Transcript MOVEMENT OF MOLECULES THROUGH CELLS

MOVEMENT OF MOLECULES
THROUGH CELLS
A cell membrane is usually permeable to substances such as
oxygen, water, and carbon dioxide, but not large molecules such as
salt.
Substances that can move into and out of a cell do so by one of
three ways: diffusion, osmosis, or active transport.
PASSIVE TRANSPORT
Diffusion and osmosis are forms of Passive Transport.
They do NOT require energy from the cell.
DIFFUSION
Diffusion is the main way molecules move in and out of a cell.
Process where molecules move from an area of higher
concentration, to an area of lower concentration.
Concentration is the amount of a substance in a given volume.
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http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion2.gif
What causes diffusion?
Molecules are constantly moving and colliding. More molecules
results in more collisions. When molecules collide they push away
from one another.
OSMOSIS
Osmosis- the diffusion of water molecules through a semi-permeable
membrane.
This process is very important because cells need adequate water.
Semi-permeable
membrane
When the concentration of water outside the cell is lower than the
concentration of water inside the cell, the cell will lose water molecules.
This may cause the cell to shrink.
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When the concentration of water outside the cell is higher than the
concentration of water inside the cell, the cell will gain water molecules.
This may cause the cell to swell.
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ACTIVE TRANSPORT
Active Transport is the movement of
materials through a cell membrane using
energy.
Special proteins called transport proteins
“pick up” molecules and carry them inside
or outside the cell, using energy.
Active Transport is required when:
– 1. The cell needs materials that are in
lower concentration outside the cell.
– 2. The materials needed are too large
to pass through the membrane by
diffusion.
Active Transport Video:
http://www.youtube.com/watch?v=STzOiRqzzL4&feature=related
ENERGY