WJEC GCSE生物 细胞 扩散 渗透 主动运输 酶
WJEC 的 GCSE Biology 在威尔士由 Qualifications Wales 监管，Unit 1 的主题名是 Cells, Organ Systems and Ecosystems，其中 1.1 一节叫 Cells and movement across membranes。这一节把细胞结构、显微观察、扩散、渗透、主动运输和酶放在一起考，纸面上只占 Unit 1 的一部分，题目却年年出现在短答、数据题和实验情境里。
下面按官方 Specification 的条目顺序，把 1.1 拆成能直接对着复习的十四个小块。每块给出考点、实验做法和常见失分方式，末尾附实验题的作答规范。
This article follows the order of topics in section 1.1 of the WJEC GCSE Biology specification, moving from cell structure through the transport processes. Each part lists what examiners ask for, how the required practical is carried out, and where marks are usually lost.
1.1 在 Unit 1 里的位置与考试结构
Unit 1 的笔试是 1 小时 45 分钟、80 分、占总成绩 45%，题型包括短答、结构化题、拓展写作和数据题，部分题目设在实验情境里。Unit 2 的规格相同，也是 1 小时 45 分钟、80 分、45%。剩下的 10% 来自 Unit 3 的实验评估，现行版本是 30 分。WJEC 官网公布的 Specification 在 2026 年 2 月更新到 Version 3，新版的 Unit 3 改为 Scientific Enquiry，2026 年 9 月起首次教学、2028 年首次颁发成绩。两个 tier 的覆盖范围不同，Higher 档给 A* 到 D，Foundation 档给 C 到 G，Unit 3 不分 tier。细胞分裂与干细胞写在 Unit 2 的 2.2，不在这一节，复习时别把两处混在一起。
The written Unit 1 paper lasts 1 hour 45 minutes and carries 80 marks, which is 45 per cent of the qualification. Unit 2 has the same shape, so the two papers together account for 90 per cent, and the remaining 10 per cent comes from the Unit 3 practical assessment; WJEC updated its specification to Version 3 in February 2026, with a new Unit 3 on scientific enquiry first taught from September 2026 and first awarded in 2028. Cell division and stem cells sit in Unit 2, so revision notes for 1.1 should stop at the cell membrane.
动物细胞：细胞膜 细胞质 细胞核 线粒体
动物细胞的图要能标出细胞膜、细胞质、细胞核和线粒体，新版材料里核糖体也常被要求。细胞膜控制物质的进出，细胞质是大多数反应发生的场所，细胞核含 DNA 并控制细胞活动，线粒体进行有氧呼吸、把葡萄糖里的能量释放出来。很多学生以为线粒体是制造能量的结构，阅卷时这种写法不给分，因为能量不会被制造，只会从一种形式转成另一种。细胞膜在光镜下看不清，画图时用一条线表示，不要画成双层。核糖体属于电子显微镜下才能分辨的层次，光镜图里标它算错。这几个结构的分工要能各用一句话写清，题目常要求把功能与结构对应。
A standard animal cell diagram needs the membrane, cytoplasm, nucleus and mitochondria, and ribosomes are increasingly accepted as well. The membrane controls what enters and leaves, the cytoplasm hosts most reactions, the nucleus holds DNA and directs activity, and the mitochondria release energy from glucose during aerobic respiration. Many students write that mitochondria make energy, which examiners reject because energy is transferred rather than created; ribosomes belong to the electron microscope level and should not appear on a light microscope drawing.
植物细胞：细胞壁 大液泡 叶绿体
植物细胞在动物细胞的基础上多出细胞壁、大液泡和叶绿体。细胞壁由纤维素构成，起支持与固定的作用，它不是选择透过性的，所以不能把它当成另一层细胞膜。大液泡里装细胞液，维持细胞的膨压，蔫掉的叶片就是细胞失水后膨压下降的结果。叶绿体只出现在能进行光合作用的部位，根细胞里没有叶绿体。常见的错误是把方形当成植物细胞的判据，形状只是细胞壁带来的外观。这一步最容易出错的地方是给根毛细胞也画上叶绿体，画错一处就会连带后面的功能解释一起丢分。
Plant cells carry three structures that animal cells lack: a cellulose cell wall, a large permanent vacuole and chloroplasts. The wall gives support and shape but is fully permeable, so it must not be described as a second membrane; the vacuole stores cell sap and keeps the cell turgid, which is why wilted leaves droop once water is lost. Chloroplasts appear only where photosynthesis happens, so root hair cells have none, and drawing them on a root cell costs marks even when the rest of the diagram is right.
指定实验：用光镜观察动物与植物细胞
Specification 列出的第一项指定实验，是用光镜观察动物与植物细胞并画出带标注的科学图。洋葱表皮要撕成单层，滴清水、盖盖玻片，斜放盖片以避免气泡；口腔上皮细胞几乎透明，要用亚甲基蓝染色才能看清细胞核。绘图用铅笔，线条连续，不画阴影，标注线平行且不交叉，图下写清放大倍数。阅卷时常见的一种失分是画出立体感或用圆珠笔，这类图直接不计分。低倍镜先找视野，再换高倍镜，换镜后只调细准焦螺旋。这一步最容易出错的地方是把盖玻片直接压下去，气泡满视野，结构一个都看不清。
The first required practical asks students to observe animal and plant cells with a light microscope and produce a labelled scientific drawing. Onion epidermis must be a single layer mounted in water with the cover slip lowered at an angle to avoid air bubbles, while cheek cells need methylene blue because the cytoplasm is almost transparent; drawings are made in pencil with continuous lines, no shading, and parallel label lines that never cross. A three dimensional sketch or a drawing in pen scores nothing, and lowering the cover slip flat traps bubbles that hide every structure.
放大倍数 分辨率 单位换算
总放大倍数等于目镜倍数乘物镜倍数，10 倍目镜配 40 倍物镜就是 400 倍。单位换算要熟：1 毫米等于 1000 微米，0.05 毫米就是 50 微米。光镜的分辨率大约 200 纳米，所以线粒体内部的嵴要用电子显微镜才看得清。放大倍数提高不会提高分辨率，这一点在数据题里反复出现。学生最常把放大倍数与分辨率当成同一件事。这一步最容易出错的地方是忘记写单位，或者把微米写成毫米，数值对但单位错照样不给分。
Total magnification is the eyepiece power multiplied by the objective power, so a 10 times eyepiece with a 40 times objective gives 400 times. Students should be fluent with the conversion that 1 millimetre equals 1000 micrometres, which makes 0.05 millimetres equal to 50 micrometres; a light microscope resolves about 200 nanometres, so the internal folds of a mitochondrion require an electron microscope. Increasing magnification never improves resolution, and answers that leave out the unit lose the mark even when the number is right.
细胞分化与特化细胞
分化是细胞变得适合特定功能的过程，分化后细胞的形状、内部结构和酶的种类都会改变。红细胞没有细胞核，为血红蛋白腾出空间；神经细胞伸出长突起传递电信号；根毛细胞把表面积拉大，便于吸收水和矿质离子；精子带大量线粒体，供尾部摆动使用。很多学生以为分化是基因发生了改变，实际上 DNA 内容不变，变的是哪些基因被表达。答题时把形状与功能连起来写，单写功能通常只得一半分。这一步最容易出错的地方是说红细胞没有 DNA，没有细胞核不等于没有 DNA 之外的遗传信息。
Differentiation is the process by which a cell becomes adapted to one particular job, and it changes cell shape, internal structure and the enzymes present. Red blood cells lose their nucleus to make room for haemoglobin, nerve cells extend long fibres to carry electrical impulses, root hair cells enlarge the surface for absorbing water and mineral ions, and sperm cells pack mitochondria to power the tail. A common mistake is to say that differentiation changes the genes themselves; the DNA stays the same and what changes is which genes are expressed.
组织 器官 器官系统 生物体
层次顺序是细胞、组织、器官、器官系统、生物体。同一类细胞分工相同就构成组织，几种组织合起来完成一项功能成为器官，器官再组合成系统。胃是一个常用例子：黏膜上皮组织分泌胃液，肌肉组织收缩搅拌，结缔组织支撑，神经组织调节，四层合起来才是一个胃。答题时若把胃写成系统，整段的层次分都拿不到。植物的层次到器官为止，叶、根、茎都是器官，没有器官系统这一层。这一步最容易出错的地方是把组织与器官的界线记反。
The hierarchy runs from cells to tissues, organs, organ systems and finally the whole organism. Cells of the same type form a tissue, several tissues working together form an organ, and organs combine into a system; the stomach illustrates this well, with epithelium secreting juice, muscle churning contents, connective tissue supporting the wall and nerve tissue coordinating the process. Writing that the stomach is a system loses the hierarchy marks, and plants stop at the organ level because leaves, roots and stems are not grouped into organ systems.
扩散：浓度梯度与四个影响因素
扩散是颗粒从高浓度区域向低浓度区域净移动，靠分子自身的随机运动，不消耗细胞的能量。影响速度的因素有浓度梯度、温度、表面积和扩散距离。肺泡壁只有一层扁平细胞，小肠绒毛把表面积扩大，都是为了让扩散更快。很多学生以为扩散一定要有细胞膜，其实在空气和液体里同样发生。考题常问绒毛细胞的形状为什么有利，答案要落到表面积与距离两个词上。这一步最容易出错的地方是只写浓度差，漏掉温度或距离对速率的影响。
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, driven by random molecular motion rather than by energy from respiration. The rate depends on the concentration gradient, temperature, surface area and diffusion distance, which explains why alveolar walls are one cell thick and why villi multiply the surface of the small intestine. Diffusion also happens in air and in water without any membrane, and answers about villi must name both surface area and short distance to gain full credit.
Visking 透析袋：膜孔与分子大小
Visking 透析袋是活体细胞膜的模型，袋壁上的孔只允许小分子通过。袋内放淀粉溶液和葡萄糖溶液，袋外放清水，静置一段时间后取袋外液体检测。加碘液不变蓝黑，说明淀粉没有过膜；加 Benedict 试剂并加热出现砖红色沉淀，说明葡萄糖已经过膜。解释结论时要把膜孔大小与分子大小对应起来写，只写它是半透膜通常只得一半分。常见的错误是只描述颜色变化而不下结论。这一步最容易出错的地方是忘记加热，Benedict 试剂不加温不会变色。
A Visking tube models a living cell membrane because the pores in its wall allow only small molecules through. Starch and glucose solutions go inside, water goes outside, and after standing the outside liquid is tested; iodine stays yellow brown, showing that starch cannot pass, while Benedict solution heated with the outside liquid turns brick red, showing that glucose has crossed. Conclusions must link pore size to molecular size, and Benedict tests that are never heated will not change colour at all.
渗透：水势方向与马铃薯条实验
渗透是水穿过选择透过性膜，从水浓度高的一侧向水浓度低的一侧移动，也就是从溶质浓度低的一侧往溶质浓度高的一侧。马铃薯条放在纯水、稀糖水和浓糖水里，纯水中的条质量增加，浓糖水中的条质量减少，与组织液浓度接近的那组几乎不变。浓糖水里的植物细胞会出现质壁分离，细胞膜与细胞壁分开。这一步最容易出错的地方是只写水进入细胞，不写方向与浓度对比。写结论时把质量变化的数字带上，比写变重变轻更稳。
Osmosis is the movement of water across a selectively permeable membrane from the side with more water to the side with less, which means from the dilute solution towards the concentrated one. Potato cylinders gain mass in pure water, lose mass in strong sugar solution, and barely change in a solution close to the concentration of the cell contents; plant cells in strong sugar solution show plasmolysis as the membrane pulls away from the wall. Answers that only say water enters the cell, without stating direction or comparing concentrations, rarely gain the explanation mark.
主动运输：载体蛋白与能量
主动运输把物质从低浓度一侧搬到高浓度一侧，需要载体蛋白，也需要呼吸作用提供的能量。根毛细胞吸收矿质离子、小肠上皮吸收葡萄糖都用这种方式，所以缺氧或低温会明显减慢吸收速率。很多学生以为所有跨膜运输都要能量，扩散和渗透都是被动的。答题时把载体蛋白与能量两个词写全，缺一个就少一半分。这一步最容易出错的地方是把它与扩散的方向记反，主动运输可以逆浓度梯度进行。
Active transport moves substances against the concentration gradient, from low to high concentration, and it needs both a carrier protein and energy released by respiration. Root hair cells take up mineral ions this way and intestinal cells absorb glucose the same way, so low oxygen or low temperature slows the process noticeably. Diffusion and osmosis need no energy at all, and answers that omit either the carrier protein or the energy source lose half the available marks.
表面积与体积比：细胞为什么小
边长 1 厘米的立方体，表面积 6 平方厘米，体积 1 立方厘米，比值 6 比 1；边长 3 厘米的立方体，表面积 54 平方厘米，体积 27 立方厘米，比值 2 比 1。细胞长大时体积增长快于表面积，物质进出就不够用，所以细胞通常保持很小，或者长出绒毛、折叠等结构。常见的错误是只算表面积或只算体积就写出比值，两个数都要算清。考题里常要求解释为什么大细胞需要更高效的运输方式，答案要落在比值下降上。
A cube with sides of 1 centimetre has a surface area of 6 square centimetres, a volume of 1 cubic centimetre and therefore a ratio of 6 to 1; a cube with sides of 3 centimetres has 54 square centimetres against 27 cubic centimetres, a ratio of only 2 to 1. As a cell grows, its volume rises faster than its surface, so exchange across the membrane becomes insufficient and cells stay small or develop folds and projections. Answers must calculate both values before stating a ratio, because a ratio taken from one measurement alone carries no credit.
酶：活性部位 变性 影响速率的因素
酶是蛋白质，作用是把反应所需的活化能降低，反应结束后酶本身不变。每种酶有一个活性部位，只与特定形状的底物结合，这就是专一性。温度过高或 pH 偏离最适值会破坏活性部位的三维结构，酶变性失活，这个过程不可逆。很多学生以为酶被杀死了，规范写法是变性或失去活性。Specification 列出的第二项指定实验就是调查影响酶作用的因素，写变量时要把自变量、因变量和控制变量分开。这一步最容易出错的地方是把低温写成使酶变性，低温只是降低活性。
Enzymes are proteins that lower the activation energy of a reaction and are unchanged at the end of it. Each enzyme has an active site that fits one substrate shape, which explains specificity, and a temperature or pH far from the optimum distorts that site so the enzyme is denatured and cannot recover; examiners reject the phrase killed because enzymes are not alive. The second required practical investigates factors affecting enzyme action, so candidates must separate the independent, dependent and controlled variables, and low temperature slows an enzyme without denaturing it.
实验题作答规范：变量 单位 对照组
实验题的分大多给在过程与解释上，不在结论上。写步骤时要写具体体积、温度、时间和重复次数，比如水浴 40 摄氏度保温 5 分钟，重复三次取平均值。对照组的设置要说清改变了哪一个变量，其余条件保持一致。结论只能落在数据支持的范围内，超出范围就要写在本实验条件下，例如本实验只测了 30 到 60 摄氏度。这一步最容易出错的地方是算完忘记写单位，或者把平均值写成了单次测量值。
Marks in practical questions are awarded for method and explanation rather than for a bold conclusion. Steps need real quantities, so write a water bath at 40 degrees Celsius for 5 minutes with three repeats and a mean, and describe the control by naming the one variable that changes while everything else stays fixed. Conclusions should stay inside the range tested, for example 30 to 60 degrees Celsius, and leaving out units or quoting a single reading as a mean is the fastest way to lose method marks.
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