Download What is homeostasis?

What is homeostasis?
“a stable, internal condition of a living organism”
materials need to be brought into the cell
and exported out of the cell to maintain
homeostasis (a stable balance)
How do you think Cell Size affects a cell’s
ability to maintain homeostasis?
Surface area to volume ratio of an object decreases,
its size increases
Small cell size makes it more efficient for the cell to
regulate flow into and out of the cell
Easier to maintain homeostasis
Size of cells: a comparison
What organelle is responsible
for maintaining homeostasis?
the cell membrane
the cell membrane- up close!
a dynamic structure
The cell membrane has a
bilipid layer. Where is that?
Proteins
Bilipid
Bilayer
Transport
Protein
Go to
Section:
Carbohydrate
chains
Phospholipids
What part of the membrane do you
think is attracted to water?
Repelled by water?
Polar heads
love water.
(Hydrophilic)
Non-polar tails
hide from
water.
(hydrophobic)
What do you think the
proteins do?
Proteins
Bilipid
Bilayer
Transport
Protein
Go to
Section:
Carbohydrate
chains
Phospholipids
What do the surface markers do? (Carbohydrate
chains and others?) What do they look like?
Proteins
Bilipid
Bilayer
Transport
Protein
Go to
Section:
Carbohydrate
chains
Phospholipids
Cell Membrane – A fluid Mosaic
Model
What is the function of cell membrane?
(Think about its structure)
Acts as a barrier between cell and its
environment
Allows cell to maintain homeostasis
Acts as selectively permeable
membrane (determines what can enter/leave the
cell)
Cell-cell communication
Surface markers – recognition (proteins,
carbs and lipids)
In your notes…
Draw and label a cell membrane
Discuss with your table partner how the
structure of the cell membrane
determines its function.
You have 5 minutes to complete this
task.
the cell regulates movement in and out
(through the membrane) by two main
methods:
NO expenditure of Energy
uses concentration gradient
• expenditure of Energy
• does NOT use
concentration gradient
What is a concentration gradient???
Types of Cellular Transport
Passive Transport
cell doesn’t use energy
HL concentration
Weeee!!!
high
low
Active Transport
cell does use energy
LH concentration
This is
gonna be
hard
work!!
high
low
Passive Transport
cell uses no energy
molecules move randomly
Molecules spread out from an area of HIGH
to an area of LOW concentration until
dynamic equilibrium is reached
What is dynamic equilibrium?
(HighLow)
3 Types of Passive Transport
1. Simple Diffusion
2. Facilitated Diffusion
3. Osmosis
Have you heard the term
diffusion before? What do
you think it means?
passive transport – simple diffusion
small molecules pass
through the lipid bilayer
no energy is used
substances move
randomly, H L
concentration
results in even distribution
of molecules
molecules move randomly from an area
where they are dense to a less dense area
Solution eventually gets evenly distributed throughout
the system.
Most transport of materials into & out of cells occurs by
diffusion
• process is random, but NET movement is from HL
concentration
• upon reaching equilibrium, molecules still move equally back &
forth across a membrane  dynamic equilibrium
diffusion leads to equal distribution of solutes (solute is
component that is dissolved in the solution, ie sugar and
water)
*dynamic equilibrium (no future NET change in
concentration)
You now know what diffusion
is, what do you think
facilitated diffusion is?
What does facilitated mean?
passive transport - facilitated diffusion
• no energy is required
• substances cross the
membrane with the help
of carrier proteins
• movement is from HIGH
to LOW concentration and
continues to equilibrium
facilitated diffusion –
carrier proteins
Transport Proteins are
specific – they “select”
only certain molecules
to cross the
membrane
Why do you think the
cell membrane is
referred as being
selectively permeable?
Cell membranes have protein channels
Selectively permeable: Allows some
molecules in and keeps other molecules
out
Pores
The structure helps it be selective!
Major membrane function: selective permeability
Truth, Truth, Lie
Write 2 truths regarding what we have
learned about the cell membrane so far,
write one lie – make it difficult!
Teams of 4, keep score!
Winner gets prize, but only if there is
one winner, so make it difficult!!
What is Osmosis?
What does Osmosis have to
do with diffusion??
Osmosis –
passive transport of water
diffusion of water
through a selectively
permeable membrane
Water moves from HL
concentration
•Water moves freely
through pores.
•Solute (green) too
large to move across.
greater
solute
concentration
NO net movement of water
Lower solute
concentration
net flow
of water
Effects of Osmosis on Life
Water is so small and there is so much of it the cell
can’t control it’s movement through the cell membrane.
Tonicity
the measure of osmotic pressure
(pressure created by concentration of
water) of two solutions separated by a
semi permeable membrane (such as a
cell membrane!)
hypotonic
hypertonic
isotonic
What does hypo mean?
Greek: Below, beneath
Hypotonic Solution
The solution outside the cell has a lower
concentration of solutes
What does that mean for the concentration of
water inside the cell vs. outside the cell?
Hypotonic Solution
A higher concentration of water outside the cell
than inside the cell.
What do you think will
happen to a cell when
immersed in a hypotonic
solution?
Result: Water moves from the solution to inside the
cell): cell swells and bursts open (cytolysis)!
What does hyper mean?
Greek: above, over
Hypertonic Solution
The solution outside the cell has a higher
concentration of solutes
What does that mean for the concentration of
water inside the cell vs. outside the cell?
Hypertonic Solution
A lower concentration of water on the outside vs.
the inside of the cell.
What do you think will
happen to a cell when
immersed in a
hypertonic solution?
Result: Water moves from inside the cell into the
solution: Cell shrinks (plasmolysis or crenation)!
What does iso mean?
Greek: equal, same
Isotonic Solution
Isotonic: The concentration of solutes in the
solution outside the cell is equal to the
concentration of solutes inside the cell.
Result: Water moves equally in both directions and
the cell remains same size! (Dynamic Equilibrium)
isotonic solutions
What type of solution are these cells in?
A
B
C
Hypertonic
Isotonic
Hypotonic
Blood cell experiencing different tonicity
Tonicity foldable
You know what passive
transport is…what are some
traits of active transport?
Why do you think it is called
“Active” transport?
active transport
• Requires energy
• Protein carriers are used to transport
substances
• Movement is from LH concentration
• does not always result in even distribution of
material
Types of active transport
1. Ion Pumps


Protein pumps
Proton Pumps
2. CoTransport
3. Bulk Transport – Exocytosis/Endocytosis
Protein Pumps
transport proteins that
require energy to do
work
•Example: Sodium /
Potassium
(Na+/K+)Pumps are
important in nerve
responses.
Protein changes
shape to move
molecules: this
requires energy!
Sodium/Potassium Pump
Sodium Potassium Pumps
Proton (H+) Pump – Hydrogen ions pumped against
their concentration gradient
Cotransport
The movement of two substances across the
membrane, either in the same direction (symport),
or opposite directions (antiport)
Bulk Transport - Exocytosis
Forces large material out
of cell membrane
surrounding the material
fuses with cell membrane
• Cell changes shape –
requires energy
Bulk Transport – Endocytosis: taking bulky material
into the cell
•
•
•
Uses energy
Cell membrane in-folds
around food particle
Three types:
•
•
•
Phagocytosis - solids
Pinocytosis - liquids
receptor mediated – certain
kinds of molecules using
specific receptors
animation
Graphic organizer
what happens to a cell in solution
is a function of the concentration
of solutes in and out of the cell
one of the most critical influences on a
cell’s function is the medium (fluid) it is
surrounded by
Because the systems of living organisms
function in a fluid environment…
…the relative concentration
of water and solutes
must be maintained
within fairly narrow limits
How Organisms Deal
with Osmotic Pressure
Paramecium
(protist) removing
excess water
video
•Bacteria and plants have cell walls that prevent them
from over-expanding. In plants the pressure exerted on
the cell wall is called tugor pressure.
•A protist like paramecium has contractile vacuoles that
collect water flowing in and pump it out to prevent them
from over-expanding.
•Salt water fish pump salt out of their specialized gills so
they do not dehydrate.
•Animal cells are bathed in blood. Kidneys keep the
blood isotonic by remove excess salt and water.
OSMOREGULATION:
The ability to regulate the osmotic
concentration of internal body fluids and keep
them constant despite fluctuations in their
external environment.
success = balancing H2O gain/loss
so…
animals have adaptations which
allow them to osmoregulate based
on the environment they live in
special vesicles and vacuoles
Helps maintain
homeostasis for water
balance (osmotic
equilibrium)
contractile vacuole
central vacuole
central vacuole
(plants ONLY)
Maintaining
internal
hydrostatic
pressure or
turgor within
the cell
contractile vacuole
(animals ONLY)
found in certain unicellular organisms
pumps fluid from in the cell to the outside by
alternately filling and then contracting