📚 Cells and Life Processes | 细胞与生命过程
In Cambridge Science, cells and life processes form the foundation of biology. The topic links the smallest unit of life to the daily functions of plants and animals. This article explains key ideas, common experiments, and exam skills you need for the Cambridge syllabus.
在剑桥科学课程中，细胞与生命过程是生物学的基础主题。它把最小的生命单位与动植物的日常功能联系起来。本文讲解剑桥课程大纲中的核心概念、常见实验和考试技巧。
1. Characteristics of Living Organisms | 生物的共同特征
All living organisms share seven characteristics, often remembered by the acronym MRS GREN: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.
所有生物都具有七个共同特征，通常用 MRS GREN 来记忆：运动、呼吸、感应、生长、繁殖、排泄和营养。
- Movement (运动): an action by an organism that changes its position or place.
- Respiration (呼吸): the chemical reaction that releases energy from food in cells.
- Sensitivity (感应): the ability to detect and respond to changes in the environment.
- Growth (生长): a permanent increase in size and dry mass.
- Reproduction (繁殖): the process that produces new individuals of the same species.
- Excretion (排泄): the removal of waste products made by metabolism, such as carbon dioxide and urea.
- Nutrition (营养): the intake of materials for energy, growth and repair.
In exam questions, you may be asked to decide whether something is living by checking these characteristics. Remember that all seven are not always visible at the same moment, but living things show them during their life cycle.
在考试题目中，你可能需要根据这些特征判断某个东西是否属于生物。要记住，这七个特征不一定在同一时刻全部可见，但生物在其生命周期中会表现这些特征。
2. Cell Theory and Microscopy | 细胞学说与显微镜使用
Cell theory states that all living organisms are made of cells, the cell is the basic unit of structure and function, and all new cells arise from pre-existing cells by cell division.
细胞学说指出，所有生物都由细胞构成，细胞是结构和功能的基本单位，新细胞来自原有细胞的分裂。
A light microscope is used to observe cells. The main parts include the eyepiece lens, objective lens, stage, coarse focusing knob, fine focusing knob and mirror or light source.
光学显微镜用于观察细胞。主要部件包括目镜、物镜、载物台、粗准焦螺旋、细准焦螺旋以及反光镜或光源。
The total magnification is calculated by multiplying the eyepiece magnification by the objective lens magnification.
总放大倍数的计算方法是用目镜放大倍数乘以物镜放大倍数。
total magnification = eyepiece magnification × objective lens magnification
For example, if the eyepiece is ×10 and the objective lens is ×40, the total magnification is ×400.
例如，如果目镜是 ×10、物镜是 ×40，那么总放大倍数就是 ×400。
3. Plant and Animal Cells | 植物细胞与动物细胞
Animal cells and plant cells both contain a cell membrane, cytoplasm, nucleus, mitochondria and ribosomes. The cell membrane controls what enters and leaves the cell. The nucleus contains genetic information as DNA. Mitochondria are the sites of aerobic respiration, and ribosomes carry out protein synthesis.
动物细胞和植物细胞都含有细胞膜、细胞质、细胞核、线粒体和核糖体。细胞膜控制物质进出细胞。细胞核含有以 DNA 形式存在的遗传信息。线粒体是有氧呼吸的场所，核糖体负责蛋白质合成。
Plant cells also have three structures that animal cells do not normally have: a cellulose cell wall, chloroplasts and a large permanent vacuole containing cell sap.
植物细胞还具有动物细胞通常没有的三个结构：纤维素细胞壁、叶绿体和含有细胞液的大液泡。
| Structure | Animal cell | Plant cell |
|---|---|---|
| Cell membrane | Present | Present |
| Cytoplasm | Present | Present |
| Nucleus | Present | Present |
| Mitochondria | Present | Present |
| Ribosomes | Present | Present |
| Cell wall | Absent | Present (cellulose) |
| Chloroplasts | Absent | Present in green parts |
| Large permanent vacuole | Absent | Present |
When drawing cells, always label the visible structures and use the correct terms. Do not confuse the cell wall with the cell membrane.
绘制细胞图时，要标注可见的结构并使用正确的术语。不要把细胞壁和细胞膜混淆。
4. Specialised Cells | 特化细胞
Specialised cells have adaptations that help them perform a particular function. You need to know several examples for Cambridge Science.
特化细胞具有帮助它们执行特定功能的适应性。剑桥科学课程中需要掌握几个实例。
- Root hair cell (根毛细胞): a long extension increases surface area for absorbing water and mineral ions from the soil.
- Red blood cell (红细胞): a biconcave disc shape and no nucleus in mature human cells allow more space for haemoglobin to carry oxygen.
- Sperm cell (精子细胞): a tail enables swimming, many mitochondria provide energy, and the acrosome contains enzymes to penetrate the egg.
- Palisade mesophyll cell (栅栏叶肉细胞): many chloroplasts near the upper surface absorb light energy for photosynthesis.
- Ciliated cell (纤毛细胞): tiny hair-like cilia move mucus and trapped particles away from the lungs.
When explaining an adaptation, always link the structural feature to its function. For example, the sperm cell has many mitochondria because it needs a lot of energy for movement.
解释适应性时，一定要把结构特征与其功能联系起来。例如，精子细胞有许多线粒体，因为它需要大量能量来运动。
5. Diffusion and Osmosis | 扩散与渗透
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient. It is a passive process, so it does not require energy from respiration.
扩散是粒子从高浓度区域向低浓度区域的净运动，沿浓度梯度进行。它是一种被动过程，因此不需要呼吸作用提供的能量。
Examples of diffusion include oxygen moving from the alveoli into the blood and carbon dioxide moving from the blood into the alveoli.
扩散的例子包括氧气从肺泡进入血液，以及二氧化碳从血液进入肺泡。
Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
渗透是水分子通过部分透性膜，从水势较高的区域向水势较低的区域净移动。
In a typical potato experiment, a potato strip placed in pure water gains mass because water enters by osmosis. In concentrated sugar solution, the strip loses mass because water leaves the cells.
在典型的马铃薯实验中，放在纯水中的马铃薯条质量增加，因为水通过渗透进入细胞。放在浓糖水中时，马铃薯条质量减少，因为水从细胞中流出。
6. Enzymes | 酶
Enzymes are proteins that act as biological catalysts. They speed up chemical reactions in living organisms without being used up or changed permanently.
酶是作为生物催化剂的蛋白质。它们能加速生物体内的化学反应，而自身不会被用完或发生永久变化。
Each enzyme has an active site with a specific shape that is complementary to its substrate. This is often described by the lock-and-key model.
每种酶都有一个活性位点，其特定形状与底物互补。这通常用锁钥模型来描述。
Enzymes become denatured at high temperatures or extreme pH levels because the shape of the active site changes, so the substrate can no longer fit.
高温或极端 pH 会使酶变性，因为活性位的形状发生改变，底物不再能够结合。
Enzymes are important in digestion, respiration, photosynthesis and many other life processes. For example, amylase breaks down starch into maltose.
酶在消化、呼吸、光合作用等许多生命过程中都很重要。例如，淀粉酶把淀粉分解为麦芽糖。
7. Photosynthesis | 光合作用
Photosynthesis is the process by which green plants make glucose from carbon dioxide and water using light energy absorbed by chlorophyll.
光合作用是绿色植物利用叶绿素吸收的光能，将二氧化碳和水转化为葡萄糖的过程。
carbon dioxide + water → glucose + oxygen
This reaction takes place in the chloroplasts. Light energy is needed, and chlorophyll is the green pigment that absorbs the light.
该反应发生在叶绿体中。需要光能，叶绿素是吸收光能的绿色色素。
The glucose produced is used for respiration, converted into starch for storage, changed into cellulose for cell walls, or combined with nitrate ions to make amino acids.
产生的葡萄糖可用于呼吸作用，转化为淀粉储存，变成纤维素构成细胞壁，或与硝酸盐离子结合生成氨基酸。
To test a leaf for starch, boil the leaf in water, then boil it in ethanol to remove chlorophyll, rinse it, and add iodine solution. A blue-black colour shows starch is present.
检测叶片中的淀粉时，先把叶片在水中煮沸，再放入乙醇中煮沸去除叶绿素，冲洗后滴加碘液。出现蓝黑色表示有淀粉存在。
8. Respiration | 呼吸作用
Respiration is a chemical reaction that releases energy from glucose. It occurs in every living cell and should not be confused with breathing.
呼吸作用是从葡萄糖中释放能量的化学反应。它发生在每一个活细胞中，不应与呼吸运动混淆。
Aerobic respiration uses oxygen and releases a relatively large amount of energy.
有氧呼吸利用氧气，释放较多的能量。
glucose + oxygen → carbon dioxide + water (+ energy)
Anaerobic respiration in muscles produces lactic acid and a relatively small amount of energy.
肌肉中的无氧呼吸产生乳酸和较少的能量。
glucose → lactic acid (+ energy)
Anaerobic respiration in yeast produces ethanol, carbon dioxide and energy. This process is used in baking and brewing.
酵母中的无氧呼吸产生乙醇、二氧化碳和能量。这个过程用于烘焙和酿酒。
glucose → ethanol + carbon dioxide (+ energy)
9. Levels of Organisation | 组织的层次
In multicellular organisms, cells are organised into tissues, tissues into organs, organs into organ systems, and organ systems make up the organism.
在多细胞生物中，细胞构成组织，组织构成器官，器官构成器官系统，器官系统组成生物体。
A tissue is a group of similar cells working together. An organ is made of different tissues working together. An organ system is a group of organs that carry out a major function.
组织是一群相似细胞协同工作的结构。器官由不同组织协同工作构成。器官系统是一组执行主要功能的器官。
For example, muscle cells form muscle tissue, muscle tissue and other tissues form the stomach, the stomach is part of the digestive system, and the digestive system is part of the whole human organism.
例如，肌细胞构成肌肉组织，肌肉组织和其他组织构成胃，胃是消化系统的一部分，消化系统又是整个人体的一部分。
10. Practical Skills: Drawing Cells | 实验技能：绘制细胞图
Biological drawings in Cambridge Science must follow clear rules. Use a sharp pencil and draw clean, continuous lines. Do not use shading or colouring.
剑桥科学课程中的生物绘图必须遵循明确的规则。使用削尖的铅笔画出清晰连续的线条。不要使用阴影或涂色。
All labels should be written neatly, and label lines should be drawn with a ruler. Include a title and state the magnification if known.
所有标注要书写工整，标注线要用尺子绘制。要写上标题，如果知道放大倍数也要注明。
Draw only what you observe under the microscope. Keep the proportions of different parts correct and label the main visible structures such as cell wall, nucleus, cytoplasm and chloroplasts.
只画你在显微镜下实际观察到的结构。保持各部分比例正确，并标注主要可见结构，如细胞壁、细胞核、细胞质和叶绿体。
11. Common Misconceptions | 常见误区
Many students confuse the cell wall and the cell membrane. The cell wall is made of cellulose and provides structural support. The cell membrane is found in all cells and controls the movement of substances into and out of the cell.
许多学生混淆细胞壁和细胞膜。细胞壁由纤维素构成，起支持作用。细胞膜存在于所有细胞中，控制物质进出细胞。
Chloroplasts are organelles found in plant cells. Chlorophyll is the green pigment inside chloroplasts. Do not write that chlorophyll is a cell structure.
叶绿体是植物细胞中的细胞器。叶绿素是叶绿体内的绿色色素。不要写错为叶绿素是一种细胞结构。
Respiration is not the same as breathing. Breathing is the movement of air into and out of the lungs. Respiration is the chemical release of energy from glucose in every cell.
呼吸作用与呼吸运动不同。呼吸运动是空气进出肺部的过程。呼吸作用是在每个细胞中从葡萄糖释放能量的化学反应。
Diffusion and osmosis are passive processes, so they do not use energy from respiration. Active transport is the process that does require energy.
扩散和渗透是被动过程，因此不使用呼吸作用提供的能量。主动运输才是需要能量的过程。
12. Exam Tips | 考试技巧
Cambridge Science questions often use command words. Define means give a precise meaning. Describe means state what is observed or what happens, without giving reasons. Explain means give reasons and link causes to effects using because.
剑桥科学题目经常使用指令词。Define 是给出精确定义。Describe 是描述观察到什么或发生了什么，不需要给出原因。Explain 是给出原因并用 because 把因果联系起来。
In magnification questions, always check whether you need to calculate total magnification or actual size. Use the correct units and show your working.
在放大倍数问题中，要确认题目是要求计算总放大倍数还是实际大小。使用正确单位并写出计算步骤。
For experiments, learn the variables: independent variable, dependent variable and control variables. Be ready to describe how to make a fair test and how to record results accurately.
对于实验题，要掌握自变量、因变量和控制变量。准备好描述如何设计公平实验以及如何准确记录结果。
Always read the question carefully and answer in full sentences where required. If a question asks for two differences, give only two clear differences.
答题时要仔细读题，需要时用完整句子作答。如果题目要求写出两个区别，就只写两个清晰的区别。
Published by TutorHao | Cambridge Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply