Mastering Diffusion, Osmosis and Active Transport | 掌握扩散、渗透与主动运输

📚 Mastering Diffusion, Osmosis and Active Transport | 掌握扩散、渗透与主动运输

Understanding how substances move into and out of cells is fundamental in biology. This article breaks down diffusion, osmosis and active transport, clarifying their differences and helping you tackle exam questions with confidence.

理解物质如何进出细胞是生物学的基础。本文深入解析扩散、渗透和主动运输，厘清三者区别，助你自信应对考试。

1. Introduction to Cell Transport | 细胞运输简介

The cell membrane is selectively permeable, meaning it allows some substances to pass through but not others. This property is crucial for maintaining the cell’s internal environment.

细胞膜具有选择透过性，即它允许某些物质通过，而阻止其他物质。这一特性对维持细胞内部环境至关重要。

Molecules can cross the membrane by passive processes (which do not require metabolic energy) or active processes (which require energy). The three main types are diffusion, osmosis and active transport.

分子可通过被动过程（无需代谢能量）或主动过程（需要能量）穿过细胞膜。三种主要类型是扩散、渗透和主动运输。

All living cells rely on these mechanisms to obtain nutrients, expel waste, and maintain the right balance of water and ions.

所有活细胞都依赖这些机制来获取营养、排出废物，并维持水分与离子的适当平衡。

---

2. What is Diffusion? | 什么是扩散？

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down the concentration gradient. This is a passive process and does not require metabolic energy (ATP).

扩散是粒子从较高浓度区域向较低浓度区域的净移动，顺着浓度梯度进行。这是一个被动过程，不需要代谢能量（ATP）。

The particles move randomly due to kinetic energy. Over time, they spread out until they are evenly distributed, reaching equilibrium. For example, oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses out of the blood into the lungs.

粒子因动能而随机运动。随着时间的推移，它们会扩散开来，直至均匀分布，达到平衡。例如，氧气从肺泡扩散进入血液，二氧化碳从血液扩散到肺部。

Diffusion can occur in gases, liquids, and even through a permeable membrane if the particles are small enough. It does not require a membrane to occur.

扩散可在气体、液体中发生，甚至如果粒子足够小，也可以通过可透性膜发生。它不需要膜即可进行。

---

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

The rate of diffusion increases with a steeper concentration gradient – the larger the difference in concentration between two regions, the faster the particles will move.

扩散速率随浓度梯度的增大而增加——两个区域间的浓度差越大，粒子移动就越快。

Higher temperatures give particles more kinetic energy, so they move faster and diffuse more quickly. Even a small rise in temperature can noticeably speed up diffusion.

更高的温度赋予粒子更多动能，因此它们运动更快，扩散也更快。即使温度的小幅升高也能明显加快扩散。

A larger surface area of the membrane allows more particles to cross at once, speeding up diffusion. For instance, the alveoli in the lungs have a huge surface area to maximise gas exchange.

更大的膜表面积允许更多粒子同时通过，从而加快扩散。例如，肺部的肺泡具有巨大的表面积，以最大限度地促进气体交换。

Reducing the diffusion distance (thinner membrane) also increases the rate. The walls of the alveoli and capillaries are only one cell thick, keeping the diffusion pathway extremely short.

缩短扩散距离（更薄的膜）同样能提高速率。肺泡壁和毛细血管壁仅有一个细胞的厚度，使扩散路径非常短。

---

4. What is Osmosis? | 什么是渗透？

Osmosis is a special type of diffusion involving water molecules. It is the net movement of water from a region of higher water potential (more free water molecules, lower solute concentration) to a region of lower water potential (fewer free water molecules, higher solute concentration) through a partially permeable membrane.

渗透是涉及水分子的特殊扩散类型。它是水通过部分透性膜，从水势较高（自由水分子多、溶质浓度低）的区域向水势较低（自由水分子少、溶质浓度高）的区域净移动。

Water potential is a measure of the tendency of water to move from one place to another. Pure water has the highest water potential (value 0 kPa). Adding solutes lowers the water potential (makes it more negative).

水势是衡量水从一个地方移动到另一个地方的倾向的指标。纯水的水势最高（值为0 kPa）。加入溶质会降低水势（使其变得更负）。

Osmosis continues until the water potential is equal on both sides of the membrane. It is a passive process and requires no energy from the cell.

渗透持续进行直到膜两侧水势相等。这是一个被动过程，不需要细胞提供能量。

---

5. Osmosis in Living Cells | 活细胞中的渗透

Animal cells lack a rigid cell wall, making them sensitive to osmotic changes. If placed in a hypotonic solution (higher water potential outside), water enters by osmosis, causing the cell to swell and possibly burst – a process called lysis.

动物细胞没有坚硬的细胞壁，因此对渗透变化很敏感。若置于低渗溶液（外部水势较高）中，水通过渗透进入，导致细胞膨胀甚至破裂——这一过程称为细胞溶解。

If an animal cell is placed in a hypertonic solution (lower water potential outside), water leaves the cell, and the cell shrinks, a change known as crenation. In an isotonic solution, there is no net movement of water, and the cell stays normal.

若将动物细胞置于高渗溶液（外部水势较低）中，水离开细胞，细胞皱缩，这种变化称为皱缩。在等渗溶液中，没有水的净移动，细胞保持正常。

Plant cells have a strong cellulose cell wall. In a hypotonic solution, water enters by osmosis, the vacuole swells and the cytoplasm pushes against the cell wall, making the cell turgid. The cell does not burst because the cell wall resists expansion.

植物细胞有坚硬的纤维素细胞壁。在低

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）