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Unit 5 Lesson 1 Homeostasis and Behavior Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company 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. Copyright © Houghton Mifflin Harcourt Publishing Company