Download The Cell in its Environment - Mother Teresa Regional School

Lesson 4, Chapter 1
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Diffusion is the main method by which small
molecules move across the cell membrane.
A cell membrane is selectively permeable,
which means that some substances can pass
through the membrane while others cannot.
Cells like castles, must let things enter and
leave. Let in oxygen and food molecules and let
out waste products, which all pass through the
cells membrane
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Molecules are always moving, and as they
move they bump in to each other. The more
molecules in one area, the more collisions there
will be.
Molecules move by diffusion from an area of
higher concentration to an area of lower
concentration.
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Because cells cannot function properly without
adequate water, many cellular processes
depend on osmosis.
Osmosis is the diffusion of water molecules
through a selectively permeable membrane
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The movement of dissolved materials through
a cell membrane without using cellular energy
is called passive transport.
Active transport is the movement of materials
through a cell membrane using cellular energy.
Active transport requires the cell to use its own
energy, while passive transport does not.
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Cells have several ways of moving materials
through active transport.
Transport Proteins
Transport by engulfing