Photosynthesis | 光合作用

📚 Photosynthesis | 光合作用

Photosynthesis is the fundamental biological process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose. This process not only sustains the organisms that perform it but also provides the basis of the food chain and maintains atmospheric oxygen levels. For IGCSE Edexcel Science students, understanding photosynthesis is crucial because it links concepts in biology, chemistry, and environmental science.

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基本生物过程。这个过程不仅维持了进行光合作用的生物体，也为食物链提供了基础，并维持了大气中的氧气含量。对于IGCSE Edexcel科学课程的学生来说，理解光合作用至关重要，因为它连接了生物学、化学和环境科学中的概念。

1. What Is Photosynthesis? | 什么是光合作用？

Photosynthesis is an endothermic reaction that takes place in the chloroplasts of plant cells. It requires energy from sunlight to convert carbon dioxide and water into glucose and oxygen. The term 'photo' means light, and 'synthesis' means putting together. Therefore, photosynthesis literally means 'putting together using light'.

光合作用是一种发生在植物细胞叶绿体中的吸热反应。它需要来自阳光的能量，将二氧化碳和水转化为葡萄糖和氧气。“photo”这个词意思是光，“synthesis”意思是合成。因此，光合作用字面意思就是“利用光来合成”。

2. The Word Equation | 文字方程式

en. This shows the reactants (left side) and the products (right side). The arrow indicates that light energy is required, and chlorophyll acts as a catalyst. It is vital to remember that the reaction cannot happen without chlorophyll and light.

描述光合作用最简单的方法是使用文字方程式：二氧化碳 + 水 → 葡萄糖 + 氧气。这显示了反应物（左侧）和生成物（右侧）。箭头表示需要光能，并且叶绿素充当催化剂。重要的是要记住，没有叶绿素和光，该反应就无法发生。

3. The Balanced Chemical Equation | 平衡化学方程式

n demonstrates that six molecules of carbon dioxide react with six molecules of water to produce one molecule of glucose and six molecules of oxygen. Note that the oxygen released comes from the water molecules, not from carbon dioxide.

在IGCSE阶段，光合作用的平衡化学方程式是：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。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气分子。请注意，释放的氧气来自水分子，而不是二氧化碳。

4. Where Photosynthesis Occurs | 光合作用发生的位置

Photosynthesis takes place inside chloroplasts, which are organelles found mainly in the palisade mesophyll cells of leaves. Chloroplasts contain a green pigment called chlorophyll. This pigment absorbs light energy, primarily in the blue and red regions of the spectrum, and reflects green light, which is why plants appear green. The internal membranes of chloroplasts, called thylakoids, provide a large surface area for the light-dependent reactions.

光合作用发生在叶绿体内部，叶绿体是主要在叶片栅栏组织细胞中发现的细胞器。叶绿体含有一种叫做叶绿素的绿色色素。这种色素吸收光能，主要是光谱中的蓝光和红光区域，并反射绿光，这就是植物呈现绿色的原因。叶绿体的内部膜，称为类囊体，为光依赖反应提供了大的表面积。

5. The Role of Chlorophyll | 叶绿素的作用

Chlorophyll is essential because it traps the light energy needed to drive photosynthesis. If a plant lacks chlorophyll, for example due to a magnesium deficiency or a genetic mutation, it cannot photosynthesise efficiently and will often appear yellow or white (chlorosis). Magnesium is a central atom in the chlorophyll molecule, so plants require magnesium ions from the soil to build chlorophyll.

叶绿素至关重要，因为它捕获驱动光合作用所需的光能。如果植物缺乏叶绿素，例如由于缺镁或基因突变，它就无法高效进行光合作用，并且通常会呈现黄色或白色（萎黄病）。镁是叶绿素分子的中心原子，因此植物需要从土壤中吸收镁离子来构建叶绿素。

6. The Limiting Factors of Photosynthesis | 光合作用的限制因素

The rate of photosynthesis is affected by several limiting factors. A limiting factor is a factor that is in short supply and prevents the rate from increasing. The three main limiting factors are light intensity, carbon dioxide concentration, and temperature. If any one of these is too low, it will limit the rate regardless of the levels of the other factors. Understanding limiting factors is key to interpreting graphs in the exam.

光合作用速率受几个限制因素的影响。限制因素是指供应不足、阻碍速率提高的因素。三个主要的限制因素是光照强度、二氧化碳浓度和温度。如果其中任何一个过低，无论其他因素水平如何，它都会限制速率。理解限制因素是考试中解读图表的关键。

广告 / Sponsored

7. Light Intensity | 光照强度

As light intensity increases, the rate of photosynthesis increases proportionally up to a certain point. Beyond this point, light is no longer the limiting factor; instead, either carbon dioxide concentration or temperature becomes the new limiting factor. The graph of rate against light intensity initially rises steeply and then levels off (forms a plateau). At very high light intensities, chlorophyll may even be damaged, causing the rate to drop.

随着光照强度增加，光合作用速率成比例增加，直到某一点。超过这个点，光不再是限制因素；取而代之的是，二氧化碳浓度或温度成为新的限制因素。速率对光照强度的图表最初急剧上升，然后趋于水平（形成平台）。在非常高的光照强度下，叶绿素甚至可能受损，导致速率下降。

8. Carbon Dioxide Concentration | 二氧化碳浓度

Carbon dioxide is a reactant in photosynthesis. The rate of photosynthesis increases with rising CO₂ concentration until another factor becomes limiting. In the natural environment, CO₂ concentration is relatively low (around 0.04%), so it is often the limiting factor on bright, warm days. In greenhouses, growers sometimes add extra CO₂ to boost crop yields, a method known as carbon dioxide enrichment.

二氧化碳是光合作用中的反应物。光合作用速率随CO₂浓度升高而增加，直到另一个因素成为限制。在自然环境中，CO₂浓度相对较低（约0.04%），因此在晴朗温暖的日子里，它常常是限制因素。在温室中，种植者有时会添加额外的CO₂来提高作物产量，这种方法称为二氧化碳富集。

9. Temperature | 温度

Photosynthesis is controlled by enzymes, so temperature has a significant effect. As temperature rises, the kinetic energy of molecules increases, and the rate of photosynthesis speeds up. However, once the temperature exceeds an optimum (usually around 25-30 °C for many plants), enzymes begin to denature. This causes the rate to fall sharply. At very high temperatures, photosynthesis can stop entirely.

光合作用由酶控制，因此温度有显著影响。随着温度升高，分子的动能增加，光合作用速率加快。然而，一旦温度超过最适温度（许多植物通常约25-30 °C），酶开始变性。这导致速率急剧下降。在极高温度下，光合作用可能完全停止。

10. Investigating Photosynthesis | 探究光合作用

In the IGCSE Edexcel Science course, you may investigate the effect of light intensity on the rate of photosynthesis using pondweed (such as Elodea). The method involves placing pondweed in a beaker of water with sodium hydrogencarbonate (to supply CO₂) and measuring the number of oxygen bubbles produced per minute at different distances from a light source. The rate is directly proportional to the number of bubbles if the volume of the bubbles is assumed constant. This experiment allows you to plot a graph and identify the limiting factor.

在IGCSE Edexcel科学课程中，你可能会使用水草（如伊乐藻）探究光照强度对光合作用速率的影响。该方法包括将水草放入含有碳酸氢钠（提供CO₂）的烧杯水中，并测量在离光源不同距离处每分钟产生的氧气气泡数。如果假设气泡体积恒定，则速率与气泡数成正比。这个实验允许你绘制图表并确定限制因素。

11. The Importance of Photosynthesis Globally | 光合作用在全球的重要性

Without photosynthesis, life on Earth as we know it would not exist. Photosynthesis is the primary source of oxygen in the atmosphere, which is essential for aerobic respiration. It also removes carbon dioxide, a greenhouse gas, helping to regulate Earth's climate. Furthermore, the glucose produced is used by plants to build cellulose, starch, and other organic compounds, which pass along food chains to consumers and decomposers.

没有光合作用，我们所知的地球生命将不复存在。光合作用是大气中氧气的主要来源，氧气对于有氧呼吸至关重要。它还移除了温室气体二氧化碳，有助于调节地球气候。此外，植物产生的葡萄糖用于构建纤维素、淀粉和其他有机化合物，这些物质通过食物链传递给消费者和分解者。

12. Photosynthesis and Respiration | 光合作用与呼吸作用

It is important not to confuse photosynthesis with respiration. Photosynthesis is an endothermic process that stores energy in glucose, occurs only in the presence of light, and uses carbon dioxide and water. Respiration is an exothermic process that releases energy from glucose, occurs in all living cells all the time, and uses oxygen and glucose. The two processes are complementary and form a cycle: photosynthesis produces the oxygen and glucose that respiration needs, and respiration returns the carbon dioxide and water needed for photosynthesis.

重要的是不要将光合作用与呼吸作用混淆。光合作用是一种吸热过程，将能量储存在葡萄糖中，仅在光存在时发生，使用二氧化碳和水。呼吸作用是一种放热过程，从葡萄糖中释放能量，在所有活细胞中一直发生，使用氧气和葡萄糖。这两个过程是互补的，并形成一个循环：光合作用产生呼吸作用所需的氧气和葡萄糖，呼吸作用则返回光合作用所需的二氧化碳和水。

Published by TutorHao | Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）