📚 KS3 CIE Plant Cell Structure, Photosynthesis and Respiration: Exam Question Practice | KS3 CIE 植物细胞结构、光合作用与呼吸作用：考试题练习
In KS3 CIE Biology, plant cell structure, photosynthesis and respiration are frequently assessed together. Exam questions often ask you to identify organelles, write word or symbol equations, interpret experiments and compare the two processes. This guide reviews the key ideas, common question types and worked examples so that you can practise effectively and pick up marks quickly.
在 KS3 CIE 生物课程中，植物细胞结构、光合作用和呼吸作用经常被放在一起考查。考试题常要求你识别细胞器、书写文字或符号方程式、解释实验并比较这两个过程。本指南回顾关键概念、常见题型和例题，帮助你有效练习并快速拿分。
All the content below follows the CIE KS3 Biology checkpoint style, where short structured answers, correct scientific vocabulary and clear reasoning matter more than long essays. Every section ends with the kind of wording that examiners expect to see on a mark scheme.
以下内容全部按照 CIE KS3 生物检查点考试（checkpoint）风格编写：短小的结构化答案、正确的科学术语和清晰的推理，比长篇大论更重要。每一节都给出了考官在评分标准中希望看到的措辞。
1. Why These Three Topics Are Examined Together | 为什么这三个主题常被合并考查
Plant cell structure, photosynthesis and respiration are linked because they describe the same living system at three levels: the parts, the food-making process and the energy-releasing process. A question that starts with a labelled cell diagram can end by asking you to explain why a mitochondrion is more common in root cells than a chloroplast.
植物细胞结构、光合作用和呼吸作用之所以被放在一起考查，是因为它们从三个层面描述了同一个生命系统：结构组成、制造有机物的过程，以及释放能量的过程。一道从细胞结构图开始的题，最后可能要求你解释为什么根细胞中线粒体比叶绿体更常见。
Typical question types include: labelling and naming organelles, matching a structure to its function, completing word and symbol equations, interpreting data from experiments such as counting oxygen bubbles, and comparing photosynthesis with respiration using a table. Very often the same six-mark question mixes all three.
常见题型包括：标注和命名细胞器、把结构与功能配对、补全文字方程式与符号方程式、解释实验数据（如数氧气气泡），以及用表格比较光合作用与呼吸作用。很多时候一道 6 分大题会同时混合这三个主题。
This guide reviews the key ideas, the common question types and worked examples in turn, so that revision is focused on what is actually tested rather than on everything in the textbook.
本指南依次回顾关键概念、常见题型和例题，让复习聚焦于真正会被考到的内容，而不是把课本上所有内容都重读一遍。
2. Plant Cell Structure: The Basics | 植物细胞结构：基础知识
A typical plant cell contains a cell wall, cell membrane, cytoplasm, nucleus, chloroplasts, mitochondria, a large permanent vacuole and ribosomes. All of these must be recognised on a diagram, and you should be able to state the job of each one in a single sentence.
一个典型的植物细胞包含细胞壁、细胞膜、细胞质、细胞核、叶绿体、线粒体、一个大的中央液泡和核糖体。你必须能在图上认出它们，并能用一句话说出每一个结构的功能。
The cell wall is made of cellulose and gives the cell a fixed shape. It is fully permeable, so it does not control what enters the cell; its main roles are support, strength and preventing the cell from bursting when it takes in water.
细胞壁由纤维素组成，使细胞具有固定形状。它是全透性的，因此并不控制物质进出；它的主要作用是支撑、提供强度，以及在水进入时防止细胞胀破。
The cell membrane is a thin partially permeable layer just inside the wall. It controls what enters and leaves the cell, allowing small molecules such as water, oxygen and carbon dioxide to pass through while restricting larger ones.
细胞膜是紧贴细胞壁内侧的一层薄的半透性结构。它控制物质的进出：水、氧气、二氧化碳等小分子可以穿过，而较大的分子则受到限制。
The chloroplasts contain chlorophyll, which absorbs light energy for photosynthesis. Mitochondria are the site of aerobic respiration, so they release the energy the cell needs. The large permanent vacuole stores cell sap and helps keep the cell firm, or turgid.
叶绿体含有叶绿素，能吸收光能进行光合作用。线粒体是有氧呼吸的场所，为细胞释放所需的能量。大的中央液泡储存细胞液，并帮助细胞保持坚挺（膨压状态）。
- Cell wall - fully permeable, supports the cell | 细胞壁 - 全透性，支撑细胞
- Chloroplast - absorbs light for photosynthesis | 叶绿体 - 吸收光能进行光合作用
- Mitochondrion - releases energy by aerobic respiration | 线粒体 - 通过有氧呼吸释放能量
- Vacuole - stores water, sugars and salts | 液泡 - 储存水、糖和盐
- Nucleus - contains genetic material and controls the cell | 细胞核 - 含有遗传物质并控制细胞
Remember the differences from an animal cell: a plant cell has a cell wall, chloroplasts and a large permanent vacuole, while animal cells have none of these. Animal cells do have a cell membrane, cytoplasm, nucleus, mitochondria and ribosomes, just like plant cells.
记住与动物细胞的区别：植物细胞有细胞壁、叶绿体和大的中央液泡，而动物细胞没有这些结构。动物细胞同样具有细胞膜、细胞质、细胞核、线粒体和核糖体。
3. Organelle Functions at a Glance | 细胞器功能速览
Examiners frequently set one-mark questions that simply ask for a structure or a function. The table below collects the answers that appear most often in mark schemes, and it is worth learning it both ways round: structure to function, and function to structure.
考官经常出一分小题，直接问某个结构或某个功能。下表汇总了评分标准中最常出现的答案，最好正反两个方向都记住：由结构说功能，以及由功能说结构。
| Structure 结构 | Function (English) | 功能（中文） |
|---|---|---|
| Cell wall 细胞壁 | Made of cellulose; supports the cell and keeps its shape | 由纤维素构成；支撑细胞并维持形状 |
| Cell membrane 细胞膜 | Partially permeable; controls what enters and leaves | 半透性；控制物质进出 |
| Cytoplasm 细胞质 | Where most chemical reactions take place | 大多数化学反应发生的场所 |
| Nucleus 细胞核 | Contains genetic material and controls the cell | 含有遗传物质并控制细胞活动 |
| Chloroplast 叶绿体 | Contains chlorophyll; absorbs light for photosynthesis | 含叶绿素；吸收光能进行光合作用 |
| Mitochondrion 线粒体 | Site of aerobic respiration; releases energy | 有氧呼吸的场所；释放能量 |
| Vacuole 液泡 | Stores cell sap; keeps the cell firm | 储存细胞液；保持细胞坚挺 |
| Ribosome 核糖体 | Site of protein synthesis | 蛋白质合成的场所 |
A useful exam habit is to count the number of marks first. If a question is worth two marks, you normally need two separate points, not one long sentence that repeats the same idea twice.
一个很实用的应试习惯是先看分值。如果一道题 2 分，你通常需要给出两个独立的要点，而不是用一句话把同一个意思说两遍。
4. Photosynthesis: Making Food in Plants | 光合作用：植物制造食物
Photosynthesis is the process by which green plants make glucose from carbon dioxide and water, using light energy absorbed by chlorophyll. Oxygen is released as a by-product. This happens mainly in the leaves, inside chloroplasts, and it is the starting point of almost every food chain on Earth.
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。氧气作为副产物释放。这一过程主要发生在叶片的叶绿体中，是地球上几乎所有食物链的起点。
The word equation should be written exactly like this, with an arrow rather than an equals sign:
文字方程式应严格写成下面的形式，用箭头而不是等号：
carbon dioxide + water → glucose + oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
The balanced symbol equation is required for higher-level questions and must be learnt with correct formulas and coefficients:
较难的题目要求写出配平的符号方程式，必须记准化学式和系数：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Four things are needed for photosynthesis to happen: light, chlorophyll, carbon dioxide and water. If any one of them is missing or in short supply, the rate of photosynthesis falls, and that factor is called a limiting factor.
光合作用的发生需要四个条件：光、叶绿素、二氧化碳和水。其中任何一个缺失或不足，光合作用速率都会下降，这个因素就称为限制因素。
The glucose made is not simply stored. Some is used immediately in respiration to release energy, some is converted into starch for storage, some is turned into cellulose for cell walls, and some combines with nitrate ions from the soil to make amino acids and then proteins.
生成的葡萄糖并不是简单储存起来。一部分立刻用于呼吸作用释放能量，一部分转化为淀粉储存，一部分转化为纤维素构建细胞壁，还有一部分与土壤中的硝酸根离子结合，生成氨基酸进而合成蛋白质。
Temperature also matters, because photosynthesis is controlled by enzymes. A very cold leaf works slowly, and an overheated leaf may have its enzymes denatured so that the rate drops sharply.
温度同样重要，因为光合作用受酶控制。叶片过冷时反应缓慢，过热时酶可能变性，速率会急剧下降。
5. Respiration: Releasing Energy from Glucose | 呼吸作用：从葡萄糖中释放能量
Respiration is the process by which living cells break down glucose to release the energy they need. It happens in every living cell, all day and all night, including in plants. Aerobic respiration takes place in the mitochondria and needs oxygen.
呼吸作用是活细胞分解葡萄糖以释放所需能量的过程。它在每一个活细胞中、白天黑夜持续进行，植物也不例外。有氧呼吸发生在线粒体中，并且需要氧气。
glucose + oxygen → carbon dioxide + water
葡萄糖 + 氧气 → 二氧化碳 + 水
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
Note that the symbol equation for respiration is the photosynthesis equation reversed. That does not mean the two processes are opposites in every way: they happen in different organelles, at different times and for different purposes.
注意，呼吸作用的符号方程式正好是光合作用方程式的逆反应。但这并不意味着两个过程在所有方面都相反：它们发生在不同的细胞器中，时间不同，目的也不同。
The energy released is used for muscle contraction, for active transport of substances across membranes, for building larger molecules such as proteins, and for keeping warm-blooded animals at a constant body temperature. Energy that is not used is released as heat, which is why a compost heap or a flask of germinating seeds warms up.
释放的能量用于肌肉收缩、物质跨膜的主动运输、合成蛋白质等大分子，以及维持恒温动物的体温。未被利用的能量以热量形式释放，这就是堆肥或发芽种子保温瓶会变热的原因。
A common exam error is to write "respiration is breathing". Breathing is the movement of air in and out of the lungs; respiration is a chemical reaction inside cells. Keeping the two words separate protects easy marks.
一个常见错误是把 respiration 写成"呼吸（breathing）"。Breathing 是空气进出肺部的运动；respiration 是细胞内的化学反应。把这两个词区分清楚可以轻松保住分数。
If oxygen is unavailable, some cells can respire anaerobically. In plants and yeast this produces ethanol and carbon dioxide, and it releases much less energy than aerobic respiration.
如果缺少氧气，某些细胞可以进行无氧呼吸。在植物和酵母中，这会生成乙醇和二氧化碳，释放的能量远少于有氧呼吸。
6. Comparing Photosynthesis and Respiration | 比较光合作用与呼吸作用
Comparison questions almost always appear as a table with four or five rows. Each row must contain a clear contrast, so it is better to revise the differences in pairs than to learn the two processes separately.
比较题几乎总是以四到五行的表格形式出现。每一行都必须体现明确的对比，因此按"成对对比"来复习，比把两个过程分开背更有效。
| Feature 对比项 | Photosynthesis 光合作用 | Respiration 呼吸作用 |
|---|---|---|
| Organelle 场所 | Chloroplast 叶绿体 | Mitochondrion 线粒体 |
| Energy 能量 | Light energy absorbed 吸收光能 | Chemical energy released 释放化学能 |
| Raw materials 原料 | Carbon dioxide and water 二氧化碳和水 | Glucose and oxygen 葡萄糖和氧气 |
| Products 产物 | Glucose and oxygen 葡萄糖和氧气 | Carbon dioxide and water 二氧化碳和水 |
| When 时间 | Only in light 只在有光时 | All the time, day and night 昼夜不停 |
| Cells 细胞 | Only cells with chloroplasts 只有含叶绿体的细胞 | All living cells 所有活细胞 |
A strong answer also explains the relationship between them: the glucose and oxygen made by photosynthesis are the raw materials for respiration, and the carbon dioxide and water made by respiration are raw materials for photosynthesis. In a leaf in bright light, photosynthesis usually happens faster than respiration, so the leaf takes in carbon dioxide and gives out oxygen overall.
高分答案还会解释两者的关系：光合作用产生的葡萄糖和氧气，正是呼吸作用的原料；呼吸作用产生的二氧化碳和水，又是光合作用的原料。在强光下的叶片中，光合作用通常快于呼吸作用，因此叶片总体表现为吸收二氧化碳、释放氧气。
7. Leaves and Gas Exchange | 叶片与气体交换
Leaves are the main organ of photosynthesis, and their structure is a favourite exam topic because every feature has a clear function. A broad, flat, thin blade gives a large surface area for absorbing light and a short distance for gases to diffuse.
叶片是光合作用的主要器官，其结构是考试热点，因为每个特征都有明确的功能。宽、扁、薄的叶片提供了吸收光的大面积，也缩短了气体扩散的距离。
Palisade cells near the upper surface are packed with chloroplasts and are close to the light. Spongy mesophyll cells below them are loosely arranged with air spaces, which allows carbon dioxide to diffuse quickly to the cells and oxygen to diffuse away.
靠近上表皮的栅栏组织细胞含有大量叶绿体，离光源最近。其下方的海绵组织细胞排列疏松，之间有空隙，使二氧化碳能迅速扩散到细胞，氧气也能迅速扩散离开。
Carbon dioxide enters and oxygen leaves through stomata, which are small pores found mainly on the lower surface. Each stoma is opened and closed by two guard cells, which control water loss as well as gas exchange.
二氧化碳进入、氧气排出都通过气孔完成，气孔是主要分布在下表皮的小孔。每个气孔由两个保卫细胞控制开闭，既调节气体交换，也控制水分流失。
The xylem supplies water and dissolved mineral ions from the roots, and the network of veins also supports the leaf blade and keeps it flat facing the light. The waxy cuticle reduces evaporation without blocking light.
木质部把水分和溶解的矿质离子从根部输送上来，叶脉网络同时支撑叶片、使其保持平展朝向光源。叶片表面的蜡质角质层能减少蒸发，又不阻挡光线。
A classic exam link is to ask why a root hair cell has no chloroplasts but many mitochondria: it is underground and in darkness, so photosynthesis is impossible, but it needs energy for active transport of mineral ions from the soil.
一个经典的考查点是问：为什么根毛细胞没有叶绿体却有很多线粒体？因为它位于地下、处于黑暗中，无法进行光合作用；但它需要能量，用于从土壤中主动运输矿质离子。
8. Required Practical: Testing Photosynthesis | 必做实验：检测光合作用
In the pondweed experiment, a piece of Cabomba or Elodea is placed in water with hydrogencarbonate solution and a lamp at a fixed distance. The number of oxygen bubbles produced per minute is counted, and this is used as a measure of the rate of photosynthesis.
在金鱼藻实验中，把一段水蕴草或伊乐藻放入加有碳酸氢钠溶液的水中，把光源固定在某一距离上。每分钟产生的氧气气泡数被计数，用来衡量光合作用的速率。
When the lamp is moved closer, the rate increases, up to a point, because light intensity is the limiting factor. Beyond that point the graph levels off, which shows that something else, usually carbon dioxide concentration or temperature, has become limiting.
把灯移近时，速率会上升，但仅到某一限度为止，因为此时光是限制因素。超过这个限度曲线变得平缓，说明其他因素（通常是二氧化碳浓度或温度）成了限制因素。
Control variables to state in answers include the distance of the lamp, the temperature, the concentration of hydrogencarbonate solution, the size of the pondweed piece and the time over which bubbles are counted. A thermometer placed in the water helps to check that the lamp is not also heating the water.
答案中要写出的控制变量包括：灯的距离、温度、碳酸氢钠溶液浓度、水草段的长度，以及计数气泡的时间。在水中放一支温度计，可以检查灯是否同时把水加热了。
The other classic practical uses a destarched plant. The plant is kept in the dark for 24 to 48 hours so that all starch is used up, then a leaf is tested. The leaf is boiled in water to kill it, boiled in ethanol to remove the green chlorophyll, washed and then tested with iodine solution.
另一个经典实验使用"去淀粉"的植株。先把植物放在黑暗中 24 到 48 小时，使淀粉耗尽，然后取叶片检测。叶片先在水浴中煮沸杀死细胞，再放入乙醇中煮以除去绿色叶绿素，冲洗后用碘液检测。
A blue-black colour shows that starch is present and therefore that photosynthesis has happened. A leaf from a part of the plant left in the dark stays brown, which acts as the control.
出现蓝黑色说明有淀粉存在，因此发生了光合作用。而一直处于黑暗部位的叶片呈棕色，作为对照。
Variegated leaves give a further comparison: only the green parts turn blue-black with iodine, proving that chlorophyll is needed for photosynthesis. A leaf with the carbon dioxide supply removed by soda lime stays brown, proving that carbon dioxide is needed.
斑叶植物提供了进一步的对照：只有绿色部分遇碘变蓝黑，证明光合作用需要叶绿素。用碱石灰除去二氧化碳处理的叶片保持棕色，证明光合作用需要二氧化碳。
9. Testing Respiration in Plants | 检测植物的呼吸作用
Students often assume that plants only respire at night, which is wrong. Plants respire continuously, and the classic demonstration uses germinating seeds because their respiration rate is high while photosynthesis is not taking place in the dark.
学生常误以为植物只在夜间呼吸，这是错误的。植物持续进行呼吸作用。经典演示使用发芽的种子，因为在黑暗中不进行光合作用，而发芽种子的呼吸速率又很高。
In the soda lime experiment, germinating seeds are sealed in a flask. Soda lime absorbs the carbon dioxide produced, and a manometer or coloured water drop moves towards the flask as oxygen is used up and not replaced. A control flask contains dead or boiled seeds, which do not respire.
在碱石灰实验中，把发芽种子密封在锥形瓶中。碱石灰吸收产生的二氧化碳，随着氧气被消耗而不再补充，U 形管或染色水柱会向瓶内移动。对照瓶装煮熟或已死亡的种子，它们不进行呼吸作用。
In the thermos flask experiment, two vacuum flasks are set up, one with germinating seeds and one with boiled seeds. Only the flask with living seeds shows a rise in temperature, because the energy released from glucose is partly transferred as heat.
在保温瓶实验中，设置两个真空保温瓶，一个装发芽种子，一个装煮熟的种子。只有装活种子的一瓶温度上升，因为葡萄糖释放的能量有一部分以热的形式散失。
In the limewater test, air is bubbled through limewater after passing over respiring material. The limewater turns milky or cloudy, showing that carbon dioxide is being produced by respiration.
在石灰水检测中，空气先通过呼吸中的材料，再通入石灰水。石灰水变浑浊，说明呼吸作用产生了二氧化碳。
For full marks, always state the control and say what it shows. A well-described control turns a vague demonstration into a valid experiment, and examiners award marks for that reasoning.
要拿满分，一定要写出对照并说明它证明了什么。一个描述清楚的对照能把含糊的演示变成有效的实验，考官会为此给出分数。
