The Cell Membrane
Moretz
Biology
Outline
Structure of the membrane
Phospholipids
Proteins
Movement across the membrane
Homeostasis
Passive transport – diffusion & osmosis
Active transport – endocytosis & exocytosis
Location
Surrounds the cell.
Present in ALL cells.
Functions
Regulates what materials enter & exit the cell.
Communicates with other cells.
Uses receptor proteins to communicate.
Structure
Made up of:
Phospholipids
Proteins
Phospholipids
Two fatty acids
Nonpolar.
Hydrophobic
Phosphate group
Polar
Hydrophilic
Phospholipids
Hydrophilic
head (water
loving)
Two
hydrophobic
tails (water
fearing)
Lipid Bilayer
Two layers of
phospholipids
make up the
cell membrane.
1
2
Proteins
Embedded throughout the cell
membrane.
Transport materials across the
membrane (carrier proteins)
Act as chemical signals to help
cells communicate (receptor
proteins)
Move around the membrane.
Fluid Mosaic Model
FLUID- proteins &
phospholipids can
move.
MOSAIC- proteins
form patterns.
Modeling the Membrane
Create a model of the cell membrane
Label each component.
On the phospholipid, label the following: hydrophobic,
hydrophilic, polar, nonpolar, phosphate heads, lipid tails.
Describe how the structure of each part of the
membrane helps it do its specific job.
Describe the function of the cell membrane.
Explain how the structure of the membrane allows it
to perform its function.
Selectively Permeable
The cell membrane controls what enters &
exits the cell.
It selects which molecules may pass through
the membrane and which ones are blocked.
Homeostasis
The cell membrane helps the cell maintain
homeostasis.
Properly balances the amount of water and
nutrients in the cell.
Concentration Gradient
Difference in concentration in two parts of a
system.
Types of movement across the membrane are
determined by the concentration gradient.
Types of movement:
Passive transport – with gradient
Active Transport – against gradient
Concentration GradientHIGH
CONCENTRATION
LOW
CONCENTRATION
Concentration
Sort the following from least concentrated to
most concentrated.
12 g of salt in 3 L of water.
12 g of salt in 12 L of water.
12 g of salt in 8 L of water.
12 g of salt in 2 L of water.
Concentration
Sort the following from least concentrated to
most concentrated.
12 g of salt in 2 L of water.
12 g of salt in 3 L of water.
12 g of salt in 8 L of water.
12 g of salt in 12 L of water.
Concentration
Which is more concentrated?
12 g of salt in 3 L water or 12 g salt in 6 L of
water?
Concentration
Which is more concentrated?
12 g of salt in 3 L water or 12 g salt in 6 L of
water?
12 g/3L vs. 12 g/6 L
4 g/L vs. 2 g / L
4 g/L is twice as concentrated.
Passive Transport
Movement WITH the concentration gradient.
Does NOT require energy.
Types:
Diffusion
Osmosis
Diffusion
Molecules move from areas of high
concentration to low concentration.
OSMOSIS – diffusion of water molecules across
the membrane.
Equilibrium
Concentration
of molecules
throughout
the solution is
equal.
Effects of Osmosis
Isotonic
Concentration outside the cell is EQUAL to the
concentration in the cell.
Effects of Osmosis
Hypertonic
Concentration outside
the cell is GREATER
than the concentration
inside of the cell.
Plasmolysis – cell
shrinks
Effects of Osmosis
Hypotonic
Concentration outside
the cell is LESS than
the concentration in
the cell.
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