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Key Idea: Feedback mechanisms maintain a living system’s internal conditions within certain limits and mediate behaviors, allowing it to remain alive and functional even as external conditions change within some range.

Students are expected to know that:

  1. The need for energy during exercise causes the rate of cellular respiration in muscle cells to increase, providing more energy for motion and releasing more energy to the cells’ surroundings.
    1. The human circulatory system responds by dilating surface capillaries, increasing blood flow to the skin where energy can be transferred to the body’s surroundings.
    2. The human integumentary system responds by sweating, which cools the body down as it evaporates from the surface of the skin.
  2. As cellular respiration speeds up, cells use reactants glucose and oxygen faster and produce products carbon dioxide and water faster.
    1. The human digestive system responds by breaking down stored glycogen to glucose (in the liver) and releasing glucose into blood vessels for transport to muscles.
    2. The human respiratory system responds by increasing the breathing rate, allowing the organism to breath in oxygen faster and breath out carbon dioxide faster.
    3. The human circulatory system responds by increasing the heart rate, allowing it to pump blood carrying glucose and oxygen to body cells faster and carbon dioxide to lungs faster (and also to transfer energy faster from muscle cells to the skin).
Percent of students answering correctly (click on the item ID number to view the item and additional data)
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As the carbon dioxide level inside a person’s body increases, the person’s body responds by increasing its breathing rate to reduce the level of carbon dioxide.




To maintain a stable amount of glucose in the blood during exercise the body breaks down glycogen molecules into glucose molecules.



No misconceptions are associated with this idea in the selected project.