Download Cell Size and Movement

Cell Size and Membrane Transport
Georgia Performance Standards:
•Explain the role of cell organelles for both prokaryotic and
eukaryotic cells, including the cell membrane, in maintaining
homeostasis and cell reproduction.
•Explain the impact of water on life processes (i.e. osmosis,
diffusion)
Essential Questions:
EQ: What limits the size of a Cell?
EQ: Why are cells small?
EQ: Why is it important to regulate what moves into and out of a cell?
EQ: How do cells maintain homeostasis?
Warm-up
How is a window screen similar to a cell membrane? Read onto
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?
Cell size and shape are
related to its function
• A large cell has a
smaller surface area
relative to its volume
than smaller cells
– Organelles near the cell
have.
• Cells must be small
in order to function
efficiently
membrane to transport
nutrients in and wastes
out.
– VERY EFFICIENT
– Organelles far from
cell membrane. Hard to
transport nutrients in
and wastes out
– NOT EFFICIENT
Cell Size with “Cube”Demo:
• The ratio of surface
area to volume
imposes and upper
limit on cell size.
• Math Example
• Larger cube has more
volume and less surface
area (not efficient).
• Smaller cube has less
volume and more surface
area (efficient)
The Cell Membrane Maintains
Homeostasis
• Structure
– Semi-permeable
– Made of a
phospholipid bilayer
– Contains proteins and
carbohydrates
– Has polar hydrophilic
(water loving) and
non-polar
hydrophobic (water
fearing) parts
• Function
– Provides support and
protection
– Controls what enters
and leaves the cell
The Structure of the Cell Membrane
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Go to
Section:
Protein
channel
Lipid bilayer
This is a cross section of
the cell membrane you
should notice two
different structures:
•The phospholipids are the round yellow structures
with the blue tails.
• The proteins are the lumpy structures that are
scattered around among the phospholipids.
This is a simple
representation of a phospholipid.
•The yellow structure represents the hydrophillic
or water loving section of the phospholipid.
•The blue tails that come off of the sphere
represent the hydrophobic or water fearing end
of the phospholipid.
If you mix phospholipids in water they will form these double
layered structures.
•The hydrophillic ends will be in contact with water.
•The hydrophobic ends will face inwards touching each
other.
1st category of proteins
Transport proteins: regulate what enters or leaves
the cell (Carrier & Channel)
B. Channel Proteins: Channel proteins simply act as
a passive pore. Molecules will randomly move
through the opening in a process called diffusion.
*
TYPES OF TRANSPORT
• PASSIVE= Requires NO Energy
HIGH concentration  LOW concentration
– Diffusion
– Osmosis
– Faciltated Diffusion
• ACTIVE= Requires Energy
LOW concentration  HIGH concentration
– Endocytosis
– Exocytosis
Passage Through Cell Boundaries
• Types of Passive Transport:
• Diffusion
– ANY substance moves from areas of HIGH
concentration to areas of LOW concentration
– Requires NO energy (ATP)
– Equilibrium is reached when the concentration is
equal on both sides of the membrane
– Rate determined by temp. and size of molecule
Passage Through Cell Boundaries
• Osmosis
– Diffusion of water through a selectively
permeable membrane, until the concentration of
substances are at an equilibrium.
– Effects of Osmosis on cells
• Isotonic (Equal amounts of solute and solvent)
• Hypertonic (more solute than solvent)
• Hypotonic (more solvent than solute)
The Effects of Osmosis on Cells
• Cells placed in an isotonic solution neither gain
nor lose water. (=)
• Cells in a hypotonic solution, animal cells swell
and burst. The vacuoles of plant cells swell,
pushing the cell contents out against the cell wall.
hypo= “hippo”
think of Violet from Willy Wonka
• In a hypertonic solution, animal cells shrink, and
plant cell vacuoles collapse.
Osmosis
Section 7-3
Higher Concentration
of Water
Water molecules
Cell
membrane
Lower Concentration
of Water
Sugar molecules
Go to
Section:
Facilitated Diffusion
Section 7-3
Glucose
molecules
High
Concentration
Cell
Membrane
Low
Concentration
Go to
Section:
Protein
channel
Facilitated Diffusion
• Some substances, such
as glucose, can not
pass through the
membrane on their
own
• Molecule move from
areas of high
concentration to
areas of low
concentration
• Protein channels
• Requires NO energy
found within the lipid
(ATP)
bilayer “facilitate” the
passage of these
substances
Active Transport
• Sometimes cells must move materials
against concentration gradients (from low
concentration to high to concentration)
• Requires energy (ATP needed)
Types of Active Transport
• Channel proteins:
– Proteins found in the lipid
bilayer can “pump” small
molecules in/out of the cell
with energy
• Endocytosis – cell can
gather large substances
and move them into the
cell by folding its cell
membrane (creating a
vesicle) around the
materials.
• Exocytosis – Vacuoles
from within the cell fuse
with the cell membrane
and force contents out of
the cell.
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
ENDOCYTOSIS
• “endo”= into or inside
• “cyto”= cell
• MOVEMENT INTO CELL
http://02b5260.netsolhost.com/videotransport.htm
EXOCYTOSIS
• “Exo”= exit, out of
• “cyto”=cell
• MOVEMENT OUT OF CELL