Download Negative feedback mechanisms maintain

BIG IDEA II
Biological systems utilize free energy and molecular building blocks
to grow, to reproduce and to maintain dynamic homeostasis.
Enduring Understanding 2.C
Organisms use feedback mechanisms to regulate growth and
reproduction, and to maintain dynamic homeostasis.
Essential Knowledge 2.C.1
Organisms use feedback mechanisms to maintain their internal
environments and respond to external environmental changes.
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Essential Knowledge 2.C.1: Organisms use feedback mechanisms to
maintain their internal environments and respond to external environmental changes.
• Learning Objectives:
–
(2.15) The student can justify a claim made about the effect(s) on a biological
system at the molecular, physiological or organismal level when a given scenario in
which one or more components within a negative regulatory system is altered.
–
(2.16) The student is able to connect how organisms use negative feedback to
maintain their internal environments.
–
(2.17) The student is able to evaluate data that show the effect(s) of changes in
concentrations of key molecules on negative feedback mechanisms.
–
(2.18) The student can make predictions about how organisms use negative
feedback mechanisms to maintain their internal environments.
–
(2.19) The student is able to make predictions about how positive feedback
mechanisms amplify activities and processes in organisms based on scientific
theories and models.
–
(2.20) The student is able to justify that positive feedback mechanisms amplify
responses in organisms.
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Negative feedback mechanisms maintain dynamic homeostasis for a
particular variable by regulating physiological processes, returning the
changing condition back to its target set point.
• Illustrative Examples Include:
–
Temperature Regulation in Animals
–
Plant Responses to Water Limitations
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Temperature Regulation in Animals
http://bcs.whfreeman.com/thelifewire/content/chp41/41020.html
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Plant Responses to Water Limitations
http://www.phschool.com/science/biology_place/labbench/lab9/guard.html
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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.
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Lactation in Mammals
http://bcs.whfreeman.com/thelifewire/content/chp42/4202s.swf
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Onset of Labor in Childbirth
http://www.johnwiley.net.au/highered/interactions/media/Foundations/content/Foundations/homeo4a/bot.htm
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Ripening of Fruit in Plants
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Alteration in the mechanisms of feedback often
results in deleterious consequences.
• Illustrative examples include:
– Diabetes mellitus in response to decreased
insulin.
– Grave’s disease (hyperthyroidism).
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Maintenance of Glucose Homeostasis
http://bcs.whfreeman.com/thelifewire/content/chp50/5002002.html
Body cells
take up more
glucose.
Insulin
Beta cells of
pancreas are stimulated
to release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Rising blood glucose
level (for instance, after
eating a carbohydraterich meal)
Blood glucose level
declines to set point;
stimulus for insulin
release diminishes.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes.
Figure 45.12
Liver breaks
down glycogen
and releases
glucose into
blood.
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STIMULUS:
Dropping blood glucose
level (for instance, after
skipping a meal)
Alpha cells of pancreas
are stimulated to release
glucagon into the blood.
Glucagon
Diabetes Mellitus
http://www.dnatube.com/video/2792/Animation-about-diabetes-and-the-body
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Thyroid Hormone: Control of Metabolism & Development
http://www.biologyinmotion.com/thyroid/index.html
• The hypothalamus and anterior
pituitary control the secretion
of thyroid hormones through
two negative feedback loops:
–
The hypothalamus secretes TSHreleasing hormone (TRH), which
stimulates the anterior pituitary to
secrete thyroid-stimulating hormone
(TSH).
–
TSH then stimulates the thyroid gland
to synthesize and release the thyroid
hormones T3 and T4.
–
These hormones exert negative
feedback on the hypothalamus and
anterior pituitary by inhibiting the
release of TRH and TSH.
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Graves’ Disease
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BIG IDEA II
Biological systems utilize free energy and molecular building blocks
to grow, to reproduce and to maintain dynamic homeostasis.
Enduring Understanding 2.C
Organisms use feedback mechanisms to regulate growth and
reproduction, and to maintain dynamic homeostasis.
Essential Knowledge 2.C.2
Organisms respond to changes in their external environments.
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Essential Knowledge 2.C.2: Organisms respond to
changes in their external environments.
• Learning Objectives:
– (2.21) The student is able to justify the selection of
the kind of data needed to answer scientific questions
about the relevant mechanisms that organisms use to
respond to changes in their external environments.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Organisms respond to changes in their environments
through behavioral and physiological mechanisms.
• Illustrative examples include:
– Photoperiodism and phototropism in plants
(physiological response)
– Shivering and sweating in humans (physiological
response) – WATCH BOZEMAN VIDEO #19!
– Taxis and kinesis in animals (behavioral response)
– Chemotaxis in bacteria (behavioral response)
– Hibernation and migration in animals (behavioral
response) – WATCH BOZEMAN VIDEO #19!
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Response & Natural Selection in Plants
• Response to information and communication
of information are vital to natural selection in
plants.
– In phototropism, changes in the light source
lead to differential growth, resulting in maximum
exposure of leaves to light for photosynthesis.
– In photoperiodism, changes in the length of
night regulate flowering and preparation for
winter.
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Phototropism and Photoperiodism in Plants
• In plants, physiological events involve interactions
between environmental stimuli and internal
molecular signals (hormones).
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Early Experiments on Phototropism
EXPERIMENT In 1880, Charles Darwin and his son Francis designed an experiment to determine
what part of the coleoptile senses light. In 1913, Peter Boysen-Jensen conducted an experiment to
determine how the signal for phototropism is transmitted.
RESULTS
Control
Boysen-Jensen (1913)
Darwin and Darwin (1880)
Shaded
side of
coleoptile
Light
Light
Light
Illuminated
side of
coleoptile
Tip
removed
Tip covered
by opaque
cap
Tip
covered
by transparent
cap
Base covered
by opaque
shield
Tip separated
by gelatin
block
Tip separated
by mica
CONCLUSION In the Darwins’ experiment, a phototropic response occurred only when light could
reach the tip of coleoptile. Therefore, they concluded that only the tip senses light. Boysen-Jensen
observed that a phototropic response occurred if the tip was separated by a permeable barrier (gelatin)
but not if separated by an impermeable solid barrier (a mineral called mica). These results suggested
that the signal is a light-activated mobile chemical.
Figure 39.5
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Fig. 39-8
Auxin
Cross-linking
polysaccharides
3 Expansins separate
Cell wall–loosening
enzymes
microfibrils from crosslinking polysaccharides.
Expansin
CELL WALL
4 Cleaving allows
microfibrils to slide.
Cellulose
microfibril
H2O
2 Cell wall
Plasma
membrane
becomes
more acidic.
Cell
wall
1 Auxin
increases
proton pump
activity.
Plasma membrane
Nucleus
Cytoplasm
Vacuole
CYTOPLASM
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5 Cell can elongate.
Photoperiodism and Responses to Seasons
Like all of us, plants have a biological clock that
maintains a circadian rhythm – a physiological
cycle that occurs in time increments roughly
equivalent to the length of one day.
Because plants are dependent on light, they
must be able to survive varying conditions of
light. This is achieved by photoperiodism –
the response by a plant to the change in the
length of days.
Flowering in plants is an example of
photoperiodism. A hormone known as florigen
is thought to assist in the blooming of flowers.
An important pigment to the process of
flowering is phytochrome, which is involved in
the production of florigen.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Photoperiodism and Responses to Seasons
Because plants differ in the conditions required for flowering to occur, different
amounts of florigen are needed to initiate this process from plant to plant.
Short Day Plants and Long Day Plants flower only if certain requirements are met:
PLANT TYPE
EXAMPLE
FLOWERING
REQUIREMENTS
FLOWERS
DURING
Short-Day
Poinsettias
Exposure to a night
LONGER than a certain
number of hours (i.e. 10
hours)
End of summer to
end of winter
Long-Day
Spinach
Exposure to a night
SHORTER than a certain
number of hours (i.e. 8
hours)
Late spring to
early summer
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Shivering & Sweating in Humans
http://education-portal.com/academy/lesson/homeostasis-and-temperature-regulation-in-humans.html#lesson
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Taxis and Kinesis in Animals
• Environmental cues not only trigger some
simple behaviors in animals, but also
provide stimuli that animals use to change
or orient both simple and complex
movements in a particular direction.
– Kinesis: a change in activity or turning rate in
response to a stimulus.
– Taxis: an oriented movement toward (positive)
or away from (negative) some stimulus.
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Kinesis
Dry open
area
Sow
bug
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Moist site
under leaf
Taxis
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Chemotaxis in Bacteria
http://www.evolutionnews.org/2013/05/visualizing_che071811.html
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Oriented Movement: Migration
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Nocturnal & Diurnal Activity
• Nocturnal activity is an animal behavior
characterized by activity during the night
and sleeping during the day.
• Diurnal animals, such as squirrels and
songbirds, are active during the daytime.
• Many times, these cycles are of adaptive
value to the organism.
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Animal Dormancy
• Torpor: a DAILY FLUCTUATION in physiological state in which
activity is low and metabolism decreases; an adaptation that
enables animals to save energy while avoiding difficult and
dangerous conditions (these organisms are easily awakened)!
• Hibernation: (winter dormancy) - a long-term physiological
state in which metabolism decreases, the heart and
respiratory system slow down, and body temperature is
maintained at a lower level than normal during winter
months.
• Estivation: (summer dormancy) - a physiological state in
which metabolism decreases, the heart and respiratory
system slow down, and body temperature is maintained at a
lower level than normal during summer months.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings