2Why 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.
3Why 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.
4Why 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.
5Why 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.
6Cells 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.
7Why 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.
8Write a definition and give some examples HomeostasisWhat does it mean?Write a definition and give some examples
9HomeostasisA system of monitoring and adjustment to keep conditions within safe limits
10HomeostasisMonitoring Controlling Internal conditions To keep them constant (or within safe limits) Despite external changesEgstemperatureblood glucose levelsblood salt concentrationrelative water potential of blood, tissue fluid and cells,pHBlood pressureCO2 levels
11Negative and Positive Feedback What’s the difference?
12Can you complete this with some real life examples? Negative FeedbackCan you complete this with some real life examples?
13Stretch and challenge questions Remember Stretch and challenge is about making synoptic linksYou 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.
14Homeostasis and Controlling Body Temperature Learning OutcomesDescribe 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
15What 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
16Control of temperature EctothermsSeek sun or shade depending on outside temperatureExpose more or less body surface to sunAlter body shape to change surface areaIncrease breathing movements to evaporate more water
17What is an Endotherm? How does an Endotherm control its body temperature? Write down as many different ways that you can think of.
18Control of temperature EndothermsSweatingPantingPiloerectionVasodilation /vasoconstrictionMetabolic rate in liverShiveringSeek sun or shadeAlter orientation of bodyAlter activity level
19Diagram to show changes to skin surface blood vessels in warm and cold conditions.
21What are the Advantages and Disadvantages of Endothermy and Ectothermy?
22Sensory Receptors and Stimuli Match the stimulus, sense and receptors in the card sort activity
23Sensory Receptors, Senses and Stimuli EyeRods and cones (light sensitive cells)Light intensity (rods) and wavelength (cones)NoseOlfactory cells lining inner surface of nasal cavityPresence of volatile chemicalsTongueTaste buds in tongue, hard palate, epiglottis and first part of oesophagusPresence of soluble chemicalsSkinPacinian corpuscles (pressure receptors)Pressure on skinEarSound receptors in cochlea (inner ear)Vibrations in airMuscleProprioceptors (stretch detectors)Length of muscle fibres
24Labelling Neurone Diagrams Use these terms to label the diagrams you have been given.Axon - specialised to conduct the action potential away from the cell bodyAxon terminals – release neurotransmitter to signal to other cellsDendrites- extend from cell body and receive neurotransmitter from axon terminals of other neuronesCell body- contains nucleus, mitochondria, ribosomesAxon Hillock - point at which the chemical signal received may reach the threshold needed to produce an action potentialMyelin sheath-insulating fatty layer composed of Schwann cellsNodes of Ranvier - Gaps between Schwann cellsDendron – branch of neurone that conduct the action potential towards the cell body
26Establishing 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 cytoplasmAs 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”
2835All 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.
29You 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.
30Reaching 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 cellThis reduces the potential difference across the membraneIf the reduction is big enough (ie reaches the threshold potential) then voltage gated channels open
31(P.d. doesn’t reach generator potential.) 35Small stimuli don’t cause a big enough change in p.d. to generate an action potential.(P.d. doesn’t reach generator potential.)
32Generating 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 differenceThis makes even more channels open (positive feedback)When potential difference reaches threshold (-50mV) the voltage gated Na+ channels open
33Generating an Action Potential (2) As more Na ions flood in the potential difference across the membrane changes to +40mVVoltage 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)
35Transmission of Action Potentials in myelinated neurones (Saltatory conduction) 3AP at 1 causes Na ions to move into axonNa ions diffuse to areas of –ve charge further down axon towards 2Voltage gated Na channels are only present at Nodes of RanvierSo new AP starts at 3 and so onThe 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)
36Transmission of Action Potentials in myelinated neurones (Saltatory conduction)