Download Passive Transport

Passive Transport
Starter
• Name a cellular organelle that possesses a membrane and
describe the purpose of the membrane.
Golgi, mitochondria, chloroplast, nucleus, lysosomes
Compartmentalise enzyme reactions/control substances in and out
• Describe the purpose of cholesterol in the plasma membrane
Prevents phospholipid tails from packing close together and preserves fluidity of membrane
• Suggest why organisms living in polar regions have a high
proportion of cholesterol in the membrane
To keep membrane fluid and functioning correctly
• List three substances that need to be transported into animal
cells in order to survive.
Oxygen, food, minerals, water
• List two substances that need to be transported out of animal
cells in order to survive
Carbon dioxide, nitrogenous wastes
Passive Transport
Learning Objectives
• Explain what is meant by
passive transport
• Explain what is meant by
facilitated diffusion
• Identify the role of
membrane proteins in
transport
Success Criteria
• Recall the definitions of
diffusion, facilitated diffusion
and osmosis (Grade D-E)
• Compare diffusion and
facilitated diffusion (Grade C)
• Construct models/diagrams to
show how the processes differ
(Grade A-B)
Transport across the cell membrane
All cells are surrounded by a partially-permeable membrane that
controls what substances can enter and exit the cell.
A cell needs to be able to import
the substances it needs to survive,
and to export waste materials and
substances that are needed outside
the cell.
There are several methods by which substances (molecules and
ions) can cross the cell membrane:

diffusion

osmosis

active transport.
On your whiteboards write
down what you understand
from KS4 about each
methods
What is diffusion?
Diffusion is the net movement of particles down a concentration
gradient: from a region of high concentration to a region of low
concentration.
net movement
of particles
No metabolic energy is expended during diffusion so it is an
example of passive transport.
One example of diffusion is gas exchange across respiratory
surfaces, such as the lungs of mammals and birds, and the gills of
fish.
Mind map – what factors affect diffusion!! Give examples where
possible
Diffusion Recap
The molecules will diffuse both ways, but the net (overall)
movement will be to the area of low concentration.
There is a concentration gradient
..... particles move down it
Diffusion is PASSIVE!
There is NO energy involved.
Diffusion occurs if the molecules involved can pass
freely through a membrane. So they have to be small. If
they’re not, facilitated diffusion is required!
What factors affect diffusion?
Rates of Diffusion
The rate at which diffusion occurs is determined by
several factors:
1. The size of the concentration gradient.
The larger the difference in concentration, the faster diffusion will
occur.
2. The thickness of the exchange surface.
The thinner the exchange surface, the faster diffusion will occur.
3. The distance between the two areas.
A shorter distance = faster diffusion.
4. The size of the molecules.
Smaller molecules such as oxygen will diffuse quicker than large
molecules like proteins.
The rate of diffusion
The rate of diffusion in a given direction across an exchange surface
can be summarized by Fick’s law, which states that:
surface area × difference in conc.
rate of diffusion is
proportional to:
length of diffusion path
(membrane thickness)
Increasing the surface area across which the particles diffuse, or
increasing the size of the concentration gradient will increase the
rate of diffusion.
Increasing the distance (or thickness of the membrane) over which
diffusion takes place will decrease the rate.
Facilitated Diffusion
Facilitated diffusion uses the same principle as ordinary
diffusion, except that protein carriers are involved.
Small molecules like O2 and CO2 can simply diffuse across a
membrane without any help.
Larger molecules like amino acids and glucose can’t diffuse
directly through the phospholipid bilayer.
They still move down a concentration gradient, but
because they’re so big, they move through carrier
proteins or channel proteins.
Facilitated diffusion is also passive (no energy).
CARRIER or transmembrane Proteins
OUTSIDE
INSIDE
Carrier proteins move large molecules in or out of the cell
down a concentration gradient.
1. Molecules attach to the carrier protein.
2. The carrier changes shape.
3. It releases the molecule on the other side.
CHANNEL Proteins
OUTSIDE
INSIDE
Channel proteins form pores in the membrane for
CHARGED PARTICLES to move down a concentration
gradient.
Only open in response to presence of molecule
Facilitated Diffusion
• Facilitated diffusion is specific.
• i.e. A certain type of molecule will have a
corresponding carrier or channel
Glucose = glucose channel
Amino acids = amino acid channel
Facilitated diffusion
Facilitated diffusion
• Write down a definition of facilitated diffusion
• What is the difference between carrier proteins
and channel proteins?
• Construct models/diagrams to show how the all
the passive processes of transport occur
- Diffusion
- Facilitated diffusion using channel proteins
- Facilitated diffusion using carrier proteins
Plenary - whiteboards