MOVEMENT THROUGH THE
MEMBRANE
Bubble Lab
Section 7-3
The cell membrane
• Function:
• Regulates what enters and leaves the cell.
Provides protection and support
• Selective permeability
• Some substances can pass across the cell
membrane and others can’t
Structure
Phospholipid Bilayer (Fluid Mosaic Model): a
double-layer sheet that makes up nearly all
membranes.
Components of the lipid bilayer
• Polar Head
– Hydrophilic
“Water Loving”
• Lipid Tails
– Hydrophobic
“Water Fearing”
Why is the lipid bilayer important?
• Tough, flexible structure
• Strong barrier between the cell
and its environment
What does it do for the cell?
• Allows only certain materials in or
out at certain times.
–Ions
–Glucose
–Water
–Electrolytes
Other membrane structures
• Protein molecules
–Form channels and pumps that help
to move material across the
membrane
Other Membrane Structures
• Carbohydrate molecules
–Act like ID markers for the cell
–Basis for blood typing: the antigens
on the blood cells (A, B, AB) are
carbohydrate chains
• Cells live in fluid environments, with
water inside and outside the cell.
• Components of plasma membrane:
–2 layers of phosphlipids
• Polar head and nonpolar tail
–Integral proteins
–Peripheral proteins
–Cholesterol
–Carbohydrates
• Proteins:
• Peripheral proteins
• On inside surface
• Held in place by cytoskeletal
filaments
• Integral proteins
• Embedded in membrane, can
move laterally
•Cholesterol - strengthens the plasma
membrane.
•Carbohydrates:
•Glycoproteins – proteins with
carbohydrates attached
•Glycolipids – phospholipids with
carbohydrates attached
Functions of membrane proteins
• Some help to transport materials across
the membrane.
•Channel Protein –
allows certain
molecules or ions to
cross membrane freely
•Carrier Protein – interacts
with certain molecule or
ions to help move it across
membrane
• Some proteins aid in cell recognition
– Glycocalyx - In animal cells, the
carbohydrate chains of cell recognition
proteins are collectively called this
Cell recognition protein
•Foreign
carbohydrate
chains are why
transplanted tissue
is often rejected by
the body
Building A Membrane
1. Using the materials provided to you, build a
model of a cell membrane.
2. Make a key explaining what pieces represent
the Polar Head, Lipid Tails, Protein Molecules,
and Carbohydrate Molecules
3. Have your teacher check your model before
you eat it!
Diffusion
Definition: The movement of molecules from
an area of higher concentration to an area
of lower concentration, until equilibrium is
reached.
Concentration?
Mass of Solute/Volume of solution (g/L)
Diffusion of Molecules
What causes diffusion?
• Diffusion is caused by the constant
movement and collision of molecules.
More molecules = More collision
• The collision cause the molecules to
spread out.
Diffusion in Cells
Molecules are able to diffuse through the
cell membrane and allow the cell to
function.
Facilitated Diffusion – some molecules need
help from protein channels to cross the
cell membrane.
Animation
Osmosis (A special kind of diffusion)
Osmosis is the diffusion of water molecules
through a selectively permeable
membrane.
Selectively Permeable - Osmosis
Osmosis
Isotonic – concentration is the same on both
sides of the membrane (equilibrium)
Hypertonic – the solution with a greater
concentration
Hypotonic – the solution with the lesser
concentration.
Osmosis Practice
The cytoplasm of Elodea cells is composed of
about 70% water molecules and 30% other
kinds of molecules.
What happens when the Elodea cells are put into
a liquid that is
a. 50 percent water.
b. 70 percent water.
c. 100 percent water .
Active Transport
Moving down a concentration
gradient is like riding a bike down
a hill. It doesn’t require energy
Osmosis and diffusion are
examples of passive transport!
Moving up a concentration gradient
is like riding up a hill. IT
REQUIRES ENERGY.
Active Transport
• Active Transport: is the movement of
materials through a cell membrane using
energy.
• Molecules move from low concentration to high
concentration.
• Proteins use ATP to pump ions and small
molecules against concentration gradient.
Types of Active Transport
1. Endocytosis – the process of taking
material into the cell by means of
infoldings of the cell membrane.
– Phagocytosis – extension of the cytoplasm
surround and engulf the particle
– Pinocytosis – similar to phagocytosis, but
cells take up liquid instead of particles.
Types of Active Transport
2. Exocytosis
– Large molecules move from inside the cell to
outside the cell.
– Contractile Vacoule – an organelle that
constantly pumps H2O out of the cell.
Animation
Specialized Cells
• Cells with a specific structure and
function and are found in multi-celled
organisms.
• We have blood cells, brain cells, bone
cells, liver cell, skin cells, etc.
We are all made of cells
Organ
System
Organs
Tissues
Cells
Tissue
• Definition: A group of similar cells
working together.
• Examples
Organs
• Definition: A groups of tissues working
together to perform a specific job.
Organ Systems
•
•
Definition: Many organs working
together to do a specific job.
Can you name all 10 organ systems?
7.3-7.4 Wrap up Questions
1.
2.
3.
4.
5.
Explain Diffusion
Explain Osmosis
What does selectively permeable mean?
What is facilitated diffusion?
Are phospholipids the only molecules in a
cell membrane?
6. What is active transport?
7. What are tissues, organs, and organ
systems? Give Examples
= cell
10%
salt
10%
salt
10%
salt
20%
salt
20%
salt
10%
salt
Label the environment around the cell in each beaker as hypertonic, hypotonic or isotonic.
Label the net flow of water and state what will happen to the cell in each beaker?
= cell 10%
salt
10%
salt
10%
salt
20%
salt
20%
salt
10%
salt
Label the environment around the cell in each beaker as hypertonic, hypotonic or isotonic.
Label the net flow of water and state what will happen to the cell in each beaker?
= cell
10%
salt
10%
salt
10%
salt
20%
salt
20%
salt
10%
salt
Label the environment around the cell in each beaker as hypertonic, hypotonic or isotonic.
Label the net flow of water and state what will happen to the cell in each beaker?
Cell membrane reading
questions
1. Compare and contrast integral and
peripheral proteins.
2. What are the differences between the two
types of transport proteins discussed in the
article (use figure 7.10 to help you)
3. Why are proteins so essential to keeping
your cells hydrated?
4. Explain how diffusion relates to a
concentration gradient.