IGCSE Biology Edexcel: Cells & Movement Across Membranes | IGCSE 生物 Edexcel：细胞与跨膜运动

📚 IGCSE Biology Edexcel: Cells & Movement Across Membranes | IGCSE 生物 Edexcel：细胞与跨膜运动

This revision guide covers the core concepts of cell structure and how substances move across cell membranes, tailored for the Edexcel IGCSE Biology specification. You will learn about the differences between prokaryotic and eukaryotic cells, the functions of key organelles, and the three main transport processes: diffusion, osmosis, and active transport.

本复习指南针对 Edexcel IGCSE 生物考纲，系统讲解细胞结构核心概念以及物质如何穿过细胞膜。你将学习原核细胞与真核细胞的区别、关键细胞器的功能，以及扩散、渗透和主动运输这三种主要运输过程。

---

1. Eukaryotic vs Prokaryotic Cells | 真核细胞与原核细胞

All living organisms are made of cells. In the Edexcel IGCSE course, you need to distinguish between eukaryotic cells (found in animals, plants, fungi, and protoctists) and prokaryotic cells (found in bacteria). Eukaryotic cells have a true nucleus surrounded by a nuclear membrane, while prokaryotic cells have no nucleus — their genetic material lies free in the cytoplasm.

所有生物体都由细胞构成。在 Edexcel IGCSE 课程中，你需要区分真核细胞（存在于动物、植物、真菌和原生生物中）与原核细胞（存在于细菌中）。真核细胞具有由核膜包围的真正细胞核，而原核细胞没有细胞核——其遗传物质游离在细胞质中。

Feature | 特征	Eukaryotic cell | 真核细胞	Prokaryotic cell | 原核细胞
Nucleus | 细胞核	Present | 有	Absent | 无
Size | 大小	10–100 μm | 10–100 微米	0.1–5 μm | 0.1–5 微米
Membrane-bound organelles | 膜包被细胞器	Present | 有	Absent | 无
Ribosomes | 核糖体	80S | 80S	70S | 70S
Cell wall (if present) | 细胞壁（如有）	Cellulose (plants) | 纤维素（植物）	Peptidoglycan | 肽聚糖
Example | 例子	Animal, plant, fungal cells | 动物、植物、真菌细胞	Bacteria | 细菌

---

2. Animal Cell Organelles | 动物细胞细胞器

You must be able to label and describe the functions of the main parts of an animal cell. The nucleus controls all cell activities and contains DNA. The cytoplasm is a jelly-like fluid where most chemical reactions happen. The cell membrane controls the movement of substances in and out of the cell.

你必须能够标注并描述动物细胞主要部分的功能。细胞核控制所有细胞活动并含有 DNA。细胞质是胶状液体，大多数化学反应在此发生。细胞膜控制物质进出细胞。

• Mitochondria | 线粒体: Site of aerobic respiration, releasing energy (ATP) for the cell. | 有氧呼吸的场所，释放能量（ATP）供细胞使用。

• Ribosomes | 核糖体: Site of protein synthesis. | 蛋白质合成的场所。

• Cell membrane | 细胞膜: Partially permeable barrier; controls transport. | 部分通透的屏障；控制物质运输。

---

3. Plant Cell Organelles | 植物细胞细胞器

Plant cells contain all the organelles found in animal cells, plus several extra structures. The cell wall is made of cellulose and provides strength and support. Chloroplasts contain chlorophyll and are the site of photosynthesis. The permanent vacuole is filled with cell sap and maintains turgidity.

植物细胞包含动物细胞中的所有细胞器，另外还有一些特殊结构。细胞壁由纤维素构成，提供强度和支撑。叶绿体含有叶绿素，是光合作用的场所。永久液泡充满细胞液，维持细胞的膨压。

Plant cell extra features: chloroplast | cell wall | permanent vacuole

植物细胞额外结构：叶绿体 | 细胞壁 | 永久液泡

---

4. The Cell Membrane: Structure & Function | 细胞膜：结构与功能

The cell membrane is described as partially permeable, meaning it allows some substances to cross but not others. Its basic structure is a phospholipid bilayer with proteins embedded. Small, non-polar molecules like oxygen and carbon dioxide pass easily through the membrane. Larger molecules like glucose and ions require transport proteins.

细胞膜被描述为部分通透，即允许某些物质通过而阻止其他物质通过。其基本结构是磷脂双分子层，其中嵌有蛋白质。小分子、非极性分子如氧气和二氧化碳容易穿过膜。较大分子如葡萄糖和离子则需要转运蛋白。

Membrane movement can be passive (no energy) or active (requires energy)

跨膜运动可分为被动（无需能量）或主动（需要能量）

---

5. Diffusion | 扩散

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. This is a passive process — it does not require metabolic energy. In biology, diffusion is important for gas exchange in the lungs and leaves, and for the movement of dissolved food molecules.

扩散是粒子从浓度较高区域向浓度较低区域沿浓度梯度的净移动。这是一个被动过程——不需要代谢能量。在生物学中，扩散对肺和叶片中的气体交换以及溶解食物分子的移动至关重要。

Rate of diffusion ∝ surface area × concentration difference ÷ membrane thickness

扩散速率 ∝ 表面积 × 浓度差 ÷ 膜厚度

• Oxygen enters the blood in the alveoli by diffusion. | 氧气在肺泡中通过扩散进入血液。

• Carbon dioxide exits the leaf through stomata by diffusion. | 二氧化碳通过气孔扩散离开叶片。

---

6. Factors Affecting Diffusion | 影响扩散的因素

You need to explain why diffusion rate changes. A larger surface area increases the rate because more particles can cross at the same time. A steeper concentration gradient causes faster net movement. A thinner membrane reduces the distance, speeding up diffusion. Higher temperature increases particle kinetic energy, so diffusion occurs faster.

你需要解释扩散速率变化的原因。较大的表面积增加速率，因为同时有更多粒子可以穿过。更陡的浓度梯度导致更快的净移动。更薄的膜缩短了距离，从而加速扩散。较高的温度增加粒子动能，因此扩散发生得更快。

Factor | 因素	Effect on rate | 对速率的影响
Temperature | 温度	Increase → faster; decrease → slower | 升高→加快；降低→减慢
Concentration gradient | 浓度梯度	Steeper → faster | 越陡→越快
Surface area | 表面积	Larger → faster | 越大→越快
Membrane thickness | 膜厚度	Thinner → faster | 越薄→越快

---

7. Osmosis | 渗透

Osmosis is a special type of diffusion. It 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. Water moves down the water potential gradient. In the IGCSE course, you must describe simple experiments using Visking tubing and plant tissues.

渗透是扩散的一种特殊类型。它是水分子穿过部分通透膜，从水势较高区域向水势较低区域的净移动。水沿水势梯度移动。在 IGCSE 课程中，你必须描述使用玻璃纸管和植物组织的简单实验。

Water moves from high water potential (dilute solution) to low water potential (concentrated solution)

水从高水势（稀溶液）向低水势（浓溶液）移动

• Animal cells in a concentrated solution lose water and shrink. | 动物细胞在浓溶液中失水并缩小。

• Plant cells in a concentrated solution become plasmolysed (membrane pulls away from wall). | 植物细胞在浓溶液中发生质壁分离（膜与细胞壁分离）。

---

8. Osmosis in Plant Cells | 植物细胞中的渗透

In plant cells, the cell wall is fully permeable, so osmosis occurs across the partially permeable cell surface membrane and the vacuole membrane. When a plant cell is placed in pure water, water enters, the vacuole swells, and the cytoplasm pushes against the cell wall. The cell becomes turgid. Turgidity supports non-woody plants.

在植物细胞中，细胞壁完全通透，因此渗透发生在部分通透的细胞表面膜和液泡膜上。当植物细胞放入纯水中时，水进入细胞，液泡膨胀，细胞质压向细胞壁。细胞变得肿胀（膨大）。膨压支撑非木本植物。

When a plant cell loses too much water, the vacuole shrinks and the cytoplasm pulls away from the cell wall. This is called plasmolysis. It causes wilting. If the plant is watered, the cells can regain turgidity.

当植物细胞失去过多水分时，液泡收缩，细胞质与细胞壁分离。这称为质壁分离。它导致萎蔫。如果植物被浇水，细胞可以恢复膨压。

---

9. Active Transport | 主动运输

Active transport is the movement of particles from a region of lower concentration to a region of higher concentration, against the concentration gradient. This process requires energy from respiration and involves carrier proteins in the membrane. It is essential for absorbing mineral ions by plant roots and for reabsorbing glucose in the kidney tubules.

主动运输是粒子从浓度较低区域向浓度较高区域逆浓度梯度的移动。这个过程需要呼吸作用产生的能量，并涉及膜中的载体蛋白。它对植物根吸收矿质离子以及肾小管重吸收葡萄糖至关重要。

Active transport: low concentration → high concentration (uphill, requires ATP)

主动运输：低浓度 → 高浓度（逆浓度，需要 ATP）

• Root hair cells use active transport to absorb nitrate ions from the soil. | 根毛细胞利用主动运输从土壤中吸收硝酸根离子。

• In the small intestine, glucose is absorbed by active transport when concentration in the gut is low. | 在小肠中，当肠内葡萄糖浓度低时，通过主动运输吸收葡萄糖。

---

10. Comparing Transport Processes | 三种运输方式对比

You need to be able to compare diffusion, osmosis, and active transport in terms of energy requirement, direction, and involvement of proteins. Many exam questions ask you to select which process is occurring in a given situation. Remember: diffusion and osmosis are passive; active transport requires energy.

你需要能够从能量需求、方向和是否涉及蛋白质方面比较扩散、渗透和主动运输。许多考试题目要求你判断给定情境中发生的是哪种过程。记住：扩散和渗透是被动的；主动运输需要能量。

Feature | 特征	Diffusion | 扩散	Osmosis | 渗透	Active transport | 主动运输
Substance | 物质	Any particles | 任意粒子	Water only | 仅水	Ions, glucose | 离子、葡萄糖
Concentration direction | 浓度方向	Down gradient | 顺梯度	Down water potential gradient | 顺水势梯度	Against gradient | 逆梯度
Energy | 能量	None | 无	None | 无	ATP required | 需要 ATP
Membrane protein | 膜蛋白	Not usually | 通常不需要	Aquaporins only | 仅水通道蛋白	Carrier proteins | 载体蛋白

---

11. Experimental Skills: Osmosis & Diffusion | 实验技能：渗透与扩散

The Edexcel IGCSE course requires familiarity with standard experiments. For osmosis, you should know how to set up Visking tubing containing a sugar solution and place it in a beaker of water. The change in mass and colour indicates movement of water. You can also use potato cylinders in different concentrations of sugar solution and measure mass changes.

Edexcel IGCSE 课程要求熟悉标准实验。对于渗透实验，你应该知道如何设置装有糖溶液的玻璃纸管，并将其放入装有水的烧杯中。质量和颜色变化表明水的移动。你也可以在不同浓度的糖溶液中放置马铃薯条，并测定质量变化。

For diffusion, a classic demonstration is placing a crystal of potassium permanganate in water and observing the purple colour spread. You should be able to state that the spreading is faster at higher temperatures due to greater kinetic energy.

对于扩散，经典演示是向水中放入高锰酸钾晶体，观察紫色扩散。你应该能说明温度越高扩散越快，因为动能更大。

---

12. Common Exam Mistakes & Summary | 常见考试错误与总结

Students often confuse osmosis with diffusion. Osmosis is always about water moving through a partially permeable membrane. Another common error is saying active transport goes ‘down’ the gradient — it must be ‘against’. Also, remember that root hair cells are adapted for absorption by having a large surface area and many mitochondria for active transport.

学生经常混淆渗透与扩散。渗透始终是关于水穿过部分通透膜。另一个常见错误是说主动运输是“顺”梯度——必须是“逆”梯度。此外，记住根毛细胞通过大的表面积和许多线粒体适应吸收，为主动运输提供能量。

Key revision points: label all cell organelles; state the functions of the nucleus, cytoplasm, cell membrane, mitochondria, ribosomes, cell wall, chloroplast, and vacuole; define diffusion, osmosis, and active transport; list factors that affect diffusion; and cite at least one biological example for each transport process.

关键复习要点：标注所有细胞器；说出细胞核、细胞质、细胞膜、线粒体、核糖体、细胞壁、叶绿体和液泡的功能；定义扩散、渗透和主动运输；列出影响扩散的因素；并为每种运输方式举出至少一个生物学实例。

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）