Osmosis

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  • Created by: zoolouise
  • Created on: 20-04-16 10:51
What is the definition of osmosis?
Osmosis is the diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential.
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What is the definition of water potential?
Water potential is the potential of water molecules to diffuse out or into a solution.
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What does osmosis require the presence of?
A partially permeable membrane and this is permeable to water molecules and other small molecules, but not to larger molecules.
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What is the definition of a solute?
A solute is any substance that is dissolved in a solvent. e.g. sugar or salt
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What is the definition of a solvent?
A solvent does the dissolving. e.g. water.
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What is water potential represented and measuredb y?
It is represented by ψ often known as psi (pronounced sigh) and it's measured in units of pressure which are kilopascals (kPa).
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What is the water potential of pure water?
Under standard conditions of temperature 25 and pressure 100kPa, pure water has the water potential of zero
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What does it mean when the solution is more concentrated?
The more concentrated a solution, i.e. the more solute that's added, the lower its water potential.
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What's the highest value of water potential?
The higher value of water potential is zero, all the other values are negative, the more negative the value, the lower the water potential.
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How do you find the water potential of cells/tissues?
Place the cells/tissue in a series of solutions of different water potentials. If no net gain/loss of water from cells/tissues, water potential inside must be same as solution
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What do red blood cells contain?
Various solutes dissolved in their watery cytoplasm.
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What happened when red blood cells are placed in pure water?
It will absorb water by osmosis, it has a lower water potential than the pure water (zero). The cell surface membranes are very thin, they can't stretch much, this results in breaking, bursting the cell and releasing its contents (haemolysis)
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How do you prevent cells from bursting?
Animal cells are normally surrounded by a liquid which has the same water potential.
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What happens when a red blood cell is placed in a solution with a lower water potential?
The water leaves and the cell shrinks and becomes shriveled.
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What is the equation used to describe the relationship between forces of water potential in plant cells?
Water potential = Solute potential + Pressure potential ψ = ψs + ψp
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How does the water potential gradient affect the rate of osmosis?
Higher water potential gradient, the faster the rate of osmosis. As osmosis takes place, the difference in water potential on either side of the membrane decreases, so the rate of osmosis levels off over time.
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How does the thickness of the exchange surface affect the rate of osmosis?
The thinner the exchange surface, the faster the rate of osmosis
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How does the surface area of the exchange surface affect the rate of osmosis?
The larger the surface area, the faster the rate of osmosis
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Card 2

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What is the definition of water potential?

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Water potential is the potential of water molecules to diffuse out or into a solution.

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What does osmosis require the presence of?

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Card 4

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What is the definition of a solute?

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What is the definition of a solvent?

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