MATERIALS MOVE ACROSS
CELL’S MEMBRANES
Chapter 2.3C
Review
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What is a cell membrane??
What is the purpose of a membrane?
What are membranes primarily made up of?
For the remainder of the powerpoint, copy words
highlighted in ORANGE!
Diffusion
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Molecules spread out from where there are many to
where there are fewer
They keep spreading until
they are evenly distributed
Examples:
 Smelling
a scent
 Oxygen (needed for respiration) and carbon dioxide
(produced by respiration)
Concentration
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The number of particles of that substance in a
specific volume
 Example:
 Dissolving
9 grams of sugar in 1 liter of water yields the
concentration 9g/L
Diffusion in Cells
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Materials are able to move into and out of the cell
 Example:
 Photosynthesis:
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produces oxygen inside the cell
Concentration of oxygen is higher on the inside than the outside
Oxygen cells move out of the cell by diffusion
**What are some daily examples of diffusion?
Types of Diffusion
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Passive transport
Active transport
Osmosis
Endocytosis
Exocytosis
Passive Transport
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Materials move without using the cell’s energy
(moving from high concentration to low
concentration)
Osmosis
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Diffusion of water through a membrane
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Example:
Unwatered plants wither
 Water leaves the plant’s roots to go to the dry soil to even out the
concentration of water molecules
 When the plant is watered,
water molecules
diffuse through
the plant’s cell
membranes to
even out the
concentration again

Active Transport
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Process of using energy to move materials through a
membrane (moving from low concentration to high
concentration)
 Examples:
 Marine
 Kidneys
iguanas
Endocytosis
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Moving materials too large to pass through a
membrane INTO the cell
 Membrane
folds inward, creating a pocket
 Membrane closes around the material, forming a
“package”
 “Package” breaks away from
cell membrane, bringing the
material into the cell
Exocytosis
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Moving materials too large to pass through a
membrane OUT OF the cell
 “Package”
carries materials to cell membrane
 Attaches to membrane and merges together
 Materials are pushed out of membrane
Cell Size (and shape) Affects Transport
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As cell grows, surface area is not large enough to
allow resources to travel to all parts of cell
As a result, the cell may:
 Stop
growing
 Divide
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Shape
 Thin
and flat cells (single-celled organisms) have
increased surface area
 Long and skinny cells (nerve and muscle) have
increased surface area