Name_____________________
KS4 Biology
(Part 2) Cell Biology
Topic Booklet
Lesson
1. Diffusion
2. Surface area to volume ratio
3. Exchanging materials
4. Osmosis
5. Osmosis RP - part 1
6. Osmosis RP- part 2
7. Active transport
8. FA2
0
,Lesson 9 Diffusion
KEYWORD DEFINITION
Diffusion Movement of particles from a high concentration to a low concentration down a
concentration gradient.
Concentration The measure of the number of particles of the solute (dissolved substance) in a
solvent (what it is dissolved in).
Surface area to The amount of surface area per unit volume of an object or collection of
volume ratio objects.
Most of the chemical reactions that occur inside the cell require some reactant products. They also
produce some reactants and waste products. Therefore, there needs to be a way for cells to obtain
the reactants such as oxygen and glucose but simultaneously get rid of any waste products such as
carbon dioxide to avoid them building up in the cells.
Concentration
In order to understand diffusion it is essential that we understand the term concentration.
Concentration is the measure of the number of particles of the solute (dissolved substance) in a
solvent (what it is dissolved in). Something that is highly concentrated will have a large number of
solute particles in the solvent and something that is more dilute (less concentrated) will have fewer
particles of the solute in the solvent.
What is diffusion?
Dissolved substances can move in and out of the cells across membranes via a process called
diffusion. Diffusion is essential for the delivery of useful products for cell processes and for the
removal of waste products. Diffusion is the movement of particles from a high concentration to a low
concentration. Diffusion occurs down a concentration gradient.
Diffusion is the net (overall) movement of particles from an area of high concentration to an area of
low concentration. Diffusion can only work if there is an area of high concentration next to an area of
low concentration. Concentration gradient is defined as the difference in concentration between two
areas. Diffusion happens because of the random nature of particle movement. The particles bump
into each other and push each other around. When there is a high concentration the particles can
bump into each other and into solute particles. This spreads out the particles in a random way.
1
,An example of diffusion of gas particles is when a smell spreads across a room. If someone sprays
air freshener in one corner of the room, the particles are in a high concentration in that corner. The
gas particles begin to bump into each other and spread across the room. Eventually, people on the
other side of the room will smell the air freshener. Similarly, when squash is mixed with water the
solutes (squash) diffuse through the water from a high concentration to a low concentration. Diffusion
also happens in biological systems which we will study in the next lesson.
TASK 1 - Comprehension questions
Answer the questions below in your books.
1. Define diffusion.
2. Draw a diagram to represent diffusion.
3. Explain in terms of solute what a high concentration is like.
4. Explain why you can smell cooking in the kitchen from a different room in the house.
Extension questions
1. Are plant and animal cells eukaryotic or prokaryotic?
2. What is a prokaryotic cell?
Factors affecting the rate of diffusion
Concentration gradient
Concentration gradient is a measure of the difference between a high and a low concentration.
Concentration gradient can be steep or less steep. The steepness of the concentration gradient
governs how quickly diffusion happens. That is, the rate of diffusion. If there is an area or very high
concentration next to an area of very low concentration, the concentration gradient would be
described as steep, and diffusion will happen quickly. If the concentration in one area is high, and is
next to an area that is fairly high there is still a concentration gradient, but a shallow one. There will
still be diffusion, but the diffusion will happen more slowly. The rate of diffusion will be lower.
2
, Temperature
An increase in temperature means the particles in a gas or a solution move around more quickly and
gain kinetic energy. When this happens, diffusion takes place more rapidly as the random movement
of particles speeds up.
Surface area
The surface area between an area of high and low concentration also affects the rate of diffusion. If
there is a larger surface area between two concentrations, there is more space for particles to mix,
giving a faster rate of diffusion. Humans, including other animals have highly folded membranes to
increase surface area.
TASK 2 - Comprehension questions
Answer the questions below in your books.
1. Explain why diffusion happens faster when there is an increase in temperature.
2. Explain why some cells have a folded membrane.
3. Male moths can track down a mate from up to 3 miles away because of the special
chemicals produced by the female. Explain how the male detects the chemical using your
knowledge of diffusion.
4. Explain why diffusion happens faster with a steeper concentration gradient.
Extension questions
1. What is a prokaryotic organism?
2. Which structures/organelles are found in prokaryotic cells?
TASK 3 - Exam style questions
Answer the questions below in your books.
Q1. In this question you will be assessed on using good English, organising information
clearly and using specialist terms where appropriate.
Diffusion is an important process in animals and plants.
3
KS4 Biology
(Part 2) Cell Biology
Topic Booklet
Lesson
1. Diffusion
2. Surface area to volume ratio
3. Exchanging materials
4. Osmosis
5. Osmosis RP - part 1
6. Osmosis RP- part 2
7. Active transport
8. FA2
0
,Lesson 9 Diffusion
KEYWORD DEFINITION
Diffusion Movement of particles from a high concentration to a low concentration down a
concentration gradient.
Concentration The measure of the number of particles of the solute (dissolved substance) in a
solvent (what it is dissolved in).
Surface area to The amount of surface area per unit volume of an object or collection of
volume ratio objects.
Most of the chemical reactions that occur inside the cell require some reactant products. They also
produce some reactants and waste products. Therefore, there needs to be a way for cells to obtain
the reactants such as oxygen and glucose but simultaneously get rid of any waste products such as
carbon dioxide to avoid them building up in the cells.
Concentration
In order to understand diffusion it is essential that we understand the term concentration.
Concentration is the measure of the number of particles of the solute (dissolved substance) in a
solvent (what it is dissolved in). Something that is highly concentrated will have a large number of
solute particles in the solvent and something that is more dilute (less concentrated) will have fewer
particles of the solute in the solvent.
What is diffusion?
Dissolved substances can move in and out of the cells across membranes via a process called
diffusion. Diffusion is essential for the delivery of useful products for cell processes and for the
removal of waste products. Diffusion is the movement of particles from a high concentration to a low
concentration. Diffusion occurs down a concentration gradient.
Diffusion is the net (overall) movement of particles from an area of high concentration to an area of
low concentration. Diffusion can only work if there is an area of high concentration next to an area of
low concentration. Concentration gradient is defined as the difference in concentration between two
areas. Diffusion happens because of the random nature of particle movement. The particles bump
into each other and push each other around. When there is a high concentration the particles can
bump into each other and into solute particles. This spreads out the particles in a random way.
1
,An example of diffusion of gas particles is when a smell spreads across a room. If someone sprays
air freshener in one corner of the room, the particles are in a high concentration in that corner. The
gas particles begin to bump into each other and spread across the room. Eventually, people on the
other side of the room will smell the air freshener. Similarly, when squash is mixed with water the
solutes (squash) diffuse through the water from a high concentration to a low concentration. Diffusion
also happens in biological systems which we will study in the next lesson.
TASK 1 - Comprehension questions
Answer the questions below in your books.
1. Define diffusion.
2. Draw a diagram to represent diffusion.
3. Explain in terms of solute what a high concentration is like.
4. Explain why you can smell cooking in the kitchen from a different room in the house.
Extension questions
1. Are plant and animal cells eukaryotic or prokaryotic?
2. What is a prokaryotic cell?
Factors affecting the rate of diffusion
Concentration gradient
Concentration gradient is a measure of the difference between a high and a low concentration.
Concentration gradient can be steep or less steep. The steepness of the concentration gradient
governs how quickly diffusion happens. That is, the rate of diffusion. If there is an area or very high
concentration next to an area of very low concentration, the concentration gradient would be
described as steep, and diffusion will happen quickly. If the concentration in one area is high, and is
next to an area that is fairly high there is still a concentration gradient, but a shallow one. There will
still be diffusion, but the diffusion will happen more slowly. The rate of diffusion will be lower.
2
, Temperature
An increase in temperature means the particles in a gas or a solution move around more quickly and
gain kinetic energy. When this happens, diffusion takes place more rapidly as the random movement
of particles speeds up.
Surface area
The surface area between an area of high and low concentration also affects the rate of diffusion. If
there is a larger surface area between two concentrations, there is more space for particles to mix,
giving a faster rate of diffusion. Humans, including other animals have highly folded membranes to
increase surface area.
TASK 2 - Comprehension questions
Answer the questions below in your books.
1. Explain why diffusion happens faster when there is an increase in temperature.
2. Explain why some cells have a folded membrane.
3. Male moths can track down a mate from up to 3 miles away because of the special
chemicals produced by the female. Explain how the male detects the chemical using your
knowledge of diffusion.
4. Explain why diffusion happens faster with a steeper concentration gradient.
Extension questions
1. What is a prokaryotic organism?
2. Which structures/organelles are found in prokaryotic cells?
TASK 3 - Exam style questions
Answer the questions below in your books.
Q1. In this question you will be assessed on using good English, organising information
clearly and using specialist terms where appropriate.
Diffusion is an important process in animals and plants.
3
