WJEC Biology for AS: Study and Rev Guide

How to use this book Knowledge and Understanding The first section of the book covers key knowledge required for the examination. There are notes on: ▪ ▪ Unit 1, Basic Biochemistry and Cell Organisation ▪ ▪ Unit 2, Biodiversity and Physiology of Body Systems. There is no practical assessment in AS, therefore you need to be able to answer practical based questions in the exam. Examples and exam tips have been included in the guide to help you prepare. You will also find: ▪▪ Key terms : many of the terms in the WJEC specification can be used as the basis of a question, so we have highlighted those terms and offered definitions. ▪▪ Quickfire/Extra questions : are designed to test your knowledge and understanding of the material as you go along. ▪▪ Pointer and Grade boost : offer extra examination advice to improve your exam technique and raise your exam performance. ▪▪ Additional practice questions : feature at the end of the book providing you with further practice at answering questions with a range of difficulty. Approximately 10% of your marks will come from the assessment of your mathematical skills. Help is provided throughout the guide, including worked examples. Gradeboost It is important to remember whichbondsare theweakest, as thesewillbreakfirstwhen enzymesareexposed tohigh temperatures. Theseare: hydrogenbonds followed by ionicbondsand lastly disulphidebridges. Pointer If an enzyme hasmany disulfide bonds present in its tertiary structure, it is likely to be able towithstand quite high temperatures. This can been seen in enzymes found in bacteria that live in hot volcanic springs. Enzyme–substrate complex : an intermediate structure formedduringan enzyme-catalysed reaction inwhich the substrate and enzymebind temporarily, such that the substrates are close enough to react. Activationenergy : the minimumenergy thatmust beput intoachemical system fora reaction to occur. KeyTerms QUICKFIRE QUICKFIRE QUICKFIRE w Drawagraph to show the effect ofanenzyme on activation energy. Enzyme structure How enzymes work Ina catabolic reaction, the substratebinds to theactive site, forming the enzyme-substrate complex .The reactionproceedsandproductsare released.Theactive site isnow free to catalyseanother reaction. Inanabolic reactions, several substratesbindandoneormoreproduct(s) are released. Asbiological catalysts,enzymes lower the activation energy (E A )needed to starta reactionbyprovidingenergy tobreakbonds inexistingmolecules sonewones can form innewmolecules.Bydoing so, chemical reactionsare speededup. The effect of enzymes on theactivation energy ofa reaction Progressof reaction Withoutenzyme Withenzyme substrate activation energy product Energy Progressof reaction substrate Energy 42 ASBiology:Study andRevisionGuide Additional practice questions 1. Inorganic ionsareneededby livingorganisms. a) Complete the functions for the following ions in the tablebelow. [2] Ion Function Magnesium Phosphate b) Explainwhyadiet lacking in ironoften results inanaemia. [2] c) Water isvital to life.Explainhow itspropertiesenable it toactasa coolant foranimals. [3] 2. a) What ismeantbya tissue? [1] b) Explainhow squamousepithelium isadapted for its function in the lungs. [2] c) Penicillin isanantibiotic thatworksbypreventing the cross linkingofpeptidoglycan in the cellwalls ofGrampositivebacteria, causing the cells tohaveweakened cellwalls.Thismakes thebacterium susceptible toosmotic lysis.Usingyourknowledgeofvirus structure,explainwhyantibioticsare ineffectiveagainstviruses suchas influenza. [1] 3. Thediagram shows thefluidmosaicmodel formembrane structureproposedbySingerandNicolson in1972. a) Why is themodel said tobefluidmosaic? [2] b) In cysticfibrosis,patientshave faulty chloride transportproteins in themembranesof the ciliated epithelium that line the tracheaandbronchioles.Asa result, chloride ionsarenot secreted from the cell,andarenotabsorbedby themucus that covers the cell. i) Usingyourknowledgeofosmosis,explainwhymucus in thesepatients isoften thick. [2] ii) Suggestwhypatientsoften report thatbreathing seaairalleviates their symptoms. [2] 145 Additionalpracticequestions 4 AS Biology: Study and Revision Guide