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What are the 4 organic compounds?
WRAP UP:
What is larger, a sugar molecule? Or a starch
molecule?
The Cell in Its Environment
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selectively permeable: some substances
can pass through the cell membrane while
others cannot (oxygen, food INTO CELL;
waste OUT OF CELL)
Diffusion
 Osmosis
 Active Transport
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MAIN method by which small molecules move
across the cell membrane
Molecules move from an area of HIGHER
concentration to an area of LOWER concentration
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Molecules are always moving and bump into one
another
The more molecules, the more collisions
Collisions cause molecules to push away
And substance spreads out
Diffusion of water molecules through a
selectively permeable membrane
 Water molecules move from highly
concentrated area to a less concentrated
area
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Moving materials through a cell that do
NOT need energy
◦ Diffusion
◦ Osmosis
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The movement of materials through a cell that
requires the cell to use its own energy
Lower concentrated area to a higher
concentrated area
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Transport Proteins
◦ Transport proteins in cell membrane “pick up”
molecules outside the cell and carry them in
 Calcium, Potassium, and Sodium
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Transport by Engulfing
 Cell membrane surrounds and engulfs a
particle, forms a vacuole within the cell
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As a cell gets larger, it takes longer for a
molecule that has entered the cell to reach
the middle of the cell