Download MOVEMENT OF SUBSTANCES

MOVEMENT OF SUBSTANCES
DIFFUSION
Learning Outcomes
After completing this chapter, you will able to :
• Define diffusion as the movement of molecules
from a region of their higher concentration to a
region of their lower concentration down a
concentration gradient
Surface area : volume ratio
Volume = _______
Surface area = ______
Volume : Surface area ratio =
___________
Volume = _______
Surface area = ______
Volume : Surface area ratio =
___________
Passive Transport
• Cell uses no energy
• Molecules move randomly
• Molecules spread out from an area of high
concentration to an area of low
concentration.
3 Types of Passive Transport
1. Diffusion
2. Facilitative Diffusion – diffusion with the
help of transport proteins
3. Osmosis – diffusion of water
Diffusion
Before
Region of high
concentration
After
Diffusion of Liquids
Diffusion in Life
Diffusion of Bromine
Diffusion of Bromine
Diffusion in Living Organisms
• 2nd Law of Thermodynamics
governs biological systems
– universe tends towards disorder (entropy)
 Diffusion

movement from high  low concentration
Diffusion in Living Organisms
Diffusion is a PASSIVE
process which
means no energy is
used to make the
molecules move,
they have a natural
KINETIC ENERGY
Cell Membrane
Structure of cell membrane
Lipid Bilayer -2 layers of
phospholipids
a.Phosphate head is polar
(water loving)
b.Fatty acid tails non-polar
(water fearing)
c. Proteins embedded in
membrane
Phospholipid
Lipid Bilayer
Fluid Mosaic
Polar heads
love water & Model of the cell
dissolve.
membrane
Non-polar
tails hide
from water.
Carbohydrate cell
markers
Proteins
Structure of the Cell Membrane
Outside of cell
Proteins
Lipid
Bilayer
Transport
Protein
Phospholipids
Inside of cell
(cytoplasm)
Go to
Section:
Carbohydrate
chains
Cell Membrane is Selectively Permeable
Diffusion Through Phospholipid Bilayer
• What molecules can get through directly?
– fats & other lipids
 What molecules can NOT
get through directly?
lipid
inside cell

 H2O
salt
NH3
polar molecules

ions
 salts, ammonia

large molecules
 starches, proteins
outside cell
sugar
aa
H2O
Passive Transport: Facilitated Diffusion
Glucose
molecules
Cellular Transport From aHigh Concentration
High
Cell Membrane
Low Concentration
Through a 
Transport
Protein
Low
Protein
channel
Passive Transport:
Facilitated Diffusion
Facilitated diffusion:
diffusion of specific particles
through transport proteins
found in the membrane
a. Transport Proteins are
specific – they “select”
only certain molecules to
cross the membrane
b.Transports larger or
charged molecules
A
B
Facilitated
diffusion
(Channel
Protein)
Diffusion
(Lipid
Bilayer)
Carrier Protein
Diffusion in Living Organisms
Diffusion of digested food
through the cell lining the small
intestine and into the blood
Diffusion of oxygen
into a root hair cell
Summary
No energy needed
Passive transport
Diffusion is a
passive transport
Diffusion in living
organism
Molecules move
from area of high to
low concentration
Across cell
membrane