1. Syllabus Point 1d,e,f HOMEOSTASIS The process by which organisms maintain a relatively stable internal environment.

2. The importance of a constant internal environment Living organisms are made of cells which must function efficiently to maintain life. All chemical reactions in cells must be coordinated to bring about optimal efficiency. Chemical reactions are driven by enzymes.

3. Cells are extremely sensitive to changes in their internal environment and any imbalance adversely affects their functioning.

4. The internal environment of an organism must be maintained within a narrow range of conditions (e.g. temperature). So that the enzymes can function effectively and metabolic efficiency can be maintained. Enzymes are very sensitive to temperature and pH of the environment and changes in these effects their activity.

5. shiveringshivering

6. Homeostasis

7. thirsty

8. Living organisms are made of cells which must function efficiently to maintain life.All chemical reactions in cells must be coordinated to bring about optimal efficiency. Chemical reactions are driven by enzymes.Cells are extremely sensitive to changes in their internal environment and any imbalance adversely affects their functioning.

9. sweating panting fast breathing

10. HOMEOSTASIS A state of balance, conditions stay the same, despite fluctuations in the external environment. The maintenance by an organism of a constant or almost constant internal environment regardless of external environmental change.

11. Consider a hospital: Needs to run smoothly despite sudden external changes.

15. Explain that homeostasis consists of two stages: detecting and counteracting In order for organisms to survive they must be able to detect information from their internal and external environments. Any information which provokes a response is called a stimulus. Receptors in the body detect changes.

16. 1e. explain that homeostasis consists of two stages: detecting changes from the stable state counteracting changes from the stable state

17. HOMEOSTASIS CONSISTS OF TWO STAGES 1.Detecting changes from the stable state This is where the receptors detect the change from the internal and external environments. Any information which provokes a response is called a stimulus. Receptors in the body detect changes. 2.Counteracting changes from the stable state. This is where the effectors counteracts the change from the stable state with an appropriate response.

18. Stimulus Light Heat and Cold Sound, touch, pressure and gravity Oxygen, CO 2, water, pH and wastes Type of Receptor Chemoreceptor Photoreceptor Thermoreceptor

19. 2.Counteracting changes from the stable state. Organisms respond to the change. Responses are brought on about effectors, these may be muscles or glands. Organisms use a control centre to coordinate a response.

20. Outline the role of the nervous system in detecting and responding to environmental changes The nervous system has receptors in the sense organs to detect changes in the external environment. For example: There are receptors in the skin to detect the increase/decrease in external temperature. The brain co-ordinates the appropriate action to maintain homeostasis.

21. Stimulus-Response Pathway Stimulus  Receptor  Control center  Effector  Response Stimulus – Any information that provokes a response eg, hot, cold, light Receptor – an organ or other part of body which receives a stimulus and transmits it to the organisms control center. eg thermoreceptors in the skin detect temperature changes Control Center – The Brain ( hypothalamus) Effector – organs/tissues which are responsible to bring about a response. Response – Body adjusts temperature back to normal. This is an example of negative feedback where the effect of the stimulus is reduced.

27. What is Negative Feedback? Negative feedback means that whenever a change occurs in a system, this automatically causes a corrective mechanism to start, which reverses the original change and brings the system back towards the set point (the constant value). This means the bigger the change, the bigger the corrective mechanism!

30. 1f. Outline the role of the nervous system in detecting and responding to environmental changes

31. The Nervous System The control centre of the body.

32. The Nervous System Consists of the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). The CNS consists of the brain and spinal cord (Control Centre) and the PNS consists of the sensory nerves and the effector nerves.

33. At which points would you find: a) the CNS b) the PNS

34. When the environmental temperature begins to exceed a comfortable level for the body, temperature sensors in the skin detect the temperature change and a sensory neuron conducts a nervous impulse to the hypothalamus found in the brain.

35. Nerve impulses pass this information from the receptors to effector neurons then onto effectors, such as blood vessels, sweat glands, endocrine glands and muscles.

36. a)Homeostasis is the process by which cells maintain their internal environment b)Homeostasis is the maintenance of the internal and external environment of the organism c)Homeostasis is the process by which animals and plants maintain their body temperature d)Homeostasis is the maintenance of a constant internal environment of the organism Which statement defines homeostasis in multicellular organisms?

37. Something to think about? What would you do if you were unable to maintain your internal environment by corrective mechanisms? Would it be possible to survive?