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 fundamental biological reaction that sustains life on Earth by producing oxygen and organic molecules.

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。它是维持地球生命的基础生物反应，通过产生氧气和有机分子为几乎所有生物提供能量来源。

1. The Word Equation | 文字方程式

The overall process of photosynthesis can be summarised using a simple word equation. Carbon dioxide and water react in the presence of light and chlorophyll to produce glucose and oxygen.

光合作用的总体过程可以用一个简单的文字方程式概括。二氧化碳和水在光照和叶绿素的存在下反应，生成葡萄糖和氧气。

Carbon dioxide + Water → Glucose + Oxygen

二氧化碳 + 水 → 葡萄糖 + 氧气

This equation is essential for understanding the raw materials and products of photosynthesis. It also shows that light energy is not a substance but an essential driving force.

这个方程式对于理解光合作用的原料和产物至关重要。它还表明光能不是一种物质，而是必要的驱动力。

2. The Balanced Chemical Symbol Equation | 平衡化学符号方程式

For a more precise understanding, the chemical equation must be balanced. Six molecules of carbon dioxide combine with six molecules of water to produce one molecule of glucose and six molecules of oxygen.

为了更精确地理解，化学方程式必须配平。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。

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

The balanced equation shows that the number of atoms of each element is conserved. This is a key requirement in all chemical reactions, and Edexcel often asks students to identify the products or balance photosynthesis equations.

该平衡方程式表明每种元素的原子数量是守恒的。这是所有化学反应的关键要求，Edexcel 考试常要求学生识别产物或配平光合作用方程式。

3. The Role of Chlorophyll and Light | 叶绿素和光的作用

Chlorophyll is a green pigment located in chloroplasts. It absorbs light energy, mainly in the red and blue-violet regions of the spectrum, and reflects green light. This absorbed energy is used to split water molecules and drive the synthesis of glucose.

叶绿素是一种位于叶绿体中的绿色色素。它吸收光能，主要吸收光谱中的红光和蓝紫光区域，并反射绿光。吸收的能量用于分解水分子并驱动葡萄糖的合成。

Light intensity affects the rate of photosynthesis. Without enough light, the process slows down or stops. Temperature also matters because photosynthesis involves enzyme-controlled reactions.

光照强度影响光合作用的速率。没有足够的光照，该过程会减慢或停止。温度也很重要，因为光合作用涉及酶控制的反应。

4. The Internal Structure of a Leaf | 叶片内部结构

Leaves are specialised organs for photosynthesis. Their flattened shape provides a large surface area for light absorption and gas exchange. The internal structure includes the epidermis, mesophyll, vascular bundles, and stomata.

叶片是进行光合作用的特化器官。其扁平形状提供了较大的表面积，用于吸收光和进行气体交换。内部结构包括表皮、叶肉、维管束和气孔。

Upper epidermis / 上表皮: Transparent layer allowing light to pass through. | 透明的层，允许光通过。
Palisade mesophyll / 栅栏叶肉: Closely packed cells containing many chloroplasts. | 排列紧密的细胞，含有大量叶绿体。
Spongy mesophyll / 海绵叶肉: Loose cells with air spaces for gas diffusion. | 疏松的细胞，具有气隙，便于气体扩散。
Stomata / 气孔: Pores controlled by guard cells for CO₂ entry and O₂ exit. | 由保卫细胞控制的气孔，用于二氧化碳进入和氧气排出。

5. Factors Affecting the Rate of Photosynthesis | 影响光合作用速率的因素

Photosynthesis rate is limited by the availability of light, carbon dioxide concentration, and temperature. The law of limiting factors states that at any given moment, the rate is limited by the factor that is in shortest supply.

光合作用速率受光照、二氧化碳浓度和温度的可用性限制。限制因子定律指出，在任何给定时刻，速率受供应最少的因素限制。

Experiments can be carried out using aquatic plants like pondweed. The number of oxygen bubbles produced per minute is a simple measure of the rate of photosynthesis.

可以使用金鱼藻等水生植物进行实验。每分钟产生的氧气气泡数量是测量光合作用速率的简单方法。

Factor 因素	Effect when limited 受限时的影响
Light intensity 光照强度	Rate increases with light, then plateaus 随光增强而增大，后趋于平稳
CO₂ concentration 二氧化碳浓度	Low CO₂ limits glucose production 低二氧化碳限制葡萄糖生成
Temperature 温度	High temperature denatures enzymes 高温使酶变性

6. Limiting Factors and Graphs | 限制因子与曲线图

Graphs of photosynthesis rate against light intensity typically show a linear increase at low light, followed by a plateau where another factor becomes limiting. This plateau is often caused by insufficient CO₂ or low temperature.

光合作用速率对光照强度的曲线通常在低光照时呈线性增加，随后出现平台期，这时另一种因子成为限制因素。该平台通常由二氧化碳不足或温度过低引起。

For example, raising CO₂ concentration when light is already saturating will still increase the rate up to a new plateau. This proves the existence of multiple limiting factors.

例如，当光已经饱和时，提高二氧化碳浓度仍会使速率上升到新的平台。这证明了多种限制因子的存在。

7. The Light-Dependent and Light-Independent Reactions | 光依赖和光独立反应

Photosynthesis occurs in two main stages: the light-dependent reaction and the light-independent reaction (Calvin cycle). In the light-dependent reaction, light energy is absorbed by chlorophyll and splits water into oxygen, protons, and electrons. This occurs in the thylakoid membranes of the chloroplast.

光合作用主要分为两个阶段：光依赖反应和光独立反应（卡尔文循环）。在光依赖反应中，光能被叶绿素吸收，将水分解为氧气、质子和电子。该过程发生在叶绿体的类囊体膜上。

The light-independent reaction uses the energy-carrying molecules from the first stage to convert carbon dioxide into glucose. This occurs in the stroma. For IGCSE level, you only need to understand the role of both stages and where they occur.

光独立反应利用第一阶段产生的能量载体分子，将二氧化碳转化为葡萄糖。该过程发生在基质中。在 IGCSE 阶段，你只需要理解两个阶段的作用及其发生位置。

8. The Importance of Photosynthesis in Food Chains | 光合作用在食物链中的重要性

Photosynthesis is the ultimate source of biomass for almost all food chains. Producers convert light energy into chemical energy stored in glucose, which is then passed on to consumers through feeding relationships.

光合作用是几乎所有食物链中生物量的最终来源。生产者将光能转化为储存在葡萄糖中的化学能，然后通过捕食关系传递给消费者。

Without photosynthesis, energy would not be available to herbivores or carnivores. The oxygen released also enables aerobic respiration to occur in most organisms.

没有光合作用，能量就无法被草食动物或肉食动物利用。释放的氧气也使大多数生物能够进行有氧呼吸。

9. Photosynthesis and the Carbon Cycle | 光合作用与碳循环

Photosynthesis removes carbon dioxide from the atmosphere and converts it into organic compounds. This process is a vital part of the carbon cycle, balancing the release of CO₂ by respiration and combustion.

光合作用从大气中去除二氧化碳并将其转化为有机化合物。该过程是碳循环的重要部分，平衡呼吸作用和燃烧排放的二氧化碳。

Deforestation and burning of fossil fuels have increased atmospheric CO₂ levels. Understanding photosynthesis helps explain why preserving green vegetation is crucial for climate stability.

砍伐森林和燃烧化石燃料增加了大气中的二氧化碳水平。理解光合作用有助于解释为什么保护绿色植被对气候稳定至关重要。

10. Investigating Photosynthesis | 探究光合作用

Classic investigations include testing a leaf for starch. A leaf exposed to light produces starch, which is a stored form of glucose. The leaf is boiled, heated in ethanol to remove chlorophyll, and then tested with iodine solution. A blue-black colour indicates starch is present.

经典探究包括检测叶片中的淀粉。暴露于光照的叶片会产生淀粉，淀粉是葡萄糖的储存形式。将叶片煮沸，用乙醇加热去除叶绿素，然后用碘液测试。蓝黑色表明存在淀粉。

To show that light is necessary, only part of a leaf is covered. To show that CO₂ is necessary, a plant can be placed in a transparent bag with soda lime to absorb CO₂. Such experiments are common in Edexcel practical exams.

为证明光的必要性，仅遮盖叶片的一部分。为证明二氧化碳的必要性，可将植物放入装有苏打石灰的透明袋中吸收二氧化碳。这类实验在 Edexcel 实践考试中很常见。

Published by TutorHao | Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Photosynthesis | 光合作用