单元 1：分子、饮食、运输与健康
Pearson Edexcel · International A-Level · 生物 知识点 1 12:42 英语旁白 · 英中内嵌字幕
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A red blood cell leaving your lung carries oxygen on haemoglobin, rides an artery, squeezes through a capillary narrower than itself, gives up the oxygen to a respiring cell, and returns through a vein.
一个红细胞离开肺，携带着血红蛋白上的氧气，沿动脉前行，挤过比自身还窄的毛细血管，把氧气交给呼吸着的细胞，再经静脉返回。
Unit one follows that whole journey, and the paper is ninety minutes, eighty marks, all compulsory, covering Topic one and Topic two together.
第一单元走完这整段旅程。 试卷90分钟、80分，全部必答，同时考查专题一和专题二。
Its habit of thought is always the same: name the structure, then say what it is for.
它一贯的思维方式是：说出结构名称，再说明它的功能。
In a water molecule, oxygen pulls the shared electrons harder than hydrogen, so each bond has a negative end and a positive end. That is the dipole nature of water.
水分子中，氧对共用电子的吸引比氢强，因此每条O-H键都有负端和正端，这就是水的偶极性。
Opposite charges between neighbouring molecules form hydrogen bonds, and polar or ionic particles - glucose, sodium ions, amino acids - dissolve because water clusters around them.
相邻分子间异号电荷形成氢键；葡萄糖、钠离子、氨基酸等极性或带电粒子会被水分子包围而溶解。
Non-polar molecules cannot break in, and that exclusion is the very reason a lipid bilayer holds together.
非极性分子无法挤入，而这种排斥正是脂双层能够稳定存在的原因。
Two monosaccharides join by a condensation reaction: a molecule of water is removed and a glycosidic bond forms.
两个单糖经缩合反应连接：脱去一分子水，形成糖苷键。
Hydrolysis is the reverse - water added, bond broken - and it is exactly what your digestive enzymes do.
水解是逆过程——加水断键——正是消化酶的工作。
Maltose is two glucose; sucrose is glucose plus fructose; lactose is glucose plus galactose.
麦芽糖是两分子葡萄糖；蔗糖是葡萄糖加果糖；乳糖是葡萄糖加半乳糖。
For storage, plants coil amylose and branch amylopectin; animals branch glycogen instead.
储存方面，植物把直链淀粉卷成螺旋、支链淀粉带分支；动物则储存糖原。
Branches mean many chain ends, and many ends mean glucose can be released fast.
分支意味着大量链末端，末端越多，释放葡萄糖越快。
Core practical one is semi-quantitative.
核心实验1是半定量的。
Heat reducing sugars with Benedict reagent and the blue turns brick-red; compare the colour against standards of known concentration, or read the tube in a colourimeter.
还原糖与班氏试剂加热，蓝色变为砖红色；与已知浓度的标准色阶比较，或用色度计读数。
The calibration curve is straight only up to about four percent, so read unknowns inside that range rather than extrapolating past it.
标准曲线只在约4%以内是直线，所以要在量程内读数，不要向外延伸。
Iodine does the same job for starch, turning blue-black in proportion to concentration.
碘液对淀粉起同样作用，随浓度升高变蓝黑色。
One glycerol joins three fatty acids by three condensation reactions, each forming an ester bond.
一分子甘油与三分子脂肪酸经三次缩合形成三个酯键，构成甘油三酯。
A saturated fatty acid has no carbon-carbon double bonds: straight chains pack closely, so the fat is solid at room temperature.
饱和脂肪酸没有碳碳双键，链是直的，排布紧密，室温下呈固态。
Unsaturated acids have one or more double bonds, each forcing a kink into the chain, so packing is loose and the oil stays liquid.
不饱和脂肪酸含一个或多个双键，每个双键都让链条弯折，排布松散，室温下呈液态。
Lipids store about twice the energy per gram of carbohydrate because their chains are more reduced.
每克脂质储存的能量约为碳水化合物的两倍，因为链条还原程度更高。
Diffusion is fast only over short distances: the time grows with the square of the distance.
扩散只在短距离内够快：所需时间随距离的平方增长。
Any cell more than about a millimetre from its supply would starve waiting.
任何离供应源超过约一毫米的细胞都会等不到营养。
So multicellular animals build a mass transport system - a pump, pipes and a medium - to deliver supplies close to every cell, and diffusion then does the last short step across walls one cell thick.
因此多细胞动物建立了大规模运输系统——泵、管道和介质——把养料送到每个细胞附近，最后一步由扩散穿过一层细胞厚的薄壁完成。
That division of labour explains every structure in this unit.
这种分工解释了本单元的每一个结构。
Arteries carry blood at high, pulsing pressure, so their walls are thick with muscle and elastic fibres that stretch with the beat and recoil between beats.
动脉输送高压脉动血流，管壁厚，含平滑肌和弹性纤维，随心跳扩张、间歇回缩。
Capillaries are where exchange happens: walls one cell thick and an enormous total cross-section that slows the flow.
毛细血管是交换场所：管壁仅一层细胞厚，总横截面积巨大，流速减慢。
Veins return blood at low pressure: wide lumens, thin walls, and pocket valves that let blood forward and stop it falling back.
静脉以低压回流：管腔宽、管壁薄，并有袋状瓣膜让血液前进、阻止倒流。
Every exam answer pairs the structure with the pressure it handles.
每道题的答案都要把结构与它承受的压力配对。
One beat has three phases.
一次心跳分三个阶段。
Atrial systole squeezes the last blood into the ventricles.
心房收缩期把最后的血液挤入心室。
Ventricular systole raises ventricular pressure above aortic pressure; the semilunar valves open and blood is driven out.
心室收缩期使心室内压超过主动脉压，半月瓣打开，血液射出。
In diastole the muscle relaxes, pressure falls, the semilunar valves slam shut for the second heart sound, and the chambers refill from the veins.
舒张期肌肉放松、压力下降，半月瓣关闭产生第二心音，心腔自静脉充盈。
Read the graph the way the examiner wants: a valve opens or shuts whenever the pressure across it changes sign.
按考官期望的方式读图：跨瓣膜两侧压力的大小关系一变，瓣膜就开或关。
Haemoglobin is a quaternary protein: four chains, each folded around a haem group whose iron carries one oxygen.
血红蛋白是四级结构蛋白：四条链各环绕一个血红素，每个铁离子携带一个氧。
Binding the first oxygen changes the protein shape so the next ones bind more easily - cooperative binding - and that gives the curve its S shape.
第一个氧的结合改变蛋白质形状，使后续结合更容易——协同结合——曲线因此呈S形。
In the lungs the curve flattens near full saturation; in tissue, where partial pressure is low, it is steep, so a small fall in oxygen partial pressure unloads a lot of oxygen.
在肺部，曲线在高饱和处平缓；在组织中，氧分压低、曲线陡峭，氧分压稍有下降就释放大量氧气。
Hard-working tissue releases carbon dioxide; hydrogen ions bind haemoglobin and shift the whole curve right - the Bohr effect - unloading even more where respiration is fastest.
剧烈活动的组织释放二氧化碳，氢离子结合血红蛋白使整条曲线右移——波尔效应——在最需要的地方卸下更多氧。
Atherosclerosis begins with damage to the endothelium.
动脉粥样硬化始于内皮损伤。
The inflammatory response grows, low-density lipoproteins invade the wall, and smooth muscle builds a plaque that narrows and stiffens the artery.
炎症反应加剧，低密度脂蛋白侵入管壁，平滑肌形成斑块，使动脉变窄变硬。
If the roughened surface triggers clotting, the cascade runs: thromboplastin, with calcium, converts prothrombin to thrombin; thrombin converts soluble fibrinogen to insoluble fibrin; the fibrin mesh traps platelets.
若粗糙表面触发凝血，级联反应启动：凝血酶原激酶在钙离子参与下把凝血酶原转化为凝血酶；凝血酶把可溶的纤维蛋白原变成不溶的纤维蛋白；纤维蛋白网困住血小板。
And remember the arithmetic of risk: factors multiply. Two moderate risks together can outweigh one severe one.
还要记住风险的算术：风险因子是相乘的，两个中等风险叠加可能超过一个严重风险。
Questions eight and nine of every WBI11 paper live on health data. Four habits cover the marks. Correlation is not causation. Judge the study design: sample size, how it was selected, what was controlled, whether it was blinded. Name the confounders - age, smoking, diet, wealth - that could produce the association without causation. And do the arithmetic carefully: percentage change, ratios in standard form, rates per hundred thousand.
每份WBI11试卷的第八、九题都考健康数据。 四个习惯覆盖所有得分点：相关不等于因果；评价研究设计——样本量、抽样方式、对照设置、是否盲法；指出混杂因素——年龄、吸烟、饮食、经济状况——它们能不经过因果就制造关联；认真做计算：百分比变化、标准形式的比值、每十万人率。
Energy balance decides mass, and two numbers screen it: BMI - mass in kilograms over height in metres squared, with twenty-five to thirty as overweight - and waist-to-hip ratio, which tracks the abdominal fat that matters most for cardiovascular risk.
能量平衡决定体重，两个数字用于筛查：BMI——千克除以米平方，25到30为超重——以及腰臀比，它最能反映与心血管风险相关的腹部脂肪。
Treatments all carry trade-offs. Statins block a liver enzyme in cholesterol synthesis, so cells clear LDL from blood - with muscle and liver side-effects to monitor. Anticoagulants cut clot risk and raise bleeding risk.
治疗都有取舍：他汀阻断肝内胆固醇合成酶，使细胞从血液清除LDL，但有肌肉和肝脏副作用需监测；抗凝药降低血栓风险却增加出血风险。
A discuss answer names a benefit, a risk, and makes a call anchored in the data given.
讨论题的答案要写出一个好处、一个风险，并依据题目数据做出判断。
The accepted picture of every membrane is the fluid mosaic model.
所有膜的公认图像是流动镶嵌模型。
A phospholipid bilayer forms automatically in water - hydrophobic tails in, polar heads out - and it is fluid: molecules slide within their layer.
磷脂双分子层在水中自动形成——疏水尾部向内、极性头部向外——且具有流动性：分子可在层内滑动。
Intrinsic proteins span the bilayer as channels and carriers; extrinsic proteins sit on its surfaces; cholesterol between the tails keeps fluidity steady when temperature changes; glycoproteins and glycolipids carry the cells identity labels.
内在蛋白横跨双层，构成通道和载体；外在蛋白附于表面；胆固醇位于尾部之间，在温度变化时稳定流动性；糖蛋白和糖脂携带细胞身份标记。
The model history - Overton, Gorter and Grendel, Davson and Danielli, finally Singer and Nicolson in 1972 - is itself an exam favourite.
从Overton、Gorter与Grendel、Davson与Danielli到1972年Singer与Nicolson的模型史，本身就是常考点。
Four routes move material across membranes.
物质跨膜有四条途径。
Simple diffusion is down the concentration gradient, no protein, no energy. Facilitated diffusion is also down the gradient but through a channel or carrier protein. Active transport runs against the gradient, powered by ATP, through carriers that change shape.
简单扩散顺浓度梯度，不需蛋白、不需能量；易化扩散也顺梯度，但要经过通道或载体蛋白；主动运输逆梯度，由ATP供能、载体变构完成；渗透是水穿过半透膜从水势高处流向低处。
Osmosis is water moving from higher to lower water potential across a partially permeable membrane. And for exchange surfaces, the Fick law - rate proportional to surface area times gradient over thickness - explains why alveoli, capillaries and gills all look the way they do.
对交换面，菲克定律——速率正比于面积乘梯度除以厚度——解释了肺泡、毛细血管和鱼鳃的形态。
An amino-acid sequence is the primary structure; hydrogen and ionic and disulfide bonds fold it into the tertiary shape, and in an enzyme that fold creates the active site.
氨基酸序列是一级结构；氢键、离子键、二硫键把它折叠成三级结构，酶的活性部位正由这一折叠形成。
Binding is induced fit: both substrate and site flex until complementary.
结合是诱导契合：底物与活性部位相互形变直至互补。
That is why temperature and pH curves have optima - they act on the tertiary structure - and why denaturation above the optimum is irreversible.
这解释了温度和pH曲线为何有最适值——它们作用于三级结构——也解释了超过最适值后变性不可逆。
A competitive inhibitor occupies the active site and is outnumbered at high substrate concentration; a non-competitive inhibitor binds elsewhere and lowers the rate everywhere.
竞争性抑制剂占据活性部位，在高底物浓度时被底物压倒；非竞争性抑制剂结合别处，在任何底物浓度下都降低速率。
A nucleotide is a pentose sugar, a phosphate and a base; phosphodiester bonds chain them into a strand.
核苷酸由五碳糖、磷酸和碱基构成；磷酸二酯键把它们连成链。
In the double helix, adenine pairs with thymine through two hydrogen bonds and guanine with cytosine through three - which is why GC-rich DNA melts at higher temperature.
双螺旋中，腺嘌呤与胸腺嘧啶以两条氢键配对，鸟嘌呤与胞嘧啶以三条配对——这也是GC含量高的DNA更难解链的原因。
Replication is semi-conservative: helicase unzips the two strands, each acts as a template, and DNA polymerase assembles the new strands.
复制是半保留的：解旋酶打开双链，各作模板，DNA聚合酶合成新链。
Meselson and Stahl grew bacteria on heavy then light nitrogen: after one round all the DNA was intermediate, after two rounds half was light - exactly what semi-conservative predicts and the alternatives forbid.
Meselson与Stahl让细菌先后在重氮和轻氮培养基中生长：复制一轮后DNA全为中等密度，两轮后一半为轻——恰好只有半保留复制能解释。
Transcription copies a gene to mRNA in the nucleus; translation reads it codon by codon on a ribosome, tRNA anticodons delivering the right amino acids.
转录在细胞核把基因抄成mRNA；翻译在核糖体上逐个密码子阅读，tRNA反密码子送来相应氨基酸。
The code is a triplet code, non-overlapping and degenerate - most amino acids have several codons.
遗传密码是三联体、非重叠且简并的——多数氨基酸有多个密码子。
So a substitution changes one amino acid or, thanks to degeneracy, nothing at all; but an insertion or deletion shifts the reading frame and rewrites every triplet that follows.
因此替换只改变一个氨基酸，或因简并而毫无影响；而插入或缺失会让突变之后的阅读框整体移位。
Three deleted bases in the CFTR gene remove one phenylalanine, the channel fails, mucus thickens - that is cystic fibrosis, the course model genetic disease, and the doorway to every screening-ethics question.
CFTR基因缺失三个碱基便失去一个苯丙氨酸，通道失效、黏液变稠——这就是囊性纤维化，本课程的模型遗传病，也是所有筛查伦理问题的入口。
Close with the paper own habit.
以试卷自己的习惯收尾。
Why do branched polysaccharides release faster?
为什么分支多糖释放更快？
Many chain ends.
链末端多。
Which valves open in ventricular systole?
心室收缩期哪些瓣膜开？
Only the semilunar, because ventricular pressure exceeds aortic.
只有半月瓣，因为心室压超过主动脉压。
What does the Bohr shift achieve?
波尔效应带来什么？
More unloading exactly where respiration is fastest.
恰在呼吸最快处卸下更多氧。
Two checks before a causal claim: confounders controlled, mechanism shown.
相信因果结论前查两件事：混杂因素是否受控、机制是否成立。
And a frameshift beats a substitution for damage because it rewrites every triplet downstream.
移码为何比替换更严重？ 它改写了下游每一个三联体。
Say the structure, then say what it is for - that sentence answers every question this paper asks.
说出结构，再说功能——这句话能回答这份试卷的所有问题。