Photosynthesis | 光合作用

📚 Photosynthesis | 光合作用

Photosynthesis is the process by which green plants, algae and some bacteria convert light energy into chemical energy stored in glucose. It is the foundation of almost all food chains on Earth and produces the oxygen we breathe.

光合作用是绿色植物、藻类和某些细菌将光能转化为储存在葡萄糖中的化学能的过程。它是地球上几乎所有食物链的基础，并产生我们呼吸的氧气。

1. What is photosynthesis? | 什么是光合作用？

Photosynthesis takes place mainly in the leaves of plants. The word ‘photosynthesis’ comes from ‘photo’ meaning light and ‘synthesis’ meaning making. During this process, carbon dioxide and water are combined using light energy to form glucose, with oxygen released as a by-product.

光合作用主要发生在植物的叶片中。“光合作用”一词源自“photo”（光）和“synthesis”（合成）。在此过程中，二氧化碳和水在光能作用下合成葡萄糖，并释放出氧气作为副产物。

Glucose can be used immediately for respiration, or converted into starch, sucrose, cellulose and other substances for storage or growth.

葡萄糖可以直接用于呼吸作用，或转化为淀粉、蔗糖、纤维素等物质用于储存或生长。

2. Word and symbol equations | 文字与符号方程式

The overall equation for photosynthesis can be written in words or as a balanced chemical equation.

光合作用的总体方程式可以用文字或平衡化学方程式表示。

Carbon dioxide + Water → Glucose + Oxygen

二氧化碳 + 水 → 葡萄糖 + 氧气

Using chemical symbols, the equation is:

用化学符号表示为：

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

This shows that six molecules of carbon dioxide react with six molecules of water to produce one molecule of glucose and six molecules of oxygen.

这个方程式表明六个二氧化碳分子与六个水分子反应，生成一个葡萄糖分子和六个氧分子。

3. The role of chlorophyll and chloroplasts | 叶绿素与叶绿体的作用

Photosynthesis occurs inside chloroplasts, which contain the green pigment chlorophyll. Chlorophyll absorbs light energy, mainly in the red and blue parts of the spectrum, and uses it to power the reactions.

光合作用发生在叶绿体内部，叶绿体含有绿色色素叶绿素。叶绿素主要吸收光谱中的红光和蓝光部分，并利用这些光能驱动化学反应。

Chloroplasts also contain enzymes and a system of membranes that increase the surface area for light absorption. Without chlorophyll, photosynthesis cannot take place.

叶绿体还含有酶和膜系统，膜系统增加了光吸收的表面积。没有叶绿素，光合作用就无法进行。

4. Light-dependent reactions | 光依赖反应

A more detailed view of photosynthesis shows two main stages. In the light-dependent stage, light energy is absorbed by chlorophyll and splits water molecules into hydrogen ions, electrons and oxygen gas.

更详细的光合作用过程包含两个主要阶段。在光依赖阶段，叶绿素吸收光能，将水分子分解为氢离子、电子和氧气。

This stage produces ATP (an energy carrier) and reduced NADP, which are used in the next stage. The oxygen released comes from water, not carbon dioxide.

该阶段产生ATP（一种能量载体）和还原型NADP，供下一阶段使用。释放的氧气来自水，而不是二氧化碳。

5. Light-independent reactions | 光不依赖反应

The light-independent stage, also called the Calvin cycle, takes place in the stroma of the chloroplast. Using ATP and NADP from the light-dependent stage, carbon dioxide is fixed and reduced to form glucose.

光不依赖阶段，又称卡尔文循环，发生在叶绿体基质中。利用光依赖阶段产生的ATP和NADP，二氧化碳被固定并还原形成葡萄糖。

This stage does not require light directly, but it depends on the products of the light-dependent stage. If light is absent for a long time, the cycle will stop because ATP and NADP are used up.

该阶段不直接需要光，但依赖光依赖阶段的产物。如果长时间无光，ATP和NADP耗尽，循环便会停止。

6. Factors affecting photosynthesis | 影响光合作用的因素

Three main factors control the rate of photosynthesis: light intensity, carbon dioxide concentration and temperature. These factors affect how quickly the reactions can proceed.

光照强度、二氧化碳浓度和温度是控制光合作用速率的主要因素。它们决定了反应进行的速度。

Light intensity: more light means more energy, so a faster rate until another factor becomes limiting.
Carbon dioxide concentration: CO₂ is a raw material; increasing it raises the rate up to a point.
Temperature: higher temperatures speed up enzyme-controlled reactions, but very high temperatures damage enzymes.

光照强度：光照越强，能量越多，速率越快，直到其他因素成为限制因素。
二氧化碳浓度：CO₂是原料，增加其浓度可在一定范围内提高速率。
温度：适当升温会加快酶促反应，但过高会破坏酶。

7. Limiting factors and graphs | 限制因素与曲线图

A limiting factor is the condition that is in the shortest supply. When one factor is increased, the rate rises until another factor becomes limiting.

限制因素是指供应最不足的条件。当某一因素增加时，速率上升，直到另一因素成为新的限制因素。

Factor	Effect on rate	Limiting example
Light intensity	Rate increases up to a plateau	In deep shade
CO₂ concentration	Rate increases until saturation	In sealed greenhouses
Temperature	Optimum around 25–35°C	Cold climates

The graph of light intensity against rate shows a steep rise then a plateau, where another factor is limiting.

光照强度与速率的曲线图先陡峭上升，然后趋于平缓，说明此时有其他因素限制。

8. Uses of glucose | 葡萄糖的用途

Glucose produced during photosynthesis is used in different ways depending on the needs of the plant.

光合作用产生的葡萄糖根据植物需求有不同的用途。

Used in respiration to release energy.
Converted to starch for storage in leaves, roots and seeds.
Converted to sucrose for transport in the phloem.
Converted to cellulose for cell walls.
Combined with nitrogen to make amino acids for proteins.

用于呼吸作用释放能量。
转化为淀粉储存在叶、根和种子中。
转化为蔗糖通过韧皮部运输。
转化为纤维素构成细胞壁。
与氮结合形成合成蛋白质所需的氨基酸。

9. Investigating photosynthesis | 探究光合作用的实验

A classic experiment uses a pondweed such as Elodea. The number of oxygen bubbles released per minute can be counted to measure the rate of photosynthesis.

经典实验使用伊乐藻等水生植物。通过计算每分钟释放的氧气气泡数量来测量光合作用速率。

Variables can be changed one at a time: light intensity (distance from lamp), temperature (water bath), or CO₂ concentration (adding sodium hydrogencarbonate).

可以逐一改变变量：光照强度（灯的距离）、温度（水浴）或二氧化碳浓度（添加碳酸氢钠）。

To test for starch in leaves, a leaf is boiled, decolourised with ethanol, softened and then tested with iodine solution. Blue-black colour indicates starch is present.

检测叶片中的淀粉时，需将叶片煮沸、用酒精脱色、软化，然后用碘液测试。出现蓝黑色说明有淀粉。

10. Mineral ions in plants | 植物中的矿质离子

Plants need certain mineral ions absorbed from the soil to make use of the glucose produced by photosynthesis.

植物需要从土壤中吸收某些矿质离子，以便利用光合作用产生的葡萄糖。

Nitrate ions are needed to make amino acids and proteins. A lack of nitrate causes stunted growth and yellowing of older leaves.

硝酸根离子用于合成氨基酸和蛋白质。缺少硝酸盐会导致生长迟缓、老叶变黄。

Magnesium ions are needed to make chlorophyll. Without magnesium, chlorophyll cannot be formed and leaves become pale or yellow.

镁离子用于合成叶绿素。没有镁，叶绿素无法形成，叶片会变得苍白或发黄。

11. Applications in agriculture | 农业应用

Farmers and gardeners can increase crop yields by managing the limiting factors of photosynthesis.

农民和园丁可以通过管理光合作用的限制因素来提高作物产量。

In greenhouses, they control temperature, add CO₂, provide artificial lighting and supply nutrients. Polythene tunnels trap heat and raise temperature in cooler months.

在温室中，他们调节温度、添加CO₂、提供人工光照并补充养分。塑料棚可保温，在较冷月份提高温度。

Understanding these factors is essential for maximising food production and reducing losses.

理解这些因素对于最大化粮食生产、减少损失至关重要。

12. Summary | 总结

Photosynthesis is an essential process that converts light energy into chemical energy. It requires carbon dioxide, water and light, and produces glucose and oxygen.

光合作用是将光能转化为化学能的重要过程。它需要二氧化碳、水和光，并产生葡萄糖和氧气。

The rate is influenced by light intensity, CO₂ concentration and temperature, with the limiting factor concept helping us predict growth. A sound understanding of photosynthesis is key for biology, agriculture and environmental science.

速率受光照强度、CO₂浓度和温度影响，限制因素概念帮助我们预测生长。深入理解光合作用对生物学、农业和环境科学至关重要。

Published by TutorHao | Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Photosynthesis | 光合作用