Download Chapter 3-Cell Membrane Diffusion Osmosis

3.3 Cell Membrane
KEY CONCEPT The cell membrane is a barrier that
separates a cell from the external environment.
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• AKA the phospholipid bilayer
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane has two major functions.
cell membrane
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane has two major functions.
– forms a boundary between inside and outside of the
cell
cell membrane
inside cell
outside cell
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane has two major functions.
– forms a boundary between inside and outside of the
cell
– controls passage of materials
cell membrane
inside cell
outside cell
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is made of a phospholipid bilayer.
cell membrane
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is made of a phospholipid bilayer.
• There are other molecules embedded in the membrane.
cell membrane
carbohydrate
chain
cholesterol
protein
protein channel
protein
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is made of a phospholipid bilayer.
• There are other molecules embedded in the membrane.
• The fluid mosaic model describes the membrane.
cell membrane
carbohydrate
chain
cholesterol
protein
protein channel
protein
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is selectively permeable.
Some molecules can cross the membrane
while others cannot.
3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is selectively permeable.
Some molecules can cross the membrane
while others cannot.
3.3 Cell Membrane
Chemical signals are transmitted across the cell
membrane, allowing materials in or out
• Receptors bind with ligands and change shape.
• There are two types of receptors.
3.3 Cell Membrane
Chemical signals are transmitted across the cell
membrane.
• Receptors bind with ligands and change shape.
• There are two types of receptors.
– intracellular receptor
3.3 Cell Membrane
Chemical signals are transmitted across the cell
membrane.
• Receptors bind with ligands and change shape.
• There are two types of receptors.
– intracellular receptor
– membrane receptor
3.4 Diffusion and Osmosis
KEY CONCEPT Materials move across membranes
because of concentration differences.
Which side of the membrane has a high concentration of
particles?
Which side of the membrane has a lower concentration?
3.4 Diffusion and Osmosis
• Diffusion: The movement of
molecules from an area of high
concentration to an area of low
concentration (Does not require a
semipermeable membrane)
*What would stop this movement?
• Concentration gradient: the difference
in concentration from one area to
another
• Molecules diffuse down a
concentration gradient.
• Why would a cell want to bring
particles in and send particles out?
Before we take anymore notes.....
Let’s talk about dinner……
3.4 Diffusion and Osmosis
• Osmosis is the diffusion of water molecules across a
semipermeable membrane.
• This is a special form of diffusion (molecules are still
moving from a region of high concentration to lower
concentration)
3.4 Diffusion and Osmosis
Osmosis is the movement of water however, water is
usually never pure…
•
• There are three types
of solutions.
•
•
Isotonic: equal concentrations of
solutes, _____ amount of H20
Hypertonic: higher solute
concentration,_____ amount of H20
Hypotonic: lower solute
concentration,_____ amount of H20
•Water will move to an area that has a higher SOLUTE
concentration (typically the area with lower water
concentration)
•Which direction will the water move? (Assume the dots
represent a solute, like NaCl)
3.4 Diffusion and Osmosis
• Water will move to an area that has a lower WATER
concentration
• Why is this important?
• http://www.glencoe.com/sites/common_assets/science/virtual_l
abs/LS03/LS03.html
Ticket out the door
Take out a sheet of paper and a pen and
answer the following in your own words:
1.
2.
3.
4.
5.
What is osmosis?
How is osmosis different that diffusion?
If a solution is hypotonic to a cell, in which direction will
water move (in or out of the cell)?
If a solution is isotonic to a cell, is there movement of
water?
What can happen to a cell if it is placed in a hypertonic
solution? How does this apply to us?
Passive Verses Active
KEY CONCEPT Materials move across membranes
because of concentration differences. This happens
two basic ways:
Passive
Active
Does
Requires
not require energy
Molecules move from high
concentration to low
Strive for balance
between cell and outside
Examples:
Diffusion
Osmosis
Facilitated
diffusion
energy
Molecules move from low
concentration to high
Examples:
Sodium
potassium pump
Endocytosis
exocytosis
3.4 Diffusion and Osmosis
Passive transport does not require
energy input from a cell.
• Molecules can move across the cell membrane
through passive transport.
• There are two types of
passive transport.
• Diffusion: movement of
molecules from high
concentration to low
• Osmosis: movement of
water to an area of high
solute content
3.4 Diffusion and Osmosis
Some molecules can only diffuse through transport
proteins.
• Some molecules cannot easily diffuse across the cell
membrane.
• Facilitated diffusion is
diffusion through transport
proteins. (like a tunnel)
3.5 Active Transport, Endocytosis, and Exocytosis
KEY CONCEPT Cells use energy to transport materials
that cannot diffuse across a membrane.
3.5 Active Transport, Endocytosis, and Exocytosis
Active transport requires energy input from a cell
and enables a cell to move a substance against its
concentration gradient.
• Passive transport requires no energy from the cell.
• Active transport is
powered by chemical
energy (ATP).
• Active transport occurs
through transport protein
pumps.
• Cells use active transport
to maintain homeostasis.
3.5 Active Transport, Endocytosis, and Exocytosis
A cell can import and export large materials or large
amounts of material in vesicles during the
processes of endocytosis and exocytosis.
• Cells use energy to transport material in vesicles.
• Endocytosis is the process of
taking material into the cell.
• Phagocytosis is a type of
endocytosis.
3.5 Active Transport, Endocytosis, and Exocytosis
A cell can import and export large materials or large
amounts of material in vesicles during the
processes of endocytosis and exocytosis.
• Cells use energy to transport material in vesicles.
• Exocytosis is the process of
expelling material from the
cell.