Syllabus Edition

First teaching 2023

First exams 2025

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Homeostasis: Maintaining the Internal Environment (SL IB Biology)

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Naomi H

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Naomi H

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Maintaining the Internal Environment

  • The process of maintaining a constant internal environment is known as homeostasis
  • Homeostasis ensures that conditions inside the body are kept within preset limits
  • Homeostasis is critically important for organisms as it ensures the maintenance of optimal conditions for enzyme action and cell function
  • Sensory cells can detect information about the conditions inside and outside the body; if conditions have changed then the body can respond to keep conditions constant
  • Examples of physiological factors that are controlled by homeostasis in mammals include
    • Core body temperature
    • Blood pH
    • Concentration of glucose in the blood
    • Osmotic concentration of the blood

Negative Feedback Loops

  • The majority of homeostatic control mechanisms in organisms use negative feedback loops to achieve homeostasis
  • Negative feedback mechanisms work to return values to a set point; they reverse the effects of any change within a system
    • Negative feedback loops are essential for maintaining conditions within set limits; this is not the case in positive feedback mechanisms which instead amplify any change
  • Negative feedback control loops involve:
    • A receptor – receptor cells detect change in a physiological factor
    • A coordination system – the brain and nervous system transfer information between different parts of the body
    • An effector – the muscles and glands bring about a response
  • Outcome of a negative feedback loop:
    • The factor / stimulus is continuously monitored
    • If there is an increase in the factor, the body responds to make the factor decrease
    • If there is a decrease in the factor, the body responds to make the factor increase

Negative feedback loops maintain conditions to a set point

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Naomi H

Author: Naomi H

Expertise: Biology

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.