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Animal Systems
Organization and Homeostasis
Which of these is the correct sequence
of levels of organization?
1. Organs -> cells ->
tissues -> organs
2. Cells -> organs ->
organ systems ->
tissues
3. Cells -> tissues ->
organs -> organ
systems
33%
1
33%
2
33%
3
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• Of all human body systems, which do
you think is most important. Discuss. Try
to explain your answer.
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Organization in Living Things
• Cells are organized into tissues
• Tissues are organized into organs
• Organs are organized into systems
• Systems form an organism
Four tissue types
• Epithelial
• Connective
• Nervous
• Muscular
Epithelial tissue
• Epithelial cells form
the outer covering,
line the internal
cavities, and make
up the glands.
• Examples: Skin,
mucous
membranes.
Connective tissue
• Consists of living
cells in a secreted
matrix.
• Examples: bone,
cartilage, blood.
Muscular tissue
• Specialized protein
fibers allow these
cells to contract.
• Examples: skeletal
muscle, smooth
muscle, cardiac
muscle.
Nervous tissue
• Neurons have the
ability to pass an
“electrical” signal
from one cell to
another, or to target
cells (muscles,
glands, organs).
Tissues form organs
• The skin is an
example of an
organ made up of
multiple tissues:
epithelial, muscular,
nervous, and
connective tissues.
A group of cells that perform a
similar function is know as:
25%
1.
2.
3.
4.
25%
25%
25%
Tissue
Organ
Organ system
Organism
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2
3
4
One cell type that must undergo
continual loss and replacement is:
25%
1.
2.
3.
4.
25%
25%
25%
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue
1
2
3
4
Which tissue type is in direct
contact with the environment?
25%
1.
2.
3.
4.
25%
25%
25%
Epithelial
Muscle
Nervous
Connective
1
2
3
4
Homeostasis
• Homeostasis is the act of keeping the
internal environment of a living organism
within an acceptable range of conditions.
• Homeostasis controls temperature, pH,
blood volume, oxygen levels, blood sugar
levels, and other conditions.
• Negative feedback maintains
homeostasis.
Negative Feedback
• Negative feedback keeps
conditions within an ideal
range.
• As conditions exceed the
limits of the ideal range,
chemical signals
(hormones) regulate
conditions. Most often this
is controlled by the
hypothalamus in the brain.
Positive Feedback
• Positive feedback
takes a condition out of
the normal range,
often to some end
point.
• During labor, oxytocin
increases contractions,
which stimulate more
oxytocin production,
until birth occurs.
Maintaining Temperature
• Ectotherms are animals
that derive body heat from
the environment. Their
body temperature may
vary widely.
• Endotherms rely on
metabolic reactions and
physiological systems to
maintain a steady body
temperature.
Maintaining Temperature
Blood Glucose Regulation
Body systems maintain homeostasis
through:
33%
33%
33%
1. Positive feedback
systems.
2. Negative feedback
systems.
3. Uncontrolled
feedback systems.
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3
True or false: “cold blooded” animals always
have a lower body temperature than “warmblooded” animals.
50%
50%
1. True
2. False
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2
• Why is positive feedback not a good way
to maintain homeostasis?
• What are some other examples of
positive feedback loops in the human
body?
• Why do young animals often have more
body fat than adults? How does this
maintain homeostasis?
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• Draw a negative feedback loop for blood
calcium regulation.
• Falling calcium level signals release of
parathyroid hormone from the
parathyroid glands. Calcium is
released from bones, increased uptake
by digestive system.
• Rising calcium level signals release of
calcitonin from the thyroid. Blood
calcium is taken up into bone tissue.
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