Coordination and Response
IGCSE Biology Topic 14 18:13 English narration · English + 中文 subtitles burned in
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Touch something hot and your hand is already moving before you feel the pain.
碰到烫的东西，你的手在你感到疼之前就已经缩回来了。
That is one of your two control systems — the fast one, made of nerves.
那是你两套控制系统中的一套——快的那套，由神经构成。
The other is slower, made of chemicals in your blood, and it can keep working for hours.
另一套慢一些，由血液中的化学物质构成，而且能持续工作好几个小时。
Your body needs both, and the exam always asks you to compare them.
你的身体两套都需要，考试总是要求你比较它们。
Welcome to coordination and response.
欢迎来到协调与反应。
Nerves, the eye, hormones, homeostasis and tropisms.
神经、眼睛、激素、稳态，还有向性。
Let's begin.
让我们开始吧。
The nervous system coordinates and regulates your body using fast electrical impulses that travel along neurones — nerve cells.
神经系统利用沿着神经元传导的快速电脉冲来协调和调节你的身体——神经元就是神经细胞。
It has two parts.
它有两个部分。
The central nervous system, the C N S, is the brain and the spinal cord.
中枢神经系统，也就是CNS，是大脑和脊髓。
The peripheral nervous system is all the nerves outside them.
周围神经系统是它们之外的所有神经。
And there are three kinds of neurone, named by where they carry the impulse.
神经元有三种，按它们把脉冲送到哪里命名。
Sensory neurones carry impulses from receptors to the C N S.
感觉神经元把脉冲从感受器送到中枢神经系统。
Relay neurones pass them on inside the C N S.
中间神经元在中枢神经系统内部传递。
Motor neurones carry them from the C N S out to effectors.
运动神经元把脉冲从中枢神经系统送到效应器。
Here is a scan of a human brain.
这是一张人脑扫描图。
The brain is one half of the central nervous system; the other half is the spinal cord running down your back.
大脑是中枢神经系统的一半；另一半是沿背部延伸的脊髓。
Together they coordinate and regulate the whole body.
它们一起协调和调节全身。
Impulses arrive from receptors, decisions are made or automatic responses are triggered, and impulses leave again to muscles and glands.
脉冲从感受器到达，作出决定或触发自动反应， 再把脉冲送到肌肉和腺体。
Everything outside this C N S is the peripheral nervous system — the long nerves that link the C N S to the rest of the body.
中枢神经系统之外的一切属于周围神经系统—— 把中枢神经系统与身体其余部分连接起来的长神经。
Under a microscope a neurone looks like a cell with long extensions.
在显微镜下，神经元看起来像一个带有长突起的细胞。
Those extensions are how electrical impulses race from one place to another.
正是这些突起让电脉冲 从一处快速传到另一处。
Remember the three kinds by the job they do.
按功能记住三种神经元。
Sensory neurones bring information in from receptors.
感觉神经元从感受器把信息带进来。
Relay neurones sit inside the C N S and pass the message on.
中间神经元位于中枢神经系统内部，把信息继续传递。
Motor neurones carry the answer out to an effector.
运动神经元把回应送到效应器。
Name the path, and you name the neurone.
说出路径，你就说出了神经元的名字。
Watch the path.
看这条路径。
The signal goes in, turns around in the spinal cord, and comes straight back out to the muscle.
信号进去，在脊髓里转个弯，然后直接回到肌肉。
A reflex action is a fast, automatic response to a stimulus — a stimulus being any change.
反射动作是对刺激的快速、自动的反应——刺激就是任何变化。
It follows a fixed path called the reflex arc, and you will be asked to write it out.
它沿着一条固定的路径，叫做反射弧，考试会要求你把它写出来。
Learn the order: receptor, sensory neurone, relay neurone, motor neurone, effector.
记住顺序：感受器、感觉神经元、中间神经元、运动神经元、效应器。
Five stages, always in that order.
五个阶段，永远是这个顺序。
And know what the ends are: a receptor detects the stimulus, and an effector is a muscle or a gland — the thing that actually does something.
还要知道两端是什么： 感受器探测刺激，效应器是肌肉或腺体——真正做事情的那个。
Trace the exam diagram.
顺着考试图走一遍。
A stimulus hits a receptor in the skin.
刺激打到皮肤里的感受器。
The impulse travels along a sensory neurone into the spinal cord.
脉冲沿感觉神经元进入脊髓。
There a relay neurone hands it to a motor neurone, and the motor neurone fires the effector muscle.
在那里中间神经元把它交给运动神经元，运动神经元再触发效应器肌肉。
Notice the path never needs the brain for the basic reflex — that is why it is so fast.
注意基本反射不必经过大脑——所以它才这么快。
Write the five stages in order every time: receptor, sensory, relay, motor, effector.
每次都按顺序写五个阶段： 感受器、感觉、中间、运动、效应器。
Miss one stage and you lose the mark.
漏一个阶段就会失分。
For the supplement paper, look at what happens between two neurones.
补充部分要看两个神经元之间发生什么。
A synapse is a junction between two neurones — a tiny gap.
突触是两个神经元之间的连接处——一个微小的间隙。
Learn the four events in order.
按顺序记住四个事件。
One: an impulse arrives and makes vesicles release neurotransmitter into the gap.
第一：脉冲到达，使囊泡把神经递质释放到间隙里。
Two: the neurotransmitter diffuses across the gap.
第二：神经递质扩散过间隙。
Three: it binds to receptor proteins on the next neurone.
第三：它结合到下一个神经元上的受体蛋白。
Four: that starts a new impulse.
第四：这引发一个新的脉冲。
And here is the consequence the exam wants: because only one side has the vesicles and only the other has the receptors, impulses can travel in one direction only.
这就是考试想要的结论：因为只有一边有囊泡，只有另一边有受体， 所以脉冲只能朝一个方向传导。
Look at the synapse drawing.
看突触图。
On the left neurone, vesicles hold neurotransmitter ready to release.
左侧神经元上的囊泡装着待释放的神经递质。
Across the tiny synaptic gap, the next neurone has receptor proteins.
跨越微小的突触间隙， 下一个神经元有受体蛋白。
When an impulse arrives, the vesicles dump their cargo into the gap.
脉冲到达时，囊泡把内容物倒进间隙。
The molecules diffuse across, bind the receptors, and start a new impulse.
分子扩散过去，结合受体，引发新脉冲。
Only one side has the vesicles and only the other has the receptors, so the signal can cross in one direction only.
只有一边有囊泡，只有另一边有受体， 所以信号只能单向通过。
That one-way rule is the mark the exam wants.
这个单向规则就是考试要的分。
Sense organs are groups of receptor cells that respond to one kind of stimulus — the eye to light, the ear to sound, the skin to touch and temperature.
感觉器官是一群感受器细胞，对一种刺激作出反应—— 眼睛对光，耳朵对声音，皮肤对触觉和温度。
Before we follow a ray through the eye, sort its parts into two jobs, because questions mix them up on purpose: some parts BEND light and some DETECT it.
在跟着一条光线穿过眼睛之前，先把它的各部分按两种职责分开， 因为题目就是故意把它们混在一起：有些部分让光弯曲，有些部分探测光。
The cornea refracts — bends — the light as it enters, and it does most of the bending, which surprises people who assume the lens does the work; the lens only fine-tunes the focus.
角膜在光进入时折射它——也就是让它弯曲——而且大部分的弯曲是它完成的， 这一点会让那些以为主要靠晶状体的人意外；晶状体只是把焦点微调一下。
The iris bends nothing at all: it just controls how much light gets in.
虹膜根本不让光弯曲：它只控制有多少光能进来。
And the retina does no bending either — it is the detector, the layer of receptor cells that turns light into nerve impulses.
视网膜同样不负责弯曲——它是探测器， 是把光变成神经冲动的那层感受器细胞。
Bending, then detecting.
先弯曲，后探测。
Keep those two jobs apart and the diagram reads itself.
把这两种职责分清楚，那张图自己就读得懂了。
Follow the light on this section of the eye.
跟着这张眼睛剖面图上的光线走。
It first hits the cornea, which refracts — bends — most of the light as it enters.
光先碰到角膜，角膜在光进入时折射——弯曲—— 大部分光线。
The iris is the coloured ring that opens or closes the pupil, the hole that lets light through.
虹膜是彩色的环，控制瞳孔开合，瞳孔是让光通过的孔。
The lens then focuses the rays onto the retina at the back.
晶状体再把光线聚焦到后方的视网膜上。
Receptor cells in the retina fire, and the optic nerve carries those impulses to the brain.
视网膜里的感受器细胞发放冲动， 视神经把这些脉冲送到大脑。
The blind spot is where that nerve leaves — no receptors sit there at all.
盲点就是视神经离开的地方——那里完全没有感受器。
This is a real eye from the front.
这是从正面看到的真实眼睛。
The black centre is the pupil — just a hole that lets light in.
黑色中心是瞳孔——只是一个让光进入的孔。
Around it is the coloured iris, which controls how wide that hole opens.
周围是有颜色的虹膜，控制这个孔开多大。
The white outer part is the sclera.
外面的白色部分是巩膜。
Sense organs are groups of receptor cells that respond to one kind of stimulus: light, sound, touch, temperature or chemicals.
感觉器官是一群感受器细胞，对一种刺激作出反应：光、声音、触觉、温度或化学物质。
The eye is the sense organ for light.
眼睛是对光的感觉器官。
When light changes, the iris adjusts the pupil so the retina is protected or still gets enough light.
光线变化时，虹膜调节瞳孔，保护视网膜或仍让足够的光进入。
The eye adjusts in two ways, and they get confused because both are muscles changing something.
眼睛用两种方式调整，而它们容易被混淆，因为两者都是肌肉在改变什么东西。
Keep them apart by what each one controls.
要靠"各自控制什么"把它们分开。
The first controls how MUCH light gets in: the pupil reflex.
第一种控制的是进来多少光：瞳孔反射。
In bright light the pupil gets smaller, protecting the retina from damage; in dim light it widens to gather more light.
在明亮的光线下瞳孔变小，保护视网膜不受损伤； 在昏暗的光线下瞳孔变大，以收集更多的光。
For the supplement paper, name the mechanism — two sets of antagonistic muscles in the iris, meaning they pull against each other, so one relaxes as the other contracts.
补充部分要说出机制——虹膜中的两组拮抗肌，意思是它们互相对抗， 一组收缩时另一组就放松。
In bright light the circular muscles contract and the pupil narrows; in dim light the radial muscles contract and it widens.
明亮时环肌收缩，瞳孔变窄； 昏暗时辐射肌收缩，瞳孔变宽。
The second adjustment does not change the amount of light at all, only WHERE it comes to a focus: accommodation is changing the shape of the lens for near or far objects, and the diagram after this takes it apart properly.
第二种调整完全不改变光的多少，只改变光在哪里聚焦： 视觉调节就是为近处或远处的物体改变晶状体的形状， 接下来的图会把它好好拆开来讲。
Amount of light, then point of focus — two jobs, two sets of muscles, never mix them.
先是光量，再是焦点——两项工作，两组肌肉，千万不要混为一谈。
Zoom in on accommodation with the same eye diagram.
用同一张眼睛图细看视觉调节。
The ciliary muscles sit around the lens, and the suspensory ligaments hold the lens in place.
睫状肌环绕晶状体，悬韧带把晶状体固定住。
For a near object the ciliary muscles contract, the ligaments slacken, and the lens becomes fatter — more refraction, so a near image focuses on the retina.
看近处时睫状肌收缩，韧带放松，晶状体变厚——折射更多，近处像落在视网膜上。
For a far object the ciliary muscles relax, the ligaments pull tight, and the lens becomes thinner — less refraction.
看远处时睫状肌放松，韧带拉紧，晶状体变薄——折射更少。
Learn both pairs: near means fat lens; far means thin lens.
记住两组对应： 近处对应厚晶状体；远处对应薄晶状体。
Also for the supplement paper: the retina holds two kinds of light receptor, and they divide the work.
同样是补充部分：视网膜有两种感光细胞，它们分工不同。
Rods are very sensitive, so they are good for vision in dim light — night vision — but they do not detect colour.
视杆细胞非常敏感，所以适合在昏暗光线下的视觉——夜视——但它们不能分辨颜色。
Cones come in three kinds, each absorbing a different colour, which is what gives you colour vision, and they work best in bright light.
视锥细胞有三种，每种吸收一种不同的颜色，这就是色觉的来源， 它们在明亮光线下工作得最好。
Cones are packed most densely at the fovea, which is why that part of the retina gives the sharpest image.
视锥细胞在中央凹处最密集， 这就是为什么视网膜的那个部分成像最清晰。
A hormone is a chemical, made by a gland and carried in the blood, that changes the activity of one or more target organs.
激素是一种化学物质，由腺体产生，通过血液运输，改变一个或多个靶器官的活动。
Learn four glands. The adrenal glands make adrenaline, which prepares the body for action.
激素来自内分泌腺，内分泌腺把它们直接释放到血液中。
The pancreas makes insulin and glucagon, which control blood glucose.
要记住四个腺体。 肾上腺产生肾上腺素，让身体做好行动准备。
The testes make testosterone; the ovaries make oestrogen.
胰腺产生胰岛素和胰高血糖素，控制血糖。 睾丸产生睾酮，用于男性发育。
Adrenaline is the one to know in detail.
卵巢产生雌激素，用于女性发育。
It is released in fight or flight situations, and it increases your breathing rate, your heart rate, your blood glucose concentration and your pupil diameter.
肾上腺素是要详细掌握的那个。 它在"战或逃"的情况下释放，比如恐惧或危险， 它会提高你的呼吸频率、心率、血糖浓度和瞳孔直径。
Hormones are made by endocrine glands, which release them straight into the blood — no ducts.
激素由内分泌腺制造，直接释放进血液——没有导管。
Adrenaline from the adrenal glands is the classic example.
肾上腺释放的肾上腺素 是经典例子。
In a fight or flight moment it hits several target organs at once.
在战或逃时刻，它同时作用于多个靶器官。
The heart beats faster, breathing deepens, the liver releases glucose for energy, and the pupils widen.
心跳加快，呼吸加深， 肝脏释放葡萄糖供能，瞳孔变大。
That multi-target chemical message is how one hormone can prepare the whole body for action in seconds, even though it is slower than a nerve impulse.
这种多靶点的化学信息，让一种激素能在几秒内 让全身做好行动准备，尽管它仍比神经冲动慢。
Now the comparison, and the useful news is that it is only three rows: speed, duration, and how the message travels.
现在做比较，而好消息是它只有三行：速度、持续时间，以及信息如何传递。
Fix those three axes in your head before the table arrives, because a compare answer that wanders between them does not score.
在表格出现之前，先把这三条轴钉在脑子里， 因为一个在三条轴之间游移的比较作答是拿不到分的。
Take speed first, because it explains the other two.
先看速度，因为它能解释另外两条。
Nervous control is very fast — an electrical impulse runs down a fixed wire straight to one target, so there is nothing to wait for.
神经控制非常快—— 电脉冲沿着一条固定的"线路"直达唯一的目标，没有什么要等。
Hormonal control is slower because a chemical has to be poured into the blood and carried everywhere before it reaches the organ it acts on.
激素控制比较慢，因为化学物质必须先倒进血液、被运送到全身， 才能到达它作用的那个器官。
A message with no wire cannot be quick, and a message in the blood cannot be brief.
没有线路的信息快不了， 而走血液的信息也短不了。
See that, and you see why you need both.
看懂这一点，你就明白为什么两者都需要。
The comparison table is three rows only.
比较表只有三行。
Speed: nervous is very fast; hormonal is slower.
速度：神经非常快；激素较慢。
Duration: nervous is short-lived; hormonal lasts longer.
持续时间：神经短暂；激素更久。
Travel: nervous uses electrical impulses along neurones; hormonal uses chemicals in the blood.
传导：神经用沿神经元的电脉冲；激素用血液中的化学物质。
Use that pattern in every compare question.
每次比较题都用这个规律。
Pulling a hand off a hot pan needs nerves.
把手从热锅上缩回需要神经。
Growing up, controlling blood glucose for hours, or a long fight-or-flight readiness needs hormones.
长大、控制血糖数小时，或长时间的战或逃准备需要激素。
The exam rewards the table, not a vague paragraph.
考试奖励表格式答案，而不是含糊段落。
Homeostasis is keeping a constant internal environment inside the body — for example a steady temperature and a steady blood glucose level.
稳态是在体内保持恒定的内环境——比如稳定的温度和稳定的血糖水平。
For the supplement paper, it works by negative feedback: when a value moves away from its set point, the body acts to bring it back.
补充部分要说，它通过负反馈工作：当一个数值偏离它的设定点时， 身体采取行动把它拉回来。
That word negative means the response opposes the change.
"负"这个字的意思是反应与变化方向相反。
The change itself triggers the correction — and that is the sentence to write.
变化本身触发了纠正——这就是要写的那句话。
The pancreas and the liver hold blood glucose steady, and it is the SHAPE of that control worth learning, because every other homeostatic control in this topic has the same shape.
胰腺和肝脏让血糖保持稳定，而真正值得学的是这套调节的"形状"， 因为这个专题里其他所有稳态调节都是同一个形状。
Two hormones pull in opposite directions around a set level.
两种激素围绕一个设定水平朝相反方向拉扯。
Insulin lowers blood glucose when a meal has pushed it up.
一顿饭把血糖推高之后，胰岛素把它降下来。
Its opposite, glucagon raises it again when the level falls between meals.
与它相反的胰高血糖素，则在两餐之间血糖下降时把它抬回去。
That is negative feedback: the change itself is what triggers the correction.
这就是负反馈：引发纠正的，正是变化本身。
Which means the level is never actually held constant — it is always overshooting a little and being pulled back, and that is why a real blood-glucose graph wobbles up and down instead of sitting flat.
这也意味着，这个水平其实从来没有被真正稳定在一个恒定值上—— 它总是稍稍冲过头，再被拉回来， 这正是真实的血糖曲线为什么是上下起伏、而不是一条平线的原因。
One naming trap before the detail: insulin is the hormone, glycogen is the store.
在讲细节之前先说一个名称陷阱：胰岛素是激素，糖原是储存物。
The two words look alike, and swapping them costs the mark every single year.
这两个词看起来很像，而弄混它们每年都在丢分。
Read the feedback loop on the diagram.
读图上的反馈回路。
If blood glucose is too high, the pancreas releases insulin and the liver stores glucose as glycogen, so the level falls back.
若血糖过高，胰腺释放胰岛素，肝脏把葡萄糖存为糖原，水平回落。
If blood glucose is too low, the pancreas releases glucagon and the liver releases glucose, so the level rises again.
若血糖过低，胰腺释放胰高血糖素，肝脏释放葡萄糖，水平回升。
Both sides return the value to normal.
两边都把数值拉回正常。
That is negative feedback: the change itself triggers the correction that opposes it.
这就是负反馈：变化本身触发了与之相反的纠正。
Insulin lowers; glucagon raises.
胰岛素降低；胰高血糖素升高。
Keep those verbs paired with the right hormone.
把这些动词和正确的激素配对。
Worked example.
例题。
Blood glucose rises sharply after a meal, then falls back over about two hours.
饭后血糖急剧升高，大约两小时后回落。
Name the organs and the hormone.
说出器官和激素。
The pancreas detects the rise and releases insulin.
胰腺察觉升高 并释放胰岛素。
Insulin makes the liver take glucose out of the blood and store it as glycogen, so the level falls back to normal.
胰岛素让肝脏从血液中取出葡萄糖，存为糖原，水平回到正常。
Between meals the opposite loop runs: the pancreas releases glucagon and the liver releases glucose again.
两餐之间运行相反回路：胰腺释放胰高血糖素，肝脏再释放葡萄糖。
Keep the words apart — insulin is the hormone, glycogen is the store.
把词分开——胰岛素是激素，糖原是储存物。
In Type one diabetes the pancreas cannot make insulin, so glucose stays high; treatment is insulin injections and a carefully planned diet.
一型糖尿病中胰腺不能造胰岛素， 血糖居高不下；治疗是注射胰岛素和精心安排的饮食。
Temperature works the same way. The brain detects your body temperature, and the skin does the work.
补充部分要说，温度的工作方式是一样的。
When you are too hot, two things happen: you sweat, and as that sweat evaporates it cools the skin; and the arterioles widen — vasodilation — so more blood flows to the skin capillaries and loses heat.
大脑察觉你的体温，皮肤来干活。 当你太热时，有两件事发生：你出汗，汗蒸发时给皮肤降温； 还有小动脉扩张——血管舒张——所以更多血液流到皮肤毛细血管并散失热量。
When you are too cold, the opposite: you shiver, and those muscle contractions make heat; and the arterioles narrow — vasoconstriction — so heat is kept in.
当你太冷时，正相反：你发抖，那些肌肉收缩产生热量； 还有小动脉收缩——血管收缩——所以到达表面的血液变少，热量被保留。 注意两者都是负反馈：变化触发了逆转它的反应。
The thermoregulation diagram shows two sides around about thirty-seven degrees.
体温调节图在大约三十七度左右展示两侧。
Too hot: sweating and vasodilation lose heat.
太热：出汗和血管舒张散失热量。
Too cold: shivering and vasoconstriction keep heat in.
太冷：发抖和血管收缩保留热量。
Both are negative feedback — a change away from the set point triggers the response that reverses it.
两者都是负反馈——偏离设定点的变化 触发了逆转它的反应。
The brain detects body temperature; the skin does the work.
大脑察觉体温；皮肤干活。
Write the pair of responses for each direction and you collect the marks.
为每个方向写出一对反应， 你就能拿到分。
The skin has four structures examiners name.
皮肤有四种考官会点名的结构。
Sweat glands make sweat; as it evaporates it cools the skin.
汗腺制造汗液；汗蒸发时给皮肤降温。
Hair erector muscles raise the hairs to trap a layer of air for insulation.
立毛肌竖起毛发，困住一层空气用于隔热。
Blood vessels change how much blood flows near the surface — widen in the heat, narrow in the cold.
血管改变靠近体表的血流量—— 热时扩张，冷时收缩。
Fatty tissue under the skin gives insulation and reduces heat loss.
皮下脂肪组织提供隔热，减少热散失。
Link each structure to heat loss or heat gain, and the temperature table is complete.
把每个结构和散热或产热联系起来，温度表就完整了。
Last, plants.
最后是植物。
A tropism is a plant's growth response to a direction — and notice the word GROWTH, because that is the whole difference from an animal response.
向性是植物对方向的生长反应——请注意"生长"这个词， 因为这正是它与动物反应的根本区别。
A plant does not move towards the light; it grows towards it, which makes the response slow and permanent where a nervous response is fast and reversible.
植物不是"移动"向光，而是"长"向光， 这使得这种反应缓慢而且不可逆，而神经反应则又快又可逆。
There are two, and each buys the plant something it cannot live without.
向性有两种，而每一种都为植物换来它离不开的东西。
Gravitropism is growth in response to gravity: roots grow down, into the water and the anchorage; shoots grow up, out of the soil.
向地性是对重力的生长反应：根向下长，长进水分和固着之处；茎向上长，长出土壤。
Phototropism is growth in response to the direction of light, which is how leaves end up where photosynthesis can actually happen.
向光性是对光的方向的生长反应，叶子正是这样才落到能真正进行光合作用的位置。
For the supplement paper both are controlled by one chemical, and the two diagrams after this trace it in detail: auxin is made in the shoot tip, and everything that follows depends on where that auxin ends up.
补充部分要说，两者都由同一种化学物质控制， 接下来的两张图会详细追踪它：生长素在嫩枝尖端产生， 而之后发生的一切，都取决于这些生长素最终去了哪里。
On the phototropism diagram, light comes from one side.
在向光性图上，光从一侧照来。
Auxin is made in the shoot tip and diffuses down.
生长素在嫩枝尖端产生并向下扩散。
Unequal light makes more auxin gather on the shaded side.
不均匀的光照 使更多生长素聚集在背光侧。
Auxin makes cells elongate, so the shaded side grows longer and the shoot bends towards the light.
生长素让细胞伸长，所以背光侧长得更长，茎朝光弯。
Write that chain: tip makes auxin, auxin moves, shaded side has more, cells elongate, shoot bends to the light.
写出这条链：尖端制造生长素，生长素移动，背光侧更多，细胞伸长，茎朝光弯。
That sentence collects the phototropism marks.
这句话能拿到向光性的分。
The same auxin idea controls gravitropism.
同样的生长素思路也控制向地性。
Gravity makes auxin spread unequally too.
重力也使生长素分布不均。
In shoots, the side with more auxin grows faster, so the shoot curves up away from gravity.
在茎中，生长素多的一侧 长得更快，所以茎向上弯曲离开重力方向。
In roots the response is different in direction — roots grow down — but the chemical is still auxin from the tip, spreading unequally and changing how fast cells elongate.
在根中方向不同——根向下长—— 但化学物质仍是尖端的生长素，不均匀分布并改变细胞伸长速度。
Phototropism is light; gravitropism is gravity; both are directional growth responses controlled by auxin.
向光性是光；向地性是重力；两者都是由生长素控制的定向生长反应。
Three marks to lock in.
锁住三个分。
First: write the reflex arc in order — receptor, sensory, relay, motor, effector.
第一：按顺序写出反射弧——感受器、感觉神经元、中间神经元、 运动神经元、效应器。
Second: insulin is the hormone, glycogen is the store; swapping them is the classic error.
第二：胰岛素是激素，糖原是储存物；弄混是经典错误。
Third: in phototropism the auxin gathers on the shaded side, and that side grows longer, so the shoot bends towards the light.
第三：向光性中生长素聚集在背光的一侧，那一侧长得更长，所以茎朝着光弯。
Master these, and this topic is yours.
掌握这些，这个专题就是你的了。
Last checklist before you leave.
离开前最后核对。
Nervous system: C N S is brain plus spinal cord; P N S is the nerves.
神经系统：中枢是大脑加脊髓；周围是神经。
Reflex arc in order every time.
每次反射弧都按顺序。
At a synapse, neurotransmitter diffuses across the gap so impulses go one way only.
突触处神经递质扩散过间隙，所以脉冲只能单向。
Eye: cornea and lens refract; the lens changes shape in accommodation; rods for dim light, cones for colour at the fovea.
眼睛：角膜和晶状体折射； 晶状体在调节中改变形状；视杆用于昏暗，视锥在中央凹负责色觉。
Hormones are slower but longer-lasting than nerves.
激素比神经慢但更持久。
Insulin lowers blood glucose; glucagon raises it.
胰岛素降低血糖；胰高血糖素升高血糖。
Too hot means sweating and vasodilation; too cold means shivering and vasoconstriction.
太热是出汗和血管舒张；太冷是发抖和血管收缩。
Auxin from the shoot tip makes cells elongate and steers both phototropism and gravitropism.
嫩枝尖端的生长素让细胞伸长， 并引导向光性和向地性。