Topic 1: Cell biology
AQA · GCSE · Biology หัวข้อ 1 48:14 การบรรยายภาษาอังกฤษ · คำบรรยายภาษาอังกฤษ + 中文 ลอยตัวบนภาพ
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Transcript
Cells are the basic unit of all forms of life.
细胞是一切生命的基本单位。
Plant and animal cells keep their genetic material inside a nucleus; bacterial cells do not, carrying a single DNA loop and sometimes plasmids instead.
动植物细胞的遗传物质包在细胞核内；细菌没有核，有环状 DNA，有时还有质粒。
This topic connects structure to function everywhere: every labelled part, every specialised cell, and three required practicals — the microscope, agar plates and osmosis.
本专题处处把结构与功能联系起来：每个结构、每种特化细胞，以及三个必做实验——显微镜、琼脂平板和渗透作用。
Here are three cell models: an animal cell, a plant cell and a bacterium.
这里有三个细胞模型：动物细胞、植物细胞和细菌。
They are not drawn to scale.
它们没有按比例绘制。
Each number marks one structure, and the key on the next frames names them.
每个数字标出一个结构，后面的表格给出名称。
Notice which numbers appear in all three cells, and which appear in only one.
注意哪些数字三种细胞都有，哪些只出现在一种细胞里。
Use the models to name two structures a bacterial cell has that an animal cell does not.
利用模型，说出细菌细胞有而动物细胞没有的两个结构。
Think about the cell boundary, and about DNA that is not inside a nucleus.
想一想细胞的边界，以及不在细胞核内的DNA。
Pause the video and try it.
暂停视频，试着回答。
Structures one to five.
结构一到五。
The nucleus holds the DNA and controls the cell's activities.
细胞核含有DNA，控制细胞的活动。
The cell membrane controls what enters and leaves.
细胞膜控制物质进出。
Most chemical reactions happen in the cytoplasm.
大多数化学反应在细胞质中进行。
Mitochondria carry out aerobic respiration, and ribosomes make proteins.
线粒体进行有氧呼吸，核糖体合成蛋白质。
Bacteria have ribosomes too: having no nucleus does not mean having no DNA.
细菌也有核糖体：没有细胞核并不等于没有DNA。
Structures six to ten.
结构六到十。
The cell wall supports the cell, and in plants it is made of cellulose.
细胞壁支持细胞，植物细胞壁由纤维素构成。
The permanent vacuole holds cell sap and keeps the cell firm.
永久液泡储存细胞液，使细胞保持坚挺。
Chloroplasts carry out photosynthesis.
叶绿体进行光合作用。
Bacteria carry their main DNA as a single loop, and many also have plasmids, small rings of DNA.
细菌的主要DNA是一个环，许多细菌还有质粒，即小的DNA环。
Not every bacterium has plasmids, and not every plant cell has chloroplasts.
并非每个细菌都有质粒，也并非每个植物细胞都有叶绿体。
First, the boundary: an animal cell has no cell wall, but a bacterium does.
第一，边界：动物细胞没有细胞壁，而细菌有。
Second, the DNA: a plasmid, or the main DNA loop outside a nucleus, is another valid answer.
第二，DNA：质粒，或者不在细胞核内的主要DNA环，也是正确答案。
The membrane, cytoplasm and ribosomes are in both cells, so they cannot tell the two apart.
细胞膜、细胞质和核糖体两种细胞都有，所以不能用来区分它们。
This exam figure shows a bacterial cell beside a yeast cell.
这幅考题图把细菌细胞和酵母细胞放在一起。
It is not drawn to scale.
它没有按比例绘制。
Look for the structures that appear in only one of the two cells.
找出只出现在其中一种细胞里的结构。
Which statement classifies the two cells correctly?
哪一项正确地给两种细胞分类？
Remember what decides prokaryotic or eukaryotic.
想一想原核与真核由什么决定。
Choose one statement.
选出一项。
Bacteria are prokaryotic: their main DNA is not enclosed in a nucleus.
细菌是原核生物：它们的主要DNA不包在细胞核内。
Yeast is eukaryotic: its genetic material is inside a nucleus, because yeast is a fungus, not a bacterium.
酵母是真核生物：它的遗传物质在细胞核内，因为酵母是真菌，不是细菌。
So the fourth statement is correct.
所以第四项正确。
A cell wall alone does not make a cell prokaryotic.
仅有细胞壁并不能说明细胞是原核细胞。
Now give two features of the yeast cell that a bacterial cell does not have.
现在说出酵母细胞有而细菌细胞没有的两个特征。
Name structures you can see in the figure: look at the large internal regions and the small membrane-bound organelles.
说出图中能看到的结构：看看大的内部区域和小的有膜细胞器。
Any two of the nucleus, the vacuole or the mitochondria earn the two marks.
细胞核、液泡、线粒体中任意两个都可以得两分。
The cell membrane, cell wall and ribosomes do not count, because bacteria have them too.
细胞膜、细胞壁和核糖体不算，因为细菌也有。
And the image is not to scale, so do not judge real size from its printed width.
图像没有按比例绘制，所以不要根据印刷宽度判断真实大小。
Why do muscle cells contain many mitochondria and many ribosomes?
为什么肌肉细胞含有许多线粒体和核糖体？
Link each structure to a process, and that process to what the muscle cell does.
把每个结构与一个过程联系起来，再把这个过程与肌肉细胞的功能联系起来。
Pause and try it.
暂停并试着回答。
Mitochondria carry out aerobic respiration.
线粒体进行有氧呼吸。
Respiration releases the energy the muscle needs to contract.
呼吸作用释放肌肉收缩所需的能量。
Ribosomes make proteins.
核糖体合成蛋白质。
Those proteins include the contractile fibres the cell needs.
这些蛋白质包括细胞所需的收缩纤维。
Four linked points explain both structures.
四个相互联系的要点解释了两种结构。
Give one structural feature of a sperm cell, and explain how it helps fertilisation.
说出精子细胞的一个结构特征，并解释它如何有助于受精。
Choose the tail or the many mitochondria, then link it to movement towards the egg.
选择尾部或大量线粒体，再把它与游向卵细胞联系起来。
One answer: the tail propels the sperm towards the egg.
一种答案：尾部推动精子游向卵细胞。
Another: many mitochondria release energy by aerobic respiration for swimming.
另一种：大量线粒体通过有氧呼吸释放游动所需的能量。
Name one feature and explain its advantage.
说出一个特征并解释它的好处。
A second, unrelated feature does not replace the explanation.
再写一个无关的特征并不能代替解释。
Three specialised animal cells.
三种特化的动物细胞。
A sperm cell has a tail and mitochondria to move towards the egg.
精子细胞有尾部和线粒体，可以游向卵细胞。
A nerve cell has a long, insulated axon to carry impulses over a distance.
神经细胞有长而绝缘的轴突，可以远距离传导冲动。
A muscle cell has contractile fibres and mitochondria for contraction.
肌肉细胞有收缩纤维和线粒体，用于收缩。
Always say how a feature helps, not only what it is.
一定要说明特征如何起作用，而不只是说它是什么。
Three specialised plant cells.
三种特化的植物细胞。
A root hair cell has a long projection with a large surface for taking up water and ions.
根毛细胞有长的突起，表面积大，用于吸收水和离子。
Xylem is hollow, with walls strengthened by lignin, so water flows and the plant is supported.
木质部是中空的，细胞壁由木质素加固，使水能流动并支撑植物。
Phloem sieve tubes have sieve plates, so dissolved sugars can flow.
韧皮部筛管有筛板，使溶解的糖能够流动。
Not every plant cell has chloroplasts: a root hair cell has none.
并非每个植物细胞都有叶绿体：根毛细胞就没有。
Explain the difference between cell differentiation and cell division.
解释细胞分化与细胞分裂的区别。
Ask yourself: what makes a cell specialised, and what increases the number of cells?
问问自己：什么使细胞特化？ 什么增加细胞的数量？
Pause and try it.
暂停并试着回答。
Differentiation means a cell gains the structures it needs for a specialised function.
分化是指细胞获得完成特定功能所需的结构。
Cell division increases the number of cells.
细胞分裂增加细胞的数量。
Most animal cells differentiate early in development, and in mature animals division is mainly for repair and replacement.
大多数动物细胞在发育早期就完成分化，成熟动物的细胞分裂主要用于修复和更新。
Many plant cells keep the ability to differentiate throughout life.
许多植物细胞终生保持分化的能力。
Magnification is image size divided by real size.
放大倍数等于像的大小除以实物大小。
Resolution is the ability to tell two close structures apart.
分辨率是区分两个相近结构的能力。
Electron microscopes have higher magnification and higher resolution, so they show finer detail.
电子显微镜放大倍数和分辨率都更高，所以能显示更精细的结构。
Enlarging a blurry image makes it bigger, but it reveals nothing new.
把模糊的图像放大只会让它变大，却不会显示新的结构。
An image is four point eight centimetres wide at a magnification of twelve hundred.
一个像宽四点八厘米，放大倍数为一千二百倍。
Find the real size in micrometres.
求实物大小，单位用微米。
Convert centimetres to micrometres first, then rearrange the magnification equation.
先把厘米换算成微米，再对放大倍数公式变形。
Pause and try it.
暂停并试着计算。
Convert first: four point eight centimetres is forty-eight thousand micrometres.
先换算：四点八厘米等于四万八千微米。
Magnification equals image size over real size, so real size equals image size over magnification.
放大倍数等于像的大小除以实物大小，所以实物大小等于像的大小除以放大倍数。
Forty-eight thousand micrometres divided by twelve hundred is forty micrometres.
四万八千微米除以一千二百，得四十微米。
Magnification has no unit, but the real size needs a length unit.
放大倍数没有单位，但实物大小需要长度单位。
Now the worksheet version: an image two point four millimetres long at a magnification of eight hundred.
现在做练习题：一个像长二点四毫米，放大倍数为八百倍。
Calculate the real size in micrometres, showing the equation and the calculation.
求实物大小，单位用微米，并写出公式和计算过程。
Pause and try it.
暂停并试着计算。
Convert: two point four millimetres is two thousand four hundred micrometres.
换算：二点四毫米等于两千四百微米。
Write the equation: real size equals image size over magnification.
写出公式：实物大小等于像的大小除以放大倍数。
Substitute: two thousand four hundred divided by eight hundred is three point zero micrometres.
代入：两千四百除以八百，得三点零微米。
Conversion, division and an answer with its unit are all visible.
换算、除法和带单位的答案都要写出来。
Centi means ten to the minus two, so one centimetre is ten thousand micrometres.
厘表示十的负二次方，所以一厘米等于一万微米。
Milli means ten to the minus three: one millimetre is a thousand micrometres.
毫表示十的负三次方：一毫米等于一千微米。
Micro means ten to the minus six: one micrometre is a thousand nanometres.
微表示十的负六次方：一微米等于一千纳米。
Nano means ten to the minus nine: one millimetre is a million nanometres.
纳表示十的负九次方：一毫米等于一百万纳米。
Convert before dividing.
先换算，再做除法。
A six-mark question.
一道六分题。
A cylinder-shaped structure has a volume of twenty-four point five million cubic nanometres and a radius of one hundred and twenty-five nanometres.
一个圆柱形结构的体积为二千四百五十万立方纳米，半径为一百二十五纳米。
Its image is four millimetres long.
它的像长四毫米。
You are given that real length equals volume divided by pi times radius squared.
题目给出：实际长度等于体积除以圆周率乘半径的平方。
First find the real length, then convert the image length and calculate the magnification.
先求实际长度，再换算像的长度并计算放大倍数。
Pause and try it.
暂停并试着计算。
Start with the given equation: length equals volume over pi r squared.
从给出的公式开始：长度等于体积除以圆周率乘半径平方。
Substitute twenty-four point five million cubic nanometres, with pi as three point one four and a radius of one hundred and twenty-five nanometres.
代入二千四百五十万立方纳米，圆周率取三点一四，半径一百二十五纳米。
The length is about four hundred and ninety-nine point four nanometres.
长度约为四百九十九点四纳米。
Keep the extra digits for the next step.
保留多余的位数，用于下一步。
The image length is given as four millimetres.
题目给出像长四毫米。
One millimetre is a million nanometres, so the image is four million nanometres long.
一毫米等于一百万纳米，所以像长四百万纳米。
Use the stated length; do not measure a resized picture on your screen.
使用题目给出的长度，不要去量屏幕上缩放过的图。
Magnification equals image size over real size.
放大倍数等于像的大小除以实物大小。
Four million nanometres divided by four hundred and ninety-nine point four nanometres is about eight thousand and ten.
四百万纳米除以四百九十九点四纳米，约为八千零一十。
So the magnification is about times eight thousand and ten.
所以放大倍数约为八千零一十倍。
The units cancel, and an answer with a unit loses the mark.
单位相互抵消，答案带单位会失分。
Required practical one, with a light microscope.
必做实验一：使用光学显微镜。
Find and focus on the specimen before you increase the magnification.
先找到标本并对焦，再提高放大倍数。
Observe the structures that are really there.
观察真实存在的结构。
Draw clear outlines, with label lines that touch the right part.
画出清晰的轮廓，标注线要准确指向相应部分。
Then show the scale, with a magnification or a scale bar.
然后标明比例：写上放大倍数或画比例尺。
Do not draw an organelle just because a model shows it.
不要因为模型里有某个细胞器就把它画上。
A printed micrograph is enlarged.
一张印刷的显微照片被放大了。
Explain why its original printed magnification may now be wrong, and how a scale bar on the image helps.
解释为什么原来标注的放大倍数现在可能不对，以及图上的比例尺有什么帮助。
Does the real object get bigger?
实物会变大吗？
Does the bar grow with the image?
比例尺会随图像一起变大吗？
Pause and think it through.
暂停并想一想。
If the image size changes but the real size does not, the magnification changes.
如果像的大小改变而实物大小不变，放大倍数就会改变。
A scale bar is resized with the image, so it still matches the object.
比例尺随图像一起缩放，所以它与实物的对应关系保持不变。
In practice, use the dimensions you are given, and put a valid scale on your practical drawings.
实际做题时，使用题目给出的尺寸，并在实验图上标出有效的比例。
One bacterium divides every twenty minutes.
一个细菌每二十分钟分裂一次。
How many cells are there after two hours?
两小时后有多少个细胞？
Convert hours to minutes, count the division intervals, then double repeatedly.
先把小时换算成分钟，数出分裂的次数，再反复加倍。
Pause and try it.
暂停并试着计算。
Two hours is one hundred and twenty minutes.
两小时是一百二十分钟。
The number of divisions is the time elapsed divided by the division time.
分裂次数等于经过的时间除以每次分裂所需的时间。
One hundred and twenty divided by twenty is six divisions.
一百二十除以二十，得六次分裂。
Six divisions is not six cells.
六次分裂并不等于六个细胞。
The final number is the starting number times two to the power of the number of divisions.
最终数量等于初始数量乘以二的分裂次数次方。
One times two to the sixth is sixty-four cells.
一乘二的六次方，得六十四个细胞。
Check by doubling: two, four, eight, sixteen, thirty-two, sixty-four.
用加倍来检查：二、四、八、十六、三十二、六十四。
Higher Tier: write sixty-four in standard form.
高阶内容：用科学记数法写出六十四。
Put one non-zero digit before the decimal point, then choose the power of ten.
小数点前只保留一位非零数字，再确定十的几次方。
Pause and try it.
暂停并试着写。
Sixty-four is six point four times ten to the one.
六十四等于六点四乘十的一次方。
Check: six point four times ten is sixty-four.
检查：六点四乘十等于六十四。
The number in front must be at least one and less than ten, and changing how you write a count must not change its value.
前面的数必须大于或等于一、小于十；改变写法不能改变数值。
This prediction rests on conditions.
这个预测依赖于条件。
Enough nutrients and a suitable temperature allow rapid binary fission.
充足的营养和适宜的温度使细菌能快速进行二分裂。
A stated, constant division time is what makes the doubling calculation possible.
给定且恒定的分裂时间才使加倍计算成为可能。
Bacteria can grow in nutrient broth or on agar.
细菌可以在营养肉汤或琼脂上生长。
If conditions change or nutrients run short, the same rate may no longer apply: twenty minutes is not a rate for every bacterium.
如果条件改变或营养不足，同样的速率可能就不再适用：二十分钟并不是所有细菌的分裂速率。
Why is the inoculating loop passed through a flame before use?
为什么接种环在使用前要在火焰上灼烧？
Say what the flame kills, and why that matters for the culture.
说明火焰杀死了什么，以及这对培养物为什么重要。
Pause and try it.
暂停并试着回答。
The action: sterilising the loop kills the microorganisms already on it.
操作：给接种环灭菌，杀死环上已有的微生物。
The reason: this reduces contamination, so only the intended bacterium is transferred.
原因：这能减少污染，使转移的只是目标细菌。
Be specific: name the loop and the treatment.
要具体：写明接种环和处理方法。
'Clean equipment' is too vague.
只写“清洁器材”太笼统。
Describe two aseptic techniques used in this investigation.
描述本实验中使用的两种无菌操作。
Use specific items and actions: which things are sterilised before use, and how is exposure to the air reduced?
要写具体的器材和操作：哪些东西在使用前灭菌？ 如何减少与空气的接触？
Pause and try it.
暂停并试着回答。
Each action has a purpose.
每项操作都有目的。
Sterilising the dishes and the culture medium kills unwanted microorganisms.
给培养皿和培养基灭菌，杀死不需要的微生物。
Sterilising the loop before a transfer reduces contamination from the loop.
转移前给接种环灭菌，减少来自接种环的污染。
Lifting the lid as little as possible, and taping it on, reduces contamination from the air.
尽量少打开盖子，并用胶带固定，减少来自空气的污染。
Storing the dish upside down stops condensation dripping onto the agar, but on its own it does not count as an aseptic technique.
把培养皿倒置存放，防止冷凝水滴到琼脂上，但单独这一项不算无菌操作。
Scientists incubated these cultures at thirty-seven degrees Celsius, but school students use a maximum of twenty-five.
科学家在三十七摄氏度下培养这些细菌，而学校学生最高只用二十五摄氏度。
Explain the difference.
解释这种差别。
What does thirty-seven degrees correspond to, and why does a school use a lower maximum?
三十七摄氏度对应什么？ 学校为什么使用较低的最高温度？
Pause and try it.
暂停并试着回答。
Thirty-seven degrees is human body temperature.
三十七摄氏度是人体体温。
The Salmonella being studied grows better at that temperature.
所研究的沙门氏菌在这个温度下生长得更好。
In school, a maximum of twenty-five degrees reduces the growth of organisms that are harmful to humans.
学校里最高二十五摄氏度，可以减少对人体有害的微生物的生长。
It does not guarantee that only harmless organisms grow.
但这并不保证只有无害的微生物生长。
This exam figure shows an agar plate with paper discs soaked in different antibiotics, plus one disc with no antibiotic.
这幅考题图展示一个琼脂平板，上面有浸过不同抗生素的纸片，还有一片不含抗生素的纸片。
The clear zones around some discs are where bacteria did not grow.
部分纸片周围的透明区是细菌没有生长的地方。
Explain the purpose of the paper disc with no antibiotic.
解释不含抗生素的纸片有什么作用。
What comparison does it allow?
它可以提供什么比较？
Could the paper itself stop the bacteria growing?
纸片本身会不会阻止细菌生长？
Pause and try it.
暂停并试着回答。
The untreated disc gives a comparison.
未处理的纸片提供对照。
It checks that any clear zone is caused by the antibiotic, not by the paper disc.
它用来检验透明区是由抗生素造成的，而不是纸片本身。
In words: this disc is a control. It is not a control variable.
术语上，这片纸是对照，而不是控制变量。
Two parts.
两个小题。
Why would you choose antibiotic A or B from this plate?
为什么从这个平板中会选择抗生素A或B？
And how could you compare their effects with numbers?
如何用数据比较它们的效果？
Look at which discs have the largest clear zones, and think about which length or area you could measure.
看看哪些纸片的透明区最大，再想想可以测量哪个长度或面积。
Pause and try it.
暂停并试着回答。
The evidence: A and B have the largest zones where bacterial growth is prevented.
证据：A和B阻止细菌生长的区域最大。
To compare them with numbers, measure each zone's diameter or radius, or calculate each zone's area.
要用数据比较，就测量每个抑菌圈的直径或半径，或计算每个抑菌圈的面积。
Use the same measuring rules and the same test conditions for every disc.
每片纸片都用相同的测量方法和相同的实验条件。
This plate is from a different exam.
这个平板来自另一份考题。
Look closely at antibiotic C, and at the area just around its disc.
仔细看抗生素C，以及它的纸片周围的区域。
A student says the bacterium is resistant to antibiotic C.
一名学生说这种细菌对抗生素C有抗药性。
Explain why the figure contradicts this.
解释为什么这幅图与他的说法相矛盾。
Is there a zone around C?
C周围有抑菌圈吗？
What would the plate look like if there were no inhibition at all?
如果完全没有抑制，平板会是什么样子？
Pause and try it.
暂停并试着回答。
There is a zone of inhibition around C, so bacterial growth was prevented there.
C周围有抑菌圈，说明那里细菌的生长受到了阻止。
If the bacteria were resistant in this test, they would grow right up to the edge of the disc, with no clear zone.
如果细菌在这个实验中有抗药性，它们会一直长到纸片边缘，没有透明区。
A smaller zone than B's does not mean no effect.
抑菌圈比B小，并不等于没有效果。
This is a simple diagram of one clear zone.
这是一个抑菌圈的简图。
Its diameter is given as twelve millimetres.
题目给出它的直径为十二毫米。
Use that stated value, not a measurement of the picture.
使用这个给定数值，而不是去量图。
A clear zone has a diameter of twelve millimetres.
一个抑菌圈的直径为十二毫米。
Calculate its area.
计算它的面积。
Find the radius first, and give the answer in square millimetres.
先求半径，答案用平方毫米表示。
Pause and try it.
暂停并试着计算。
The radius is half the diameter: twelve divided by two is six millimetres.
半径是直径的一半：十二除以二等于六毫米。
Area equals pi r squared.
面积等于圆周率乘半径的平方。
Pi times six squared is about one hundred and thirteen square millimetres.
圆周率乘六的平方，约为一百一十三平方毫米。
Using the diameter as the radius would give four times the correct area.
如果把直径当作半径，得到的面积会是正确答案的四倍。
To make the comparison fair, use the same type of bacteria and the same agar.
为了使比较公平，使用同一种细菌和同样的琼脂。
Use matching discs, with the same amount and concentration of each treatment.
纸片要一致，每种处理的用量和浓度相同。
Keep the time and temperature the same.
时间和温度保持一致。
Repeat the test and compare the means, which reduces the effect of random variation.
重复实验并比较平均值，以减少随机波动的影响。
The nucleus contains the chromosomes.
细胞核里有染色体。
Each chromosome is a DNA molecule carrying many genes.
每条染色体是一个携带许多基因的DNA分子。
A gene is a section of DNA.
基因是DNA的一个片段。
In body cells, chromosomes are normally in pairs: humans have twenty-three pairs, forty-six in all.
体细胞中的染色体通常成对存在：人类有二十三对，共四十六条。
These pairs are not the same thing as the copies made when DNA replicates.
这些成对的染色体与DNA复制产生的副本不是一回事。
Where are chromosomes found in a body cell, and what are genes?
在体细胞中，染色体位于哪里？
Answer the location and the definition separately.
基因是什么？ 位置和定义分开回答。
Pause and try it.
暂停并试着回答。
Location: chromosomes are in the nucleus.
位置：染色体在细胞核内。
Definition: genes are sections of DNA, and one chromosome carries many genes.
定义：基因是DNA的片段，一条染色体携带许多基因。
Do not confuse the nucleus, a chromosome and a gene.
不要把细胞核、染色体和基因混为一谈。
The cell cycle has three overall stages.
细胞周期总体分三个阶段。
First, preparation: the cell grows, makes more ribosomes and mitochondria, and its DNA replicates.
第一，准备：细胞生长，合成更多核糖体和线粒体，DNA复制。
Second, mitosis: one set of chromosomes is pulled to each end of the cell, and the nucleus divides.
第二，有丝分裂：每套染色体被拉向细胞的一端，细胞核分裂。
Third, the cytoplasm and cell membrane divide, forming two identical cells.
第三，细胞质和细胞膜分裂，形成两个相同的细胞。
You do not need the names of the phases inside mitosis.
不需要记住有丝分裂内部各期的名称。
The question already tells you that DNA replicates before the cell divides.
题目已经告诉你，细胞分裂前DNA会复制。
Describe one other change.
请描述另一种变化。
Think about the cell's size, or its ribosomes and mitochondria.
想一想细胞的大小，或者它的核糖体和线粒体。
Pause and try it.
暂停并试着回答。
Accepted answers: the cell grows, or it makes more ribosomes or more mitochondria.
可接受的答案：细胞生长，或者合成更多核糖体或线粒体。
Repeating DNA replication gives no new change.
重复写DNA复制不算另一种变化。
And describe preparation, not something that happens while the cell divides.
要描述准备阶段的变化，而不是细胞分裂时发生的事。
Describe cell division by mitosis, for three marks.
描述有丝分裂过程中的细胞分裂，共三分。
Where does each set of chromosomes move?
每套染色体移向哪里？
What divides before the cytoplasm?
在细胞质分裂之前，什么先分裂？
Pause and try it.
暂停并试着回答。
After DNA replication, one set of chromosomes is pulled to each end of the cell.
DNA复制后，每套染色体被拉向细胞的一端。
Then the nucleus divides.
然后细胞核分裂。
Then the cytoplasm and cell membrane divide, forming two cells.
接着细胞质和细胞膜分裂，形成两个细胞。
DNA replication is preparation, so it does not replace any of these three points.
DNA复制属于准备阶段，不能代替这三点中的任何一点。
This exam figure shows chromosomes being pulled apart.
这幅考题图展示染色体被拉开的过程。
Its numbered stages all happen within division itself, so they are not the three overall stages of the cell cycle.
图中编号的各阶段都发生在分裂过程中，并不是细胞周期的三个总体阶段。
Drug X stops fibres attaching to the replicated chromosomes.
药物X阻止纤维附着在复制后的染色体上。
Explain why division cannot finish.
解释为什么细胞分裂无法完成。
What movement do the fibres cause, and what must happen before two cells can form?
纤维引起什么运动？ 形成两个细胞之前必须发生什么？
Pause and try it.
暂停并试着回答。
Without the fibres, the chromosomes cannot be pulled to each end of the cell.
没有纤维，染色体就不能被拉向细胞两端。
So the nucleus cannot divide, and two genetically identical cells cannot form.
因此细胞核不能分裂，也不能形成两个遗传上相同的细胞。
Just saying 'the cell cannot divide' only repeats the question.
只说“细胞不能分裂”只是在重复题目。
Why does a drug that stops cell division help treat cancer?
为什么阻止细胞分裂的药物有助于治疗癌症？
Think about what happens to the number of tumour cells, then state the effect on the tumour.
想一想肿瘤细胞的数量会怎样，再说明对肿瘤的影响。
Pause and try it.
暂停并试着回答。
A tumour grows by producing more and more cells.
肿瘤靠不断产生更多细胞而长大。
Stopping cell division prevents the tumour growing or spreading.
阻止细胞分裂可以阻止肿瘤生长或扩散。
The mark needs that tumour outcome, not only 'it stops division'.
得分需要写出对肿瘤的影响，而不只是“它阻止分裂”。
Suggest and explain one side effect of a drug that stops cell division.
提出并解释阻止细胞分裂的药物的一种副作用。
Choose a healthy tissue whose cells normally divide, and link the reduced cell production to a symptom.
选择一种细胞通常会分裂的健康组织，把细胞生成减少与一种症状联系起来。
Pause and try it.
暂停并试着回答。
Living cells in hair follicles divide to make hair grow.
毛囊中的活细胞分裂使头发生长。
Blocking their division can cause hair loss.
阻止它们分裂可能导致脱发。
Another answer: less division in repair tissue can slow wound healing.
另一种答案：修复组织中的细胞分裂减少，会使伤口愈合变慢。
Note that the hair shaft itself is dead and does not divide.
注意头发的毛干本身是死细胞，不会分裂。
A stem cell is undifferentiated: it is not yet specialised for any particular function.
干细胞是未分化的细胞：它还没有特化出某种特定功能。
It can divide to make more stem cells. And it can differentiate to produce specialised cells of different types.
它可以分裂产生更多干细胞，也可以分化产生不同类型的特化细胞。
Dividing alone does not make a cell a stem cell.
仅仅能分裂并不能使一个细胞成为干细胞。
Which property of embryonic stem cells makes them useful for treating liver disease?
胚胎干细胞的哪种特性使它们可用于治疗肝病？
Name the specialised cell that is needed, and explain how it can arise.
说出所需的特化细胞，并解释它如何产生。
Pause and try it.
暂停并试着回答。
Embryonic stem cells can differentiate into liver cells. That provides exactly the specialised cell type the patient needs.
胚胎干细胞可以分化成肝细胞，正好提供患者所需的特化细胞类型。
'They can divide' on its own does not explain where liver cells come from.
只说“它们能分裂”并不能解释肝细胞从何而来。
Three sources of stem cells.
干细胞的三种来源。
Embryonic stem cells can become most human cell types.
胚胎干细胞可以分化成人体大多数类型的细胞。
Adult stem cells from bone marrow form many types, including blood cells, but a narrower range.
骨髓中的成体干细胞可以形成多种细胞，包括血细胞，但范围较窄。
Plant meristems can produce any type of plant cell, throughout the plant's life.
植物分生组织在植物一生中都能产生任何类型的植物细胞。
Suggest one ethical reason for refusing an injection of embryonic stem cells.
提出拒绝注射胚胎干细胞的一个伦理理由。
Think about what happens to the embryo, and explain the objection rather than just naming a religion.
想一想胚胎会怎样，要解释反对的理由，而不只是写出某种宗教。
A risk of passing on a virus is a safety issue, not an ethical one.
传播病毒的风险属于安全问题，不是伦理问题。
Pause and try it.
暂停并试着回答。
One answer: obtaining the cells may destroy an embryo, a potential life.
一种答案：获取这些细胞可能会破坏胚胎，也就是一个潜在的生命。
Another: the embryo cannot give consent, or the procedure conflicts with beliefs that you explain.
另一种：胚胎无法表示同意，或者这一做法与你所解释的信念相冲突。
Viral infection is a biological risk, and the word 'religion' on its own is not enough.
病毒感染属于生物学风险，只写“宗教”是不够的。
Give one benefit and one risk of therapeutic cloning.
说出治疗性克隆的一个好处和一个风险。
Why do the patient's own genes matter here, and does matching remove every safety risk?
为什么患者自身的基因在这里很重要？ 基因匹配能消除所有安全风险吗？
Pause and try it.
暂停并试着回答。
The benefit: the embryo has the patient's own genes, so its stem cells are not rejected by the patient's body.
好处：胚胎带有患者自己的基因，所以它的干细胞不会被患者身体排斥。
The risk: a viral infection may still be passed on.
风险：仍可能传播病毒感染。
Matching applies to therapeutic cloning; stem cells from a donor may still be rejected.
基因匹配只适用于治疗性克隆；来自捐献者的干细胞仍可能被排斥。
Compare embryonic and adult bone-marrow stem cells criterion by criterion.
按标准逐项比较胚胎干细胞和骨髓成体干细胞。
Range: embryonic cells make most human cell types; marrow cells a narrower range, such as blood cells.
范围：胚胎干细胞能形成人体大多数类型的细胞，骨髓干细胞范围较窄，例如血细胞。
Ethics: using embryos raises the objection that they are destroyed, which adult cells avoid.
伦理：使用胚胎会引起胚胎被破坏的反对意见，成体干细胞则可避免。
Safety: both still need assessing before use.
安全：两者在使用前都需要评估。
Name the tissue in a plant's root tip that contains stem cells.
说出植物根尖中含有干细胞的组织。
The root tip is only the location; the question asks for the tissue.
根尖只是位置，题目问的是组织名称。
Pause and try it.
暂停并试着回答。
The tissue is meristem.
这种组织叫分生组织。
Its stem cells can differentiate into any type of plant cell, throughout the plant's life.
它的干细胞在植物一生中都能分化成任何类型的植物细胞。
The name and the ability answer two different demands.
名称和能力回答的是两个不同的要求。
Explain why meristem cells can be used to clone plants, and give two benefits of cloning rare plants this way.
解释为什么分生组织细胞可以用来克隆植物，并说出用这种方法克隆珍稀植物的两个好处。
Link undifferentiated cells to differentiation, then link conservation to producing many plants quickly.
把未分化细胞与分化联系起来，再把保护物种与快速大量繁殖联系起来。
Pause and try it.
暂停并试着回答。
Meristem cells are undifferentiated, so they can still differentiate into any plant cell.
分生组织细胞是未分化的，所以仍能分化成任何植物细胞。
Cloning rare species helps protect them from extinction.
克隆珍稀物种有助于防止它们灭绝。
Large numbers of the rare plant can be produced quickly and cheaply.
可以快速而经济地大量繁殖珍稀植物。
Cloning crop plants with disease resistance is a separate application.
克隆具有抗病性的农作物是另一种应用。
Three particle models of transport.
三种物质运输的粒子模型。
Open circles are water molecules, and filled circles are solute particles or ions.
空心圆代表水分子，实心圆代表溶质粒子或离子。
The arrows show net movement: the overall direction, even though particles move both ways.
箭头表示净移动方向，即总体方向，尽管粒子在两个方向上都在运动。
In diffusion, a substance moves from high to low concentration, with no energy from respiration.
扩散中，物质从高浓度移向低浓度，不需要呼吸作用提供能量。
In osmosis, water moves from a dilute solution to a more concentrated one, through a partially permeable membrane, again with no respiration energy.
渗透作用中，水通过部分透性膜从稀溶液移向较浓的溶液，也不需要呼吸作用的能量。
In active transport, a substance moves from low to high concentration, and that does need energy from respiration.
主动运输中，物质从低浓度移向高浓度，需要呼吸作用提供能量。
Concentration always refers to the solute.
浓度始终是指溶质的浓度。
Define diffusion.
给扩散下定义。
Name what moves, where it moves, and the net direction.
说出什么在移动、在哪里移动，以及净移动的方向。
Pause and try it.
暂停并试着回答。
Particles of a substance spread out in a solution or a gas.
物质的粒子在溶液或气体中散开。
The overall movement is from a higher to a lower concentration.
总体移动方向是从高浓度到低浓度。
The particles still move both ways; net movement is the difference between the two.
粒子仍在两个方向上运动；净移动是两者之差。
Four changes speed up diffusion.
四种变化可以加快扩散。
A steeper concentration gradient gives more net transfer.
浓度梯度更大，净转移更多。
A higher temperature makes the particles move faster.
温度更高，粒子运动更快。
A larger membrane area lets more particles cross at once.
膜面积更大，同时能通过的粒子更多。
A thinner barrier gives a shorter path.
屏障更薄，扩散路径更短。
Blood flow and breathing keep the gradient steep; they do not power diffusion.
血液流动和呼吸维持陡峭的梯度，但并不为扩散提供能量。
Why does a root hair cell use active transport to absorb mineral ions?
为什么根毛细胞用主动运输吸收矿质离子？
Compare the concentration of the same ion inside and outside the cell, and name the energy source.
比较同一种离子在细胞内外的浓度，并说出能量来源。
Pause and try it.
暂停并试着回答。
The mineral ion is less concentrated in the soil water than in the root hair cell.
这种矿质离子在土壤溶液中的浓度低于根毛细胞内。
So uptake runs from low to high concentration for that ion, against its gradient.
所以对这种离子来说，吸收是从低浓度到高浓度，逆着浓度梯度进行的。
Respiration supplies the energy.
能量由呼吸作用提供。
Diffusion could not produce this uptake.
扩散不能完成这种吸收。
Give one difference between active transport and osmosis.
说出主动运输与渗透作用的一个区别。
One precise contrast is enough: compare the energy needed, or the substances moved.
一个准确的对比就够了：比较所需的能量，或者被运输的物质。
Pause and try it.
暂停并试着回答。
Energy: active transport needs energy from respiration, and osmosis does not.
能量：主动运输需要呼吸作用提供能量，渗透作用不需要。
Substance: active transport can move ions or glucose, while osmosis is the movement of water.
物质：主动运输可以运输离子或葡萄糖，而渗透作用是水的移动。
Direction: active transport moves a substance against its concentration gradient.
方向：主动运输使物质逆浓度梯度移动。
Saying only that active transport is 'active' earns nothing.
只说主动运输是“主动的”不得分。
A potato cube is placed in distilled water, and its mass increases.
把一块马铃薯放入蒸馏水中，它的质量增加了。
Why?
为什么？
Choose one statement.
选出一项。
It is the concentration that decides the direction of osmosis, not the total volume of water.
决定渗透方向的是浓度，而不是水的总体积。
The answer: the cell solution is more concentrated than distilled water.
答案：细胞液的浓度高于蒸馏水。
So water enters the cells by osmosis, through the partially permeable membrane.
所以水通过部分透性膜，以渗透作用进入细胞。
The net water entry increases the mass.
水的净进入使质量增加。
This exam graph shows the mean change in mass of potato pieces against the concentration of the solution.
这幅考题图表示马铃薯块的平均质量变化与溶液浓度的关系。
Read the vertical axis carefully: it is mean mass change in grams.
仔细看纵轴：它是平均质量变化，单位是克。
Here is the upper part of the same graph, with the same curve and axis values.
这是同一幅图的上半部分，曲线和坐标值不变。
Find where the curve crosses zero.
找出曲线穿过零的位置。
Name the quantity on the vertical axis, with its unit, and estimate the concentration where the mass change is zero.
说出纵轴表示的物理量及其单位，并估计质量变化为零时的浓度。
Use the graph itself; do not assume it plots percentages.
要读图本身，不要以为它画的是百分数。
Pause and try it.
暂停并试着回答。
The vertical axis is mean change in mass, in grams, not percentage change.
纵轴是平均质量变化，单位是克，而不是百分比变化。
The curve crosses zero at about zero point three moles per cubic decimetre.
曲线在约零点三摩尔每立方分米处穿过零。
There, the potato shows no net water movement, though water molecules still move both ways.
在这个浓度下，马铃薯没有水的净移动，但水分子仍在双向运动。
That concentration roughly matches the inside of these cells.
这个浓度大致与这些细胞内部的浓度相当。
The lower part of the graph shows the negative results.
图的下半部分显示负值结果。
Compare the mass changes at zero point six and at one point zero moles per cubic decimetre.
比较零点六和一点零摩尔每立方分米时的质量变化。
Explain the result at zero point six moles per cubic decimetre, for three marks.
解释零点六摩尔每立方分米时的结果，共三分。
Which way does water move, and how do the solute concentrations inside and outside compare?
水向哪个方向移动？ 细胞内外的溶质浓度相比如何？
Pause and try it.
暂停并试着回答。
Water leaves the potato cells, so the mass goes down.
水离开马铃薯细胞，所以质量下降。
The cell solution is less concentrated than the solution outside.
细胞液的浓度低于外面的溶液。
This net movement of water through the partially permeable membrane is osmosis.
水通过部分透性膜的这种净移动就是渗透作用。
The outside is the more concentrated side: do not reverse the comparison.
外面是浓度较高的一侧，不要把比较弄反。
Why is the mass loss at one point zero greater than at zero point six?
为什么一点零时的质量损失比零点六时更大？
Explain the difference, not just each result on its own.
要解释两者的差别，而不只是分别解释每个结果。
Compare the concentration differences, then link them to water loss.
比较浓度差，再把它与失水联系起来。
Pause and try it.
暂停并试着回答。
At one point zero, the concentration difference between the outside and the inside is greater.
在一点零时，外面与里面的浓度差更大。
So more water leaves the potato by osmosis, and the mass loss is greater.
所以更多的水通过渗透作用离开马铃薯，质量损失更大。
A comparative cause gives a comparative effect.
比较性的原因带来比较性的结果。
A potato piece starts at two point five grams and ends at two point nine grams.
一块马铃薯开始时二点五克，最后二点九克。
Calculate the percentage change.
计算百分比变化。
Subtract initial from final, then divide by the initial mass, not the final one.
用最终质量减去初始质量，再除以初始质量，而不是最终质量。
Pause and try it.
暂停并试着计算。
The change in mass is final minus initial.
质量变化等于最终质量减去初始质量。
Two point nine minus two point five is plus zero point four grams.
二点九减二点五，得正零点四克。
Percentage change is the change divided by the initial mass, times one hundred.
百分比变化等于质量变化除以初始质量，再乘一百。
Zero point four over two point five, times one hundred, is plus sixteen percent.
零点四除以二点五再乘一百，得正百分之十六。
The plus sign records a gain.
正号表示增加。
A three point zero gram piece loses zero point four five grams.
一块三点零克的马铃薯失去零点四五克。
Calculate the percentage change.
计算百分比变化。
Use a negative change, and the initial three point zero grams as the denominator.
质量变化用负值，分母用初始质量三点零克。
Pause and try it.
暂停并试着计算。
We know the initial mass is three point zero grams, and the change is minus zero point four five grams.
已知初始质量为三点零克，质量变化为负零点四五克。
Use the same equation: change over initial mass, times one hundred.
使用同一个公式：质量变化除以初始质量，再乘一百。
Minus zero point four five over three point zero, times one hundred, is minus fifteen percent.
负零点四五除以三点零再乘一百，得负百分之十五。
A loss and a gain must never have the same sign.
质量减少和增加绝不能用同一个符号。
Required practical three, step by step.
必做实验三，逐步进行。
Prepare equal peeled pieces from the same potato.
从同一个马铃薯上切下大小相同、去皮的小块。
Blot them the same way, and record each initial mass.
用同样的方法吸干表面，记录每块的初始质量。
Put them in known concentrations, with the same time, volume and temperature.
把它们放入已知浓度的溶液中，时间、体积和温度相同。
Then blot again, record the final mass, and calculate the change.
然后再吸干，记录最终质量，计算变化。
Repeat, plot the means at each concentration, and label the axis with the correct quantity and unit.
重复实验，画出各浓度下的平均值，坐标轴标上正确的物理量和单位。
A six-mark evaluation.
一道六分评价题。
A student weighed a potato cube, put it in salt solution, reweighed it after 'some time', calculated the mass change, and used three concentrations.
一名学生称了一块马铃薯的质量，把它放进盐溶液，过了“一段时间”后再称，计算质量变化，并使用了三种浓度。
Evaluate how valid this method is.
评价这个方法的有效性。
Start with a strength from what was actually done, then link each improvement to its reason.
先从实际做法中找出一个优点，再把每项改进与其理由联系起来。
Pause and plan your answer.
暂停并构思你的答案。
A strength: weighing before and after measures the mass change, and several concentrations test the effect.
优点：前后称重测出了质量变化，几种浓度检验了浓度的影响。
Size: the cubes should have stated, equal dimensions, because 'a cube' does not guarantee the same area or volume.
大小：马铃薯块应有规定且相同的尺寸，因为“一块”不能保证面积或体积相同。
Time: use the same stated immersion time, because 'some time' can give different exposures.
时间：使用相同的规定浸泡时间，因为“一段时间”可能导致浸泡时长不同。
The judgement: a useful starting method, but uncontrolled variables limit how valid it is.
结论：这是一个有用的初步方法，但未控制的变量限制了它的有效性。
More improvements, each with its reason.
更多改进，每项都有理由。
Blot before weighing, so surface solution is not included in the mass.
称重前吸干表面，使测得的质量不包括表面溶液。
Control the temperature and the volume, to isolate concentration and keep the pieces covered.
控制温度和溶液体积，以单独研究浓度的影响，并使马铃薯块浸没。
Repeat and calculate means, to reduce random variation and spot anomalies.
重复实验并计算平均值，以减少随机波动、发现异常值。
Calculate percentage change, to compare pieces with different starting masses.
计算百分比变化，以比较初始质量不同的马铃薯块。
More concentrations would show the curve in more detail, but they do not replace repeats.
增加浓度数目可以使曲线更详细，但不能代替重复实验。
Plan how to get the mean mass-change results shown on the graph.
设计实验，得到图中的平均质量变化结果。
Give a sequence someone else could repeat, with measurements before and after, and explain how repeats become means.
写出别人可以重复的步骤，包括前后的测量，并说明如何由重复数据求平均值。
Remember the graph shows mean mass change in grams.
记住，这幅图显示的是以克为单位的平均质量变化。
Pause and plan it.
暂停并构思。
One possible setup: one-centimetre peeled cubes, in salt solutions from zero to one mole per cubic decimetre, in steps of zero point two.
一种可行的设计：用边长一厘米、去皮的马铃薯块，盐溶液浓度从零到一摩尔每立方分米，每隔零点二取一个浓度。
Blot and weigh each cube, then immerse it in thirty millilitres of solution for twenty minutes at twenty degrees, then blot and reweigh.
先吸干并称重，然后在二十摄氏度下浸入三十毫升溶液中二十分钟，再吸干并称重。
Use three pieces at each concentration, and calculate final minus initial mass and the mean change.
每种浓度用三块，计算最终质量减去初始质量，并求平均变化。
Plot concentration on the x-axis and mean mass change on the y-axis.
横轴为浓度，纵轴为平均质量变化。
Two cube models, one with sides twice as long as the other.
两个立方体模型，其中一个的边长是另一个的两倍。
Use the stated side lengths in your calculations, not a ruler on the picture.
计算时使用给出的边长，不要用尺子量图。
Compare cubes with sides of two millimetres and four millimetres.
比较边长为二毫米和四毫米的两个立方体。
Calculate the surface area, the volume, and the surface area per unit volume.
计算表面积、体积，以及单位体积的表面积。
A cube has six square faces, and volume uses three dimensions.
立方体有六个正方形面，体积要用三个维度。
Pause and try it.
暂停并试着计算。
Surface area is six times the side squared.
表面积等于六乘边长的平方。
Six times two squared is twenty-four square millimetres.
六乘二的平方，得二十四平方毫米。
Volume is the side cubed.
体积等于边长的立方。
Two cubed is eight cubic millimetres.
二的立方，得八立方毫米。
For the four millimetre cube, the surface area is six times four squared, ninety-six square millimetres.
对于边长四毫米的立方体，表面积等于六乘四的平方，即九十六平方毫米。
Its volume is four cubed, sixty-four cubic millimetres.
体积等于四的立方，即六十四立方毫米。
The small cube's ratio is twenty-four over eight, three per millimetre.
小立方体的比值是二十四除以八，等于每毫米三。
The large cube's ratio is ninety-six over sixty-four, one point five per millimetre.
大立方体的比值是九十六除以六十四，等于每毫米一点五。
Doubling the side multiplies area by four and volume by eight, so the ratio halves.
边长加倍，面积变为四倍，体积变为八倍，所以比值减半。
Why can a single-celled organism rely on exchange across its surface, while a human needs a transport system?
为什么单细胞生物可以靠表面进行物质交换，而人类需要运输系统？
Compare surface area per unit volume, and think about the distance to the cells deep inside.
比较单位体积的表面积，并想一想到达深处细胞的距离。
Pause and try it.
暂停并试着回答。
A single cell is small, so it has a large surface area to volume ratio. Enough exchange happens across its cell surface.
单个细胞很小，所以表面积与体积之比很大，通过细胞表面就能完成足够的物质交换。
A human is large, with a smaller ratio and long paths to the cells inside.
人体很大，比值较小，到达体内细胞的路径也很长。
So humans need specialised exchange surfaces, and a circulation to deliver substances to every cell.
所以人类需要特化的交换表面，以及把物质运送到每个细胞的循环系统。
Exchange surfaces share four features.
交换表面有四个共同特征。
A large surface area allows more transfer at once.
表面积大，同时能交换更多物质。
A thin barrier gives a short diffusion path.
屏障薄，扩散路径短。
A good blood supply keeps the gradient steep and carries substances away.
血液供应充足，维持陡峭的浓度梯度并运走物质。
Ventilation replaces the air or water and keeps the gas gradients steep.
通气不断更新空气或水，维持气体的浓度梯度。
Look for these in the lungs, small intestine, gills, roots and leaves.
在肺、小肠、鳃、根和叶中都能找到这些特征。
Alveoli are numerous, thin-walled and surrounded by capillaries.
肺泡数量多、壁薄，并被毛细血管包围。
Explain each feature.
解释每个特征。
Link each one to a different effect: area, path length and gradient.
把每个特征与不同的效果联系起来：面积、路径长度和浓度梯度。
Do not just write 'faster diffusion' three times.
不要把“扩散更快”写三遍。
Pause and try it.
暂停并试着回答。
Numerous alveoli give a large total surface area, so more gas exchange can happen.
大量的肺泡提供很大的总表面积，可以进行更多气体交换。
Thin walls give a short diffusion path, which speeds up transfer.
薄的肺泡壁使扩散路径短，加快交换。
The capillaries' blood flow keeps the concentration gradients steep and carries the gases away.
毛细血管中的血液流动维持陡峭的浓度梯度，并把气体运走。
Diffusion itself needs no energy from respiration.
扩散本身不需要呼吸作用提供能量。
A disease halves the number of working alveoli.
一种疾病使能正常工作的肺泡减少一半。
Explain why the patient becomes breathless.
解释为什么患者会气喘。
Follow the chain from area, to oxygen transfer, to the body's demand.
沿着这条链条思考：面积、氧气交换，再到身体的需求。
Pause and try it.
暂停并试着回答。
Fewer working alveoli means less surface area for gas exchange.
能工作的肺泡减少，气体交换的表面积就减少。
So less oxygen can diffuse into the blood each second.
所以每秒扩散进入血液的氧气减少。
The supply may not meet the tissues' demand, so breathing speeds up to ventilate the remaining alveoli.
氧气供应可能满足不了组织的需求，于是呼吸加快，使剩下的肺泡通气更多。
Each breath does not contain half the oxygen; the transfer rate is what falls.
每次呼吸所含的氧气并没有减半，下降的是交换速率。
Final checklist. Label all three cells and match structures to functions. Give one feature per specialised cell. Convert units before every magnification sum. Give the four aseptic-technique whys and count bacterial divisions. Order the cell cycle and evaluate stem cells from both sides. Define the three transports with energy and examples, and calculate surface-area-to-volume ratios and percentage change in mass.
最后清单：标出三种细胞并配功能；每种特化细胞一个结构一个功能；放大倍数计算前先换算单位；说出无菌操作四条及原因并计算细菌分裂；排好细胞周期顺序，两面评价干细胞；用能量和例子区分三种运输，并计算表面积体积比和质量变化百分比。