end show slide 1 of 47 copyright pearson prentice hall outline 7-3: cell boundaries
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Outline 7-3: Cell Boundaries
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7-3 Cell Boundaries
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7-3 Cell Boundaries
I. Cell Boundaries
A. Cell membrane
1. Thin, flexible barrier around cells
B. Cell Wall
1. Strong supporting layer around the membrane
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7-3 Cell Boundaries
II. Cell Membrane Functions
A. Regulates what enters and leaves cells
B. Provides support
C. Provides protection
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7-3 Cell Boundaries
III. Cell Membrane Structure
A. Cell membranes are fluid
1. This fluidity is caused by lipids which make up the basic structure of the membrane
2. Proteins are embedded in the lipids and are free to move around
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7-3 Cell Boundaries
B. Fluid Mosaic Model of Membrane
1. Main structure is a double layer of special lipids called phospholipids.
a. Phospholipids are made of a:
● phosphate head which is polar
● fatty acid tails which are non-polar
b. Heads are attracted to water (hydrophilic)
c. Tails are repelled by water (hydrophobic)
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d. Phospholipids arrange themselves d. Phospholipids arrange themselves into a double layer known as the into a double layer known as the phospholipid bilayer.phospholipid bilayer.
● ● Nonpolar tailsNonpolar tails are are located on inside located on inside layer. layer.
● ● Polar phosphate Polar phosphate heads heads are found on are found on the outsidethe outside
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7-3 Cell Boundaries
2. Embedded Proteins: a. Different types of proteins are found
embedded throughout the lipid bilayer ● They are free to float around
b. Proteins come in different types & play different roles: ● Channel, or transport, proteins – help to bring substances into & out of cell
● Marker proteins – help to identify cells like chemical ID cards
● Receptor proteins – bind to substances outside of cell
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Cell Membrane
Fluid Mosaic Model of the Cell Membrane
Outside of cell
Cell membrane
Inside of cell (cytoplasm)
Protein channel
Proteins
Lipid bilayer
Carbohydrate chains
Marker proteins
Receptor
Transport protein
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7-3 Cell Boundaries
IV. Cell Wall Structure & FunctionA. Structure: 1. Found outside of cell membrane 2. Composed of cellulose in plants
B. Function:
1. Provide support & protection for cell 2. Found in cells of plants, algae, fungi &
many prokaryotes 3. Porous enough to allow small molecules to pass through easily (water, O2, CO2, etc.)
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Plant Cell WallsPlant Cell Walls
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Diffusion Through Cell Boundaries
V. Diffusion Through Cell Boundaries
A. Every living cell exists in a liquid environment.
1. Cell membrane regulates movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side.
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Diffusion Through Cell Boundaries
B. Measuring Concentration of Solutions
1. Concentration is the mass of solute in a given volume of solution, or
mass/volume (grams/liter).
2. Frequently shown as % of solute or in units known as molarity (M).
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Diffusion Through Cell Boundaries
C. Diffusion
1. Particles tend to move from areas where they are more concentrated to
areas where they are less concentrated. This is called
diffusion.
2. When the concentration of the solute is the same throughout a system, the system has reached equilibrium.
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Diffusion Through Cell Boundaries
Solute Solute concentration concentration higher on one higher on one side of side of membranemembrane
Solute will move across membrane towards lower concentration
Once equilibrium is reached, solute moves in both directions
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Diffusion Through Cell Boundaries
3. Diffusion depends upon random particle movements.
a. Therefore, substances diffuse across membranes without requiring the cell to use energy.
b. This is called passive transport.
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Diffusion Through Cell Boundaries
D. Membrane Permeability
1. If a substance is able to diffuse across a membrane, the membrane is
said to be permeable to it.
2. Membranes are impermeable to many substances.
3. Most membranes are selectively permeable, meaning that only
some substances can cross them.
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Diffusion Through Cell Boundaries
E. Osmosis
1. Water molecules are small enough to diffuse through cell membranes
2. The diffusion of water through a selectively permeable membrane
is called osmosis.
3. Water tends to move from regions with a higher concentration of water to regions with a lower concentration
of water.
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Osmosis
How Osmosis Works
Movement of water
Dilute sugar solution (Water more concentrated)
Concentrated sugar solution (Water less concentrated)
Sugar molecules
Selectively permeable membrane
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Osmosis
4. When you compare two solutions:
a. The region with a higher concentration of solute will have a lower concentration of water. This will be called a hypertonic solution.
b. The region with a lower concentration of a solute will have a higher concentration of water. This will be called a hypotonic solution.
c. When concentrations are the same on both sides of a membrane this is called an isotonic solution.
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Osmosis
How Osmosis Works
Movement of water
Dilute sugar solution (Water more concentrated)
Concentrated sugar solution (Water less concentrated)
Sugar molecules
Selectively permeable membrane
Hypertonic Side
Hypotonic side
Water will move towards hypertonic side
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Osmosis
5. If you put cells in these 3 kinds of solutions you will get different responses:
a. Hypertonic solutions
• Water will move from inside cell to outside and the cell will shrink
b. Hypotonic solutions
• Water will move from outside of cell to inside and the cell will swell and possibly burst
c. Isotonic solutions
• Water will diffuse in & out of cell equally and cell will stay the same size
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Osmosis
Solutions outside of cells are:
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Facilitated Diffusion
Do Osmosis Situations
from transparencies now
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Facilitated Diffusion
F. Facilitated Diffusion
1. Cell membranes have protein channels that act as carriers, making it easy for certain molecules to cross.
2. The movement of specific molecules across cell membranes through
protein channels, without the use of extra energy, is known as facilitated
diffusion.
3. Molecules move from area of higher concentration to lower concentration
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Facilitated Diffusion
Facilitated Diffusion
Protein channel
Glucose molecules
This is how glucose enters
cells
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Active Transport
G. Active Transport
1. Sometimes cells move materials in the opposite direction from which the
materials would normally move—that is against a concentration difference. This process is known as active transport.
2. Active transport requires energy.
3. Small molecules and ions are carried across membranes by proteins in the membrane.
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Active Transport
Molecule to be carried
Active Transport
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4. Sodium-potassium pumpa. This transports 3 sodium ions, Na+,
OUT of cellb. Transports 2 potassium ions, K+, INTO
cellc. Both of these are transported AGAINST their concentration gradientsd. Energy is supplied by ATPe. This pump can use up much of the ATP in a given cell
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Sodium-potassium pump animation
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html
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Active Transport
H. Using Membranes in Active Transport
1. Endocytosis
a. Process of taking material into the cell by means of infoldings, or
pockets, of the cell membrane.
b. The pocket breaks loose from the outer portion of the cell
membrane and forms a vacuole, or vesicle, within the cytoplasm.
c. This takes considerable amounts of energy.
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Endocytosis
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Active Transport
d. Two examples of endocytosis are:
•Phagocytosis – bringing in solid food
•Pinocytosis – bringing in liquid
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PHAGOCYTOSIS
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Active Transport
2. Exocytosis
a. Many cells also release large amounts of material from the cell.
b. During exocytosis, the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.
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