如果你看到了这篇推文，很有可能你是“入坑”了。生物作为最难的国际课程之一，很多人都是避而远之的。
一来文字表述多，读题费时；二来，太多“主观性”的东西，答案不好把握；三来，难拿分，从每年的boundary就可以知道。
以October 2022 PDF Grade Boundaries为例，大概拿到50%原始分就可以a了。
但其实换句话来说，只要你够强，分分钟拿a*/A*，因为a*/A*原始分够低。
那么alevel生物到底学什么呢？根据爱德思考纲，这一节课你要掌握：
考点一：The importance of water
1.1、understand the importance of water as asolventintransport, including its dipole nature
1.Dipole and Hydrogen bond
The separation of charge is calleddipole
Therepolar covalent bondbetweenHydrogenandoxygen.
Water is a polar molecule and exhibitdipolarity--— it has apartialnegative (δ–) chargeon one side and apartial positive (δ+)chargeon the other .
2.Properties of water(所有的“properties都来自于氢键”)
2.1 Water is apolar solvent.
Water can formhydrogen bondswith a variety of different substances(eitherpolarorcharged ioniccompunds)
2.2Water is an excellenttransport medium
glucose
amino acid
sodium chloride
chloesterol
fat
oxygen
2.3 As water cools to 4 °C, it reaches itsmaximum density.
--This unusualproperty enables organisms to live in water, even in countrieswhere itgets cold enoughto freeze in winter
2.4Water is slow to absorb and release heat – it has ahigh specificheat capacity.
High specific heat(高比热容)-- water can absorb or give offa great deal of energywithout changing temperature a lot.
when water evaporates, large amount of heat energy are used to break hydrogen bonds and allow water molecule to seperate.
2.5 Water is a liquid – itcannot be compressed.
Water molecules arecohesiveandadhesive
Cohesive--water attracting toeach otherby hydrogen bond.
Eg. surface tension; drinking draw; droplet
Adhesive--the attraction between water andother substance.
Eg. capillary action; meniscus; water climbs up paper towel or cloth
2.6 Water has avery high surface tensionbecause the attractionbetween the water molecules
1.Mass Transport Systems
Single-celled organisms:glucoseandoxygencandiffuse directlyacross the cell membranebecause of theshort distance
Multicellularorganisms: diffusion across the outer membrane would betoo slowbecause of the
large distance
Themass transport systemsare used tocarry raw materialsfrom specialisedexchange organs(e.g. the lungs and the digestive system) to the body cells,and toremove metabolic waste(e.g. carbon dioxide)Eg.circulatory system
资料来自《Edexcel International ALEVEL Biology EXAM GUIDE 》
