📚 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 fundamental basis for almost all life on Earth, providing oxygen and organic compounds for heterotrophs.
光合作用是绿色植物、藻类和一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生命的基础，为异养生物提供氧气和有机化合物。
1. Overall Equation | 总反应方程式
Photosynthesis can be summarised by the word equation: carbon dioxide + water → glucose + oxygen, with light energy and chlorophyll as required conditions.
光合作用可用文字方程式概括：二氧化碳 + 水 → 葡萄糖 + 氧气，需要光能和叶绿素作为条件。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
In the balanced chemical equation, six carbon dioxide molecules react with six water molecules to produce one glucose molecule and six oxygen molecules.
在配平的化学方程式中，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气分子。
2. The Role of Chlorophyll | 叶绿素的作用
Chlorophyll is a green pigment located in chloroplasts, primarily in the mesophyll cells of leaves. It absorbs light energy, mainly in the red and blue-violet regions of the spectrum, and reflects green light, which is why leaves appear green.
叶绿素是一种位于叶绿体中的绿色色素，主要存在于叶肉细胞中。它吸收光能，主要是光谱中的红光和蓝紫光区域，并反射绿光，因此叶子呈现绿色。
Chlorophyll acts as an electron donor and catalyst in the light-dependent reactions. It is essential for converting light energy into chemical energy in the form of ATP and reduced NADP.
叶绿素在光依赖反应中充当电子供体和催化剂。它对于将光能转化为ATP和还原型NADP形式的化学能至关重要。
3. Light-Dependent Reactions | 光依赖反应
These reactions occur in the thylakoid membranes of chloroplasts. They require light directly and produce ATP, reduced NADP, and oxygen.
这些反应发生在叶绿体的类囊体薄膜上。它们直接需要光，产生ATP、还原型NADP和氧气。
During photolysis, water molecules are split by light energy into protons, electrons, and oxygen gas. The oxygen is released as a by-product of photosynthesis.
在光解过程中，水分子被光能分解为质子、电子和氧气。氧气作为光合作用的副产物释放出来。
The electrons move through an electron transport chain, releasing energy that pumps protons across the thylakoid membrane, creating a gradient used to synthesise ATP.
电子沿电子传递链移动，释放能量驱动质子跨膜运输，形成用于合成ATP的梯度。
4. Light-Independent Reactions | 光非依赖反应
These reactions occur in the stroma of the chloroplast and do not require light directly. They are sometimes called the Calvin cycle.
这些反应发生在叶绿体的基质中，不直接需要光。它们有时被称为卡尔文循环。
Carbon dioxide is fixed by combining with ribulose-1,5-bisphosphate (RuBP), a five-carbon compound, catalysed by the enzyme rubisco, to form two molecules of 3-phosphoglycerate (3-PGA).
二氧化碳被固定，与五碳化合物1,5-二磷酸核酮糖（RuBP）结合，在酶Rubisco催化下生成两个分子的3-磷酸甘油酸（3-PGA）。
Using ATP and reduced NADP from the light-dependent reactions, 3-PGA is reduced to glyceraldehyde-3-phosphate (G3P), which is then used to produce glucose and regenerate RuBP.
利用光依赖反应产生的ATP和还原型NADP，3-PGA被还原为甘油醛-3-磷酸（G3P），然后用于产生葡萄糖并再生RuBP。
5. Factors Affecting Photosynthesis | 影响光合作用的因素
Light intensity, carbon dioxide concentration, and temperature are the three main limiting factors. The rate of photosynthesis increases until another factor becomes limiting.
光强度、二氧化碳浓度和温度是三个主要限制因素。光合作用速率会增加，直到另一个因素成为限制因素。
- Light intensity: increasing light intensity up to a saturation point increases the rate.
- Carbon dioxide concentration: increasing CO₂ concentration up to a saturation point increases the rate.
- Temperature: increasing temperature increases enzyme activity up to the optimum, then decreases due to enzyme denaturation.
- 光强度：在饱和点之前增加光强度，反应速率增加。
- 二氧化碳浓度：在饱和点之前增加CO₂浓度，反应速率增加。
- 温度：在达到最适温度前，升温加快酶活性，之后因酶变性而速率下降。
6. Limiting Factors and Their Graphs | 限制因素及其图表
The concept of limiting factors is important in understanding agricultural practices. For example, in a greenhouse, farmers may use artificial lighting, CO₂ generators, and heaters to optimise photosynthesis.
限制因素的概念对理解农业实践很重要。例如，在温室中，农民可能使用人工照明、CO₂发生器和加热器来优化光合作用。
When light intensity is low, it is the limiting factor; increasing CO₂ concentration has no effect. When light intensity is high, CO₂ concentration or temperature may become the limiting factor.
当光强度低时，它是限制因素；增加CO₂浓度没有效果。当光强度高时，CO₂浓度或温度可能成为限制因素。
| Factor | Effect on rate |
|---|---|
| Light intensity ↑ | Rate ↑ until saturation |
| CO₂ concentration ↑ | Rate ↑ until saturation |
| Temperature ↑ | Rate ↑ to optimum, then ↓ |
| 因素 | 对速率的影响 |
|---|---|
| 光强度 ↑ | 速率↑直至饱和 |
| CO₂浓度 ↑ | 速率↑直至饱和 |
| 温度 ↑ | 速率升至最适，然后↓ |
7. Leaf Adaptations for Photosynthesis | 叶片对光合作用的适应
Leaves are adapted to maximise light capture and gas exchange. The broad, flat shape provides a large surface area for light absorption.
叶片适应于最大化光捕获和气体交换。宽大的扁平形状提供了大的表面积来吸收光。
The palisade mesophyll layer contains numerous chloroplasts and is located near the upper surface. Stomata allow CO₂ to enter and O₂ to leave, while internal air spaces facilitate gas diffusion.
栅栏叶肉层含有大量叶绿体，位于靠近上表面的位置。气孔允许CO₂进入和O₂释放，内部气隙促进气体扩散。
- Thin cuticle reduces water loss but allows light penetration.
- Veins supply water and carry away sugars.
- Chloroplasts contain starch grains and chlorophyll.
- 薄的角质层减少水分流失，但允许光穿透。
- 叶脉输送水分并带走糖类。
- 叶绿体含有淀粉粒和叶绿素。
8. Measuring the Rate of Photosynthesis | 测量光合作用速率
The rate can be measured by the volume of oxygen produced, the volume of carbon dioxide absorbed, or the increase in biomass over time.
速率可以通过产生的氧气体积、吸收的二氧化碳体积或随时间增加的生物量来测量。
A common experiment uses aquatic plants such as Elodea. The number of oxygen bubbles released per minute can be counted, or the gas can be collected in a measuring cylinder.
常见实验使用水生植物如伊乐藻。可以计算每分钟释放的氧气气泡数，或者将气体收集在量筒中。
Variables such as light intensity (distance from lamp), temperature, and CO₂ concentration (sodium hydrogencarbonate solution) can be changed to investigate their effects.
可以改变光强度（与灯的距离）、温度和CO₂浓度（碳酸氢钠溶液）等变量来研究其影响。
9. Photosynthesis and Respiration | 光合作用与呼吸作用
Photosynthesis is anabolic, storing energy in glucose. Respiration is catabolic, releasing energy from glucose. They are complementary processes in the carbon and oxygen cycles.
光合作用是合成代谢，将能量储存在葡萄糖中。呼吸作用是分解代谢，从葡萄糖中释放能量。它们在碳循环和氧循环中是互补过程。
At night, plants cannot photosynthesise but continue to respirate. During the day, photosynthesis usually exceeds respiration, resulting in net oxygen release.
在夜间，植物不进行光合作用但继续呼吸。在白天，光合作用通常超过呼吸作用，导致净氧气释放。
Photosynthesis: CO₂ + H₂O → Glucose + O₂
Respiration: Glucose + O₂ → CO₂ + H₂O
10. Importance of Photosynthesis | 光合作用的重要性
Photosynthesis is essential for maintaining atmospheric oxygen levels, providing food chains with energy, and serving as the ultimate source of fossil fuels.
光合作用对于维持大气氧含量、为食物链提供能量以及作为化石燃料的最终来源至关重要。
It removes carbon dioxide from the atmosphere, helping to regulate the greenhouse effect. Agricultural productivity depends on optimising photosynthesis.
它从大气中移除二氧化碳，有助于调节温室效应。农业生产力依赖于优化光合作用。
Without photosynthesis, most life on Earth would not exist, as heterotrophs depend on the organic compounds produced by autotrophs.
没有光合作用，地球上大多数生命将不复存在，因为异养生物依赖自养生物产生的有机化合物。
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