9.1-9.3

• What must organisms be able to monitor in their environment?

  Both internal and external changes
• How do organisms survive changes in their environment?

  Through anatomical, physiological, and behavioural adaptations
• What is homeostasis?


  Maintenance of a constant internal environment
• What is the role of homeostasis in organisms?

  To ensure that all metabolic reactions occur at a rate that ensures survival
• What does irritability refer to in living organisms?

  The ability to detect and respond to changes in the environment
• What occurs during coordination in organisms?

  Different body parts work together to maintain homeostasis
• What is a stimulus?


  A detectable change in the environment
• How do cells detect changes in the environment?

  By using molecules that change due to the stimulus
• What are the different roles of specialized cells in response to stimuli?

  Some receive external stimuli, others send/receive signals, and some determine if changes are needed for homeostasis
• What is the role of receptors in sensory organs?


  To detect input from the environment
• What happens after a chemical message is transmitted to a coordinating center?

  The regulator determines if a change is required
• What occurs if a change is required after a chemical message is received?

  Another chemical message brings about a response within an effector organ
• What do plants release when an appropriate stimulus acts on them?

  A chemical transmitter (hormone)
• How is the efficiency of the animal control system measured?

  By the displacement from the optimal level and the speed at which it is restored
• What activates the control system in response to fluctuations from the set point?


  Fluctuations from the set point activate the control system
• What are the two types of feedback in biological systems?

  Positive feedback and negative feedback
• How does positive feedback differ from negative feedback?

  Positive feedback continues the same response, while negative feedback reverses it
• What is the relationship between the effector's response and the original stimulus in most systems?

  The effector's response typically removes the original stimulus
• What are the two coordinating systems in multicellular animals?

  The nervous system and the hormonal (endocrine) system
• What are hormones?


  Chemical messengers produced in small quantities to regulate cell and organ activity
• What are the three ways a hormone may effect a change?

  Autocrine, paracrine, and endocrine hormones
• How do autocrine hormones function?

  They bind to receptors in the same cell that produced them
• What is the function of paracrine hormones?

  They bind to receptors on neighbouring cells
• How do endocrine hormones operate?

  They travel long distances through the blood supply to reach target cells
• What are pheromones?


  Hormones that act over a distance
• How is input from the external environment relayed to hormone-excreting cells?

  Via the nervous system in most animals
• How do hormone-secreting cells respond to changes?

  They respond directly to changes in their immediate internal environment
• What must be activated for a cell to respond to a stimulus?

  A signal transduction pathway must be activated
• What happens when a hormone binds to its specific receptor?

  The receptor rearranges its shape
• What do secondary messenger molecules do in response to a hormone?

  They cause changes in chemical pathways throughout the cell
• What are some responses to a hormone message?


  Activating or inactivating enzymes, exocytosis of molecules, switching genes on or off, and opening or closing protein channels
• How is the type of receptor on a cell's surface determined?

  By DNA
• What is down-regulation in terms of cell receptors?

  When fewer receptors are present, reducing the cell's sensitivity to signals
• What is up-regulation in terms of cell receptors?

  When more receptors are synthesized to increase the cell's sensitivity to a weak signal
• What are some structures specialized to respond to stimuli?

  Nerve endings, sense organs, mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, and nociceptors
• Where are hormones produced in mammals?

  In ductless endocrine glands
• How do endocrine organs function?

  They do not work in isolation; many hormones interact to bring about a response
• What stimuli control the release of hormones?

  The presence of specific metabolites, other hormones, and stimulation by the autonomic nervous system
• How can a hormone influence a target cell?

  By changing membrane permeability, influencing enzymes, affecting organelles, or activating genes
• What role does the hypothalamus play in hormone regulation?

  It collects information from other parts of the brain and monitors hormone levels