IGCSE生物 生命特征 干重 排泄 分类检索表
上一篇讲细胞结构，回答的是生物由什么组成；这一篇回到课程内容的第一章第一节，回答另一个更基础的问题：凭什么说一个东西是活的。CAIE 官方 syllabus 0610 适用于 2026、2027 与 2028 三年的考试，1.1 列出七条特征，每一条都用一个英文术语命名，考试要求你按官方措辞复述。这一节的题量不大，却几乎每张卷都会露面，位置多数在开头的两三道小题。下面按定义、易混对、判断题陷阱和分类收尾的顺序排一遍复习路线。
The previous article dealt with cell structure, which answers what a living thing is made of; this one returns to the very first section of the subject content and asks a more basic question, namely what entitles something to be called alive. CAIE syllabus 0610, which covers examinations in 2026, 2027 and 2028, lists seven characteristics in 1.1, and every one of them carries an official English term that has to be reproduced in the answer. The questions on this section are short, yet they turn up in almost every paper, usually in the first two or three items; the revision route below covers the definitions, the two pairs that get confused, the traps in judgement questions, and classification.
1.1 在三张卷里的位置
所有考生都考三张卷，Core 方向考 Paper 1 与 Paper 3，Extended 方向考 Paper 2 与 Paper 4，两张选择题卷各 45 分钟、40 分、占 30%，两张理论卷各 1 小时 15 分钟、80 分、占 50%。实验技能再从 Paper 5（1 小时 15 分钟）与 Paper 6（1 小时）里选一张，各 40 分、占 20%。CAIE 官方 syllabus 给出的评分目标权重是 AO1 占 50%、AO2 占 30%、AO3 占 20%，而 Papers 1 到 4 的内部权重是 AO1 63%、AO2 37%。七条生命特征落在 AO1，也就是回忆与理解那一档。阅卷时这一段很少单独出大题，通常以两分填空或一道四选一的形式出现。很多学生以为这是最简单的开篇，考完才发现定义里的限定词一个都不能少。考试季是 6 月与 11 月，印度另有 3 月场次。
Every candidate sits three papers; Core candidates take Papers 1 and 3 while Extended candidates take Papers 2 and 4, with each multiple-choice paper worth 40 marks in 45 minutes and each theory paper worth 80 marks in 75 minutes. The practical element is one paper from a choice of two, since Paper 5 runs for 1 hour 15 minutes and Paper 6 for 1 hour, and both carry 40 marks, which is 20% of the total. Assessment objective weightings published by CAIE give AO1 50%, AO2 30% and AO3 20% overall, with AO1 at 63% inside Papers 1 to 4, and the seven life processes all sit in that first objective; examiners usually test them with a two-mark gap fill or a single multiple-choice item.
七个特征与官方措辞
七条依次是 movement、respiration、sensitivity、growth、reproduction、excretion、nutrition，顺序本身不必背成口诀，但每条定义必须按 syllabus 的口径写。CAIE 官方 syllabus 0610 的 1.1 把 respiration 定义为细胞内分解营养分子、释放能量供代谢使用的化学反应。sensitivity 是察觉并对内部或外部环境变化作出反应的能力，internal 这个词经常被漏掉。reproduction 写成产生更多同类生物的过程，并不单指有性生殖。nutrition 是摄取物质用于能量、生长与发育。学生最常把定义题当成翻译题，写出大意就交卷，阅卷时只看关键词给分。
CAIE fixes the order of the seven characteristics as movement, respiration, sensitivity, growth, reproduction, excretion and nutrition, but marks are awarded for the wording of each definition rather than for the sequence. Respiration is defined as the chemical reactions in cells that break down nutrient molecules and release energy for metabolism; sensitivity is the ability to detect and respond to changes in the internal or external environment, and the word internal is easy to forget. Reproduction covers the processes that make more of the same kind of organism, so it is broader than sexual reproduction, while nutrition means the taking in of materials for energy, growth and development.
排泄与排遗这一对
excretion 是移除代谢废物与超出需要的物质，所以二氧化碳、尿素与汗液里的盐都算。egestion 在 syllabus 里单独列在 7.2 节，指把未消化的食物残渣以粪便形式排出体外，分界线是这种物质有没有参与细胞内的化学反应。很多学生把粪便写进排泄的答案里，这一分就丢了。常见的错误是把有害当成判据，旧教材写有毒物质，现行措辞是 waste products of metabolism and substances in excess of requirements，水与盐因此也算。叶片排出的氧气同样属于排泄，因为它是光合作用与呼吸作用的产物。答题时写移除代谢废物这几个字最稳妥。
Excretion is the removal of the waste products of metabolism and substances in excess of requirements, which is why carbon dioxide, urea and the salts in sweat all count. Egestion appears separately in the syllabus, where it covers the removal of undigested food from the body as faeces, and the dividing line is whether the substance took part in cellular reactions. Many students lose the mark here by listing faeces among the excretory products, and the older textbooks, which used the phrase toxic materials, are the usual source of that confusion.
呼吸不是呼吸动作
respiration 指细胞内释放能量的化学反应，breathing 或 gas exchange 指把空气吸进肺里再呼出去的动作。选择题常把两者放进同一题的四个选项，问哪种过程在所有活细胞里都发生，答案只能是 respiration。皮肤细胞、根毛细胞、干种子里的胚都不做气体交换动作，但它们每一个都在呼吸。厌氧条件下酵母把葡萄糖转成酒精与二氧化碳，人体肌肉细胞转成乳酸，两种都算 respiration，只是没有氧气参与。很多学生以为呼吸一定要氧气，看到无氧两个字就判它不是呼吸。写答案时用细胞内化学反应、释放能量供代谢这类措辞，比写吸入氧气安全得多。
Respiration means the chemical reactions inside cells that release energy, whereas breathing, or gas exchange, is the mechanical movement of air into and out of the lungs. A multiple-choice item often places both processes among the four options and asks which one happens in every living cell, and only respiration survives that test. Skin cells, root hair cells and the embryo inside a dry seed do not move air at all, yet all of them respire, and anaerobic respiration in yeast and in human muscle follows exactly the same definition without oxygen.
生长为什么强调干重
现行定义把 growth 写成体积与干重的永久性增加，dry mass 指样品烘干到恒重之后剩下的质量。吸水膨胀的细胞体积变大但干重没变，所以不算生长，干种子泡一夜膨大同样不算。测干重的做法是先称鲜重，再放烘箱烘到两次质量不变，然后称第二次，两者之差就是含水量。题目常给你连续三天的干重读数，要你判断哪一组体现生长，只要看数字是不是每一步都在增加。常见的错误是只看高度不看质量，把浇过水的植株判成生长。细胞数量增加与细胞体积增大是生长的两层含义，根尖与茎尖的分生区负责前一层。
The current wording treats growth as a permanent increase in size and dry mass, and dry mass is what remains after a sample has been dried to constant mass. A cell that swells with water becomes larger without gaining dry mass, so a bean that doubles in volume overnight has not grown in the sense the syllabus intends. An examination item often supplies dry mass readings taken on three consecutive days and asks which set shows growth, and the answer is the set that rises at every step; measuring height alone is the mistake that costs marks here.
敏感性看内部与外部
sensitivity 的官方措辞包含 internal or external environment 两半，血糖浓度升高与体温偏离设定值都属于内部环境的变化。植物向光弯曲、根系顺着重力方向生长是对外部环境的反应，syllabus 把它们归在后面的 tropic responses 一节。含羞草叶片被触碰后合拢、瞳孔在强光下缩小，是同一类反应的另外两个例子。很多学生以为敏感性必须依赖神经系统，植物没有神经就答不出例子。答题时先写察觉变化，再写作出反应，两个动作都出现才算完整。单细胞生物没有神经，靠细胞膜上的受体察觉化学梯度并改变运动方向。这一条在 Paper 1 与 Paper 2 的选择题里出现得比理论卷频繁。
Sensitivity is defined as the ability to detect and respond to changes in the internal or external environment, so both halves of that phrase need an example. A shoot bending towards light and a root growing downwards are responses to the external environment and are examined under tropic responses later in the course; a pupil narrowing in bright light and blood glucose drifting away from its set point belong to the internal side. Students who assume that sensitivity requires a nervous system usually leave the example blank on a plant question, even though a single-celled organism with no nerves can detect a chemical gradient and change direction.
运动在植物身上怎么算
定义是生物体或生物体的一部分产生位置改变的动作，organism or part of an organism 这半句给植物与单细胞生物留了答题空间。向日葵幼茎随太阳转动、气孔保卫细胞改变形状让气孔开闭、种子萌发时胚根向下钻，都算 movement。单细胞生物靠纤毛或伪足整体移动，草履虫是常见的例子。血液在血管里流动属于体内运输，不是 syllabus 要的 movement 例子，写上去不合适。很多学生以为植物完全不动，这一条干脆空着交卷。阅卷时只要求给出一个可以观察的动作，不需要解释背后的机制。
Movement is an action by an organism or part of an organism causing a change of position or place, and the second half of that definition is what makes plants answerable. A young sunflower stem following the sun, guard cells changing shape to open and close a stoma, and a radicle pushing downwards as a seed germinates are all acceptable examples. Circulating blood is internal transport rather than movement in this sense, so it is not a safe example, and examiners ask only for one observable action without requiring the mechanism behind it.
营养与自养的界限
nutrition 写成摄取物质用于能量、生长与发育，绿色植物靠光合作用自己制造有机物，动物与真菌摄取现成的有机物。比较题常要求写出一处不同与一处相同，相同点是两者都要从外界获得原料与能量。植物的原料是二氧化碳与水，还需要光能；动物的原料是有机物，能量来自食物里化学键的释放。很多学生以为植物不需要摄取，其实矿物质离子与水分同样要从土壤里吸收。常见的错误是把营养与呼吸塞进同一道题，一个负责获取原料，一个负责释放能量。食用真菌既不是植物也不是动物，它在五界系统里属于 fungus 这一界。
Nutrition is the taking in of materials for energy, growth and development, and it covers both the green plant that manufactures its own organic molecules and the animal or fungus that takes them ready-made. Comparison questions usually ask for one difference and one similarity, and the similarity is that both sides must obtain raw materials and energy from outside themselves; the plant needs carbon dioxide, water and light, while the animal needs food whose chemical bonds can be broken. Mineral ions and water are still taken in by a plant, so the claim that plants take nothing in is wrong, and fungi sit in their own kingdom in the five-kingdom system rather than among plants.
繁殖与生命的延续
reproduction 写成产生更多同类生物的过程，细菌二分裂、酵母出芽、草莓走茎都算。不育的个体仍然是活的，工蜂不产卵，马与驴的后代骡不能生育，所以能不能繁殖不能当作判断个体是否活着的标准。判断物种用的是另一句定义，能够相互交配并产生可育后代的群体。很多学生把这两个层次混在一起，问个体就答物种，问物种就答个体。写答案之前先看清题目问的是个体还是种群。这一条常与 growth 并列出题，一个讲复制同类，一个讲数量与体积的增加。
Reproduction covers the processes that make more of the same kind of organism, and binary fission in bacteria, budding in yeast and runners in strawberry plants all qualify. A sterile individual is still alive, so the ability to reproduce is not a test of whether a single organism is living, since the fertile-offspring criterion belongs to the separate definition of a species. Many students mix these two levels up, answering a question about an individual with the species definition or the other way round, and the safe habit is to check whether the question says individual or population before writing.
判断题里的四类陷阱
最容易踩的一类陷阱是把非生物写进生物名单，火焰会动也会消耗氧气，但它没有细胞，也不排出代谢废物。病毒是第二处坑，syllabus 在 1.3 里只要求写它由蛋白质外壳与遗传物质组成，五界系统里没有它的位置。休眠种子与干种子代谢极慢，仍然是活的，泡水之后会萌发，很多学生以为不发芽的就是死的。机器人能移动也能对光作出反应，但它不生长、不繁殖、不排泄，用两条特征一问就露馅。回答病毒为什么不算生物这类题，写蛋白质外壳加遗传物质、离开宿主不能独立繁殖，两句就够。阅卷时这段的分数通常只有一到两分，写多了反而容易自相矛盾。
Non-living things that appear to move or respond cause the most errors, because a flame moves and consumes oxygen yet has no cells and produces no metabolic waste. Viruses are treated separately in the syllabus, which asks only for a protein coat and genetic material, and they have no place in the five-kingdom system, while a dormant or dry seed is alive even though its metabolism has almost stopped. A machine that moves and reacts to light still fails the test, since it does not grow, reproduce or excrete.
分类与双名法落到卷面上
1.2 的核心是三个句子：生物按共同特征分组、物种指能相互交配并产生可育后代的群体、双名法用属名加种名。属名首字母大写，种名全小写，印刷体排斜体，手写时在名字下面划一条横线。五界是 animal、plant、fungus、prokaryote、protocist，动物界里的节肢动物再分成 myriapods、insects、arachnids、crustaceans 四支。检索表按可辨认的特征一问一答分叉，每一步只能有两个出口，某一步写出三个出口就是设计错误。很多学生把属名与种名写反，Homo 是属，sapiens 是种，顺序颠倒这一分就没有了。
Section 1.2 rests on three statements, since organisms are grouped by the features they share, a species is a group of organisms that can reproduce to produce fertile offspring, and the binomial system gives every organism a genus name and a species name. The genus takes a capital letter, the species name is written in lower case, and printed names are italicised while handwritten ones are underlined; the five kingdoms are animal, plant, fungus, prokaryote and protocist. A dichotomous key splits on identifiable features and offers exactly two options at each step, so an entry with three branches at one point is a design error, and reversing the genus and the species name is one of the most frequent slips in a classification question.
三周复习排期
第一周把七条定义抄成两列表格，左边英文术语、右边自己写的中文解释，每天遮住一边默写一遍。第二周专攻例句，每条特征准备两个不同生物的例子，植物一个、动物或微生物一个，遇到选择题直接调取。第三周做真题，把近五年 Paper 1 与 Paper 2 里涉及 1.1 到 1.4 的题目挑出来，统计自己错在哪一类，错得最多的那一类单独再练一天。每次做题之后把定义里的限定词圈出来，permanent、internal、excess of requirements 这三个词错一次就记一次。考前一周只看自己的错题表，不再翻整本书。复习节奏按每天二十分钟分配，比一次性背两小时有效。
Weeks one and two split the work in two, starting with definitions as a two-column table carrying the English term on one side and your own Chinese explanation on the other, then moving to examples with two organisms per characteristic. In the third week, pull every question on sections 1.1 to 1.4 out of the last five years of Papers 1 and 2 and count which category you keep missing, because the category with the highest count deserves a full day of its own. Circle the qualifiers in each definition as you revise, since permanent, internal and excess of requirements are the three words that quietly decide whether an answer scores.
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