Download Chapter 7 III. Cell Boundaries

Chapter 7 III. Cell Boundaries
• All cells have a
_____________________________and
some have a cell wall
Cell membrane
Interest Grabber
Section 7-3
• How is a window screen similar to a cell membrane? Read on to
find out.
• 1. What are some things that can pass through a window
screen?
• 2. What are some things that cannot pass through a window
screen? Why is it important to keep these things from moving
through the screen?
• 3. The cell is surrounded by a cell membrane, which regulates
what enters and leaves the cell. Why is it important to regulate
what moves into and out of a cell?
Go to
Section:
A. Cell Membrane
• Regulates what enters and leaves the cell and also provides
_____________________________.
• Almost all cell membranes are made of a double layered sheet
called a ___________________________-flexible,yet strong
barrier
• Cell membranes usually have a protein molecule imbedded in
the bilayer w/ carbohydrate molecules attached
• Called a _________________model
• Some of the proteins form channels or pumps to move material
across the membranes
• Some of the carbs act as ____________________tags
Protection
and support
Phospholipid
bilayer
Fluid mosaic
Chemical id tags
Figure 7-15 The Structure of the
Cell Membrane
Section 7-3
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Go to
Section:
Protein
channel
Lipid bilayer
B. Cell Walls
• In plants,algae,fungi, and many prokaryotes
• Lie _______________the cell membrane
• Usually porous enough to let water,O2,CO2 and
certain other substances to pass through easily
• Main function is support and protection
• Usually made of fibers of ____________________produced in cell and secreted to surface
• Mostly _____________________-tough carb fibers
Carbohydrate
and protein
outside
cellulose
C.Diffusion Through Cell
Boundaries
• Every cell is in a liquid environment
• Cell membrane regulates the movement of
cell materials from one side to the other
1.Measuring concentration
–
•
Cytoplasm is a solution of various substances
in water
_____________of a solution is the mass of solute
in given volume of solution---ie. Mass/volume…..If
you have 15 g salt in 3 mL water,what is the
concentration?------_______….If you have 24 g salt
in 2mL water you would have 12 g/mL salt….Which
solution is more concentrated?______________
12 g/mL
5g/mL
concentration
2. Diffusion
–
•
In a solution the particles move
constantly,spreading out randomly….tending to
move where more concentrated to an area less
concentrated…This is called
__________________.
– ____________________= concentration of a
solute is the same throughout a system
– does not require energy because random
movement
if equilibrium is reached,particles keep moving
across the membrane,still balancing concentration
isotonic
D. Osmosis
Figure 7-17 Osmosis
Section 7-3
Higher Concentration
of Water
Water molecules
Cell
membrane
Lower Concentration
of Water
Sugar molecules
Go to
Section:
D. Osmosis
– Some molecules are too large or too strongly
charged to make it across the lipid bilayer----thus
impermeable to it
– Most membranes are selectively permeable
– _____________________is the diffusion of water
across a selectively permeable membrane
– water moves easily and will move to balance the
concentration of a solute,water moving from area
of higher to lesser conc. For the WATER
– ____________________-same strength of a solute
on both sides of a cell membrane
osmosis
isotonic
– more concentrated side of solute is
____________________
– less concentrated side is____________________
– Osmosis exerts a pressure known as
____________________________on the
hypertonic side of a membrane….This could
results in a cell bursting
– Bursting not so much a problem in larger
organisms….tend to be in isotonic environments
• Osmotic pressure may not allow a plant or bacterial
cell to burst , but could weaken the cell wall
hypertonic
hypotonic
Osmotic pressure
E.Facilitated Diffusion
»
»
»
Protein channels
Some molecules,like glucose ,diffuse quickly
across due to ________________________
These allow only certain molecules to pass
Since it is diffusion it does not require energy and
still goes from area of higher to lower
concentration
F.Active Transport--– ____________________________________________
___________________________________
– Requires much energy
– Usually carried out by proteins or pumps
found in the membrane
Moves materials across a
concentration gradient,or
difference
1. Molecular Transport
– Small molecules and ions carried by
proteins that act like energy requiring pumps
•
Ca ,K,and Na ions are carried
Endocytosis and Exocytosis
•
•
•
Transports larger molecules and even clumps of
matter
________________________is the process of
taking material inward by enfolding,or pockets
In endocytosis ,the pocket breaks loose from the
cell membrane and forms a vacuole…large
molecules,food and even whole cells can be taken
in this way
endocytosis
2 examples of endocytosis are
– ___________________-extensions of cytoplasm
surround a particle and package it in a food
vacuole,then the cell engulfs it ---This is how
amoebas eat-----is a form of active transport
• _______________-Cells use this to take up liquids in
the environment—tiny pockets filled w/ liquid form
along the cell membrane and pinch off to form
vacuoles
phagocytosis
pinocytosis
– ___________________________--releases
large amounts from the cell by pinching off
or a contractile vacuole as in paramecium--also active transport
exocytosis
Figure7-20 Active Transport
Section 7-3
Molecule to
be carried
Low
Concentration
Cell
Membrane
High
Concentration
Molecule
being carried
Low
Concentration
Cell
Membrane
High
Concentration
Energy
Go to
Section:
Energy