Igcse biology edexcel 2.77 2.90

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Edexcell ppt Biology 2.77 - 2.90 Used in lessons to scaffold class teaching and as a revision resource for students

Transcript of Igcse biology edexcel 2.77 2.90

  • 1. Coordination and ResponseHomeostasis: the maintenance of a constantinternal environment

2. The S in MRS GREN2.77 understand that organisms are able to respond to changes in their environmentM Movement All living things move, even plantsR Respiration Getting energy from foodS Sensitivity Detecting changes in the surroundingsG Growth All living things growR Reproduction Making more living things of the same typeE Excretion Getting rid of wasteN Nutrition Taking in and using foodSENSITIVITYA stimulus is a change in the environment of an organism.Animals respond to a stimulus in order to keep themselves in favourable conditions.Examples of this include: moving to somewhere warmer if they are too cold moving towards food if they are hungry moving away from danger to protect themselvesAnimals that do not respond to a stimulus do not survive for long. 3. Homeostasis2.78 understand that homeostasis is the maintenance of a constant internal environment and that body water content and bodytemperature are both examples of homeostasisAll organisms try and maintain a constantinternal environment. This is calledhomeostasis.Examples of homeostasis include:1) The regulation of water levels.2) The regulation of body temperature. 4. Stimulus > Receptor> Coordination >Effector > Response2.79 understand that a coordinated response requires a stimulus, a receptor and an effector Both systems respond to stimuli(i.e. events that change the internal environment). Both systems have a:1) Receptor, which detects the stimulus.2) Effector, which carries out a response to correct the effect ofthe stimulus.The message from detector to effector is carried either via anelectrical nerve impulse or as a hormone, depending whichhomeostatic system is being used. 5. STIMULI2.79 understand that a coordinated response requires a stimulus, a receptor and an effector 6. Examples of Receptors and Effectors2.79 understand that a coordinated response requires a stimulus, a receptor and an effectorReceptorORGAN RECEPTORskin Temperature Receptorskin Pressure / Pain ReceptorBrain (hypothalamus) Water Concentration ReceptorEye (retina) Light Receptors (Rods & Cones)EffectorsORGAN EFFECTORHeart Muscle cellSkin Sweat glandKidney Collecting duct walls 7. STIMULI2.79 understand that a coordinated response requires a stimulus, a receptor and an effectorReceptors detect Stimuli. Some examples are:a) Light Eye (retina)b) Sound Ear (hearing)c) Movement (K.E) Ear (balance) / Skind) Chemical Nose / Tonguee) Heat Skin 8. Response in Plants2.80 understand that plants respond to stimuliPlants also respond to stimuli. As plants dont havenerves their responses are limited to hormones only.Plants respond to the following stimuli: Gravity: Roots grow towards gravitational pull andstems grow away. This is Geotropism. Water: Roots grow towards water. This isHydrotropism. Light: Shoots grow towards light. This is Phototropism. 9. GEOTROPISM2.81 describe the geotropic responses of roots and stemsShoot tips and Root tips respond to GRAVITY. Shoot tips grow away from gravity (NegativeGeotropism) Root tips grow in the direction of gravity (PositiveGeotropism) 10. WHYYou only need to know that plants respond to achemical hormone calledAUXINBUT if you want more2.81 describe the geotropic responses of roots and stems 11. 2.81 describe the geotropic responses of roots and stems 12. 2.81 describe the geotropic responses of roots and stemsYou do need to know some funexperiments with plants 13. 2.81 describe the geotropic responses of roots and stemsWhat happens when you grow a plantin space? 14. Positive Phototropism2.82 describe positive phototropism of stemsPositive Phototropism is controlled by hormonesreleased by the growing tip of the shoot.(Only the tip makes the hormone)If you remove the tip, the shoot stops growing.The hormone made by the tip is calledAuxin(which part of the plant would be controlled byNegative Phototropism?) 15. 2.82 describe positive phototropism of stems 16. MOREEXPERIMENTS2.82 describe positive phototropism of stems 17. 2.82 describe positive phototropism of stemsWhat if you grow a plant in the dark? 18. Response Systems2.83 describe how responses can be controlled by nervous or by hormonal communication and understand the differencesbetween the two systemsHumans have two systems which carry outdetection and response: Nervous System Chemical electrical systemusing NeuronsExample: Iris dilation, movement, ventilation Endocrine System Chemical system usingproteins called hormones in the blood.Example: Osmoregulation, Fight or Flight,Menstruation. 19. Differences2.83 describe how responses can be controlled by nervous or by hormonal communication and understand the differencesbetween the two systemsNervous System Endocrine SystemWorks by nerve impulses(has chemicals in synapses though)Works by hormones transmittedin blood streamTravel fast and usually haveinstant effectTravel slowly and may take longerto askResponse is short lived Response is usually longer lastingImpulse act on individual cells(localised effect)Widespread effects on differentorgans (still only work oncells/organs with correctreceptors) 20. Nervous System2.84 understand that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nervesThe Central Nervous System(CNS) consists of1) the brain2) the spinal cordThere are also PeripheralNerves System (PNS)1) Sensory Nerves/organs(e.g. pain receptors inskin, or photoreceptorsin the eye)2) nerves that link brainand sense organs3) Motor Nerves 21. 2.85 understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervousStimulation of the sense organs results in an electrical signal(a nerve impulse) being sent along the nerve to the brain.Nerve impulses are very quick (~120m/s), allowing rapidresponses to the stimulus.nerve impulseNerve Impulsesynaptic cleftreceptorsystem, resulting in rapid responses 22. DIFFUSION AGAIN??2.85 understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses(You do not have to know the terms just the ideas)1) An electrical impulse travels along a nerveending.2) This triggers the nerve-ending of a neuronto release chemical messengers calledneurotransmitters.3) These chemicals diffuse across thesynapse (the gap) and bind with receptormolecules on the membrane of the nextneuron.4) The receptor molecules on the secondneuron bind only to the specific chemicalsreleased from the first neuron. This stimulatesthe second neuron to transmit the electricalimpulse. 23. REFLEXS2.86 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot objectSome sense organs are not connected directly tothe brain.This is a defence mechanism allowing almostinstant responses to threatening or dangerousstimuli (e.g. pain/hot object).These instant responses are controlled by nervesin the spine, rather than the brain and are calledreflexes 24. REFLEX ARC2.86 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot objectRelay Neuron 25. STEP BY STEP REFLEX ARC2.86 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object1) A stimulus is detected by a receptor2) The receptor initiates a nerve impulse in the sensorynerve3) The sensory nerve (which runs from the receptor to thespine) passes the message/impulse onto aninterneuron/Relay Neuron in the spine4) The interneuron/relay neuron passes the message on thea motor nerve5) The motor nerve (which runs from the spine to a musclein the same limb as the receptor) passes the messageonto the effector muscle6) The effector muscle carries out the response (musclecontraction). 26. Reflex Arc Timing2.86 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot objectThe entire process (stimulus to response)happens in less than a second and does notinvolve the brain.The purpose of the interneuron is also to informthe brain of what has happened.Reflex Summary1) Immediate response to stimulus2) Automatic reactions3) Limits damage to organism 27. THE EYE 28. EyE WebSites2.87 describe the structure and function of the eye as a receptora) Label the eyehttp://www.kscience.co.uk/animations/eye_drag.htmb) Function of the eyehttp://www.kscience.co.uk/animations/eye_function_drag.htmc) Label the eyehttp://www.freezeray.com/flashFiles/eye.htmd) Light and the eyehttp://www.kscience.co.uk/animations/eye.htme) Fun with your blind spothttp://www.med.yale.edu/neurobio/mccormick/fill_in_seminar/figure1.htm 29. EYE DIAGRAM2.87 describe the structure and function of the eye as a receptorConjunctiva 30. Define these Terms2.87 describe the structure and function of the eye as a receptor Ciliary Body (muscle) Iris Pupil Cornea Lens Suspensory Ligament Sclera Choroid Retina Fovea Optic Disk (blind spot) Optic Nerve ConjunctivaContracts to Relaxes to change shape of lensColoured muscular part of eye that controls pupils sizeOpening in the iris that lets light through to the retinaTransparent front part of the eye that refracts lightTransparent part of the eye that bends light (refracts)Ligament that controls the shape of the lensDense white covering of the eyeVascular membrane of the eyeball between the sclera and the retina& stops light reflecting around in the eyeLight sensitive membrane that converts light to electrical signals to the brainPart of the retina with a high density of cones for very sharp visionArea of retina that is insensitive to lightWhere electrical impulses from retina travel to brainhelps lubricate the eye by producing mucus and tears 31.