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Notes on Homeostasis
Homeostasis – “biological balance”
cell(s) keeping a steady state with or in spite of the environment
• homeo - same
• stat - steady
Homeostasis Regulation of the internal environment to
maintain constant, favorable conditions
Every cell, tissue & organ in the human body contributes toward total body homeostasis
Ex: Body is cold (low temp), you begin to shiver to raise body temperature
Ex: Your blood oxygen level is low**, your respiratory rate increases to meet this O2 need (raise blood O2)
**generalization
Ex: Blood collects & carries wastes from all tissues toward kidneys, which then filter blood & send waste materials toward excretory system
Ex: Enzymes used in producing sperm function best at 2-3° lower than regular body temperature.
What determines a cell’s set of homeostatic conditions?
The metabolic needs of the cell.
• In the human body, these are the conditions of homeostasis:
–pH of human blood is: 7.4
–Normal body temp is: 98.6 ºF (or 37 ºC)
–Saline concentration in blood is: 9g salt per liter
–Regular blood glucose level is: 100-150 mg/dL
• Clearly, homeostasis does NOT mean conditions are equal to the conditions of the environment
Homeostasis
Write down the key ideas from the following video clip dealing with metabolism and homeostasis; use these
for your Frayer Model in comp book!.
Because the cell membrane is
the interface between the cell
and the external environment,
the cell membrane plays a
MAJOR role in governing
homeostasis for the cell.
The BIG idea:
Review….Solute: Any substance that is dissolved in water is a solute.
Example: salt
Solvent: The liquid in which a solute is dissolved Example: water (of the saltwater )
Solution: A liquid that contains one or more solutesExample: Water with sugar and/or salt
Concentration: The mass of solute in a given volume ofsolution.
Concentration, then, just means how “salty” the water is.What are two methods for changing a solution’s concentration?
New idea: Concentration Gradient• A concentration gradient is a difference between
two solutions that are separated by space or a barrier.
Notice these two “salt” solutions:
One solution is saltier than the other. What do you think will happen to the salt particles over time?
K concentration gradient
Definition
A separation of two different concentrations of a solution. Outs
ide th
e cell
Insid
e the cell
Outsid
e the cell
Insid
e the cell
K
K KK
K
KK
KK
K
K
K
KK
K
K
K
K
K
KK
KK
K
Na
Na
Na
NaNaNa
Na
Na
NaNa
NaNa NaNaNa
Na
NaNaNa
Na
Na
NaNa
NaNa
Equilibrium /Equal on both sides
In cells, concentration gradients occur at the cell membrane—between the intracellular and extracellular environments.
Interacting with the concentration gradient is how the cell membrane helps to maintain homeostasis.
Cell membrane – regulates what enters and leaves the cell
Semipermeable membrane – keeps out some molecules but allows others to enter
Structure of the Cell membrane
• composed of a bilayer of phospholipids and proteins
Structure of
Non-polar
• regulates what enters and leaves the cell – selectively permeable (semipermeable)
• Keeps out some molecules but allows others to enter
Movement across the cell membrane:
2 types:
1. passive transport
2. active transport
1. Passive transport – does not require cellular energy
A. Diffusion – movement of molecules from areas of greater concentration to areas of lesser concentration
Particles move WITH the concentration gradient.
Diffusion with no membrane:
Diffusion across a membrane:
Once the concentration of the molecules is the same, dynamic equilibrium has been reached…
There is no NET change of concentrationMolecule of dye Membrane Equilibrium
Human body examples of Diffusion:•Oxygen diffusing from lungs to blood
•Carbon dioxide diffusing from blood to lungs
•Nitrogenous waste diffusing from blood in the kidneys into urine
•Food particles absorbed in the small intestine from the digestive tract.
What is the homeostatic role of the cell membrane in processes of
diffusion?
B. Facilitated diffusion – molecules that can not cross the cell membrane’s lipid bilayer directly are guided through the protein channels
• example: glucose
Cell Membrane
Protein Channel
Solute
What is the homeostatic role of the cell membrane in processes of facilitated
diffusion?
C. Osmosis – diffusion of water across a membrane
Hypotonic – concentration of solute molecules in the environment is lower than in the cell
HYPO could make a cell POP
In osmosis, solute isn’t moving, but the solute is the reason for water movement
• water comes in and the cell swells
• “hypo” means lower
Hypertonic – concentration of solute molecules in the environment is greater than in the cell
• “hyper” means higher
• water leaves and the cell shrinks
HYPER will make a cell SHRINK
Isotonic – concentration of solute molecules in the environment is equal to the inside of the cell
• “iso” means equal
• cells neither gain nor lose water
Examples:
Salty water will be hypertonic to a cell
Distilled water will be hypotonic to a cell
Plant cells swell until they are restricted by the cell wall
• this sets up turgor pressure and result in the cell becoming rigid
Water leaves (loss of turgor pressure) the plant cell wilts
• This condition is known as plasmolysis
If too much water enters an animal cell, the cell will burst
- this is called cytolysis
What is the homeostatic role of the cell membrane in processes of
osmosis?
ISOTONIC SOLUTION HYPOTONIC SOLUTION HYPERTONIC SOLUTION
(1) Normal
(4) Flaccid
(2) Lysing
(5) Turgid
(3) Shriveled
(6) Shriveled
ANIMALCELL
PLANTCELL
Plasmamembrane
Type of cell - ___________
Type of solution - _____________
How will water move? _____
By what process? ______________
How will salt move? ______
By what process? _______________
What will happen to the cell? _____________
Biological term - __________________
45% NaCl
8.5% NaCl
91.5% H2O
55% H2O
Animal
hypertonic
out
osmosis
in
diffusion
shrink in size
plasmolysis
Type of cell - ___________
Type of solution - _____________
How will water move? _____
By what process? ______________
How will salt move? ______
By what process? _______________
What will happen to the cell? _____________
Biological term - __________________
Distilled water
8.5% NaCl
91.5% H2O
0% NaCl
Plant
hypotonic
in
osmosis
out
diffusion
swell and become rigid
turgor pressure
100% H2O
Passive Transport
low
high
2. Active transport – requires cellular energy
• materials move from an area of lesser concentration to an area of greater concentration
• In active transport, materials are moved against the concentration gradient.
• Types of active transport are found in:
– protein pumps– endocytosis– exocytosis
Types of Active TransportA. A Protein Pump pushes substances
against their concentration gradient in order to keep the amounts that the cell prefers.
Example: Nerve cells use a sodium-potassium pump to keep desirable concentrations inside the cell.
During a nerve impulse, protein channels OPEN, all solutes diffuse with the concentration gradients, but away from the desired levels…oh no!!!
That’s where the sodium-potassium pump comes in…see next slide…--pumping things back so that there IS the desired concentration gradient.
• example: the sodium-potassium pump
• sodium (out) and potassium (in)
Active Transport
Endocytosis vs. ExocytosisOnline link to video clip
B. Endocytosis – passage of large molecules into the cell through the cell membrane
• The material is enclosed in a vesicle which pinches off from the cell membrane
• 2. Phagocytosis is the process of large particles being taken into the cell by means of extensions of cytoplasm that go out and engulf the large particles.
• This is a leukocyte (white blood cell) in • your blood that is shooting out extensions • to get the large particles that you see.
a. pinocytosis – movement of solutes or fluids
• pino = to drink
b. phagocytosis – movement of large food particles or whole organisms
• phago = to eat
• example: WBCs, amoeba
C. Exocytosis – passage of unwanted and/or large molecules through the cell membrane to the outside
• excretions and secretions; Golgi body
• Excess water; contractile vacuole of some protists.
What is the homeostatic role of the cell membrane in processes of
active transport?
Active Transport
low
high
ENERGY
True/False Discussion“The cell membrane maintains homeostasis by allowing solutes to reach equilibrium.”
“The cell membrane maintains homeostasis by preventing solutes from reaching equilibrium.”
“The cell membrane maintains homeostasis by preventing the diffusion of large molecules.”
W2W
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