Download Notes 3-4

Notes 3-4
The Cell in Its Environment
Cell Membrane
• Provides protection for the cell
• Chooses what comes in and out of cell
• It is selectively permeable, which means it lets
some substances pass through the membrane,
and other substances cannot
Cell Membrane
• Here is the cell
membrane magnified
• Remember it surrounds
the entire cell
• Notice it is made up of
lipids, proteins, and
carbs (3 of the organic
molecules from section
3-3)
Passive Vs. Active Transport
Passive Transport:
• Movement of materials
through cell membrane
WITHOUT energy
• Materials move from a high
concentration of the
material to a lower
concentration of material
• Its like rolling down a hill
(no energy is needed)
Active Transport:
• Movement of materials
through cell membrane
WITH energy
• Materials move from a low
concentration of the
material to a higher
concentration of material
• Its like trying to roll up a hill
(imagine how hard that
would be and how much of
your energy it would take)
Passive and Active
Transport
• Passive and active transport
are two processes by which
materials pass through the
cell membrane. Active
transport requires the cell to
use its own energy, while
passive transport does not.
• When looking at the images,
pay attention to what is
meant by low concentration
of materials versus high
concentration of materials.
Diffusion
• Molecules move across cell membrane without
energy (passive transport)
• Move from high concentration to low
concentration
• Molecules continue to pass through membrane
until there are equal amounts of molecules inside
the cell as outside the cell
• Remember, Molecules can only diffuse through
the membrane if the membrane is permeable to
it (if the membrane chooses to let it in!)
Diffusion
• In diffusion, molecules move from an area of
higher concentration to an area of lower
concentration.
Osmosis
• Special example of diffusion- Osmosis is the diffusion
of WATER!
• Passive transport, no energy required
• Water will move from a high concentration of water to
an area of low concentration of water until amount of
water is equal inside and outside the cell
• If too much water moves out of cell, the cell will shrivel
(not good)
• If too much water moves into cell, cell will burst (not
good)
• Cell needs to maintain a balance to function properly
Osmosis
Notice how the different
concentrations of water
choose whether water
moves into or out of cell
A selectively permeable
membrane separates the
2 sides of the solution.
The arrow shows that
water is moving towards
the right side. WHY?
Water is moving from an
area where water is high
to an area where water is
low, and the membrane
is permeable to water.
Why are the sugar molecules not moving across the membrane?
The membrane must not be permeable to sugar (otherwise the sugar
would be moving to the left side, from high to low concentrations of sugar)
Transport Proteins
• There are proteins embedded in the cell
membrane that pick up materials and bring
them into cell or carry them out of cell
• Active transport, so requires energy
• Brings materials from low concentration to
high concentration
• Each protein recognizes and carries a specific
molecule such as calcium, potassium, or
sodium.
Transport Proteins:
Why does this process require energy (ATP)?
• This proton pump
is a transport
protein.
• ATP is the energy
its using.
• Notice its pumping
Hydrogen Ions out
of the cell (from
low concentration
to high
concentration)
Because it is using active transport (it is transporting materials from low to high
concentration).
Engulfing
• Cell extends its cytoplasm and cell membrane,
surrounds molecule, and engulfs it (encloses it)
• A vacuole is formed around molecule in this process
• Process known as endocytosis (meaning inside cell)
• A form of active transport, requires energy
Cell Size
• Cells must be small in order to function
properly
• If cells were too big, it would take too long for
molecules to pass from one side of the cell to
the other
• Also, if cells were too big, it would take too
long for wastes to be removed
Let’s Review
• Passive transport
requires energy- True or
False?
False! Active transport
does! Think of it like this…
you need energy to be
active!
• Does diffusion require
energy?
No, because it is an
example of passive
transport.
Let’s Review
• What are some
examples of active
transport?
• Osmosis is the diffusion
of _________?
WATER
Engulfing (or endocytosis)
and transport proteins