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
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
Movement of Materials
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?
What is the structure of cell
membranes?
Draw a basic diagram of the
cell membrane with your
group.
• Label the 2 or 3 major structures.
• What is the function of the
•
membrane? What do the major
structures have to do with the
function?
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
Structure and Function
Structure and Function
Function: The membrane is selectively permeable
Structures:
• Pores in the Membrane/Fluid Mosaic Model
• Water diffuses through openings called pores located in cell membranes
• Process of water diffusing into cells is called osmosis
• Small molecules such as Oxygen and Carbon Dioxide dissolve and pass
through lipid layers
• Proteins/Channels in the membrane
• Chemical make-up of particles determines which channels it can go through
• Whether or not particles are soluble in water determine which channels it can go
through
• Conditions inside and outside the cell (concentrations) determine which way
molecules will flow
Osmosis and Living Cells
Equilibrium: When concentrations of two solutions
separated by a membrane is the same
• Brownian Motion: Constant movement of molecules
• Video
• Water and solutes continues to move back and forth
across a membrane even when equilibrium is reached
Concentration of water on each side of membrane is
determined by number of solutes (dissolved solids) in that
water solution (For example a sugar water solution that is
20% water would be 80% sugar)
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
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
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
• A simple rule to
remember is “Solute
Sucks”
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
Comprehension Check
Which of the following eggs was placed in a isotonic, hypotonic,
hypertonic solution? How do you know?
Which was a “stronger” solution, the hypertonic or isotonic
solution? How do you know?
Plant versus Animal Cells
Multicellular versus Unicellular
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?
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.
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 that change shape to 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: Specialized carrier molecules 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.
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
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 Potassium 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 impulses