Understanding Communication and Homeostasis in Living Organisms

1. Unit 1 Communication, Homeostasis and Energy Communication

2. Test Yourself • What effect does temperature change have on enzyme action? • What other environmental factors inhibit the action of enzymes? • List three changes to the external environment to which we might need to respond. • What is the main role of the • Heart • The lungs • The kidneys

3. Keep testing yourself • What is meant by cell signalling? • In what other process in the body is cell signalling particularly important? • Explain the role of cell surface receptors in cell signalling.

4. Learning Outcomes • Outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the internal and external environment and to coordinate the activities of different organs.

5. Key words • Sensitivity • Stimulus • Internal communication • Plants • Animals • Receptor • Effector

6. The need for a constant internal environment • All living things need to maintain a certain limited set of conditions inside their cells. • Why?

7. The need for a constant internal environment • Cellular activities rely on the action of enzymes • Specific limited set of conditions • Suitable temperature • Suitable pH • Aqueous environment • No toxins / inhibitors

8. External environments • As the external environment changes it places stress on the living organism. • The environmental change is a stimulus and the way in which the organism changes its behaviour or physiology is its response to the stress.

9. Definitions • Stimulus • Any change in environment that causes a response • Response • A change in behaviour or physiology as a result of a change in the environment.

10. Learning outcomes • State that cells need to communicate with each other, which they do by a process called cell signalling. • State that neuronal and hormonal systems are examples of cell signalling

11. Internal Environments • The internal environment of the cells in animals is tissue fluid. • Activity of the cell alters its environment • Use up substrates • Produce products, some of which may be toxic • Accumulation of excess waste acts as a stimulus to cause the removal of these wastes

12. Maintaining internal environment • Summary • Composition of the tissue fluid is maintained by the blood • Wastes accumulating in tissue fluid enter the blood • Excretion prevents the accumulation of wastes in the blood • Concentrations of all substances in the blood are monitored

13. Coordination • In a multicellular organism cells become differentiated (specialised) forming tissues and organs. • A good communication system is required • List the features of a good communication system

14. Good communication system • Whole body • Cell communication • Specific • Rapid • Short term and long term

15. Cell signalling • How cells communicate with each other • The neuronal system and the hormonal system work by cell signalling.

16. Learning Outcomes • define the terms negative feedback, positive feedback and homeostasis; • explain the principles of homeostasis in terms of receptors, effectors and negative feedback;

17. Homeostasis • Maintaining a constant internal environment despite external changes • Examples • Body temperature • Blood glucose concentrations • Blood salt concentration • Water potential of blood • Blood pressure • Carbon dioxide concentration

18. Negative feedback • Reversal of any change in internal environment to return to an optimum steady state.

19. Negative Feedback Optimum condition Change away from optimum Receptor detects change Return to optimum conditions Effector reacts to reverse change Communication system informs effector

20. Negative feedback • Structures required for pathway to work • Sensory receptors • Communication system • Effector cells

21. Examples of Negative feedback • Control of room temperature • Control of body temperature • Control of blood glucose levels • Control of body water concentration

22. Positive Feedback • Increases any change that is detected by receptors • Does not lead to homeostasis

23. Positive Feedback Optimum condition Change away from optimum Receptor detects change Effector reacts to increase change Communication system informs effector

24. Examples of positive feedback • If core temperature drops too low • Dilation of the cervix at the end of pregnancy

25. Stretch and Challenge • Enzyme action and temperature regulation • As core body temperature rises the increase will affect the activity of enzymes. This can lead to heat exhaustion and even death. • Describe the effect of increasing body temperature on enzyme action. • Suggest what actually causes death as body temperature rises.

26. Answers • Temperature increase – rate of enzyme action increases • 10oC increase will double the rate of reaction • Above 50oC enzymes denature – rate of reaction falls quickly • Death

27. Stretch and challenge • The stress response • The usual response to stress is to release the hormone adrenaline. This hormone has a wide range of target cells and prepares the body for activity. The activity may be to stay and fight or it may be to run away. The hormone is known as the “fight or flight” hormone.

28. Stretch and challenge • The stress response • When under stress women also release the hormone oxytocin. This results in a tendency to pacify or protect. It has been called the “tend and befriend” hormone. Oxytocin prompts a mother to protect her children.

29. Stretch and challenge • Suggest how these responses to adrenaline and oxytocin may have evolved.

30. Learning Outcome • describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms

31. Maintaining body temperature • Changes in body temperature affects the structure of proteins • Endotherms • Maintain body temperature within strict limits • Independent of external temperature • Ectotherms • Body temperature fluctuates with external temperature

32. Ectotherms • Advantages • Use less food in respiration • Need less food • Greater proportion energy used for growth • Disadvantage • less active in cooler temperatures • May not be capable of activity in winter months

33. Temperature regulation in ectotherms • Increasing the heat exchange with their environment • Expose body to sun • Orientate body to sun • Orientate body away from sun • Hide in burrow • Alter body shape • Increase breathing movements

34. Student Activity • Design an A4 poster to summarise behavioural and physiological adaptions of ectotherms for temperature regulation.

35. Stretch and challenge • Temperature regulation in bee swarms • Bees are ectothermic. • However, it has been shown that the temperature of a bee swarm can be maintained accurately to within one degree of 35oC. • This is achieved by bees moving to different parts of the swarm and by allowing passages for air flow through the swarm.

36. Question • Suggest how movement of bees within a swarm and air movement through the swarm can help to maintain the temperature of the swarm.

37. Answer • Bees in the centre of the swarm will be warmer than those on the outside. • Warmer bees move towards the outer parts of the swarm while colder bees move toward the centre. • This transfers heat from the centre to the outer parts of the swarm.

38. Answer • In hot weather the bees create more passages for air flow; the passages are also wider • Thus more air can pass through the swarm and carry heat away. • In cooler weather there are fewer air passages and they are narrower.

39. Quick Questions • Why is it important to maintain body temperature? • Make a list of 5 ectotherms • Explain how basking on a hot rock in the sun can help an ectotherm to regulate its body temperature.

40. Learning Outcome • describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms and endotherms, with reference to peripheral temperature receptors, the hypothalamus and effectors in skin and muscles

41. Endotherms • Use internal sources of heat to maintain body temperature • Many chemical reactions in the body are exergonic • Endotherms also show behavioural and physiological adaptations

42. Endotherm Advantages disadvantages Energy used up to maintain constant temp. More food required Less energy used in growth • Constant body temp. • Activity possible even when cool • Inhabit colder parts of planet

43. Physiological Adaptations

44. Behavioural adaptations Too hot Too cold Move into sunlight Increase exposed surface area Move about to generate heat in muscles Extreme cold – roll into a ball to decrease surface area • Move into shade • Decrease exposed surface area • Remain inactive / increase surface area

45. Change in core temperature Thermoregulatory centre in hypothalamus detects change. Nervous and hormonal systems carry signals to skin, liver and muscles Fall in core temperature Rise in metabolic reactions Release more heat from exergonic reactions Release heat through muscle contractions Decrease loss of heat, temperature rises

46. Control of body temperature Skin temperature External Core Temperature HYPOTHALAMUS Thermoregulatory centre • TOO COLD • Shivering • Increased metabolism • Vasoconstriction • Reduced sweating • Skin hairs erected • TOO HOT • Reduce metabolism • Vasodilation • increased sweating

47. Detecting changes in body temperature • Thermoregulatory centre in the Hypothalamus • Monitors blood temperature • Detects changes in core temperature • Peripheral temperature receptors • “early warning” system • Detect changes in temperature of the extremities • Sends signals to the brain to initiate behavioural mechanisms to maintain core temperature.

48. Stretch and challenge • Should mountain rescue dogs carry brandy? • In early part of the twentieth century St Bernard dogs were used for mountain rescues. • Traditionally they carried a small container of brandy for the lost or injured climber to drink. • Alcohol causes vasodilation.

49. Question • Explain why drinking brandy is not a good idea for someone who is lost or injured and exposed to cold weather.

50. Answer • If the climber is unable to find shelter, the low temperature could reduce the body temperature to the point where enzyme activity is severely reduced. • Vasodilation caused by the alcohol in the brandy will increase the rate of heat loss from the body, because more blood carries heat from the body’s core to the surface where it can be lost. • Hypothermia and death will happen sooner in a person who has drunk alcohol.