1. Communication and Homeostasis
A2 Biology F214

2. Why do multi cellular organisms need communication systems?
Organisms need to detect changes in their external environment eg: pressure on skin, light, sounds, temperature, chemicals etc. The receptor cells need to signal these changes to the organism so it can respond and maintain its safety.

3. Why do multi cellular organisms need communication systems?
Organisms need to detect changes in internal environments such as temp, pH, water potential of blood , tissue fluid, level of toxins, etc as these can affect the ability of cells to function efficiently. Enzymes, dehydration, lack of respiratory substrate, toxins inhibiting metabolism, etc.

4. Why do multi cellular organisms need communication systems?
Organs work together to maintain a constant internal environment with different organs having different functions. These functions have to be co-ordinated to keep the environment constant (Homeostasis)
Pancreas, liver, muscles, digestive system organs are all used to maintain blood glucose levels.

5. Why do multi cellular organisms need communication systems?
Cell Signalling: one cell releases a chemical that is detected by another cell. The second cell may respond to the chemical signal in any of a large number of ways depending on the type of cell and the chemical stimulus recieved.

6. Cells signal using hormones (the Endocrine system) that travel in the blood stream and are picked up by their target cells. The endocrine system enables long-term responses.

7. Why do multi cellular organisms need communication systems?
Nerve impulses are transmitted by neurone networks across synapses using neurotransmitters. This allows fast signalling and responses to rapidly changing stimuli.

8. Write a definition and give some examples
Homeostasis
What does it mean?
Write a definition and give some examples

9. Homeostasis
A system of monitoring and adjustment to keep conditions within safe limits

10. Homeostasis
Monitoring Controlling Internal conditions To keep them constant (or within safe limits) Despite external changes
Egs
temperature
blood glucose levels
blood salt concentration
relative water potential of blood, tissue fluid and cells, pH
Blood pressure
CO2 levels

11. Negative and Positive Feedback What’s the difference?

12. Can you complete this with some real life examples?
Negative Feedback
Can you complete this with some real life examples?

13. Stretch and challenge questions
Remember Stretch and challenge is about making synoptic links
You need to access information from previous work and use it in your explanations in this module.
In the questions asked you need to use information from the sections on enzymes and natural selection.

14. Homeostasis and Controlling Body Temperature
Learning Outcomes
Describe the physiological and behavioural responses that maintain a constant body temperature in Ectotherms and Endotherms.
In Endotherms refer to the role of peripheral temperature receptors, Hypothalamus and effectors in the skin and muscles

15. What is an Ectotherm? How does an Ectotherm control its body temperature?
Write down as many different ways that you can think of.
Complete the card sort to see how different Ectotherms deal with regulation of temperature

16. Control of temperature
Ectotherms
Seek sun or shade depending on outside temperature
Expose more or less body surface to sun
Alter body shape to change surface area
Increase breathing movements to evaporate more water

17. What is an Endotherm? How does an Endotherm control its body temperature?
Write down as many different ways that you can think of.

18. Control of temperature
Endotherms
Sweating
Panting
Piloerection
Vasodilation /vasoconstriction
Metabolic rate in liver
Shivering
Seek sun or shade
Alter orientation of body
Alter activity level

19. Diagram to show changes to skin surface blood vessels in warm and cold conditions.

21. What are the Advantages and Disadvantages of Endothermy and Ectothermy?

22. Sensory Receptors and Stimuli
Match the stimulus, sense and receptors in the card sort activity

23. Sensory Receptors, Senses and Stimuli
Eye
Rods and cones (light sensitive cells)
Light intensity (rods) and wavelength (cones)
Nose
Olfactory cells lining inner surface of nasal cavity
Presence of volatile chemicals
Tongue
Taste buds in tongue, hard palate, epiglottis and first part of oesophagus
Presence of soluble chemicals
Skin
Pacinian corpuscles (pressure receptors)
Pressure on skin
Ear
Sound receptors in cochlea (inner ear)
Vibrations in air
Muscle
Proprioceptors (stretch detectors)
Length of muscle fibres

24. Labelling Neurone Diagrams
Use these terms to label the diagrams you have been given.
Axon - specialised to conduct the action potential away from the cell body
Axon terminals – release neurotransmitter to signal to other cells
Dendrites- extend from cell body and receive neurotransmitter from axon terminals of other neurones
Cell body- contains nucleus, mitochondria, ribosomes
Axon Hillock - point at which the chemical signal received may reach the threshold needed to produce an action potential
Myelin sheath-insulating fatty layer composed of Schwann cells
Nodes of Ranvier - Gaps between Schwann cells
Dendron – branch of neurone that conduct the action potential towards the cell body

25. Structure of neurones

26. Establishing the “Resting Potential”
At rest, the inside of a neuron's membrane has a relatively negative charge.
As the figure shows, a Na+ / K+ pump in the cell membrane pumps 3 sodium ions out of the cell and 2 potassium ions into it.
However, because the cell membrane is a bit leakier to potassium than it is to sodium, more potassium ions leak out of the cell, increasing the positive charge outside.
There are also many organic anions (-ve charged) in the cytoplasm
As a result, the inside of the membrane builds up a net negative charge relative to the outside. (-70mV is the resting potential, the cell is “polarised”

27. Sodium – Potassium pump online tutorial

28. 35
All stimuli produce generator potentials but some don’t cause a big enough change in p.d. to reach threshold potential so no action potential is generated.

29. You should be able to: Describe and explain how an action potential is generated. Interpret graphs of the voltage changes taking place during the generation and transmission of an action potential.

30. Reaching the threshold potential
Any stimulation of a receptor cell causes some of the sodium channels to open.
So some Na+ions diffuse down their concentration gradient back into the cell
This reduces the potential difference across the membrane
If the reduction is big enough (ie reaches the threshold potential) then voltage gated channels open

31. (P.d. doesn’t reach generator potential.)35
Small stimuli don’t cause a big enough change in p.d. to generate an action potential.
(P.d. doesn’t reach generator potential.)

32. Generating an Action Potential
Stimulation of the receptor causes Na+ channels to open. The bigger the stimulus the more channels open.
Na+ ions diffuse into cell lowering potential difference
This makes even more channels open (positive feedback)
When potential difference reaches threshold (-50mV) the voltage gated Na+ channels open

33. Generating an Action Potential (2)
As more Na ions flood in the potential difference across the membrane changes to +40mV
Voltage gated K channels open and Na channels close (2&3)
K ions diffuse out of cell repolarising the cell (4)
So many ions diffuse out that the cell is hyperpolarised (5)
The Na/K pump re-establishes the resting potential (6)

34. Local Current

35. Transmission of Action Potentials in myelinated neurones (Saltatory conduction)3
AP at 1 causes Na ions to move into axon
Na ions diffuse to areas of –ve charge further down axon towards 2
Voltage gated Na channels are only present at Nodes of Ranvier
So new AP starts at 3 and so on
The impulse moves in one direction only as it takes time to re-establish distribution of ions using the Na/K pump.
So the neurone cannot depolarise again immediately in that region (refractory period)

36. Transmission of Action Potentials in myelinated neurones (Saltatory conduction)

40. Extension: Animation showing the linking of an action potential to muscle movement

41. Animation to explain a synapse

42. Use your new knowledge to create a script to describe and explain the following animation: