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Passive Transport
vs.
Active Transport
Remember that all cells have …
• Plasma or cell membranes that are
selectively permeable and very fluid…
• (Click the animation below)
fluid membrane
Passive Transport
• Does not require energy
• Moves substances from a higher
concentration to a lower
concentration
• Moves with the concentration
gradient
Types of Passive Transport
• Diffusion
• Osmosis
• Facilitated Diffusion
Diffusion
• Movement of matter (particles) from a high
concentration to a low concentration
• Moves particles that are small in size such
as …
Carbon dioxide
diffusion of particles
ions
diffusion of ink
wastes
Food (glucose)
oxygen
water
Osmosis
• Movement of water across a membrane
from higher to lower concentration
Osmosis animation
How do cells react to different
environments?
•
Because cells have cell membranes they will
be affected by various concentrations of
substances in fluids. (think about the egg
experiment)
There are three environments
a. Isotonic- same concentrations of water in and
out of the cell
b. Hypotonic- higher concentration of water
outside the cell than inside
c. Hypertonic- lower concentration of water
outside the cell than inside
animations for various environments (click here to observe changes)
Facilitated Diffusion
• Passage of particles across the plasma
membrane by means of transport proteins
called channel or carrier proteins
• Used in the movement of small sugars and
large amino acids across the cell
membrane
faciitated diffusion animation
Facilitated Diffusion
carrier protein
Active Transport
• Requires energy in the form of
ATP (adenosine triphosphate)
• Moves substances from a lower
concentration to a higher
concentration
• Moves molecules against the
concentration gradient
Types of Active Transport
• Sodium-Potassium pump
• Endocytosis
• Exocytosis
Cell membrane pumps (ion
pumps)
1. Transport proteins embedded in the
plasma membrane act as “pumps”
2. Each pump can bond to a particular
particle whose shape fits it.
3. Chemical energy (ATP) alters the shape
of the pump and this releases the particle
to the other side.
4. Once the particle is released, the pump
returns to its original shape.
Sodium-Potassium Pump
• Animal cells have a high concentration or K+
ions and a low concentration of Na+ ions
compared to the environment
• A pump maintains these concentrations by
moving 2 K+ ions into the cell for every 3 Na+
ions that it moves out of the cell
sodium-potassium pump
Endocytosis
The membrane engulfs particles and takes in
substances from the environment. Part of the
membrane breaks away and becomes a
vesicle.
Phagocytosis: Engulfing
food and particles,
“cell eating”
Pinocytosis: Engulfing
liquids, “cell drinking”
Examples: large particles,
cholesterol, bacteria,
oil droplets
pinocytosis animation
phagocytosis animation
Exocytosis
The reverse of endocytosis. This is how the cell exports
substances and gets rid of wastes.
Examples: toxic wastes, hormones, proteins,
carbohydrates
exocytosis animation
An amoeba is a unicellular organism
that eats by endocytosis and releases
wastes by exocytosis.