Essential knowledge 2.C.1:
Essential knowledge 2.C.1:Organisms use feedback mechanisms to
maintain their internal environments and respond to external
environmental changes.
Negative FeedbackNegative feedback mechanisms maintain dynamic
homeostasis for a particular condition (variable) by regulating
physiological processes, returning the changing condition back to
its target set point.Negative Feedback..is the mechanism by which
the body maintains conditions within particular limits. The body
will do this by opposing a change that deviates from the
normal.Example 1: Body Temperature Regulation Body temperature in
mammals is regulated by a sensor that consists of cells within the
hypothalamus of the brain.
Endotherms: have internal control of body termpterature
Example 2: Blood GlucoseThe amount of glucose in your blood is
carefully controlled.After you have eaten a meal, the blood glucose
levels will begin to rise because the carbohydrates in the food are
digested and absorbed. This rise is detected by beta cells, which
then will produce more insulin. This insulin then binds to receptor
proteins in cell membranes (particularly in the liver). This causes
more protein channels to open so that more glucose can enter the
cell.
Also, insulin encourages enzymes to convert glucose to glycogen
for storage.If however, you have been doing a lot of exercise, and
glucose is being used up, then alpha cells will produce glucagon,
this causes the release of an enzyme that breaks glycogen to
glucose
Example 3: Operons in Gene RegulationThe trp operon is a
repressible operonA repressible operon is one that is usually on;
binding of a repressor to the operator shuts off transcription
Positive Feebackb. Positive feedback mechanisms amplify
responses and processes in biological organisms. The variable
initiating the response is moved farther away from the initial
set-point. Amplification occurs when the stimulus is further
activated which, in turn, initiates an additional response that
produces system change.
Example 1: Lactation in mammalsLactation involves positive
feedback in that as the baby suckles on the nipple there is a nerve
response into the spinal cord and up into the hypothalamus of the
brain, which then stimulates the pituitary gland to produce more
prolactin to produce more milk.Example 2: Onset of labor in
childbirthwhen a contraction occurs, the hormone oxytocin causes a
nerve stimulus, which stimulates the hypothalamus to produce more
oxytocin, which increases uterine contractions. This results in
contractions increasing in amplitude and frequency.
Example 3: Ripening of fruitthe first fruit that begins to ripen
emits ethylene triggering the surrounding fruit to ripen- One bad
apple
Alteration in the mechanisms of feedback often results in
deleterious consequences.Example 1: Diabetes: a person has high
blood sugar, either because the pancreas does not produce enough
insulin, or because cells do not respond to the insulin that is
produced
Example 2: Dehydration in response to decreased antidiuretic
hormone (ADH) In the kidneys, water is first filtered from the
blood (along with waste products). Much of this water is reabsorbed
and delivered back to the blood. ADH stimulates this reabsorption
of water.
alcohol inhibits the release of ADH. This is why excess alcohol
consumption can lead to frequent urination and dehydration.
Example 3: Graves disease (hyperthyroidism)affects the thyroid
causing it to grow 2 to 3X its size (goiter); leads to increased
heartbeat, muscle weakness, disturbed sleep, and irritability
Essential knowledge 2.C.2:
Organisms respond to changes in their external
environments.Photoperiodism Photoperiodism
TropismsPhototropismGravitropismThigmotropism
Taxis and Kinesis in AnimalsKinesis random movement of
organismsTaxix movement toward or away from a stimulus Chemotaxis
in bacteria, sexual reproduction in fungi
Other Responses worthy of mentioning:Hibernation and migration
in animalsNocturnal and diurnal activity: circadian rhythms
(roughly 24 hour cycle in the physiological processes of living
beings, including plants, animals, fungi and
cyanobacteria)Shivering and sweating in humans
