协调与应答
生物学· 2.80–2.95B· 25 分钟阅读
1. 协调与内稳态的核心基础★★☆☆☆⏱ 4 min
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内稳态
即使外部或内部条件发生变化，仍在狭窄限定范围内维持稳定内部环境的过程。核心实例包括体内含水量调节与核心体温调节。
所有生物都会对环境变化作出应答以维持生存。一次协调应答需要三个核心组成部分：刺激（环境的变化）、感受器（检测到刺激的结构）和效应器（作出应答的肌肉或腺体）。
一只狗闻到食物气味后开始分泌唾液，请指出该应答过程中的刺激、感受器和效应器。
- 1
- 刺激：空气中来自食物的化学分子。
- 2
- 感受器：狗鼻腔内的嗅觉感受器。
- 3
- 效应器：狗口腔内分泌唾液的唾液腺。
Exam tip:
在分值为2-3分的简答题中，请务必明确写出协调应答的所有三个组成部分，才能拿到全部分数。
2. 植物的协调作用：向性与生长素的作用机制★★☆☆☆⏱ 4 min
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向性
植物针对定向刺激作出的定向生长应答，可分为正向（朝向刺激生长）和负向（远离刺激生长）两类。
Shoots (stems): Positively phototropic (grow towards light), negatively geotropic (grow away from gravity)
Roots: Positively geotropic (grow towards gravity), negatively phototropic (grow away from light)
生长素是在植物茎尖合成的生长激素。当茎部受到来自单侧的光照（单侧光）时，生长素会移动到茎的背光侧。背光侧更高的生长素浓度会使该侧细胞比向光侧细胞伸长速度更快，因此茎会向光源方向弯曲。
将一株幼苗种植在花盆中，放置在只有一个小孔透光的黑暗橱柜里，解释为什么5天后幼苗会朝向小孔方向生长。
- 1
- 光线仅能从小孔进入，使幼苗的茎尖受到单侧光照射。
- 2
- 由茎尖产生的生长素会移动到茎上距离光源最远的一侧（即背光侧）。
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- 背光侧更高的生长素浓度会刺激该侧的细胞伸长速率快于向光侧。
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- 背光侧更快的生长速度会使茎朝向光源（小孔）弯曲。
Exam tip:
切勿将植物的应答描述为「神经性」或「肌肉性」——植物仅通过化学（激素）方式进行协调，使用这类表述不会获得分数。
3. 人体神经系统与反射弧★★★☆☆⏱ 5 min
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中枢神经系统（CNS）
由脑和脊髓组成，通过外周神经与感觉器官相连，负责协调机体的所有应答反应。
Feature | Nervous System | Hormonal System |
|---|---|---|
Type of signal | Electrical impulses along neurones | Chemical messengers in blood |
Speed of response | Very fast | Slower |
Duration of response | Short-lived | Long-lived |
Target | Precise, specific effectors | Widespread, multiple target organs |
突触是两个神经元之间的间隙。当电冲动到达第一个神经元的末梢时，会释放神经递质类化学物质。该物质扩散穿过突触间隙，与下一个神经元上的受体结合，在第二个神经元中触发新的电冲动。
反射是无需大脑有意识参与的快速、自动的应答，可保护机体免受伤害。考试作答要求的标准反射弧通路为：刺激 → 感受器 → 感觉神经元 → 中间神经元（位于脊髓/中枢神经系统） → 运动神经元 → 效应器 → 应答。
儿童触碰到尖锐的针后立刻缩手。请按正确顺序描述该应答的完整反射弧。
- 1
- 刺激：针尖刺穿皮肤。
- 2
- 感受器：儿童手指皮肤中的痛觉感受器。
- 3
- 感觉神经元将电冲动从感受器传导至脊髓（中枢神经系统）。
- 4
- 脊髓内的中间神经元将冲动传递给运动神经元（无需大脑进行有意识的处理）。
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- 运动神经元将冲动传导至效应器（负责缩手的手臂肌肉）。
- 6
- 应答：肌肉收缩，将手指从针尖处移开以避免进一步受伤。
Exam tip:
作答时务必按照考纲规定的准确顺序列出反射弧的步骤以获得满分，混淆神经元类型会被扣分。
4. 人眼的结构与功能★★★☆☆⏱ 4 min
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人眼是感知光刺激的感觉器官，它执行两项关键调节功能：调节作用（对焦近处/远处物体）和瞳孔反射（调节进光量以保护视网膜）。
Accommodation for near objects: Ciliary muscles contract → suspensory ligaments slacken → lens becomes thicker/more convex, increasing light refraction to focus on the retina.
Accommodation for distant objects: Ciliary muscles relax → suspensory ligaments become taut → lens becomes thinner/flatter, reducing light refraction.
Pupil reflex in bright light: Circular iris muscles contract, radial iris muscles relax → pupil constricts, reducing light entry to avoid retinal damage.
Pupil reflex in dim light: Radial iris muscles contract, circular iris muscles relax → pupil dilates, increasing light entry to improve vision.
驾驶员正看着（离面部很近的）速度表，随后抬头看向100米外的路牌。请解释人眼是如何调节以看清远处路牌的。
- 1
- 眼内的睫状肌舒张。
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- 睫状肌舒张将悬韧带拉紧。
- 3
- 绷紧的悬韧带将晶状体拉成更薄、更扁平的形态。
- 4
- 更扁平的晶状体对光的折射程度更低，因此来自远处路牌的平行光线可以准确聚焦在视网膜上。
Exam tip:
不要写睫状肌在看远处物体时“收缩绷紧”，实际上它们是舒张的，这是考试中常见的失分错误。
5. 皮肤在体温稳态中的功能★★★☆☆⏱ 4 min
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皮肤在将核心体温维持在约37°C（酶发挥功能的最适温度）的过程中起到关键作用。控制产热和散热的三个核心机制为：血管舒张/血管收缩、出汗和寒战。
When core temperature is too high: 1. Vasodilation: Arterioles supplying skin capillaries widen, increasing blood flow to the skin surface, so more heat is lost via radiation. 2. Sweat glands produce more sweat; evaporation of sweat from the skin surface transfers heat away from the body.
When core temperature is too low: 1. Vasoconstriction: Arterioles supplying skin capillaries narrow, reducing blood flow to the skin surface, so less heat is lost. 2. Sweat production stops. 3. Shivering: Uncontrolled muscle contractions release heat from respiration to warm the body.
解释为什么在温暖天气下跑完5公里后，跑步者会面色潮红且大量出汗。
- 1
- 肌肉收缩所需的呼吸作用释放出多余热量，使跑步者的核心体温升高。
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- 温度感受器检测到该变化，触发皮肤小动脉舒张。
- 3
- 流向皮肤表面的血流量增加，使皮肤呈现潮红状态，更多热量通过辐射散失到环境中。
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- 汗液分泌增加，汗液从皮肤表面蒸发会进一步降低体温。
Exam tip:
切勿表述为血管在炎热环境下“移动到皮肤表面”，只有提及小动脉的血管舒张/血管收缩才能得分。
6. 人体的激素调节（核心内容+仅生物学要求）★★★☆☆core / Paper 2 专属⏱ 4 min
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激素
由内分泌腺产生的化学信使，直接分泌进入血液，作用于靶器官以产生特定应答。
Hormone | Source Gland | Key Role |
|---|---|---|
Adrenaline | Adrenal glands | Fight or flight response: raises heart rate, breathing rate and blood glucose levels to prepare the body for activity |
Insulin | Pancreas | Lowers blood glucose levels by stimulating the liver to convert excess glucose into glycogen for storage |
Testosterone | Testes (males) | Controls development of male secondary sexual characteristics during puberty |
Oestrogen | Ovaries (females) | Controls development of female secondary sexual characteristics, and regulates the menstrual cycle |
Progesterone | Ovaries (females) | Maintains the lining of the uterus during pregnancy |
Hormone | Source Gland | Key Role |
|---|---|---|
ADH | Pituitary gland | Controls water reabsorption in the kidney tubules to regulate body water content |
FSH | Pituitary gland | Stimulates egg maturation in the ovaries, and oestrogen production |
LH | Pituitary gland | Triggers ovulation (release of a mature egg from the ovary) |
解释人被巨大声响惊吓时，肾上腺素释放产生的作用。
- 1
- 肾上腺释放肾上腺素进入血液。
- 2
- 心率和呼吸频率上升，为肌肉细胞输送更多氧气和葡萄糖。
- 3
- 血糖水平升高，为肌肉收缩提供更多能量，支撑战或逃应答。
Exam tip:
针对本考纲的胰岛素相关问题作答时不要提及胰高血糖素，该内容超出考试范围，作答了也不会得分。
7. 常见陷阱
错误做法:
Mixing up tropism directions (stating roots are positively phototropic)
原因:
Students confuse shoot and root responses to light and gravity stimuli
正确做法:
Memorise: Shoots = +phototropic, -geotropic; Roots = +geotropic, -phototropic
错误做法:
Stating ciliary muscles contract to focus on distant objects
原因:
Students mix up muscle action for accommodation of near vs distant objects
正确做法:
Remember: Near objects = ciliary muscles contract; Distant objects = ciliary muscles relax
错误做法:
Writing that blood vessels move up to the skin surface when hot
原因:
Incorrect description of heat loss mechanism that is not accepted in mark schemes
正确做法:
Only refer to vasodilation of skin arterioles, increasing blood flow to the skin surface
错误做法:
Reordering reflex arc steps (e.g. putting motor neurone before sensory neurone)
原因:
Students forget the exact sequence required by the specification mark scheme
正确做法:
Memorise the exact sequence: stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response
错误做法:
Comparing nervous and hormonal systems without pairing contrasts
原因:
Mark schemes require direct, paired comparisons to award full marks for comparison questions
正确做法:
Pair each contrast point: Nervous = electrical impulses / hormonal = chemical messengers; Nervous = fast / hormonal = slow, etc.
错误做法:
Mentioning glucagon when explaining insulin function
原因:
Glucagon is explicitly out of scope for this specification point
正确做法:
Only discuss insulin's role in lowering blood glucose by converting glucose to glycogen in the liver
8. 速查表
Topic | Key Exam Facts |
|---|---|
Homeostasis | Maintenance of constant internal environment: e.g. body temp, water content |
Tropisms | Shoots: +phototropic, -geotropic; Roots: +geotropic, -phototropic |
Auxin | Accumulates on shaded side of shoot → faster elongation → bends to light |
Nervous vs Hormonal | Nervous: electrical, fast, short, precise; Hormonal: chemical, slow, long, widespread |
Reflex Arc Order | Stimulus → Receptor → Sensory neurone → Relay neurone → Motor neurone → Effector → Response |
Accommodation (Near) | Ciliary muscles contract → suspensory ligaments slack → lens thick |
Accommodation (Distant) | Ciliary muscles relax → suspensory ligaments taut → lens thin |
Pupil Reflex | Bright light: pupil constricts; Dim light: pupil dilates |
Temp Regulation | Hot: vasodilation, more sweat; Cold: vasoconstriction, no sweat, shivering |
Core Hormones | Adrenaline (fight/flight), Insulin (lower blood glucose), Testosterone (male characteristics), Oestrogen (female characteristics), Progesterone (uterus lining) |
Biology Only Hormones | ADH (water reabsorption), FSH (egg maturation), LH (ovulation) |
9. 常见问题
神经调节与激素调节的区别是什么？
神经调节使用经神经元传递的电脉冲，反应速度快、持续时间短，且靶向特定效应器。激素调节使用血液中的化学信使，反应速度更慢、持续时间更长，且会对多个靶器官产生广泛作用。
生长素如何使茎部产生正向向光性？
生长素在茎尖合成。当受到单侧光照射时，生长素会移动到茎的背光侧，刺激该侧的细胞更快伸长，因此茎会向光源方向弯曲。
反射弧的正确顺序是什么？
获得满分所需的标准顺序为：刺激 → 感受器 → 感觉神经元 → （中枢神经系统内的）中间神经元 → 运动神经元 → 效应器 → 应答。
深入阅读
下一步
Now that you have mastered coordination and response, you are ready to move on to related topics in the Edexcel IGCSE Biology specification. The concepts of homeostasis you learned here will underpin your study of osmoregulation and excretion, while hormonal control content will be expanded in the reproduction topic. For Biology-only students, you will explore the role of FSH and LH in the menstrual cycle in more detail in the organism reproduction unit. Practice past paper questions focused on reflex arc pathways, eye accommodation and temperature regulation to consolidate your knowledge, and make sure you can differentiate between nervous and hormonal control for 3-4 mark comparison questions.