In or Out?
1. What are some things that can pass
through a window screen?
2. What are some things that cannot pass
through a window screen? Why is it
important to keep these things from
moving through the screen?
3. The cell is surrounded by a cell
membrane, which regulates what enters
and leaves the cell. Why is it important to
regulate what moves into and out of a cell?
Sec 7-3: Cell Boundaries
Two Types of Cell Boundaries
1. Cell wall (outer)
Strong supporting layer outside cell membrane
Only in some organisms
-plants, algae, fungi, prokaryotes
Porous
2. Cell membrane (inner)
Thin, flexible layer that surrounds all cells
Plant Cell: Has Cell Wall and Cell Membrane
(Cell)
Functions of Cell Membrane
1. Regulates what goes in and
what comes out of a cell
2. Protects cell
3.Supports cell, but also
flexible
Figure 7-12 The Structure of the
Cell Membrane
Structure of Cell Membrane
Outside
Section 7-3
of cell
Carbohydrate
chains
Proteins
Cell
membrane
Inside
of cell
(cytoplasm) Protein
channel Lipid bilayer
Main Parts of Cell Membrane
Section 7-3
Phospholipid
• 1. Phospholipid bilayer – 2 layers
– Phosphate “head” = is polar = likes water
– Lipid “tails” = are non-polar = do not like water
(is why phospholipids align a certain way)
Phosphate head: is in water
Lipid tails: point away from water
Phosphate head: is in water
• 2. Proteins
– Embedded in lipid bilayer
– Form channels and pumps
• 3. Carbohydrates
– Allow individual cells to identify one another
• 4. Cholesterol
– Regulates membrane fluidity over wide
range of temperatures
• Warm temp. = Prevents membrane from
becoming too fluid
• Cold temp. = Prevents membrane from
becoming frozen
Membrane = Fluid Mosaic Model
Why?
Fluid = is flexible and moveable
Mosaic = made of so many kinds of molecules
Like mosaic artwork made of so many different tiles
Terms to Know
• A solution is a mixture of two or more
substances, evenly mixed
– Solutes = substances dissolved in the solution
• The cytoplasm is a solution of many different
substances
• Concentration = mass of solute in a given
volume of solution
– Mass/volume
Passive Transport [High] to [Low]
Does not require energy!!!!!
• DIFFUSION • FACILITATED • OSMOSIS
DIFFUSION
DIFFUSION: Definition
High Concentration
MOVE from an AREA OF
HIGH CONCENTRATION
to
an AREA of LOW
CONCENTRATION
Low Concentration
Diffusion
• Def. of permeable = membrane that lets
substances pass through it
• Cell membrane is selectively permeable,
which means that it lets some things in but
does not let other things in
• Substances keep moving till there is about
equal amounts of them on both sides of the
membrane = at equilibrium
Factors that Affect Diffusion
• Amounts of substances involved
• Temperature
• Pressure
• Stirring
-speeds up the rate of diffusion
OSMOSIS
• Deals with movement of water
– From greater to lesser area of water
• Particles can’t move because membrane won’t
allow it!
Types of Solutions
(refers to solution outside of cell)
• Hypotonic (“hypo” = less)
– Less solutes outside cell = more water
– More solutes inside cell = less water
Water rushes into cell
(cell swells up like a hippo = hypo)
• Hypertonic (“hyper” = more)
– More solutes outside cell = less water
– Less solutes inside cell = more water
Water leaves cell
• Isotonic (“iso” = same)
– Same amount of solutes inside and outside cell
Water stays where it is
Types of Solutions Examples
Osmotic Pressure
• Pressure exerted on hypertonic side of a
selectively permeable membrane
– Cell walls prevent the cell from expanding
• Some organisms fight osmotic pressure
by using a contractile vacuole – pumps
excess water out of the cell
– Ex. paramecium
Facilitated Diffusion
• Passive
– Proteins used in facilitated diffusion are called
channels
– Channels are specific to certain molecules
– 100 different protein channels
RECAP
• What are 3 major types of passive
transport?
• What characterizes these as passive?
• Describe how the concentration of
molecules moves within this type of
transport.
• What would happen to a red blood cell
placed in a hypertonic solution?
Active Transport
• ENERGY NEEDED! Molecule to
be carried
• Molecules go from lesser to
greater concentration
“against concentration gradient”
Energy
• Also used for when LARGE
molecules need to get Molecule
through membrane being carried
• May or may not need channel
proteins – called pumps
Endocytosis and Exocytosis
• Endocytosis = process by which cells take
in large molecules from the outside
-eg.: pinocytosis – large amounts of liquid
phagocytosis – large amounts of solid
• Exocytosis = process by which cells get rid
of large molecules in the cell; leaves cell.
• Vacuole fuses with membrane to dispel
Pinocytosis
Pinocytes are pockets on the cell
membrane.
Subtances are engulfed and a
vacuole forms around them
Phagocytosis: Engulfing
• This is when large
molecules are surrounded
and pulled into the cell
• Examples: amoeba, white
blood cells called
phagocytes
• This is the same method
used by white blood cells
to trap bacteria in our
blood
RECAP
What are some examples of active
transport?
Describe the concentration gradient
involved in active transport
How is active transport different
from passive transport?
Exit Questions
When is equilibrium reached?
What is the difference between
osmosis and diffusion?
What is the difference between
active and passive transport?