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Unit 5 Lesson 1 Homeostasis and Behavior
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Unit 5 Lesson 1 Homeostasis and Behavior
Oh, Behave!
What is behavior?
• A stimulus is anything that causes a reaction or
change in an organism.
• A response is an organism’s reaction to a
stimulus.
• A set of actions taken by an organism in response
to a stimulus is called a behavior.
• Homeostasis is maintaining a stable balance in
the body.
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Unit 5 Lesson 1 Homeostasis and Behavior
How are stimuli detected?
• Multicellular organisms have sensory cells in their
bodies that detect specific stimuli.
• Sensory receptors are found in sensory organs.
Sensory organs include eyes, noses, skin,
whiskers, and ears.
• Sensory receptors are sensitive to changes in
specific stimuli.
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Unit 5 Lesson 1 Homeostasis and Behavior
Where do responses come from?
• When an animal’s sensory receptors detect
stimuli, they send messages along the nervous
system.
• Responses are also caused by hormones. A
hormone is a chemical signal produced in one
part of an organism that affects cell activity in
another part of the organism.
• Hormones move more slowly than electrical
signals. An organism’s response is usually the
result of the action of both hormones and
electrical signals.
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Unit 5 Lesson 1 Homeostasis and Behavior
Outside Influence
What is an external stimulus?
• An external stimulus is any stimulus that comes
from outside the body of an organism and that
influences the behavior of the organism.
• Taxis is the movement of organisms toward or
away from an external stimulus. An organism
shows positive taxis when it moves toward a
stimulus.
• An organism shows positive taxis when it moves
toward a stimulus.
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Unit 5 Lesson 1 Homeostasis and Behavior
What is an external stimulus?
• Tropism is the movement of a plant in response
to an external stimulus, such as light or gravity.
• Phototropism is a plant’s response to light.
• Geotropism is a plant’s response to gravity.
• Roots show positive geotropism because they
grow in the direction of gravity.
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Unit 5 Lesson 1 Homeostasis and Behavior
What is an internal stimulus?
• An internal stimulus is a stimulus that comes from
inside an organism’s body. Hunger and thirst are
internal stimuli that influence behavior.
• Certain responses to internal stimuli, such as the
gradual change during insect metamorphosis or
puberty in humans, are controlled by hormones.
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Unit 5 Lesson 1 Homeostasis and Behavior
I Will Survive!
How does homeostasis work?
• To maintain homeostasis, organisms must
constantly respond to external and internal
stimuli.
• Homeostasis responses allow individual cells and
complete body systems to function properly.
• If the body cannot maintain homeostasis, illness
or disease may occur.
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Unit 5 Lesson 1 Homeostasis and Behavior
What are some behaviors that improve
survival?
• Maintaining homeostasis allows an organism’s
body to function well, but to survive, organisms
need to avoid predators and find food and space
to live.
• Other behaviors such as finding a mate,
reproducing, and raising young help with the
overall survival of a species.
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Unit 5 Lesson 1 Homeostasis and Behavior
What are some behaviors that improve
survival?
• When faced with a threatening stimulus such as a
predator or natural disaster, organisms display
they fight-or-flight response.
• This response is characterized by changes such as
an increased heart rate, anxiety, decreased blood
supply to certain muscles, and a release of
hormones and other chemicals in the body.
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Unit 5 Lesson 1 Homeostasis and Behavior
What are some behaviors that improve
survival?
• Hunger is an internal stimulus that affects the
behavior of an animal.
• Searching for food becomes increasingly
important as the hunger stimulus grows.
• A positive result to a food-seeking response
enhances the survival of an animal.
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Unit 5 Lesson 1 Homeostasis and Behavior
What behaviors help animals survive
environmental changes?
• Animals that live in environments where it is
difficult to survive year-round will move to
environments where conditions are more
favorable for survival. This movement is called
migration.
• Migration helps animals to avoid harsh conditions
that can come with seasonal changes.
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Unit 5 Lesson 1 Homeostasis and Behavior
What behaviors help animals survive
environmental changes?
• A deep sleep during which an animal slows down
its body processes to save energy is called
hibernation.
• The animal’s heart rate rate, body temperature,
and nutritional needs are lowered so that energy
is conserved during periods of unsuitable weather
or food shortage.
• When internal processes slow down during hot,
dry weather, it is called estivation.
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Unit 5 Lesson 1 Homeostasis and Behavior
What behaviors help plants survive
environmental changes?
• Unlike animals, plants cannot move to another
location to avoid harsh conditions. Instead, plants
maintain homeostasis and conserve energy in
other ways.
• Some plants have specialized structures, such as
bulbs, to store food.
• During dormancy, a plant conserves energy and
stops growing.
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Unit 5 Lesson 1 Homeostasis and Behavior
White-Nose Syndrome
• White-nose syndrome is a disease caused by the
fungus Geomyces destructans. It kills bats by
disrupting their hibernation.
• It is possible that humans exploring the caves
where bats hibernate may pick up the fungus on
their equipment and carry it to another cave.
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