Maintaining Dynamic
Equilibrium
Unit 4
Homeostasis
Nervous System
Endocrine System
Equilibrium
Every natural process strives to achieve
physiological balance
Equilibrium is the state of balance between
opposing processes, resulting in a stable
condition.
How is this achieved?
Diffusion
The constant movement of molecules from
areas of high concentration to areas of low
concentration until each molecule is a
maximum distance from every other similar
molecule (uniform distribution)
Example: Chlorine in a pool
Rate of Diffusion
All chemical and physical processes move
towards equilibrium at a speed determined by
the amount of energy added.
The rate of diffusion increases as thermal
energy input increases
Example:
A
B
C
Dye in gelatin
incubator (300 C)
room temperature (200C)
refrigertor (30C)
*most diffused
*least diffused
Osmosis
Water follows the Concentration Gradient
(diffusing from an area of high water
concentration to an area of low water
concentration)
Water moves to balance the concentration of the
solutions on both sides of a membrane when
the solute particles are unable to diffuse to
establish equilibrium.
Turgor Pressure
In plant cells, water within a cell puts pressure on the
cell wall to give the cell rigidity.
As a plant cell loses water Plasmolysis occurs
The cytoplasm within the cell shrinks away from the
cell wall and turgor pressure is reduced
 the plant wilts
This can be reversed by adding water  osmosis
moves water into the cell, the cytoplasm swells
putting pressure on the cell wall again
Deplasmolysis
Dynamic Equilibrium
Any system in a biosphere that remains stable
within fluctuating limits
Living systems are designed to maintain balance
within an environment (open system) using a
variety of processes
 adapt to changes without disturbing balance
Homeostasis is an organisms ability to maintain a
constant internal environment while the external
environment’s conditions are changing
*This system of active balance requires constant monitoring
Homeostasis and Metabolism
Cells exchange matter and energy with their
surroundings through a
semipermeable membrane
(some substances may pass through while
others may not)
Example: starch vs water in dialysis tubing
Starch molecules are too big to move across the membrane,
so water moves in
Sugar is small enough to diffuse, so it leaves the tubing
Tonicity
Ideally, cells want to maintain the same
concentration of solutes inside the cell as
outside
Isotonic condition
“iso”
“tonic”
equal
concentration
* The movement of water (osmosis) into the cell
should balance the movement of water out
the cell
Imbalance
Hypotonic
“hypo”
below
Hypertonic
“hyper”
above
The concentration of
dissolved molecules is
lower on this side of
the membrane
The concentration of
dissolved molecules is
greater on this side of
the membrane
Water will move away
from this solution
Water will move toward
this solution
Metabolism
Cells cycle material in and out constantly to
be used for energy conversion in the cell
Metabolism
is the sum of all chemical reactions within a
cell, or the sum of all cellular activities in
an organism
Special conditions are necessary (ideal) for
metabolic chemical reactions
But exterior conditions change constantly
from ideal
Homeostasis is a feedback system that
maintains interior stability
(balance/ ideal conditions)
so the organism can survive regardless of
external changes
In animals…
The brain coordinates homeostasis.
Special receptors in the body’s organs signal
the brain once an organ begins to operate
outside its normal limits.
The brain relays the information to the
appropriate regulator, which helps restore
the normal balance.
Assignment
Read page 117
2.
Read page 222-227
Answer questions 1-6 on page 228
Copy the flow chart from page 225
(fig.10.3) and page 229 (fig.10.10).
Compare these.
1.
3.
4.