Movement of Substances Through Cell Membrane
Movement of
Substances through
a Cell Membrane
BIOLOGY
Unit 1.1
Double Award
Unit 1.1
How do substances enter and leave
cells?
M
o
l
e
c
u
l
e
s
m
o
v
e
q
u
i
c
k
l
y
a
n
d
a
t
r
a
n
d
o
m
f
r
o
m
a
r
e
g
i
o
n
o
f
h
i
g
h
c
o
n
c
e
n
t
r
a
t
i
o
n
t
o
l
o
w
c
o
n
c
e
n
t
r
a
t
i
o
n
d
o
w
n
a
c
o
n
c
e
n
t
r
a
t
i
o
n
g
r
a
d
i
e
n
t
-
t
h
i
s
i
s
c
a
l
l
e
d
D
I
F
F
U
S
I
O
N
.
Diffusion
Here the pink molecules
will move from the left to
the right until there are
the same number of
pink molecules on both
sides.
Flow
Flow
Flow
Flow
D
i
f
f
u
s
i
o
n
d
o
e
s
n
o
t
r
e
q
u
i
r
e
a
n
i
n
p
u
t
o
f
e
n
e
r
g
y
…
i
t
i
s
a
p
a
s
s
i
v
e
p
r
o
c
e
s
s
.
The orange molecules
move in the opposite
direction. This is how
substances such as
oxygen and carbon
dioxide enter and leave
cells.
The Effect of the Cell Membrane on
Diffusion
If a cell membrane was totally permeable
(allows everything in and out), the cell would
die in no time. Even though useful substances
would enter the cell easily, the cell’s content
would diffuse out. In order to survive, the cell
membrane has to be selectively permeable
(allows only some substances to enter and
leave).
Osmosis
Here we can see the water diffusing through a selectively permeable
membrane, from a region of high concentration to a region of lower
water concentration.
water
sugar
Selectively permeable
Selectively permeable
Membrane
Membrane
High water concentration
High water concentration
Low sugar concentration
Low sugar concentration
Low water concentration
Low water concentration
High sugar concentration
High sugar concentration
W
e
a
k
s
o
l
u
t
i
o
n
S
t
r
o
n
g
s
o
l
u
t
i
o
n
Osmosis
Here we can see the water diffusing through a selectively permeable
membrane, from a region of high concentration to a region of lower
water concentration.
water
sugar
Selectively permeable
Selectively permeable
Membrane
Membrane
High water concentration
High water concentration
Low sugar concentration
Low sugar concentration
Low water concentration
Low water concentration
High sugar concentration
High sugar concentration
W
e
a
k
s
o
l
u
t
i
o
n
S
t
r
o
n
g
s
o
l
u
t
i
o
n
Osmosis
Here we can see the water diffusing through a selectively permeable
membrane, from a region of high concentration to a region of lower
water concentration.
water
sugar
Selectively permeable
Selectively permeable
Membrane
Membrane
High water concentration
High water concentration
Low sugar concentration
Low sugar concentration
Low water concentration
Low water concentration
High sugar concentration
High sugar concentration
W
e
a
k
s
o
l
u
t
i
o
n
S
t
r
o
n
g
s
o
l
u
t
i
o
n
Practical Work
We can use a special plastic called
Visking tubing to demonstrate osmosis.
Here we can see that the water
molecules can move through the tubing
but the sucrose molecules are
prevented. The reason for this is to do
with the size of the molecules. The
sucrose molecule is larger than the
water and cannot fit through the tiny
holes in the wall of the tubing. Water
can move into the sucrose solution, but
the sucrose cannot go into the water.
After about half an hour, the solution’s
level in the tube will have risen, and the
water level will have dropped.
water
Visking tube
sucrose solution
capillary tube
tight
knot
Practical Work
Potatoes can be used to demonstrate
osmosis in living tissue.
Potato cylinders of the same length and
diameter are each placed in different
concentrations of sucrose solutions for 20
minutes.
The length and mass of each cylinder
should then be re-measured. The potatoes
that have been in strong sucrose solutions
will have reduced in length and mass, whilst
the ones placed in weak sucrose solutions
will have gained length and mass.
Cylinders showing no change will have cells
with cytoplasm of equal strength to the
sucrose solution that they were placed in.
Distilled
Water
0.1M
0.2M
0.5M
1M
Labelled Petri dishes
50mm
5mm
Potato
cylinder
The Importance of Osmosis to Cells
If a red blood cell was in a solution containing
less water than itself (hypertonic) then the cell
would lose water. It would shrivel and die.
H
H
i
i
g
g
h
h
e
e
r
r
Homeostasis
It is very important therefore to keep the
blood constant so that the cells in it do not
gain or lose too much water.
T
h
e
t
e
r
m
f
o
r
k
e
e
p
i
n
g
t
h
e
s
e
i
n
t
e
r
n
a
l
c
o
n
d
i
t
i
o
n
s
c
o
n
s
t
a
n
t
i
s
H
o
m
e
o
s
t
a
s
i
s
.
H
H
i
i
g
g
h
h
e
e
r
r
The importance of Osmosis to Cells
If a red blood cell was in a solution that had more water
in it than was in the cell (hypotonic), then it would gain
water. It would expand, burst and die.
H
H
i
i
g
g
h
h
e
e
r
r
Active Transport
I
n
m
a
n
y
c
a
s
e
s
s
u
b
s
t
a
n
c
e
s
a
r
e
m
o
v
e
d
i
n
t
o
o
r
o
u
t
o
f
c
e
l
l
s
a
g
a
i
n
s
t
a
d
i
f
f
u
s
i
o
n
g
r
a
d
i
e
n
t
i
.
e
.
o
p
p
o
s
i
t
e
t
o
t
h
e
m
o
v
e
m
e
n
t
o
f
t
h
e
m
o
l
e
c
u
l
e
s
.
E
n
e
r
g
y
i
s
n
e
e
d
e
d
f
o
r
t
h
i
s
p
r
o
c
e
s
s
,
a
n
d
s
o
i
t
’
s
c
a
l
l
e
d
a
c
t
i
v
e
t
r
a
n
s
p
o
r
t
.
H
H
i
i
g
g
h
h
e
e
r
r
Examples of Active Transport
In the body we see active transport in the
small intestine, when digested food is
absorbed into the blood in the opposite
direction to diffusion.
In a plant, rare minerals from the soil are
pulled into the roots opposite to the
direction of diffusion.
H
H
i
i
g
g
h
h
e
e
r
r
Summary
D
i
f
f
u
s
i
o
n
i
s
t
h
e
m
o
v
e
m
e
n
t
o
f
p
a
r
t
i
c
l
e
s
d
o
w
n
a
c
o
n
c
e
n
t
r
a
t
i
o
n
g
r
a
d
i
e
n
t
.
O
s
m
o
s
i
s
i
s
t
h
e
d
i
f
f
u
s
i
o
n
o
f
w
a
t
e
r
m
o
l
e
c
u
l
e
s
t
h
r
o
u
g
h
a
s
e
l
e
c
t
i
v
e
l
y
p
e
r
m
e
a
b
l
e
m
e
m
b
r
a
n
e
.
A
c
t
i
v
e
t
r
a
n
s
p
o
r
t
i
s
t
h
e
m
o
v
e
m
e
n
t
o
f
m
o
l
e
c
u
l
e
s
a
g
a
i
n
s
t
a
c
o
n
c
e
n
t
r
a
t
i
o
n
g
r
a
d
i
e
n
t
–
t
h
i
s
r
e
q
u
i
r
e
s
e
n
e
r
g
y
.
Substances enter and leave cells through diffusion and osmosis processes, driven by concentration gradients. The cell membrane plays a crucial role in selectively allowing substances to pass, ensuring cell survival. Osmosis can be demonstrated using Visking tubing, showing water molecules moving while larger sucrose molecules are blocked.
Download Presentation
Please find below an Image/Link to download the presentation.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author.If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.
You are allowed to download the files provided on this website for personal or commercial use, subject to the condition that they are used lawfully. All files are the property of their respective owners.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author.
E N D
Presentation Transcript
Movement of Substances through a Cell Membrane BIOLOGY Unit 1.1 Double Award Unit 1.1
How do substances enter and leave cells? Molecules move quickly and at random from a region of high concentration to low concentration down a concentration gradient - this is called DIFFUSION.
Diffusion Here the pink molecules will move from the left to the right until there are the same number of pink molecules on both sides. Flow The orange molecules move in the opposite direction. This is how substances such as oxygen and carbon dioxide enter and leave cells. Flow Diffusion does not require an input of energy it is a passive passive process.
The Effect of the Cell Membrane on Diffusion If a cell membrane was totally permeable (allows everything in and out), the cell would die in no time. Even though useful substances would enter the cell easily, the cell s content would diffuse out. In order to survive, the cell membrane has to be selectively permeable (allows only some substances to enter and leave).
Osmosis Here we can see the water diffusing through a selectively permeable membrane, from a region of high concentration to a region of lower water concentration. Selectively permeable Membrane water sugar High water concentration Low sugar concentration Low water concentration High sugar concentration Weak solution Strong solution
Osmosis Here we can see the water diffusing through a selectively permeable membrane, from a region of high concentration to a region of lower water concentration. Selectively permeable Membrane water sugar High water concentration Low sugar concentration Low water concentration High sugar concentration Weak solution Strong solution
Osmosis Here we can see the water diffusing through a selectively permeable membrane, from a region of high concentration to a region of lower water concentration. Selectively permeable Membrane water sugar High water concentration Low sugar concentration Low water concentration High sugar concentration Weak solution Strong solution
Practical Work We can use a special plastic called Visking tubing to demonstrate osmosis. capillary tube Here we can see that the water molecules can move through the tubing but the sucrose molecules are prevented. The reason for this is to do with the size of the molecules. The sucrose molecule is larger than the water and cannot fit through the tiny holes in the wall of the tubing. Water can move into the sucrose solution, but the sucrose cannot go into the water. sucrose solution level tight knot sucrose solution Visking tube After about half an hour, the solution s level in the tube will have risen, and the water level will have dropped. water
Practical Work Potatoes can be used to demonstrate osmosis in living tissue. Distilled Water Potato cylinders of the same length and diameter are each placed in different concentrations of sucrose solutions for 20 minutes. 0.1M 0.2M 1M 0.5M The length and mass of each cylinder should then be re-measured. The potatoes that have been in strong sucrose solutions will have reduced in length and mass, whilst the ones placed in weak sucrose solutions will have gained length and mass. Labelled Petri dishes 5mm 50mm Cylinders showing no change will have cells with cytoplasm of equal strength to the sucrose solution that they were placed in. Potato cylinder
Higher Higher The Importance of Osmosis to Cells If a red blood cell was in a solution containing less water than itself (hypertonic) then the cell would lose water. It would shrivel and die.
Higher Higher Homeostasis It is very important therefore to keep the blood constant so that the cells in it do not gain or lose too much water. The term for keeping these internal conditions constant is Homeostasis.
Higher Higher The importance of Osmosis to Cells If a red blood cell was in a solution that had more water in it than was in the cell (hypotonic), then it would gain water. It would expand, burst and die.
Higher Higher Active Transport In many cases substances are moved into or out of cells against a diffusion gradient i.e. opposite to the movement of the molecules. Energy is needed for this process, and so it s called active transport.
Higher Higher Examples of Active Transport In the body we see active transport in the small intestine, when digested food is absorbed into the blood in the opposite direction to diffusion. In a plant, rare minerals from the soil are pulled into the roots opposite to the direction of diffusion.
Summary Diffusion is the movement of particles down a concentration gradient. Osmosis is the diffusion of water molecules through a selectively permeable membrane. Active transport is the movement of molecules against a concentration gradient this requires energy.
