Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

What is the water potential of pure water, and why is it the highest possible value?

The water potential of pure water is zero kPa, and no solution can exceed it because adding any solute lowers the water potential to a negative value.

Why does adding a solute to water lower its water potential?

Water molecules form hydrogen bonds with and cluster around the solute particles, so fewer of them are free to move out of the solution and the tendency of water to leave is reduced.

Why does a solution of sodium chloride have a lower water potential than a glucose solution of the same molar concentration?

Sodium chloride is an electrolyte and dissociates into two ions per formula unit, so it produces twice as many dissolved particles as the same concentration of glucose and lowers the water potential twice as much.

Give the equation relating the water potential of a plant cell to its solute and pressure potentials.

Water potential equals solute potential plus pressure potential.

OCR A-Level Biology B H422

The Developing Cell: Cell Division and Cell Differentiation

Topic overview The cell cycle and mitosis Apoptosis in growth and repair Stem cells and cell differentiation

The Developing Individual: Meiosis, Growth and Development

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The Development of Species: Evolution and Classification

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Cells and Microscopy

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Water and Its Importance in Plants and Animals

Topic overview The properties of water Water as a transport medium and the composition of body fluids Detecting and measuring sugars and proteins Monomers, polymers and the carbohydrates Osmosis and water potential

Proteins and Enzymes

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Nucleic Acids

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Patterns of Inheritance

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Gene Technologies

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Gas Exchange in Mammals and Plants

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Transport Systems in Plants

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Water and Its Importance in Plants and Animals

Osmosis and water potential

3 things to know
Components 01, 02 and 03

Overview

Recall questions on water potential and its units, why solutes lower it, the solute and pressure equation, plant cells and erythrocytes in strong solutions, and percentage change in potato mass.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What happens to a plant cell placed in pure water?

Key term

Why does an erythrocyte burst in pure water when a plant cell does not?

Key term

What is water potential and what units is it measured in?

Questions from this subtopic

Each one with the model answer underneath.

1
Define osmosis.
Model answer
Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
2
What is water potential and what units is it measured in?
Model answer
Water potential is the tendency of water molecules to move out of a system, and it is measured in kilopascals, kPa.
3
What is the water potential of pure water, and why is it the highest possible value?
Model answer
The water potential of pure water is zero kPa, and no solution can exceed it because adding any solute lowers the water potential to a negative value.
4
Why does adding a solute to water lower its water potential?
Model answer
Water molecules form hydrogen bonds with and cluster around the solute particles, so fewer of them are free to move out of the solution and the tendency of water to leave is reduced.
5
Why does a solution of sodium chloride have a lower water potential than a glucose solution of the same molar concentration?
Model answer
Sodium chloride is an electrolyte and dissociates into two ions per formula unit, so it produces twice as many dissolved particles as the same concentration of glucose and lowers the water potential twice as much.
6
Give the equation relating the water potential of a plant cell to its solute and pressure potentials.
Model answer
Water potential equals solute potential plus pressure potential.

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Osmosis and water potential

Overview

What you need to know

What happens to a plant cell placed in pure water?

Why does an erythrocyte burst in pure water when a plant cell does not?

What is water potential and what units is it measured in?

Questions from this subtopic

Define osmosis.

What is water potential and what units is it measured in?

What is the water potential of pure water, and why is it the highest possible value?

Why does adding a solute to water lower its water potential?

Why does a solution of sodium chloride have a lower water potential than a glucose solution of the same molar concentration?

Give the equation relating the water potential of a plant cell to its solute and pressure potentials.

Other ways to work this

What is inside Levo

The 3-step method, run for you

Cram a whole paper in one sitting

Blank Blitz makes facts automatic

Build It gets the exam shape right

Test It catches misconceptions

Brain Breaks between sessions

Every question in Water and Its Importance in Plants and Animals, on a schedule.