When a change occurs in an animal’s environment, an adjustment must be made. Even an animal that is apparently inactive is maintaining this homeostatic equilibrium. It is equilibrium because body functions are kept within specific ranges. It is dynamic because it is constantly adjusting to the changes that the body’s systems encounter. Homeostasis means to maintain dynamic equilibrium in the body. These changes might be in the level of glucose or calcium in blood or in external temperatures. Organisms use feedback mechanisms to regulate growth and reproduction, and to maintain dynamic homeostasis.Ģ.C.1 Organisms use feedback mechanisms to maintain their internal environments and respond to external environmental changes.ħ.2 The student can connect concepts in and across domain(s) to generalize or extrapolate in and/or across enduring understandings and/or big ideas.Ģ.16 The student is able to connect how organisms use negative feedback to maintain their internal environments.ĥ.3 The student can evaluate the evidence provided by data sets in relation to a particular scientific question.Ģ.17 The student is able to evaluate data that show the effect(s) of changes in concentrations of key molecules on negative-feedback mechanisms.Ħ.4 The student can make claims and predictions about natural phenomena based on scientific theories and models.Ģ.18 The student is able to make predictions about how organisms use negative-feedback mechanisms to maintain their international environments.Ģ.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.Ħ.1 The student can justify claims with evidence.Ģ.20 The student is able to justify that positive-feedback mechanisms amplify responses in organisms.Īnimal organs and organ systems constantly adjust to internal and external changes through a process called homeostasis-steady state. Big Idea 2īiological systems utilize free energy and molecular building blocks to grow, to reproduce, and to maintain dynamic homeostasis. A learning objective merges required content with one or more of the seven Science Practices. The AP ® Learning Objectives listed in the Curriculum Framework provide a transparent foundation for the AP ® Biology course, an inquiry-based laboratory experience, instructional activities, and AP ® exam questions. Information presented and the examples highlighted in the section support concepts outlined in Big Idea 2 of the AP Biology® Curriculum Framework. However, the loss of internal equilibrium due to positive feedback can be detrimental for example, a small area of damaged heart tissue can precipitate a heart attack which, in turn, damages even more cardiac muscle. There are fewer examples of positive feedback, but one is the onset of labor in childbirth when uterine contractions increase in strength with the secretion of oxytocin, another hormone. By comparison, positive feedback amplifies responses in the same direction, with the variable initiating the response moving the system even further away from the set point. For example, if you were to consume a dozen jelly donuts, your blood sugar level would rise, and your pancreas would release insulin, a hormone involved in the conversion of glucose to glycogen, thus returning your blood glucose level to its appropriate set point. Negative-feedback mechanisms result in slight fluctuations above and below the set point. Consequently, negative- and/or positive-feedback loops regulate homeostasis. You can probably hypothesize how your liver will respond if you eat a dozen jelly donuts! The failure to maintain homeostasis can be detrimental and can even cause death. Your blood glucose levels also remain fairly constant because the liver removes glucose from the blood and converts it to glycogen when the body cells require glucose, glycogen is broken down. If your temperature climbs above the set point, you sweat to cool off if your temperature drops below the set point, you shiver to warm up. For example, as an endotherm, your body temperature remains fairly constant around 37 ☌ or 98.6 ☏. Animals must be able to maintain homeostasis-the ability to maintain dynamic equilibrium around a set point-while also being able to respond to changing conditions.
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