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1. Levels of Biological Organisation

1. Levels of Biological Organisation. An introduction to homeostasis. 2. How homeostasis works. The role of feedback systems. Homeostasis: . A definition: the maintenance of a stable internal environment despite fluctuations in the external environment. Components of homeostasis.

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1. Levels of Biological Organisation

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  1. 1. Levels of Biological Organisation An introduction to homeostasis

  2. 2. How homeostasis works The role of feedback systems

  3. Homeostasis: • A definition: • the maintenance of a stable internal environment despite fluctuations in the external environment

  4. Components of homeostasis • A system requires three components for homeostasis: • - A receptor; • - A control centre; • - An effector. • These components do specific jobs that allow regulation of the internal environment.

  5. Feedback systems • May be negative or positive • Discuss how these devices work: • A toilet cistern when you flush • A hot water cylinder when you run the shower

  6. What upsets the balance? • Various factors apply stress on the internal environment: • Internal factors - within the body, eg pain, high or low blood pressure • External factors - outside the body, eg extremes of temperature

  7. negative feedback... causes the system to respond to reverse the direction of change. .. which tends to keep things constant… so it allows the maintenance of homeostasis. eg, if there is a fall in calcium in the blood, the parathyroid glands sense the decrease and secrete more parathyroid hormone, thereby increasing calcium release from the bones;

  8. Negative feedbackin incubator Temperature sensor Heater (switched off) Thermostat system with switch • temperature • Temp too high • Temp too low Temp fallsi Rise in Incubator temperature at 32 C Temp risesi Temperature sensor Thermostat system with switch Heater (switched on)

  9. Negative feedbacka fridge Temperature sensor cooling (switched off) Thermostat system with switch • Fall in Drop in temperature Rise in temperature Fridge temperature varies to setting C Drop in temperature Rise in temperature Temperature sensor Thermostat system with switch cooling (switched on)

  10. Positive feedback… • increases the variable in the same direction… • a destabilising effect that does not result in homeostasis. • Positive feedback is used when rapid change is needed. • eg in childbirth the hormone oxytocin is produced to stimulate and enhance labour contractions • eg clotting mechanism when skin is cut

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