Transcript Unit 4: Cells

Unit 4: Cells
Learning Goal D: Explain how the
structure of the cell membrane relates to
how materials are transported through it
and identify those modes of
transportation.
Cell Membrane
 The cell membrane regulates what enters and leaves the
cell and also provides protection and support.
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Composed of a double-layered sheet called a lipid bilayer (two
layers of lipids).
Contains many different molecules.
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Proteins, carbohydrates, etc.
The different molecules help regulate what enters and leave a cell.
Cell Wall
 A strong supporting layer around the
membrane found in some types of cells.
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The main function of the cell wall is to
provide support and protection for the cell.
Most cell walls are porous enough to allow
water, oxygen, carbon dioxide, and certain
other substances to pass through the cell
wall.
Diffusion:
 A particle moving
from an area of
higher concentration
to an area lower
concentration until it
reaches equilibrium.
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Equilibrium is when
the concentration of a
solute is the same
throughout a system.
Diffusion
 Diffusion depends upon random particle
movements; substances diffuse across
membranes without requiring the cell to use
energy.
 Particles still move
after equilibrium is
reached. They move
at an equal rate in
each direction.
Osmosis
 The diffusion of water across a
selectively permeable membrane.
Osmosis
 Isotonic means that there
is an equal concentration
on both sides of the
membrane.
 Hypertonic means there
is a higher concentration
of the solute than of the
water (strong solution).
 Hypotonic means there is
more water molecules
than other molecules
(weak solution).
Facilitated Diffusion
 Some molecules are too big or too
strongly charged to pass through the
membrane. There are protein channels
that allow certain molecules to pass
through the membrane.
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This is a fast process, but it is specific to the
molecules it lets through.
This does not require energy.
Active Transport
 Requires energy to move molecules into or out of the cell.
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Molecules are moved from an area of low concentration
to an area of high concentration.
 Proteins act as pumps forcing molecules into or out of
cells.
Endocytosis
 The process of taking
material into the cell by
means of enfolding, or
pockets, of the cell membrane.
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Phagocytosis is when food particles are taken in by
an organism surrounding the food and breaking off in
the cell.
Pinocytosis is when liquid is taken in by an organism
surrounding the liquid and breaking off in the cell.
Exocytosis
 The membrane of the vacuole
surrounding the material fuses with the
cell membrane, forcing the contents out
of the cell.