Characteristics & Classification
IGCSE Biology Topic 1 15:02 English narration · English + 中文 subtitles burned in
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A car moves.
汽车会移动。
It uses fuel, gives off waste gases, and responds when you turn the wheel.
它使用燃料、排出废气，你转动方向盘时它会做出反应。
So is a car alive?
那么汽车是活的吗？
No — and biology can tell you exactly why.
不是——生物学能准确告诉你为什么。
Living things share seven processes, and a car only imitates a few of them.
生物共有七种生命过程，而汽车只模仿了其中几种。
Once you know those seven, you can sort every living thing on Earth into groups — from bacteria to blue whales.
一旦你掌握了这七种，你就能把地球上所有生物分类——从细菌到蓝鲸。
Let's start with what it means to be alive.
让我们从"什么才算活着"开始。
Welcome to characteristics and classification.
欢迎来到生物的特征与分类。
The seven life processes, naming species, keys, and the five kingdoms.
七种生命过程、物种命名、检索表，还有五界。
Let's begin.
让我们开始吧。
Every living organism carries out seven life processes, and one mnemonic holds all of them: MRS GREN — Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.
每个生物体都进行七种生命过程，而一个口诀就能把它们全装下： MRS GREN——运动、呼吸作用、应激性、生长、生殖、排泄、营养。
Getting the seven names back is the easy part.
把这七个名字背出来是容易的部分。
The marks are in the wording, because two of these mean something narrower than everyday English suggests.
分数在措辞上， 因为其中有两个的含义比日常英语窄得多。
Respiration — the chemical reactions in cells that break down nutrients to release energy.
呼吸作用——细胞中分解营养物质、释放能量的化学反应。
That is not breathing, and writing "breathing" scores nothing.
那不是呼吸动作，写"呼吸"一分也拿不到。
And Nutrition is not eating; it is taking in materials for energy, growth and development, which is why a plant making its own food still counts.
而营养也不等于吃东西；它是摄取用于能量、生长和发育的材料， 所以植物自己制造食物同样算数。
We will take all seven definitions properly in a moment.
这七个定义，我们马上就来逐条过一遍。
Here are the seven characteristics in one chart.
这张图把七个特征放在一起。
Movement is an action by an organism, or part of it, that changes its position or place.
运动是生物体或其一部分改变位置或场所的动作。
Respiration is the chemical reactions in cells that break down nutrient molecules and release energy for metabolism.
呼吸作用是细胞中分解营养物质分子、为新陈代谢释放能量的化学反应。
Metabolism means all the chemical reactions inside an organism's cells.
新陈代谢是指生物体细胞内发生的全部化学反应。
Sensitivity is detecting and responding to changes in the internal or external environment.
应激性是察觉并响应内外环境的变化。
Growth is a permanent increase in size and dry mass — not just swelling with water.
生长是大小和干重的永久性增加，不只是吸水变大。
Reproduction makes more of the same kind.
生殖产生更多同类生物。
Excretion removes the waste products of metabolism, and substances the body has in excess.
排泄排出新陈代谢的废物，以及体内过量的物质。
Nutrition takes in materials for energy, growth and development.
营养摄取用于能量、生长和发育的材料。
Write each definition as a clear full sentence.
把每个定义写成一句完整清楚的话。
Two traps lose easy marks.
两个陷阱很容易丢分。
Digestion is not one of the seven characteristics — it is only part of nutrition.
消化不是七个特征之一，它只是营养的一部分。
Breathing is not one either; breathing is just the movement of air in and out of the lungs, while respiration is the chemical energy release in cells.
呼吸动作也不是；那只是空气进出肺的运动，而呼吸作用是细胞里释放能量的化学反应。
A car moves and uses fuel, but it does not grow, does not reproduce, and does not carry out all seven processes.
汽车会移动、会用燃料，但它不生长、不生殖，也不完成全部七种过程。
Only living organisms do all seven.
只有生物体才做齐这七种。
If a question asks you to list the characteristics of life, write the full MRS GREN list with the exam wording, not everyday words like eating or breathing.
若题目要求列出生命特征，就用考试措辞写全七个， 不要用吃东西或喘气这类日常说法。
There are millions of kinds of living thing, so scientists classify them — sorting them into groups by shared features.
生物有数百万种，所以科学家给它们分类——按共同特征把它们分组。
The smallest group is the species: organisms that can reproduce to make fertile offspring.
最小的群体是物种：能繁殖出可育后代的生物。
Every species gets a two-part scientific name — the binomial system, used worldwide.
每个物种都有一个两部分的学名—— 双名法，全世界通用。
The first part is the genus, with a capital letter; the second is the species, with a small letter; and the whole name is in italics.
第一部分是属，用大写字母开头；第二部分是种，用小写字母开头； 整个名字用斜体。
Modern classification also uses DNA: organisms with more similar base sequences share a more recent ancestor, so they are more closely related.
现代分类学还使用DNA：碱基序列越相似的生物， 共有的祖先越近，亲缘关系就越近。
Look at this scientific name.
看这个学名。
The first word is the genus, starting with a capital letter.
第一个词是属，大写字母开头。
The second word is the species, starting with a small letter.
第二个词是种，小写字母开头。
The whole name is written in italics.
整个名字用斜体书写。
Humans are Homo sapiens — genus Homo, species sapiens.
人类的学名是智人，，属名在前，种名在后。
Two rats named Rattus norvegicus and Rattus rattus share the same genus, Rattus, but they are different species.
两种老鼠同属不同种：它们属名相同，种名不同。
Fertile offspring means the young can themselves go on to have young.
可育后代的意思是， 这些后代自己也能继续生育。
Organisms in the same group share more features with each other than with organisms in other groups.
同一组里的生物彼此共有的特征， 比与其他组生物共有的更多。
That is why classification is useful: it puts related living things together.
这就是分类的用处：把亲缘近的生物放在一起。
Modern classification tries to show evolutionary relationships — how closely different organisms are related.
现代分类试图展示进化关系，也就是不同生物亲缘有多近。
Organisms that are more closely related share a more recent ancestor.
亲缘更近的生物共有更近的祖先。
Scientists compare the base sequence of DNA: the order of the chemical letters that make up an organism's genes.
科学家比较基因的碱基序列：组成基因的化学字母的排列顺序。
The rule is simple.
规则很简单。
Organisms that share a more recent ancestor have more similar DNA base sequences.
共有更近祖先的生物，碱基序列更相似。
Organisms that share only a distant ancestor have less similar base sequences.
只共有遥远祖先的生物，碱基序列差异更大。
So a DNA base sequence can be used both to classify organisms and to work out how closely two species are related.
因此碱基序列既能给生物分类，也能判断两个物种亲缘有多近。
On the exam, more similar DNA means more closely related — they share a more recent common ancestor.
考试里，碱基序列越相似，亲缘关系就越近，，它们共有更近的共同祖先。
To identify an unknown organism, use a dichotomous key.
要鉴定一个未知生物，就用二歧检索表。
Dichotomous means splitting into two.
二歧的意思是分成两支。
At each step the key gives exactly two choices about a feature; you pick the one that fits, and it sends you to the next pair.
每一步检索表都给出恰好两个关于某个特征的选择；你选择符合的那个， 它就把你带到下一对选择。
Suppose an insect has two pairs of wings.
假设一只昆虫有两对翅膀。
Step one asks only: wings, or no wings?
第一步只问：有翅膀还是没翅膀？
It has wings, so go to step two.
它有翅膀，所以去第二步。
Step two asks: one pair, or two pairs?
第二步问：一对还是两对？
Two pairs — so it is a butterfly.
两对——所以它是蝴蝶。
Follow the route one step at a time, and never jump ahead to the name that looks right.
一步一步跟着路线走，绝不要直接跳到看起来对的名字。
This flowchart is a dichotomous key.
这张流程图就是二歧检索表。
Each numbered step splits into two choices, and each choice leads to the next step or to a named organism.
每个编号步骤分成两个选择， 每个选择通向下一步或通向某个命名的生物。
When you build a key yourself, choose clear features you can see — for example has wings or has no wings — not features that change, such as size.
自己编检索表时， 要选看得见的清晰特征，，例如有翅膀或没有翅膀，，不要选会变化的特征，比如大小。
A worked example from the handout: step one, has wings go to two; no wings go to three.
手稿里的例题：第一步，有翅膀去第二步；无翅膀去第三步。
Step two, one pair of wings means housefly; two pairs means butterfly.
第二步，一对翅膀是家蝇；两对翅膀是蝴蝶。
An unknown insect has two pairs of wings.
未知昆虫有两对翅膀。
Step one only asks wings or no wings, so wings sends you to step two.
第一步只问有没有翅膀，所以有翅膀就去第二步。
At step two, two pairs gives butterfly.
在第二步，两对翅膀对应蝴蝶。
Always start at the first pair and follow the route step by step.
一定要从第一对选择开始，一步一步跟着路线走。
The biggest groups are kingdoms, and there are five: animals, plants, fungi, prokaryotes and protoctists.
最大的分组是界，共有五个：动物、植物、真菌、原核生物和原生生物。
Naming them is the easy half.
把名字说出来只是容易的那一半。
A question never tells you "this is a fungus" — it hands you a description and expects you to sort it, so what you actually need is which feature settles which case.
题目从不会告诉你"这是真菌"—— 它给你一段描述，要你自己归类，所以你真正需要的是：哪一个特征能定哪一桩案子。
And the trap is that a shared feature settles nothing.
而陷阱在于：共有的特征什么也定不了。
Plants are many-celled, but so are animals, so "many cells" alone can never separate those two — you have to reach for the cell wall, or for whether it makes its own food.
植物是多细胞的，可动物也是， 所以单凭"多细胞"永远分不开这两者——你必须去看细胞壁， 或者看它能不能自己制造食物。
Prokaryotes, like bacteria, are the one kingdom whose cells have no nucleus at all, which makes that single feature decisive on its own.
原核生物，比如细菌， 是唯一细胞里完全没有细胞核的一个界，所以这一个特征本身就能定案。
Let's put all five against the features that separate them.
我们把五个界和真正能区分它们的特征摆在一起看。
Living organisms split into five kingdoms by their main features.
生物按主要特征分成五界。
Animals are made of many cells, have no cell wall, cannot make their own food, and most can move their whole body.
动物多细胞、无细胞壁、不能自己制造食物， 多数能整体移动。
Plants are many-celled with a cell wall, and they photosynthesise using chloroplasts.
植物多细胞、有细胞壁，用叶绿体进行光合作用。
Fungi, such as moulds, mushrooms and yeast, have cell walls but cannot photosynthesise; they feed on dead or living matter.
真菌，例如霉菌、蘑菇和酵母，有细胞壁但不能光合作用；它们以死物或活物为食。
Prokaryotes, for example bacteria, are single-celled with no nucleus.
原核生物，例如细菌，是单细胞且没有细胞核。
Protoctists, for example amoeba and algae, are usually single-celled and do have a nucleus.
原生生物，例如变形虫和藻类，通常是单细胞且有细胞核。
At Core level you place organisms into animals and plants; the fungus, prokaryote and protoctist kingdoms are Supplement only.
核心水平只需把生物放进动物界和植物界；真菌、原核生物和原生生物属补充内容。
Decide where an organism belongs by looking at its main features.
根据主要特征判断生物属于哪一界。
This is a fungus — the fly agaric, a mushroom.
这是一种真菌，，毒蝇伞，一种蘑菇。
Fungi include moulds, mushrooms and yeast.
真菌包括霉菌、蘑菇和酵母。
They have cell walls, but they cannot photosynthesise, so they do not make their own food the way plants do.
它们有细胞壁，但不能进行光合作用，所以不能像植物那样自己制造食物。
Instead they feed on dead or living matter.
它们以死物或活物为食。
That is the exam contrast with plants: both may have cell walls, but only plants use chloroplasts and photosynthesis.
这是和植物的考试对比：两者都可能有细胞壁， 但只有植物用叶绿体进行光合作用。
If you see a mushroom in a question, place it in the fungus kingdom, not with plants.
题目里若出现蘑菇，应归入真菌界，不要归到植物。
These rod-shaped cells are bacteria — a prokaryote seen under an electron microscope.
这些杆状细胞是细菌，，电子显微镜下的原核生物。
Prokaryotes are single-celled and their cells have no nucleus.
原核生物是单细胞的，细胞没有细胞核。
That is the key difference from protoctists.
这是与原生生物的关键区别。
Protoctists, like amoeba and algae, are usually single-celled too, but their cells do have a nucleus.
原生生物，如变形虫和藻类，通常也是单细胞，但细胞有细胞核。
So if a single cell has no nucleus, it is a prokaryote. If a single cell has a nucleus, it is often a protoctist.
所以单细胞且无核的是原核生物；单细胞且有核的往往是原生生物。
Animals and plants are many-celled, so they never sit in either of these two single-celled kingdoms.
动物和植物是多细胞的，不会落在这两个单细胞界里。
The animal kingdom splits first by one feature: a backbone.
动物界首先按一个特征划分：脊柱。
Vertebrates have one, and their five groups get the diagram to themselves in a moment.
脊椎动物有脊柱， 而它们的五个类群，马上会有一整张图专门来讲。
Arthropods have no backbone — instead a hard exoskeleton on the outside and jointed legs — and they are told apart by COUNTING, not by looking, which makes them the easier half if you know what to count.
节肢动物没有脊柱——而是在外面有坚硬的外骨骼，还有分节的腿—— 而且区分它们靠的是"数"，不是"看"， 所以只要知道该数什么，它们反而是容易的那一半。
Insects have three body parts and three pairs of legs.
昆虫有三个体部和三对腿。
Arachnids have two body parts and four pairs.
蛛形类有两个体部和四对腿。
Crustaceans have many legs and two pairs of antennae.
甲壳类有很多腿和两对触角。
Myriapods have many segments, each one carrying legs.
多足类有许多体节，每一节都带着腿。
Body parts, leg pairs, antennae — count those three and every arthropod question answers itself.
体部数、腿的对数、触角——把这三样数清楚， 节肢动物的题目就自己有了答案。
The left side shows vertebrates — animals with a backbone.
左侧是脊椎动物，，有脊柱的动物。
Memorise the five groups with their features.
记住五个类群及其特征。
Mammals have fur or hair and feed their young on milk.
哺乳动物有毛发或绒毛，用乳汁喂养幼崽。
Birds have feathers and a beak, and lay eggs with hard shells.
鸟类有羽毛和喙，产硬壳蛋。
Reptiles have dry skin covered with scales and lay eggs with leathery shells on land.
爬行动物皮肤干燥覆盖鳞片，在陆地上产革质壳的蛋。
Amphibians have moist skin, lay eggs in water, and the young live in water.
两栖动物皮肤湿润，在水中产卵，幼体也生活在水中。
Fish have wet scales and fins, breathe using gills, and lay eggs in water.
鱼类有湿鳞和鳍，用鳃呼吸，在水中产卵。
Notice the egg and habitat clues: reptiles on land with leathery shells; amphibians and fish eggs in water.
注意卵和栖息地线索：爬行动物在陆地产革质壳卵；两栖动物和鱼的卵在水中。
Those details win marks.
这些细节能得分。
The right side shows arthropods — animals with no backbone.
右侧是节肢动物，，没有脊柱的动物。
They have a hard outer skeleton, an exoskeleton, and legs that bend at joints.
它们有坚硬的外骨骼，腿在关节处弯曲。
There are four main groups.
主要有四个类群。
Insects: body in three parts, three pairs of legs, usually two pairs of wings, and one pair of antennae.
昆虫：身体分三部分，三对腿，通常两对翅，一对触角。
Arachnids: body in two parts, four pairs of legs, no wings, and no antennae.
蛛形类：身体分两部分，四对腿，无翅，无触角。
Crustaceans: many pairs of legs, two pairs of antennae, and most live in water.
甲壳类：多对腿，两对触角，多数生活在水中。
Myriapods: a long body made of many segments, with one or two pairs of legs on each segment.
多足类：身体细长由许多体节组成，每节有一对或两对腿。
Count body parts and leg pairs carefully — that is how the exam separates insects from arachnids.
仔细数体部和腿的对数，，考试就靠这些把昆虫和蛛形类分开。
Plants are grouped too, and one question makes the first cut: does it make seeds?
植物也要分组，而第一刀由一个问题来切：它结不结种子？
Ferns have roots, stems and leaves like any plant, but no flowers and no seeds — they reproduce by spores instead, which is why you find them in damp, shady places.
蕨类植物和别的植物一样有根、茎和叶，却不开花、不结种子—— 它们用孢子繁殖，所以你总在潮湿背阴的地方见到它们。
Flowering plants do make seeds, inside flowers, and they divide again by their seed-leaves, the cotyledons — the diagram after this takes that split properly.
开花植物确实结种子，种子长在花里， 而它们再按子叶——也就是种子里的叶——继续划分， 接下来那张图会好好讲这个划分。
Finally, viruses, which are the odd ones out completely.
最后是病毒，它们完全是异类。
They belong to no kingdom at all, because they are not made of cells: a virus is just a protein coat around its genetic material.
它们不属于任何一界，因为它们根本不是由细胞构成的： 病毒只是包裹着遗传物质的一层蛋白质外壳。
It cannot reproduce by itself, only inside a host's living cells.
它无法自己繁殖，只能在宿主的活细胞里繁殖。
That is why "is a virus alive?" is a real question, and why nobody asks it about a fern.
这正是"病毒算不算活的"会成为一个真问题的原因， 也是没有人拿这个问题去问蕨类的原因。
Flowering plants split by their seed-leaves, the cotyledons.
开花植物按子叶划分。
Monocotyledons have one cotyledon.
单子叶植物有一片子叶。
Their leaves are long and narrow, and the veins run side by side — parallel veins.
叶子细长，叶脉并排而行，，平行叶脉。
Dicotyledons have two cotyledons.
双子叶植物有两片子叶。
Their leaves are broad, and the veins form a branching net with a midrib.
叶子宽阔，叶脉形成带主脉的分枝网。
Look at this pair of leaves: parallel lines mean monocot; a branching net means dicot.
看这两片叶子：平行线是单子叶；分枝网是双子叶。
Ferns are different again — they have roots, stems and leaves, but they make no flowers or seeds and reproduce using tiny spores.
蕨类又不同，，它们有根、茎和叶，但不开花不结种子，用微小孢子繁殖。
If a plant has flowers and seeds, it is a flowering plant; then check the cotyledons or the vein pattern.
若植物有花和种子，就是开花植物；再查子叶数或叶脉样式。
Viruses are not placed in any kingdom.
病毒不归入任何一界。
They are not made of cells, so many scientists do not count them as living.
它们不是由细胞构成的，所以许多科学家不把它们算作生物。
A virus is very simple, with only two parts: an outer protein coat, and genetic material — its genes — inside.
病毒非常简单，只有两部分：外面的蛋白质外壳，以及里面的遗传物质，，它的基因。
Look at the diagram: a hexagonal coat around a strand of genetic material.
看图：六边形外壳包着一股遗传物质。
A virus cannot carry out the life processes on its own.
病毒不能独自完成生命过程。
It can only reproduce inside the living cells of a host — the organism it infects.
它只能在宿主的活细胞内繁殖，，宿主就是被它感染的生物。
That is why viruses sit outside the five kingdoms: no cells, no independent life processes, only host-cell reproduction.
这就是病毒落在五界之外的原因：没有细胞，没有独立的生命过程，只能靠宿主细胞繁殖。
Three marks to lock in.
锁住三个分。
First: learn the seven characteristics with their exact definitions — and remember digestion is not one of them; it is only part of nutrition, and breathing is not one either.
第一：背熟七个特征及其准确定义——记住消化不是其中之一， 它只是营养的一部分，呼吸动作也不是。
Second: in a scientific name, the genus takes a capital letter, the species a small one, and both are italic.
第二：学名中，属用大写字母开头， 种用小写字母，两者都用斜体。
Third: more similar DNA base sequences mean the organisms are more closely related — they share a more recent ancestor.
第三：DNA碱基序列越相似，生物的亲缘关系越近—— 它们共有更近的祖先。
Master these, and this topic is yours.
掌握这些，这个专题就是你的了。
One more exam habit for keys.
检索表还有一个考试习惯。
To use a dichotomous key, start at the first pair of choices and follow the route step by step.
使用二歧检索表时，从第一对选择开始，一步一步跟着路线走。
Do not jump ahead to a name that looks familiar.
不要跳到看起来熟悉的名字。
When you write a key, use visible features that do not change with age or growth.
编写检索表时，要用不会随年龄或生长而改变的可见特征。
And when you define a species, say organisms that can reproduce to make fertile offspring — the word fertile matters.
定义物种时，要说能繁殖出可育后代的生物，，可育这个词很关键。
Put those three ideas with the seven life processes, binomial naming, and DNA relatedness, and Topic One is secure.
把这三点连同七种生命过程、双名法命名和碱基序列亲缘关系一起掌握， 第一专题就稳了。