Constant Internal Environment (OCR Gateway GCSE Biology)

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The Importance of Homeostasis

  • Homeostasis is the regulation of the internal conditions of a cell or organism
  • Some examples of these internal conditions include:
    • Water content (of an individual cell or of the body fluids of an organism)
    • Body temperature
    • pH
    • Blood pressure
    • Blood glucose concentration
  • It is important for an organism to respond to internal and external environmental changes whilst maintaining optimum internal conditions for enzyme action and healthy cell functions
  • If the homeostatic limits are exceeded, the organism may die

Control of homeostasis

  • Maintaining controlled conditions within the body is under involuntary (automatic) control
  • This means that the brain stem (or non-conscious part of the brain) and the spinal cord are involved in maintaining homeostasis – you don’t consciously maintain your body temperature or blood glucose level
  • These automatic control systems may involve nervous responses or chemical responses
  • All control systems include:
    • Cells called receptors, which detect stimuli (changes in the environment)
    • Coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors
    • Effectors (muscles or glands) which bring about responses which restore optimum levels

Negative Feedback

  • The majority of homeostatic control mechanisms in organisms use negative feedback to maintain homeostatic balance (ie. to keep certain physiological factors, such as blood glucose concentration, within certain limits)
  • 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
    • The system is restored to its original level
  • Negative feedback mechanisms are usually a continuous cycle of bringing levels down and then bringing them back up so that overall, they stay within a narrow range of what is considered ‘normal’

Negative feedback loop

A negative feedback control loop

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Ruth

Author: Ruth

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Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. She gained 10 years of teaching experience across the 3 key science disciplines and physical education. Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.