材料科学英语Unit 2 Lecture 3 Main chemical components of wood.ppt

MainchemicalcomponentsofwoodUnit2

Readingstrategy:Dealingwithunknownwords.1.GuessingbyexampleExample:Inbrief,mechanicalproperties,suchasdeformationandfracture,amongothers,areresponsestoappliedmechanicalforces.Maybe“mechanicalproperties”isunfamiliarforyou,butbasedontheexamplesmentioned:deformationandfacture,wecanknowthatitreferstothephysicalchangescausedbymechanicalforces.

2.GuessingbyaffixExample:Solarcellsrelyonsemiconductorstoabsorbsunlight.Theaffixsemi-meanshalf,andconductormeansasubstancethatallowsheat,electricity,etc.topassalongorthroughit.Therefore,wecanguessthatsemiconductormeansasolidmaterialthathaselectricalconductivitybetweenthatofaconductor.Readingstrategy:Dealingwithunknownwords.

3.GuessingbythepartofspeechofawordExample：Graphenecouldalsohaveapplicationsforcamerasensors,DNAsequencing,gassensing,materialstrengthening,waterdesalinationandbeyond.Afterwemeetdesalination,wecantellthewordmustbeanounbecauseitisparallelwithsequencing,sensingandstrengthening.Besides,itmustbeatreatmentdonetowater.Readingstrategy:Dealingwithunknownwords.

ReadtextBandapplytheskillsdealingwiththeunderlinedwords.Thecharacteristicfeatureofwoodycellsisthespecialnatureoftheircellwalls.Woodtissueiscomposedprincipallyofagroupofpolymersubstancesthatmakeupthecellwalls.Thesecompoundsaremixedinthewallinacomplexandhighlyorderedmanner,whichisdirectlyreflectedinthephysicalandmechanicalpropertiesofwood.

Wooddoesnothaveachemicalformulabecauseitisnotanindividualchemicalcompoundbutismadeupofmanychemicalstructures.Withinitscellularstructure,therearethreechemicalcomponents–cellulose,hemicellulose,andlignin,whichareprincipallycomposedofcarbon,oxygenandhydrogen.

ResearchingTaskUnit2Workwithyourgroupmembers,andtr