Unit 4

• Biological components


  • Chromosomes
  • Chromatids
  • Cyto
  • Canis
  • Cyclin
  • CDKs
• Organisms have two types of feedback mechanisms: negative and positive
• Negative feedback


  Returns conditions back to normal range
• Positive feedback


  Sends conditions further past the normal range
• If the response reverses the stimulus


  The system is operating by negative feedback
• Negative feedback


  Often results in the stopping or slowing down of a process in order to return to a set point maintaining homeostasis
• Negative feedback examples


  • Maintaining body temperature
  • Keeping blood sugar levels constant
• Maintaining blood sugar levels

  1. Liver stores sugar as glycogen

  2. Glycogen converted to glucose when blood sugar is low

  3. Pancreas releases glucagon

  4. Pancreas releases insulin when blood sugar increases
• Positive feedback


  Mechanism that results in the amplification or growth of an output signal, moving the organism further past the set point disrupting homeostasis
• Positive feedback examples


  • Lactation in mammals
  • Ripening of fruit
• Positive feedback is a less common pathway but has specific circumstances for which greater change is necessary
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