Transport in
Cells
1
Simple Diffusion
2
What is diffusion?
The movement of particles from an
area of high concentration to an
area of low concentration.
3
What is diffusion?
◎ Particles in fluids (liquids and
gases - not solids) are not in
fixed positions, so are able to
randomly move freely over one
another.
◎ The particles move randomly
until they reach equilibrium (are
evenly spread).
◎ This type of movement is
PASSIVE and does NOT require
energy.
4
What is diffusion?
Concentration Gradient
5
Diffusion in cells
◎
◎
Diffusion can occur across the plasma membrane
For example, a cell will need to allow oxygen
molecules in and carbon dioxide molecules out.
6
Why is diffusion useful?
◎
◎
◎
◎
Cells can use diffusion as a way
of getting important particles in
and out of them.
Diffusion is particularly useful as
it does not use any energy.
To get into a cell, particles have
to pass through a
selectively-permeable
membrane.
This is only good for small
molecules, though – like oxygen
and carbon dioxide.
7
“
8
Real-life examples of simple
diffusion
◎ You can smell perfume because
it diffuses into the air and
makes its way into your nose.
◎ A tea bag placed in a cup of hot
water will diffuse into the water.
◎ Placing food coloring in a liquid
will diffuse the color.
◎ Cigarette smoke diffuses into
the air.
9
Demonstration
How does diffusion work?
10
Factors that influence diffusion
◎ Many factors can increase the
rate of diffusion.
◉ Temperature
◉ Molecule size
◉ Medium of diffusion
◉ Concentration gradient
11
12
2
Facilitated Diffusion
13
What is facilitated diffusion?
The process by which proteins in a
cell membrane help particles
diffuse through.
14
What is facilitated diffusion?
◎ This type of diffusion is still
passive as NO energy is required.
◎ It is needed to help larger
molecules such as charged ions
pass through the membrane.
◎ The two types of proteins
involved in this process are carrier
proteins and channel proteins.
15
Carrier Proteins
◎ Open and close areas along the
plasma membrane
◎ When they are open, molecules
and particles can pass through
◎ They bind to specific molecules or
ions on one side of the
membrane, change shape and
release them on the other side
16
Carrier Proteins
17
Channel Proteins
◎ Form narrow passageways
through which small ions can
diffuse
◎ Only ions of specific size and
shape can pass through particular
protein channels
◎ Transport is selective and channel
proteins only open when they
receive a signal to do so
18
Channel Proteins
19
“
20
3
Active Transport
21
What is active transport?
◎ Sometimes, molecules will need
to move AGAINST the
concentration gradient (from low
to high).
◎ It is called active transport as it
requires an input of energy.
22
How does active transport work?
◎ Involves carrier proteins similar to
the ones used in facilitated
diffusion.
◎ They are selective and can
become saturated.
◎ In this process, the protein is
coupled with ATP (energy) to
transport molecules against the
concentration gradient.
23
How does active transport work?
24
“
25
Transport in Cells
Simple
diffusion
Active
transport
Facilitated
diffusion
26
True/ False?
Diffusion occurs when particles move from areas of high
concentration to low concentration.
27
True/ False?
Diffusion is an example of passive transport (it
does not require energy).
28
True/ False?
Oxygen, carbon dioxide and water are easily diffused across
the plasma membrane via simple diffusion.
29
True/ False?
Active transport uses carrier proteins and does not require
energy.
30
True/ False?
Carrier proteins and channel proteins are the same thing.
31
True/ False?
Heat has no effect on diffusion.
32
True/ False?
Diffusion requires the random movement of molecules.
33
True/ False?
Cell membranes allow any molecule to pass through freely
as long as they need it.
34
True/ False?
Cell membranes are selectively permeable
35