Transport of molecules in living
organisms
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey 22/10/2019
Learning Outcomes
• Recall and explain the different ways cells
use to transport molecules
• Explain some physiological important
examples of passive and active transport.
• Compare and contrast diffusion, facilitated
diffusion, osmosis and active transport
• Be able to predict what would happen to an
animal or plant cell when its extracellular
solute concentration is reduced or increased.
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey 22/10/2019
Learning Outcomes
•
Recall and explain the different ways cells
use to transport molecules
•
Explain some physiological important
examples of passive and active transport.
•
Compare and contrast diffusion, facilitated
diffusion, osmosis and active transport
•
Be able to predict what would happen to an
animal or plant cell when its extracellular
solute concentration is reduced or increased.
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey 22/10/2019
Key words
Diffusion
Osmosis
Facilitated Diffusion
Active transport
Semi-permeable membrane
Solvent
Solute
Dynamic equilibrium
Hyopotonic, isotonic,
hypertonic
The kinetic model of matter
The particles in solids, liquids and gases above absolute zero (-273
°C) will all exhibit some degree of movement.
Diffusion
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Diffusion is the net movement of particles
from an area of high concentration to an
area of low concentration until the particles
are evenly spread out.
Diffusion
o Diffusion happens in liquids and gases,
through cell cytoplasm and across
membranes
o It happens because the particles move
randomly from place to place.
o It is passive-no energy is required.
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Diffusion
Dynamic equilibrium is
achieved when there is no
net change in concentration
between two areas.
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Factors affecting diffusion
o Concentration gradient
o Shape & size of the molecules
o Temperature
o Distance
o Surface area
Why is diffusion important?
All living cells rely on diffusion to live. They use it for:
o obtaining raw materials for respiration (oxygen)
o removing waste products (e.g. carbon dioxide from
respiration)
Examples of diffusion
In breathing
you exchange
carbon
dioxide (CO2)
and oxygen
(O2) between
alveoli in the
lungs and the
blood.
Photosynthesis & Diffusion
carbon dioxide + water  oxygen + glucose
Inside leaf
Outside
Osmosis is special example of
diffusion.
Osmosis
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Osmosis is the diffusion of water
molecules from a region where the
water molecules are in higher
concentration, to a region where they
are in lower concentration, through a
partially permeable membrane.
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Examples of osmosis
Water uptake by plant roots,
Roots have hairs, which increases
the surface area.
Examples of osmosis
The intestines absorb water
and nutrients by osmosis.
Examples of osmosis
Slugs and snails-death by salt!
Examples of osmosis
Kidneys use osmosis to
recover water from waste
material.
Solvent
(water)
Solute (e.g.
glucose)
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Concentrated,
hypertonic solution
outside (low water
concentration)
Equal water
concentrations inside &
out
H2O
H2O
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Pure water (hypotonic)
outside (High water
concentration)
H2O
Equal water
concentrations inside &
out
Concentrated,
hypertonic solution
outside (low water
concentration)
Pure water (hypotonic)
outside (High water
concentration)
Animal cells have no cell wall to stop the swelling, just a flexible cell
membrane.
Sports drinks
o Normal sugary drinks (i.e. hypertonic)
good for recovery after exercise but
slow to absorb and can result in
dehydration
o Isotonic or hypotonic drinks quickly
absorbed by osmosis so can quickly
replace fluid lost by sweating and
provide a boost of carbohydrate.
Some definitions
o Hypotonic-has a lower solute concentration compared
to another solution, e.g. water
o Hypertonic-has a higher solute concentration
compared to another solution, e.g. syrup
o Isotonic-has a similar solute concentration compared to
another solution.
Facilitated
diffusion
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Facilitated diffusion is the movement of
molecules along their concentration
gradient, guided by the presence of
another molecule – usually an integral
membrane protein forming a pore or
channel.
Selective permeability of a cell membrane
The hydrophobic
core of the plasma
membrane helps
some materials
move through the
membrane, while it
blocks the
movement of
others.
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey 01/10/2019
Facilitated diffusion
o Channel proteins
o Gated channel proteins
o Carrier proteins
Facilitated diffusion-channel protein
Channel proteins
e.g.
Aquaporins
(water
channels)
Facilitated diffusion-gated channel protein
Gated channel proteins have
a binding site specific for a
molecule or ion. A stimulus
causes the gate to open or
shut
The stimulus may be chemical or electrical signals, temperature, or
mechanical force, depending on the type of gated channel.
Facilitated diffusion-carrier protein
Carrier proteins "carry" the
ion or molecule across the
membrane by changing
shape after the binding of
the ion or molecule. Carrier
proteins are involved in
passive and active
transport.
Summary so far
Diffusion, facilitated diffusion and osmosis are all passive
forms of transport.
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Active
transport
There are many occasions when cells need
to take in substances that are present only
in small quantities- that is, the desired
direction of movement is against the
diffusion gradient
Active transport is the movement of
ions or molecules across a cellular
membrane from a lower to a higher
concentration, requiring the
consumption of energy.
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Active transport
Active transport uses
energy released during
respiration.
Carrier proteins pick up specific
molecules and take them through
the cell membrane against the
concentration gradient.
Examples of active transport
Examples of active transport include:
o Sodium-potassium pump in brain cells (neurons)
o uptake of glucose by epithelial cells in the villi of
the small intestine
o uptake of ions from soil water by root hair cells in
plants
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Diffusion
Facilitated transport
Access to HE Diploma (Science Pathway) Level 3 Dr PV Massey October 2019
Osmosis
Active transport