STANDARD 2
Organization & Development of
Living Systems
Unit 6 – Homeostasis & Health
Objectives
• B2.3B: Describe how the maintenance of a
relatively stable internal environment is required
for the continuation of life.
• B2.3C: Explain how stability is challenged by
changing physical, chemical, and environmental
conditions, as well as the presence of disease
agents.
• B2.3f: Explain how human organ systems help
maintain human health.
What is Human Nutrition?
• The balance between the amount of
calories a person takes in (eats) and the
amount of calories burned (physical
activity).
– Calorie
• The amount of heat required to raise the
temperature of one gram of water one
degree Celsius, heat-producing or energyproducing value in food
Essential Nutritional Processes
• Diffusion = movement of a substance from an area of greater
concentration to an area of lesser concentration
Example – spray Windex
• Osmosis = diffusion through a semi-permeable membrane
• Hypotonic Solution = solute concentration is greater in the
environment than in the cell, so water enters the cell
• Isotonic Solution = solute concentration is equal
in the environment and in the cell
• Hypertonic Solution = solute concentration is
lower in the environment than in the cell, so water
exits the cell – it dehydrates and dies
Internal Environment
Physical Conditions
• Cell function in a narrow range of physical conditions, such as temperature
and pH (acidity), to perform life functions. When these physical conditions
are not maintained, the cell will die.
• pH - Lysosomes and peroxisomes are often referred to as the garbage
disposal system of a cell. Both organelles are somewhat spherical, bound
by a single membrane, and rich in digestive enzymes, naturally occurring
proteins that speed up biochemical processes.
• All of these enzymes work best at a low pH, reducing the risk that these
enzymes will digest their own cell should they somehow escape from the
lysosome. Here we can see the importance behind compartmentalization
of the eukaryotic cell. The cell could not house such destructive enzymes
if they were not contained in a membrane-bound system.
• The term pH derives from a combination of "p" for the word power and "H"
for the symbol of the element hydrogen. pH is the negative log of the
activity of hydrogen ions and represents the "activity" of hydrogen ions in a
solution at a given temperature. The term activity is used because pH
reflects the amount of available hydrogen ions, not the concentration of
hydrogen ions. The pH scale for aqueous solutions ranges from 0 to 14 pH
units, with pH 7 being neutral. A pH of less than 7 means that the solution
is acidic, whereas a pH of more than 7 means that the solution is basic.
Physical Conditions
• Temperature also affects how a cell can perform and function.
If the appropriate temperature is not maintained, the cell will
die.
• For example – Sperm cells are made in the testes; it takes
about 72 days to produce a sperm cell. The temperature in the
testes is about four degrees below body temperature; that's
why they hang outside the body. The scrotum containing the
testes helps maintain this temperature by raising or lowering
the testicles (in and out of the body cavity) depending on the
outside temperature.
Internal Environment
• In order to stay alive and functioning, cells must interact with
their environment to obtain nutrients, water, ions, etc., and to
get rid of wastes and to export materials.
• This is accomplished by the processes of diffusion, and
osmosis, which are passive mechanisms. Other passive
mechanisms which allow materials to pass in and out of cells
such as facilitated transport.
• There are also active transport mechanisms, which require the
expenditure of ATP energy. They include ion "pumps",
endocytosis, and exocytosis.
Maintaining Internal Environments
•←• Endocytosis = the uptake of external
materials by a cell; The process by
which materials enter a cell without
passing through the cell membrane.
The membrane folds around material
outside the cell, resulting in the
formation of a saclike vesicle into
which the material is incorporated. This
vesicle is then pinched off from the cell
surface so that it lies within the cell.
See phagocytosis; pinocytosis.
•←• Exocytosis = the release of materials
by the cell. It is when the cell releases
vesicular materials to the outside of a
cell. The opposite of endocytosis.
•Active Transport (05:33)
• Active Transport = the pumping of a
substance across a cellular membrane
from a point of lower concentration to
one of higher concentration; requires
energy.
Internal Environment
• It is necessary for the cell to maintain a relatively stable internal
environment for the continuation of life.
• The internal environment of cells is challenged by physical,
chemical, and environmental conditions as well as the presence
of disease agents.
• The metabolic activities of organisms produce highly reactive
chemicals, including strong oxidizing agents. The internal
structure of the cell, however, minimizes the harmful effects of
such agents; the critical reactions take place within enclosed
structures such as ribosomes, membranes, or mitochondria,
and counteractive enzymes such as peroxidases and
lysosomes enzymes.
• How is this balance achieved and maintained? Putting filtration by the kidney
aside, for small molecules such as sugars and amino acids, transport
equilibria—spontaneous, reversible processes of equalization between
opposing forces—across the membranes of the cells of perfused tissues are
responsible. The movement of water-soluble molecules through pores
embedded in cell membranes or by means of membrane carrier proteins
exemplify these processes.
• The stable concentrations that result are the consequence of the equilibrium
process itself.
Diffusion vs Osmosis vs Active Transport
• DIFFUSION → The spontaneous movement of particles from an
area of higher concentration to an area of lower concentration.
The movement of molecules occurs along a concentration
gradient, i.e. from areas of high concentration to a low
concentration until their is an equilibrium.
•Diffusion
and Osmosis
(02:04)
•Cell
Membrane:
Diffusion
(00:53)
• OSMOSIS → The movement of water through a selectively
permeable membrane across a concentration gradient (from a
high concentration to a low concentration).
• ACTIVE TRANSPORT → Molecules and ions can be moved
against their concentration gradient, but this process requires
the expenditure of energy (usually from ATP).
Internal Environment
• What would happen to the stability of a cell
if a disease agent was present?
Internal Environment
• Molecules move back and forth, from and into each cellular source
compartment and from and into each destination compartment, in response
to the concentration gradient between them and blood, until movement in
both directions, entry and exit, across each affected membrane, becomes
equal though opposite.
• When this occurs, the concentration of the substance in blood becomes
unchanging as a matter of course. This holds true whether the substance is
passively distributed across the membrane, as in simple equilibria, or
whether special transport processes maintain a concentration gradient
across it at the cost of metabolic energy.
• Similarly, it pertains whether movement is due to nonspecific leakage or the
presence of specific receptors, transporters, or pore-forming proteins.
Whatever the particular circumstances, fluxes in both directions across the
various membranes become equal when the stationary state applies—that
is, when the concentration of the substance in blood is constant.
• From our perspective, these processes have two critical features. First, entry
and exit commute—each fully affects and determines the other. Second,
attaining and sustaining the resultant concentration in blood is an intrinsic
property of the physical mechanism by which it is achieved. No additional
mechanisms are needed.
Maintaining Internal Environments
• Hypertonic solutions
• Solutions that have more solute dissolved than another one are said to be
hypertonic to the solution they are being compared to.
• A solution which contains more dissolved particles than cellular content.
• In biology, a hypertonic cell environment has a higher concentration of
solutes than in cytoplasm. In a hypertonic environment, osmosis causes
water to flow out of the cell. If enough water is removed in this way, the
cytoplasm can become so concentrated that the cell has difficulty
functioning.
•Cells in Hypertonic Solution
•Photomicrograph of blood cells
in a hypertonic solution; the
puckered effect comes from the
loss of fluid from inside the cell
Maintaining Internal Environments
• Isotonic solutions
• If both solutions being compared have equal amount of dissolved solutes
then the solutions are isotonic to each other.
• A solution that has the same salt concentration as the normal cells of the
body and the blood. An isotonic beverage (such as Gatorade) may be drunk
to replace the fluid and minerals that the body uses during physical activity.
• An isotonic cellular environment occurs when an equal solute concentration
exists inside and outside the cell. Molecules flow in and out at an equal rate
by osmosis, causing the cell size to stay the same. It will not lose or gain any
solutes.
• When red blood cells are placed in a 0.9% salt solution, they neither gain
nor lose water by osmosis. Such a solution is said to be isotonic.
•Normal Cells in Isotonic Solution
•Photomicrograph of blood c
Maintaining Internal Environments
• Hypotonic solutions
• The solution with the lower solute concentration is hypotonic.
• A solution which contains less dissolved salt than cellular content.
• In biology, a hypotonic cell environment is one with a lower concentration of
solutes than the cytoplasm. In a hypotonic environment, osmosis causes
water to flow into the cell. Plants thrive in hypotonic environments. Their
cells have rigid cell walls that prevent bursting. In fact, the pressure of the
cytoplasm against the cell wall keeps the plant from wilting and losing its
shape.
• A red blood cell placed in a hypotonic solution (e.g., pure water) bursts
immediately ("hemolysis") from the influx of water.
• Plant cells and bacterial cells avoid bursting in hypotonic surroundings by
their strong cell walls. These allow the buildup of turgor within the cell.
When the turgor pressure equals the osmotic pressure, osmosis ceases.
•Cells in Hypotonic Solution
•Photomicrograph of blood cells
in a hypotonic solution; the
bloated effect comes from the
swelling of the cell.
Plant Cell Internal Balance
•Equilibrium (05:56)
•http://www.tvdsb.on.ca/westmin
/science/Sbi3a1/cells/Osmosis.h
Normal Cells in Isotonic
Solution
Cells in Hypertonic
Solution
Cells in Hypotonic Solution
Photomicrograph of
blood cells
in an isotonic solution.
Photomicrograph of
blood cells
in a hypertonic
solution; the
puckered effect
comes from the
loss of fluid from
inside the cell.
Photomicrograph of
blood cells
in a hypotonic solution;
the
bloated effect comes
from the
swelling of the cell.
Internal Balance
• Homeostasis = Equilibrium or balance of internal environment.
• In biology, the term homeostasis is used to describe a condition where an
organism maintains a stable structure where in fact a constant flux of
molecules occurs. Although many organisms can live for years, all cellular
components like proteins, membranes, sugars, and nucleic acids are
constantly recycled while never compromising the integrity of the organism
as a whole.
• In a living organism just about everything, from Arterial blood pressure to
Zymogen granules, is subject to homeostatic regulation. Homeostasis
occurs in single cell organisms and at every level of organization in a
multicellular organism (such as yourself) from the single cell up to the entire
body.
• The most common way of exploring the principles of homeostasis is to look
at how hormones regulate the function of different organs and integrate
these functions to the best advantage of the organism as a whole.
• A most literal definition of "internal environment" is the actual salts and water
that form the basis of both the cytoplasm and the fluid space between the
cells.
•The condition in which
the internal environment
of the body remains within
physiological limits.
•Cell
Membrane:
Homeostasis
WHY MUST CELLS BE SMALL?
• Cells must be small – gives them more surface area.
• If a cell gets too large – the cells surface area would be too
small and the cell will die because it is unable to remove
toxic substances quick enough or receive needed
substances quick enough.
•Amoeba, intestinal cells with microvilli Extending the outer surface of a cell into
folds, fingers or indentations can increase
the total surface area by a factor of several
times
•Bacillus bacteria, red blood cells, a
sphere has a low SA/V ratio. Cells
that are drawn out (e.g. cylinder), or
flattened have much more
membrane per unit of cytoplasm