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• What does a cell need to survive
and how does it get that?
Lipid Bilayer- a double-layered group
of lipids (fats) that protect the cell,
allowing only some things in and out
of the cell.
Semipermiable- A membrane that can
select what materials can move
through.
•All cells have a liquid inside
•Reminder: liquid = solvent
other = solute
•Concentration- the amount of solute
in an area.
•When solutes move from areas of
high to low concentration, across the
cell’s membrane, the process is
called diffusion.
•In other words, things move across
a membrane from areas of “a lot” to
areas of “a little”.
•It’s all about size and shape
• chemicals are too big or the wrong
shape, they cannot pass through
the membrane
**This does not cost the cell energy!
Most semipermiable membranes allow
water to cross.
When WATER moves from high to
low concentration, the process is
called osmosis.
Animation: http://www.colorado.edu/eeb/web_resources/osmosis/
Molecules need to get in, but can’t
by diffusion.
Many proteins in the cell membrane
act to let recognize these molecules
and allow them into the cell.
**This does not require energy!
Many cells need certain chemicals in
high concentrations.
Many small molecules are pumped
into a cell by special proteins.
*This requires energy!
**What makes that energy?
•Endocytosis- Taking IN molecules by
cell membranes folding into pockets.
• Phagocytosis- When large particles
are taken in through endocytosis
• Pinocytosis- Cell taking in liquid
•Exocytosis- Vacuoles fuse with cell
membranes, forcing molecules OUT.
Some Examples…
• Salt on a cell
• What happens?
• If concentration of things in and out
of cell are very different and remain
that way, what does that tell you about
the cell’s functioning?
•Breaking down glucose to create energy
in the form of ATP
•Aerobic
• uses oxygen, makes 36 ATP
• Anaerobic
• when oxygen is absent, makes 2 ATP
• What are 2 factors that allow some
things to cross a membrane while
others cannot?