Osmosis | Osmolarity | Osmotic Equilibrium | Transport Across the Cell Membrane | Cell Physiology
Summary
TLDRThis video from Byte Size Med explains osmosis, a type of passive transport where solvents like water move across a semi-permeable membrane to balance solute concentrations. It differentiates between isotonic, hypotonic, and hypertonic solutions, illustrating how they affect cell size. The video also covers osmotic pressure, osmolarity, and osmolality, emphasizing the importance of understanding these concepts for maintaining cellular equilibrium.
Takeaways
- š§ Passive transport moves substances along a concentration gradient, requiring no metabolic energy like ATP.
- ā” Active transport moves substances against a concentration gradient, requiring ATP for energy.
- š Osmosis is a type of passive transport involving the movement of water (solvent) across a semi-permeable membrane.
- š¬ In osmosis, water moves from an area of low solute concentration to an area of high solute concentration to reach equilibrium.
- š§ The solute is the substance dissolved in a solvent; for example, salt in salt water.
- āļø Osmotic pressure is the pressure needed to stop the movement of water, depending on the number of solute particles.
- š Osmolarity measures solute concentration in terms of osmoles per liter of solution, while osmolality measures it per kilogram.
- š Isotonic solutions have equal concentrations inside and outside the cell, causing no change in cell size.
- ā¬ļø In a hypotonic solution, water enters the cell, causing it to swell due to a higher solute concentration inside.
- ā¬ļø In a hypertonic solution, water leaves the cell, causing it to shrink due to a higher solute concentration outside.
Q & A
What is the difference between passive and active transport across a cell membrane?
-Passive transport does not require extra metabolic energy and occurs along a concentration gradient from high to low. Active transport requires energy, like ATP, because it moves substances against the concentration gradient, from low to high.
What is osmosis and how does it differ from diffusion?
-Osmosis is the movement of the solvent (water) across a semi-permeable membrane, from an area of lower solute concentration to higher solute concentration. Diffusion, on the other hand, is the movement of the solute from high to low concentration until equilibrium is reached.
What role does a semi-permeable membrane play in osmosis?
-A semi-permeable membrane allows only certain substances to pass through. In osmosis, it lets water (the solvent) pass but prevents the solute from moving, allowing water to move towards higher solute concentrations to reach equilibrium.
How is osmotic pressure defined, and what does it depend on?
-Osmotic pressure is the pressure needed to stop the movement of water across a membrane. It depends on the number of solute particles in the solution, meaning the higher the number of solute particles, the greater the osmotic pressure.
What is the difference between osmolarity and osmolality?
-Osmolarity refers to the number of osmoles per liter of solution, while osmolality refers to the number of osmoles per kilogram of solvent. Both measure the concentration of solutes in a solution.
What is meant by the terms isoosmotic, hyposmotic, and hyperosmotic?
-Isoosmotic refers to solutions with equal osmolarity. Hyposmotic refers to a solution with lower osmolarity compared to another, while hyperosmotic refers to a solution with higher osmolarity.
What is an ineffective osmole, and why is it called so?
-An ineffective osmole is a solute that can freely cross the membrane, which allows it to equalize concentrations quickly, preventing the formation of a sustained osmotic gradient. This makes it ineffective in driving osmosis.
What is tonicity and how is it different from osmolarity?
-Tonicity refers to the effect of a solution on cell volume and takes into account the concentration of solutes that cannot cross the membrane, thus contributing to the osmotic gradient. Osmolarity includes all solutes, regardless of their ability to cross the membrane.
How do isotonic, hypotonic, and hypertonic solutions affect cell size?
-In an isotonic solution, the concentration of solutes is equal inside and outside the cell, so the cell size remains unchanged. In a hypotonic solution, water enters the cell, causing it to swell. In a hypertonic solution, water leaves the cell, causing it to shrink.
Why does water move towards higher solute concentrations during osmosis?
-Water moves towards higher solute concentrations to dilute the solute and achieve equilibrium, where the concentrations of the solute are equal on both sides of the membrane.
Outlines
š Introduction to Osmosis and Transport Mechanisms
This paragraph introduces the concept of transport across the cell membrane, emphasizing two main types: passive and active transport. Passive transport, such as osmosis, occurs without the need for extra energy and follows the concentration gradient (high to low). In contrast, active transport requires ATP because it moves substances against the gradient (low to high). Using an analogy of pushing a boulder up a hill, the paragraph explains that osmosis is a type of passive transport that involves the movement of water (the solvent) across a semi-permeable membrane to equalize solute concentrations on both sides. This process is compared with diffusion, where solutes move along the gradient.
š§Ŗ Osmotic Pressure, Osmolarity, and Osmolality Explained
The second part introduces osmotic pressure, the force required to stop the movement of water, and explains how this pressure depends on the number of solute particles in the solution. The terms osmolarity and osmolality are defined, with osmolarity referring to osmoles per liter and osmolality to osmoles per kilogram. It also explains how solutes like sodium chloride, which dissociate into multiple particles, contribute to osmotic pressure. The paragraph concludes with a discussion on isoosmotic, hyposmotic, and hyperosmotic solutions, and introduces the concept of an effective osmole, a solute that cannot freely cross the membrane and thus contributes to an osmotic gradient.
Mindmap
Keywords
š”Osmosis
š”Passive transport
š”Active transport
š”Concentration gradient
š”Semi-permeable membrane
š”Osmotic pressure
š”Osmolarity
š”Tonicity
š”Isotonic solution
š”Hypertonic solution
Highlights
Introduction to passive and active transport across the cell membrane.
Passive transport moves along a concentration gradient from high to low.
Active transport requires energy like ATP because it moves against the concentration gradient.
Osmosis is a type of passive transport where water moves through a semi-permeable membrane.
In osmosis, water moves from lower solute concentration to higher solute concentration.
Osmotic pressure can stop the movement of water by applying pressure on the more concentrated side.
Osmolarity measures the concentration of solutes in a solution in osmoles per litre.
Osmolality measures the concentration of solutes per kilogram of solvent.
If two solutions have the same osmolarity, they are isoosmotic; if different, they are hyposmotic or hyperosmotic.
Osmolarity doesn't account for the permeability of the membrane, whereas tonicity does.
Tonicity includes only solutes that are not freely permeant and contribute to the osmotic gradient.
Isotonic solutions do not change cell size, while hypotonic solutions cause cells to swell, and hypertonic solutions cause cells to shrink.
Tonicity impacts cell size by determining whether the cell swells or shrinks based on the surrounding fluid.
Osmotic equilibrium is the end goal of osmosis, balancing solute concentrations inside and outside the cell.
Conclusion and encouragement to subscribe for more educational videos.
Transcripts
Hello. Welcome to Byte Size Med.Ā This video is on osmosis.Ā Ā
Transport across the cell membrane, it couldĀ be passive or active. Passive transport doesĀ Ā
not require extra metabolic energy like ATP. ActiveĀ transport does, and why? That is is because passiveĀ Ā
transport is along a concentration gradient fromĀ high to low, while active transport is against theĀ Ā
gradient from low to high. So like pushingĀ a boulder up a hill, it needs extra energyĀ Ā
when compared to letting it roll down. OsmosisĀ is a type of passive transport, like diffusion.Ā Ā
To understand it we take two solutions separatedĀ by a membrane. The solution has a solute and aĀ Ā
solvent. For example, in a solution of salt water,Ā salt is the solute and water is the solvent. So theĀ Ā
concentrations of the solute in these solutionsĀ are different. One is high and one is low. TheĀ Ā
difference creates a concentration gradient. Now ifĀ this membrane were permeable to the solute, meaningĀ Ā
it lets the solute pass through, then the soluteĀ will diffuse from higher to lower concentrations.Ā Ā
So along the gradient, until the concentrationsĀ are equal. That is equilibrium, when there willĀ Ā
be no more net diffusion. Now that was diffusion.Ā It's the movement of the solute along its gradient.Ā Ā
Osmosis is the movement of the solvent. So let'sĀ say the membrane is semi-permeable, that it letsĀ Ā
the solvent pass through, which is water hereĀ and not the solute. So water can get through butĀ Ā
the solute cannot. Which way will water move? TheĀ ultimate goal is equilibrium. The concentrationsĀ Ā
have to become equal. So water moves from lowerĀ solute concentration to higher, diluting the higherĀ Ā
one, making the two concentrations equal. So thisĀ is equilibrium, after which there'll be no more netĀ Ā
movement of water. So water moved along itsĀ gradient from high to low, but in terms of theĀ Ā
solute, it moved from lower to higherĀ concentrations of the solute. This movement ofĀ Ā
the solvent is called osmosis. If we were to applyĀ pressure to the more concentrated side, we couldĀ Ā
stop the movement of water. This pressure that canĀ just stop the solvent from migrating, that is theĀ Ā
osmotic pressure. This osmotic pressure dependsĀ upon the number of particles in the solution.Ā Ā
The concentrations of solutions areĀ expressed in moles, it's a molar concentration.Ā Ā
Here we're talking about osmoles. The solute, onceĀ dissolved in a solution can dissociate or not.Ā Ā
If it doesn't dissociate, like glucose, then oneĀ mole of glucose is one osmole. If it doesĀ Ā
dissociate, like sodium chloride, which splitsĀ into a sodium ion and a chloride ion, that'sĀ Ā
two osmotically active particles. So assumingĀ it completely dissociates, that's two osmoles.
The number of osmoles per litre of a solution,Ā that's the osmolarity or the osmotic concentrationĀ Ā
of that solution. Osmolarity with an 'r'. SoĀ it's osmoles per litre, or if it's smaller,Ā Ā
milliosmoles per litre. If the same thing isĀ expressed per kilogram, then it's osmolality,Ā Ā
with an 'l'. So osmoles per kg or milliosmolesĀ per kg. So we have two solutions and if theĀ Ā
osmolarity of the two solutions are equal, thenĀ they are isoosmotic. But what if they're different?Ā Ā
Then the lower one is hyposmotic, and the higherĀ one is hyperosmotic. So iso-, hypo- and hyper-.Ā Ā
Osmolarity and osmolality, they take intoĀ account the concentrations of the solutions, yesĀ Ā
but they don't include the characteristics ofĀ the membrane. It includes solutes that are bothĀ Ā
freely permeant and those that are not. IfĀ a solute is freely permeant, it means it canĀ Ā
easily cross the membrane. So what will happen?Ā It'll diffuse along its concentration gradient,Ā Ā
from high to low and the concentrations becomeĀ equal. Water moves as well, but since the soluteĀ Ā
moved, it creates equal concentrations fasterĀ and when there's no concentration difference,Ā Ā
there's no more osmotic gradient.Ā Such a solute is an ineffective osmole.Ā Ā
So for osmoles to be effective, they should notĀ be freely permeant. That maintains a differenceĀ Ā
in concentration and so an osmoticĀ gradient, allowing the solvent to move.
Tonicity is a similar term toĀ osmolarity, but is not the same.Ā Ā
It takes into account the solute concentrationsĀ and also their ability to cross the membrane.Ā Ā
It only includes solutes that are notĀ freely permeant and so are capable ofĀ Ā
contributing to the osmotic gradient.Ā It's a measure of effective osmolality.
This is the term used when fluids are comparedĀ to the plasma. Isotonic, hypotonic and hypertonic.Ā Ā
Tonicity determines the effect that a fluid canĀ have on cell size, whether it swells or shrinks.
If we consider one of these solutions to beĀ fluid inside the cell and one to be fluidĀ Ā
outside, the two are separated byĀ a cell membrane. The cell membraneĀ Ā
is semi-permeable. It is freely permeable toĀ water, but is impermeable to a lot of solutes.
So we're going to take a cell in aĀ solution. The end goal is equilibrium,Ā Ā
which means that the concentrationĀ inside and outside have to be equal,Ā Ā
and that happens by fluidĀ moving across the membrane.Ā Ā
Let's put this cell in three different kindsĀ of solutions. Isotonic, hypotonic and hypertonic.Ā Ā
An isotonic solution means the concentrationĀ is equal between inside and outside the cell.Ā Ā
There's no need for water to move across theĀ membrane and the cell size stays the same.Ā Ā
But if it's a hypotonic solution, there's aĀ lower concentration outside than inside. SoĀ Ā
water moves towards higher concentration of theĀ solute. It enters the cell and the cell swells.Ā Ā
On the other hand, if it were a hypertonic solution,Ā Ā
there's higher concentration outside than inside.Ā Water again moves towards higher concentrationĀ Ā
of the solute. So it leaves the cell and the cellĀ shrinks. So in hypotonic solutions, the cell swells.Ā Ā
In hypertonic solutions, the cellĀ shrinks. The end goal, osmotic equilibrium.
And that is osmosis. If this video helped you,Ā give it a thumbs up and subscribe to my channel.Ā Ā
Thanks for watching andĀ I'll see you in the next one! :)
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