that facilitate the diffusion of water through the cell membrane, allowing water to travel across it.
What is tonicity and why is it important for understanding water movement?
-Tonicity describes the concentration of dissolved materials or the amount of water in a solution relative to the cell's interior. It is important for understanding water movement because it helps predict the direction of water flow via osmosis, which is from a high concentration to a low concentration.
What happens to a cell in a hypotonic solution?
-In a hypotonic solution, where there is a high amount of water outside the cell and a low amount inside, water will diffuse through the cell membrane into the cell, causing the cell to swell, which in plant cells can lead to turgor and in animal cells can cause the cell to burst.
What is the difference between an isotonic and a hypertonic solution in terms of water movement?
-In an isotonic solution, the amount of water inside the cell is equal to the amount outside, resulting in no net movement of water. In a hypertonic solution, there is less water outside the cell and more inside, causing water to diffuse out of the cell, leading to cell shrinkage or plasmolysis in plant cells.
How can the change in mass (Ξmass) be used to predict the direction of water movement in different solutions?
-By knowing the concentrations of solutions, one can predict the change in mass of a system. If the internal solution has a higher concentration than the external, the system will lose water and have a lower Ξmass. Conversely, if the internal solution has a lower concentration, it will gain water and have an increased Ξmass.
What are the two main components of water potential in a plant cell, as discussed in the video?
-The two main components of water potential in a plant cell, as discussed in the video, are pressure potential and solute potential.
Why is the solute potential always negative?
-The solute potential is always negative because the presence of solutes in water reduces the potential for water movement. Solutes form hydrogen bonds or attractions that limit the ability of water molecules to move freely, thus decreasing the water's potential energy.
How is the solute potential calculated?
-The solute potential is calculated using the equation: Ξ¨s = -(RT/i) * ln(c), where 'i' is the number of particles the solute dissociates into, 'R' is the gas constant, 'T' is the temperature in Kelvin, and 'c' is the molar concentration of the solute.
What is the significance of reaching water potential equilibrium?
-Reaching water potential equilibrium signifies that there is no net movement of water across the cell membrane. This is due to the internal solute potential being balanced by the internal pressure potential, resulting in a stable state for the cell.
Outlines
π Understanding Water Potential and Osmosis
This paragraph introduces the concept of water potential, symbolized by the Greek letter Psi (Ξ¨), which dictates the movement of water into or out of a system. It discusses the structure of the cell membrane, including phospholipids, proteins, and carbohydrates, and their roles in water movement. The paragraph also explains the terms 'hypotonic', 'isotonic', and 'hypertonic' in relation to water concentration and osmosis, illustrating how water moves across the cell membrane and the effects on cells, such as turgid in hypotonic conditions and plasmolysis in hypertonic conditions. The speaker acknowledges the choppy recording quality due to the use of an iPad and emphasizes the importance of the visual slides for understanding the topic.
π Predicting Water Movement with Water Potential
The second paragraph delves into predicting water movement using the concept of water potential. It explains that water potential is a mathematical model based on observations and evidence, aiming to describe the movement of water at a cellular level. The discussion includes the impact of distilled water on cells, highlighting that pure water has a high tendency to move into cells due to the presence of solutes within them. The paragraph also introduces the idea of dynamic equilibrium in water potential, where the pressure inside the cell balances the water's movement, leading to no net change in water distribution. Examples of beakers with different solute concentrations are used to illustrate predictions of mass changes due to water movement.
π§ Exploring Components of Water Potential
This paragraph focuses on the two main components of water potential: pressure potential and solute potential. It explains that pressure potential arises from the rigid cell wall limiting water uptake and increases as the cell takes on water. On the other hand, solute potential is always negative, as solutes in the solution decrease the water's ability to move freely, thus lowering the water potential. The paragraph provides a clear definition of solute potential and emphasizes its negative impact on water movement. It also touches on the importance of understanding the difference between ionic and covalent compounds when calculating solute potential, using the equation that includes the number of particles (i), molar concentration (c), the pressure constant (s), temperature (T), and the gas constant (R).
βοΈ Calculating and Applying Solute Potential
The final paragraph provides a deeper understanding of how to calculate solute potential using the provided equation and discusses its significance in reaching equilibrium in water potential. It emphasizes the negative nature of solute potential and the need to negate the calculated product. The paragraph also offers tips for remembering key concepts, such as the zero pressure potential in an open container and the impact of solutes on lowering water potential. It concludes with an invitation for viewers to ask questions and engage with the content, reinforcing the importance of understanding these concepts in the study of biology.
Mindmap
Keywords
π‘Water Potential
π‘Osmosis
π‘Cell Membrane
π‘Phospholipids
π‘Aquaporins
π‘Tonicity
π‘Hypotonic Solution
π‘Isotonic Solution
π‘Hypertonic Solution
π‘Pressure Potential
π‘Solute Potential
Highlights
Introduction to water potential, a key concept in osmosis.
Explanation of the Greek letter Psi (Ξ¨) as the symbol for water potential.
Overview of the cell membrane structure including phospholipids, proteins, and carbohydrates.
Role of aquaporins in facilitating water diffusion through the cell membrane.
Definition and importance of tonicity in understanding cell behavior in different solutions.
Description of hypotonic, isotonic, and hypertonic solutions and their effects on cells.
Prediction of water movement based on concentration differences using beaker models.
Introduction of the mathematical model for water potential to describe osmotic processes.
Explanation of how distilled water's high water potential affects cell hydration.
Dynamic equilibrium concept in relation to water potential and cell pressure.
Differentiation between pressure potential and solute potential in the context of water potential.
The always negative nature of solute potential and its effect on water movement.
Calculation of solute potential using the equation involving solute concentration and temperature.
Importance of understanding the ionization of solutes in calculating solute potential.
The impact of temperature on solute potential and water movement.
Practical application of water potential in predicting osmotic movement and equilibrium.
Tips for remembering key concepts of water potential, including pressure and solute effects.
Conclusion summarizing the significance of water potential in cellular processes.
Transcripts
hey everyone we're gonna do a video
saying water potential on this video is
gonna be a little bit different it's
actually of slides set up so recording
on an iPad and the way it records is a
little bit choppy so forgive that
forgive me that my flow isn't as good to
be as good as it normally is but the
slides are important because I've got
some good visuals for you and so water
potential is pasted on osmosis so we're
gonna be describing this thing called
water potential this is visual you're
symbolized by the Greek letter Sai so
you're seems a little Trident looking
things I think the official I've never
taken Greek but I think it has a little
loops there all the times I'll just see
this kind of that tried it looking guy
but this describes how waters going to
move into or out of a system based on a
few factors so let's do some quick
review and to start with so this is a
diagram of the cell wall or a cell
membrane excuse me you've seen this
before
remember the red particles in this are
the phospholipids the phospholipid has
two components it has a negatively
charged head made of a phosphate
molecule or phosphate ion and then it
has neutral or uncharged tails these are
fatty acids attached to a glycerol
molecule here in the head the
phospholipids are amphiphilic meaning
the heads are hydrophilic they like to
be they will orient themselves to the
equus solution or polar these tails are
hydrophobic they will orient themselves
away from the aqueous environment and
that's why we have a bilayer here on our
membrane also integral to are also
important in the cell membrane are these
proteins so there are multiple kinds of
proteins that line the cell membrane so
this would be a peripheral protein
there's a surface level protein here and
then we have these integrated proteins
these are integrins some of them may be
aquaporins which allow water to travel
right through they facilitate diffusion
on the outside of the membrane there are
these glyco sugars the carbohydrates so
we can have a glycol lipids these are
attached to the lipids themselves or we
can have a glycoprotein these are mainly
used for cell identification in cell
signaling
also as a point of review we've got
tenacity and tenacity describes the the
solution that a cell is placed in and
this is important that we identify the
reference point so when all of Tennessee
our reference point is the cell right is
the reference so in a hypotonic solution
remember we are looking at the
concentration of dissolved materials or
the concentration of water essentially
and that's a little bit misleading
because water is a pure liquid it
doesn't have a concentration so this
maybe is the amount of water is a better
way to say it in a hypotonic solution we
have a high amount of water on the
outside meaning then we have a low
amount of water on the inside because
osmosis goes from a high concentration
to a low concentration water is going to
diffuse through the cell membrane and
into the cell in a plant cell it will
actually burst like a blue you know
plant cell excuse me in an animal cell
that will burst like a balloon in a
plant so we get what's called turgid and
turgid means there's pressure on the
cell wall it's bulging just a little bit
isotonic means that the concentration or
the amount of water inside is equal to
the amount of water outside or the
quantity of water outside is equal to
the quantity of water inside water is
moving in it's moving out at the same
rate there's no net movement and that's
important for isotype no net movement
hypertonic is the opposite of hypotonic
so we have low water on the outside and
high water on the inside we defuse some
via osmosis from the inside across the
membrane to the outside in that cell
will actually shrivel up in a plant cell
we call that classman plasmolysis
so applying that principle if I know
what the concentration is we can predict
which direction water will travel via
osmosis so we've got five beakers here
we're gonna make a prediction and we're
gonna look at the change or Delta mass
so if I know the concentrations I could
predict what's gonna happen to the mass
of this this is what I'm assuming is
that house is too many but some kind of
membrane so in this first system
actually let's look at this middle
system first so I have a point two molar
solution on the inside and a point to my
lure solution on the outside there are
equal amounts equal quantities of water
and so we have an equal net movement
into and out of that bag so blue is
really hard to see those change to red
and let me make my pen just a little bit
bigger we have equal movement into the
cell into that bag and out of that bag
this would be an isotonic solution you
would expect zero change no change in
mass and a bag there B it might be some
negligible change there abundant for the
most part the mass is gonna stay the
same there's no appreciable quantity if
we look at this particular system next
we have a high or a low concentration of
material inside meaning we have a lot of
water and a high concentration of
material on the outside meaning lower
water so we move from high to low so
this bag is going to be losing water to
the surrounding solution it would be
hypertonic and so this one would have a
lower Delta mass if we compare that to
let's say this bag number four it's just
the opposite we have a high
concentration of stuff inside and a low
concentration of stuff outside so this
one would have in low water and outside
would have high water so our direction
is reversed water's going to enter the
bag and so this wouldn't be increase
Delta minus now we'd have an increase in
the mass of that bag because water is
flowing in so this is a very simple you
know low-level qualitative prediction of
what's going to happen we can use this
to describe the system in general but
water potential it takes us to the next
step it's important to recognize that we
are modeling with water potential this
is not the exact thing this is based on
evidence
it's based on observations but we are
giving a mathematical model of what is
happening and why it's happening so it
tries to describe what's happening so
let's take a look at this model I've got
another diagram showing tonicity but
this time we've got cells and we're
using distilled water okay this is
important so distilled water this is
pure there are no solutes okay it is
straight h2o so that is as high of a
quote/unquote concentration remember
water liquid water does not have a
concentration but this is straight water
that means that in any cell no matter
what cell it is plant animal whatever
there's stuff dissolved inside of
ourselves so water is going to net
across the board move into that cell
remember if you have an animal it's just
a cell membrane and you typically lyse
and lakes in a plant cell though we have
this wall and that cell wall provides a
little bit of structure so when we take
a plant cell and place it into a
distilled water aqueous environment
there is a net movement of water into
that plant cell and then we get this
buildup of pressure to check this out
this is really interesting when we're
looking at water potential you're not
going to equal out your concentrations
just because the quantities of water
inside of the cells are very very small
and so when we reach equilibrium it's
not necessarily a concentration
equilibrium what we call it as a water
potential equilibrium we have canceled
out the movement of water we have
resisted that further movement of water
because of other factors so in a plant
cell the pressure inside of the cell
pushing back out is equal to the
pressure of the water trying to diffuse
into the cell and that's where we reach
our dynamic equilibrium and this is how
we're going to describe water potential
so here's our simple model for water
potential from a plant's point of view
we're only focusing on two things at
this point we're going to be looking at
the pressure potential and of the solute
potential there are other variables
involved with plants especially when
you're looking at a macro scale so if
you're looking at a tree there's also
gravity that's a major major influenced
the water potential of a plant and
that's important when that plant is
trying to draw water through its root
system up to its leaves so we've talked
about transpiration this is manipulating
water potential as well but for today
we're talking at the cellular level all
we're gonna look at is the pressure and
the solute potential pressure is pretty
easy so pressure comes from the rigid
cell wall that limits further water
uptake so our system remember is our
cell and so the pressure potential
increases as the cell takes on water
that pressure inside the cell on the
cell wall is increasing so this
increases as the cell takes on water
pressure starts at zero at atmospheric
pressure that's an open container there
is zero pressure as water starts to fold
to flow into that cell it's taking on
water there's a higher pressure on them
on the plant cell wall and so that
pressure potential is increasing well
look at what that means on the next
slide when I clear this out just so we
have a clean slide to work with if you
need to go back you can just rewind it
pause it but essentially pressure
increases as the cell takes on water
solute potential is always negative
always negative it is reducing the
potential for that water to move so
here's why it's negative if I'm a water
molecule so here's some of Mickey Mouse
ear or water molecules very there's a
certain amount of hydrogen bonding
between us so simple like a hydrogen
bond it's an attraction it's a positive
negative attraction right we have
positive hydrogen's negative oxygens
there's a source of magnetic attraction
but essentially there is nothing keeping
me from doing what I want to is a water
molecule the other way to think about it
is there is the highest level of entropy
the highest level of disorder that we
could
in a particular system when there is
nothing else dissolved so this would be
like distilled pure water as soon as we
start to add some solutes so maybe these
are salt ions they can be sugar
molecules as soon as we add solutes
these guys are also going to start to
form hydrogen bonds or use those
attractions this is going to limit the
ability of water to move the other way
you can think about it is that this is
now decreasing entropy right lower
entropy equals lower energy free energy
Gibbs free energy so that we're moving
back to this idea from last semester so
lower entropy means the lower energy
means a lower potential that's why
solute potential is always negative in
nature it's going to limit the ability
of water to move from one place to the
other and this is a very very important
concept so you really have to make sure
you understand it so let's take a look
at the definition this is the effect of
a solute right the dissolved material
pure water has a solute potential of
zero meaning that it is not it's going
to move as much as it can as solute is
added those water molecules move less
they're less able to move around so the
water potential becomes more negative
the water potential decreases that water
is less likely to move just because of
the inhibition of other stuff in total
the solute is added water potential of a
solution drops this is hugely important
please make sure you understand this
let's take a look at an example remember
we've reached equilibrium when there is
no net movement so we've already talked
about the factors that can impact water
potential distilled water in an open
container has zero pressure potential
and zero solute potential giving me a
system that has zero water potential
there's not going to be any movement
there's a plant cell immediately put
into distilled water there is solutes
inside my plants other stuff sugar salts
different things dissolved that's why
this solute potential is negative to
water potential moves from a high
potential to a low potential so that
distilled water is zero is going to
force water into
to that plant cell by osmosis until
notice the pressure look at this as
water moves in this pressure is
increasing we have a positive value here
solute potential is still the same
concentration hasn't changed but we've
now reached in equilibrium the water
potential is back to zero because the
internal solute pressure is equal to the
internal pressure potential on that cell
wall and this is water potential we can
use this to model reaching equilibrium
a question we need to answer as well if
I need a no solute potential how do we
calculate solute potential you can use
this equation this is on your ap bio
formula sheet but let's just talk about
how to interpret it solute concentration
further scuse me saw your potential is
more than just concentration right so
concentration you have to do with it but
we have to actually calculate this sy s
the potential due to the solute so I
little I is the number of particles that
that the molecule will create when is
dissolved
remember sodium chloride this is a
salted ionic so he actually gets sodium
ions and chlorine ions I'd from this
single molecule this ionic compound we
get two ions that's why it's two here
for sucrose or glucose these do not high
and I so the number stays and so on so
pay attention is that ionic or is it a
covalent compound if it's ionic we have
a metal right sodium is a metal on your
periodic table on the left and Cori is
in a nonmetal those will perform ions
anything else is covalent it does not on
eyes sees the molar concentration you
know how to calculus remember that
molarity is equal to moles of solute per
liter solution so you can calculate to
see if it's not given to you or is a
pressure constant this is also on your
formula sheet so you don't need to
memorize it but it is good to have as
much committed to memory as you can and
then T is the temperature in Kelvin and
Kelvin is 273 plus your temperature in
degrees Celsius so as we increase
temperature right those particles move
faster they have more energy and so the
potential for moving also increases so
remember though there's a negative right
there in front of this because saw your
potential is always negative right we
are decreasing the likelihood that water
is going to move so do not forget to
negate your product so there's a lot
there this is a big video night I do
apologize for the length but some tips
just remember don't forget to pressure
an open container is zero
okay pressure comes from the water
pressure entering the cell and pushing
on that cell wall solutes always lower
the water potential tip pressure
typically raise
the water potential in an open system
solute potential has to be calculated
and we just looked at the equation for
that this is sy is negative I see RT and
then ionization constant matters so do
not forget about I right there this is
very very important so pay close
attention to what kind of substance you
have dissolved in your water thanks for
watching if you have questions please
feel don't leave feel free to leave a
comment below or if you're in my class
you can shoot me an email or send me
something on canvas everybody else thank
you again for watching
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