Cell Membranes and
Transport
Honors Biology
Chapter 5
Important Root Words
Root Word
Meaning
hypo
below
hyper
above
ton
tension
-ic
pertaining to
iso
lysis
cytendoexo-osis
phag
plasm
same
loosening, splitting
cell
within
outside
condition
feed, eat
to form or develop
1
What is homeostasis?
Review this term with your group.
Come up with a great definition!
Relate this term (and its importance) to
cells! How do cells maintain
homeostasis?
The Cell and its Environment
Biological Balance – Homeostasis
• Every organism must constantly adjust in
•
•
order to survive
Homeostasis occurs at all levels of living
things
For homeostasis to occur, the cell must keep
necessary balance within the limits of
environmental changes
2
Movement of Materials
Brownian Motion: Constant
movement of molecules
Diffusion: Process by which
molecules of a substance
move from areas of high
concentration to areas of
low concentration.
• One of the major means of
molecular transport in cells
Movement of Materials
Concentration gradient: Difference in
concentration of molecules across a
membrane
What factors affect the rate of diffusion?
How would you design an experiment to
test these factors?
3
What is the structure of cell
membranes?
Draw a basic diagram of
the cell membrane with
your group.
• What are the important
•
•
components?
Why does it have this
structure?
Can you name any
important characteristics?
Structure of the Cell
Membrane
Double layer of lipids with
proteins that control passage
of some molecules into and
out of the cell
“Fluid-Mosaic” Model
Selectively Permeable:
Controls passage of materials
into and out of the cell
Cell Membrane Animation
4
Characteristics of cell
membranes
Factors that let selectively permeable membranes operate:
• Structure of Plasma Membrane itself
•
•
•
•
• Water diffuses through openings called pores located in cell membranes
• Process of water diffusing into cells is called osmosis
Size of Particles
• Oxygen and Carbon Dioxide dissolve and pass through lipid layers
• Water molecules do dissolve and pass through lipid
Chemical make-up of particles
Whether or not particles are soluble in water
Conditions inside and outside the cell
Osmosis and Living Cells
Equilibrium: When concentrations of two
solutions separated by a membrane is the same
Water continues to move back and forth across a
membrane until equilibrium is reached
Concentration of water on each side of
membrane is determined by number of solutes
(dissolved solids) in that water solution
5
Comprehension Check
Here is a sample cell in a beaker of water, we placed
monosaccharide and polysaccharide inside the cell. We also
took iodine (the indicator for ____?_____) and placed it into
the beaker.
• What diffused into/out of the dialysis tubing and why?
• How did you know what had moved through the tubing?
Isotonic Solutions
A simple rule to
remember is “Solute
Sucks”
Isotonic Solution:
Concentration of solutes
outside of cell
membrane is same as
that inside of cell
membrane
•
Ex: Plasma in blood is
isotonic with the red
blood cells
6
Hypotonic Solutions
Hypotonic Solutions:
Concentration of
solutes outside the cell
membrane is lower
than inside the cell
membrane
•
Ex: Freshwater plants
and animals living in
lakes and streams where
water is constantly
flowing
Hypertonic Solutions
Hypertonic Solutions:
The concentration of
solutes outside the cell
is greater than that
inside the cell
•
Ex: drinking sea water
causing cells to lose water
7
Plant versus Animal Cells
Review the major differences between
plant cells and animal cells with your
group.
•
•
How would a plant cell react to a hypertonic
solution? How is this different than an animal
cell?
How would an animal cell react to a hypotonic
solution? How is this different than a plant
cell?
Would changes in solutions affect
unicellular or multicellular organisms
more?
8
Types of solutions
•
•
•
•
Turgor Pressure: Pressure that
builds in a plant cell as a result
of osmosis
Cytolysis: The bursting of an
animal cell membrane in a
hypotonic environment
Plasmolysis: The shrinking of
cells as a result of water loss.
Contractile Vacuoles: Tiny
vacuoles found in one-celled
animals which pump out
excess water
Passive and Active Transport
Talk to your group about the difference
between passive and active transport.
Decide what these terms mean and
come up with reasons why passive and
active transport would be used by cells.
9
Passive and Active Transport
Both diffusion and facilitated diffusion are forms of passive transport
of molecules down their concentration gradient, while active transport requires an
investment of energy to move molecules against their concentration gradient.
Passive Transport
Passive Transport: Passing of materials into and out of the cell
without the use of energy (ATP)
• Diffusion
• Facilitated Diffusion: Proteins assist certain molecules to
move through cell membrane
• Carrier Molecules: The proteins that assist in facilitated
diffusion
• Ex: Glucose molecules going in/out of the cell
• Ion Channels: Membrane proteins that help such ions as
Na+, Ca2+, Cl-,K+, to cross the cell membrane. These ions
are not soluble in lipids and need assistance to cross.
10
Active Transport
Transport of materials into or out of the cell with the use of
cell energy (ATP)
•
Active transport using carrier molecules involves actual movement
of materials in a cell from regions of low concentrations to regions
of higher concentrations.
•
Ex: Moving glucose from blood stream into our liver cells
Bulk Transport
A type of active transport where materials into or out of the cell
that cannot normally pass through the cell membrane
Exocytosis: The bulk transport of substances out of the cells
Endocytosis: Bulk transport of substances into the cell
• Phagocytosis: solids or larger particles
• Pinocytosis: liquids
11
Comprehension Check
Requires Energy
Requires NO Energy
Place the following terms into one of the boxes above:
Diffusion
Osmosis
Active Transport
Facilitated Diffusion
Passive Transport
Exocytosis
Endocytosis
Sodium-Potassium Pump Video
Real World Example: Active
Transport
Sodium Potassum Pump
The movement of Na+ and K+ against
their concentration gradients
Typically, an animal cell has higher
concentrations of K+ and lower
concentrations of Na+ inside the cell.
The sodium-potassium pump uses the
energy of one ATP to pump three Na+
ions out and two K+ ions in.\
At top speed, the Na+/K+ Pump
can transport about 450 Na+ and
300 K+ ions per second
Used in the conduction of nerve
12