単位 5：呼吸、体内環境、調節、遺伝子技術
Pearson Edexcel · International A-Level · Biology トピック 5 10:22 英語ナレーション・英語＋中文字幕 burning-in
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Transcript
Sprint for a bus and your body performs a symphony: muscles burn glucose faster, the heart doubles its output, ventilation deepens, sweat starts, the kidney re-tunes its water recovery - all without a conscious thought.
追赶公交车时，身体奏响交响乐：肌肉更快分解葡萄糖、心输出量翻倍、通气加深、出汗、肾脏调整水的重吸收——全都不假思索。
This unit follows that machinery.
本单元追踪这套机器。
The paper is one hour forty-five, ninety marks, and one twenty-mark question is built on the pre-released scientific article you will have studied in advance.
试卷105分钟、90分，其中一道20分大题基于你提前研读的预发布科学文章。
Respiration releases energy in enzyme-controlled steps.
呼吸作用经酶控步骤释放能量。
Glycolysis in the cytoplasm phosphorylates a hexose and splits it to pyruvate, making a little ATP and reduced NAD.
细胞质中的糖酵解把己糖磷酸化并裂解为丙酮酸，产生少量ATP和还原NAD。
The link reaction and the Krebs cycle, in the mitochondrial matrix, strip the remaining hydrogens to reduced NAD and FAD and release carbon dioxide.
基质中的链接反应与三羧酸循环把剩余的氢转给NAD和FAD并释放二氧化碳。
On the cristae, the electron transport chain pumps hydrogen ions into the intermembrane space and chemiosmosis through ATP synthase makes most of the ATP; oxygen accepts the spent electrons and forms water.
嵴上，电子传递链把氢离子泵入膜间隙，经ATP合酶的化学渗透产生大部分ATP；氧接受耗尽的电子生成水。
Without oxygen the chain stops - so pyruvate accepts the hydrogen instead and becomes lactate, which the liver rebuilds afterwards at the cost of the oxygen debt.
没有氧气，传递链停摆——丙酮酸转而接受氢生成乳酸，事后由肝脏重建，代价是氧债。
Respiration rate against temperature follows the enzyme curve: rising to an optimum near body temperature, collapsing above it as tertiary structure breaks.
呼吸速率随温度呈酶曲线：在接近体温的最适值处达到峰值，超过后因三级结构破坏而崩塌。
The respiratory quotient reveals what is being burned: carbon dioxide produced over oxygen consumed.
呼吸商揭示燃烧的底物：产生的二氧化碳除以消耗的氧。
Carbohydrate gives one point zero, protein about zero point nine, lipid about zero point seven - a germinating seed with RQ zero point seven is living on its lipid reserves, and any value above one means some anaerobic respiration is adding carbon dioxide without matching oxygen use.
碳水化合物为1.0，蛋白质约0.9，脂质约0.7——呼吸商0.7的萌发种子正在动用脂质储备；超过1.0则说明存在无氧呼吸，额外释放二氧化碳而不消耗相应的氧。
A skeletal muscle fibre is a fused, multinucleate cell packed with myofibrils - actin filaments anchored at the Z-lines, myosin filaments between them with globular heads.
骨骼肌纤维是含多核的融合细胞，充满肌原纤维——肌动蛋白锚在Z线，肌球蛋白居间并带球形头部。
Contraction is a cycle: calcium ions bind troponin and move tropomyosin off the actin binding sites; the energised myosin head attaches, pulls the actin, and releases only when a fresh ATP binds - which is why no ATP after death means rigor.
收缩是一个循环：钙离子结合肌钙蛋白，原肌球蛋白移开暴露肌动蛋白结合位点；储能的肌球蛋白头部结合、拉动肌动蛋白，只有新ATP结合时才脱离——这就是死后没有ATP便尸僵的原因。
Fast-twitch fibres are thick and few-mitochondria for sprint power; slow-twitch are mitochondria-rich and vascularised for endurance.
快肌纤维粗大、线粒体少，适合爆发；慢肌线粒体丰富、血供充足，适合耐力。
Cardiac muscle is myogenic: it beats without nerve input.
心肌是自主性的：无需神经输入即可搏动。
The excitation starts at the sino-atrial node, spreads across the atria, is delayed at the atrio-ventricular node, then runs along the Purkyne fibres to the ventricle walls - atria first, ventricles a fraction later.
兴奋从窦房结开始，扩布两心房，在房室结短暂延迟，再沿浦肯野纤维传至心室壁——心房先收缩，心室稍后。
The medulla adjusts the rate to demand through the autonomic system.
延髓经自主神经系统按需调节心率。
Cardiac output is stroke volume times heart rate: at rest seventy cubic centimetres times seventy-two beats is about five litres a minute; in exercise a hundred and twenty times a hundred and fifty is eighteen - the table the exam loves, alongside minute ventilation from the spirometer trace.
心输出量等于每搏输出量乘心率：静息时70毫升乘72次约每分5升；运动时120乘150达18升——正是考题钟爱的表格，连同呼吸曲线得到的每分钟通气量。
Homeostasis holds the internal environment in dynamic equilibrium - variables oscillate inside narrow limits rather than standing still.
稳态使内环境处于动态平衡——变量在窄范围内波动而非静止。
Negative feedback corrects deviations in both directions: too hot and too cold, too high and too low, as insulin and glucagon hold blood glucose.
负反馈向两个方向纠正偏差：太热与太冷、太高与太低，正如胰岛素和胰高血糖素共同稳住血糖。
Positive feedback amplifies a deviation - a fever spiking, an action potential opening ever more sodium channels - and cannot stabilise anything.
正反馈放大偏差——发热失控、动作电位打开越来越多的钠通道——无法使任何东西稳定。
Thermoregulation runs through the hypothalamus: vasodilation and sweating to lose heat, vasoconstriction and shivering to keep or make it, with adrenaline as the fight-or-flight accelerant.
体温调节由下丘脑统辖：血管扩张与出汗散热，血管收缩与寒战保温产热，肾上腺素则是战斗或逃跑的加速器。
Blood enters the glomerulus at high pressure - the afferent arteriole is wider than the efferent - and everything except cells and large proteins is forced through into the capsule.
血液以高压进入肾小球——入球小动脉比出球宽——除细胞和大蛋白外的一切被压入肾小囊。
The proximal tubule reabsorbs all glucose and amino acids plus most salts and water.
近曲小管重吸收全部葡萄糖和氨基酸以及大部分盐和水。
The loop of Henle builds a water-potential gradient down the medulla.
亨勒环在髓质建立水势梯度。
The collecting duct makes the final decision: antidiuretic hormone from the pituitary inserts aquaporins, so water leaves the filtrate to the medullary blood - concentrated urine when dehydrated, dilute when over-watered.
集合管做最终决定：垂体的抗利尿激素插入水通道蛋白，水从滤液进入髓质血液——脱水时尿少而浓，水过多时尿多而稀。
Excess amino acids are deaminated in the liver; the ammonia becomes urea.
多余的氨基酸在肝内脱氨，氨转化为尿素。
A transcription factor binds a gene promoter and switches transcription on or off - that is most of differentiation.
转录因子结合基因启动子，开关转录——这是分化的主要机制。
Steroid hormones are lipid-soluble, so they cross the membrane and their receptor complex acts directly as a transcription factor.
固醇类激素脂溶性高，穿过膜后其受体复合物直接充当转录因子。
Epigenetics silences genes without changing the base sequence: methyl groups on a promoter block the machinery, and histone changes pack the DNA out of reach.
表观遗传在不改变碱基序列的情况下使基因沉默：启动子上的甲基基团阻断转录机器，组蛋白变化把DNA压缩到够不着。
Failures matter - a methylated tumour suppressor gene cannot hold cell division in check, and imprinting errors explain Prader-Willi syndrome.
失效后果严重——被甲基化的抑癌基因无法约束细胞分裂，印记错误导致普拉德–威利综合征。
The resting neurone holds about minus seventy millivolts with the sodium-potassium pump.
静息神经元靠钠钾泵维持约−70毫伏。
A stimulus past threshold - about minus fifty-five - opens voltage-gated sodium channels: depolarisation to plus thirty, all-or-nothing.
超过阈值（约−55毫伏）的刺激打开电压门控钠通道：去极化至+30，全或无。
Potassium channels then restore the potential and the refractory period resets the channels and stops backward travel.
随后钾通道复极化，不应期重置通道并阻止逆向传导。
Myelinated axons carry the impulse node to node - saltatory conduction - far faster than continuous depolarisation.
有髓轴突让冲动在郎飞氏结间跳跃传导——远快于连续去极化。
At the synapse, calcium entry triggers vesicles of transmitter; the transmitter crosses the cleft and binds receptors.
突触处，钙内流触发递质囊泡；递质越过间隙结合受体。
Drugs act there: SSRIs block re-uptake, lidocaine blocks sodium channels.
药物在此起作用：SSRI阻断重摄取，利多卡因阻断钠通道。
Phytochrome is a light switch.
光敏色素是一个光控开关。
Pr absorbs red light and converts to Pfr; Pfr absorbs far-red and converts back.
Pr吸收红光转为Pfr；Pfr吸收远红光转回。
Daylight contains more red than far-red, so Pfr accumulates through the day - and Pfr is the active form that triggers germination in light-sensitive seeds and flowering in long-day plants; a far-red flash last is the classic reversal experiment.
日光中红光多于远红光，白天Pfr累积——而Pfr正是触发需光种子萌发和长日植物开花的活性形式；最后照射远红光会使效果逆转，这是经典实验。
Auxin from the shoot tip elongates cells by acidifying their walls, bending shoots toward light when it accumulates on the shaded side.
茎尖产生的生长素使细胞壁酸化而伸长，在背光侧积累后使茎向光弯曲。
Gibberellin from the embryo induces amylase in the aleurone layer, mobilising the starch that feeds germination.
胚产生的赤霉素诱导糊粉层合成淀粉酶，调动淀粉供萌发所需。
Five regions, five jobs: the cerebral hemispheres for voluntary movement and thought, the cerebellum for balance and coordination, the hypothalamus and pituitary below them for homeostasis and hormones, the medulla for heart rate and breathing.
五个区域五份职责：大脑半球管随意运动与思维，小脑管平衡与协调，其下的下丘脑和垂体管稳态与激素，延髓管心率与呼吸。
MRI gives detailed structure; fMRI tracks oxygenated blood to show activity; CT is fast structure; PET shows metabolism with a radioactive tracer - match the method to the question.
MRI给出精细结构；fMRI以含氧血流显示活动；CT快速成像结构；PET用放射性示踪显示代谢——按问题选方法。
And chemistry first: Parkinson disease is a dopamine deficit, treated with L-Dopa because dopamine itself cannot cross the blood-brain barrier; low serotonin links to depression, the target of SSRIs.
化学先行：帕金森病是多巴胺缺乏，用左旋多巴治疗，因为多巴胺本身不能穿越血脑屏障；血清素过低与抑郁相关，是SSRI的作用靶点。
The insulin recipe: isolate the messenger RNA from pancreatic cells and copy it back to DNA without introns - bacteria cannot splice.
胰岛素配方：从胰腺细胞分离mRNA，逆转录成不含内含子的DNA——细菌不能剪接。
Cut the copy and a plasmid with the same restriction enzyme, so their sticky ends match; seal with DNA ligase.
用同一种限制酶切割目的DNA和质粒，使黏性末端匹配；用DNA连接酶连接。
Transform bacteria by heat shock or electroporation, and plate on antibiotic medium: only cells carrying the plasmid - with its resistance marker - survive.
通过热激或电穿孔转化细菌，在抗生素培养基上筛选：只有携带质粒（连同抗性标记）的细胞存活。
Grow them in a fermenter and harvest the human protein.
在发酵罐中培养，收获人源蛋白。
Microarrays read which genes are active by the mRNA that hybridises to the chip; bioinformatics compares sequences to measure relatedness and find drug targets.
微阵列凭与芯片杂交的mRNA读出活跃基因；生物信息学比较序列以度量亲缘并寻找药物靶点。
Close with the numbers again.
仍以数字收尾。
Lactate forms when oxygen runs short - reduced NAD is recycled by reducing pyruvate - and the liver rebuilds it to glucose afterwards, spending oxygen.
乳酸在缺氧时形成——还原NAD靠还原丙酮酸再生——事后肝脏把它重建为葡萄糖，消耗氧气。
Eighty-five cubic centimetres times one hundred and forty is about eleven point nine litres per minute.
85毫升乘140次约每分11.9升。
High ADH means permeable collecting ducts, so water is reabsorbed: a small volume of concentrated urine.
ADH高意味着集合管通透，水被重吸收：尿量少而浓。
L-Dopa crosses the blood-brain barrier and is converted to dopamine inside the brain; dopamine cannot cross.
左旋多巴能穿过血脑屏障并在脑内转为多巴胺；多巴胺本身不能。
And the insulin gene is copied from messenger RNA because bacteria cannot remove introns from genomic DNA.
胰岛素基因从mRNA拷贝而来，因为细菌无法去除基因组DNA中的内含子。