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 ultimate source of almost all food and oxygen on Earth.

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和氧气的最终来源。

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1. Importance of Photosynthesis | 光合作用的重要性

Photosynthesis produces oxygen, which is essential for aerobic respiration in most living organisms. It also produces glucose, which forms the basis of food chains and supplies energy to herbivores and carnivores.

光合作用产生氧气，而氧气是大多数生物进行有氧呼吸所必需的。它还产生葡萄糖，葡萄糖构成食物链的基础，并为草食动物和肉食动物提供能量。

• Releases oxygen into the atmosphere | 向大气释放氧气

• Removes carbon dioxide from the air | 从空气中吸收二氧化碳

• Provides organic compounds for all heterotrophs | 为所有异养生物提供有机化合物

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2. The Word and Symbol Equation | 字方程式和符号方程式

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

整个过程可以用字方程式概括。二氧化碳和水在光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

The balanced chemical equation shows the exact ratio of molecules involved:

平衡化学方程式显示了所涉及分子的精确比例：

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Six carbon dioxide molecules combine with six water molecules to form one glucose molecule and six oxygen molecules.

六个二氧化碳分子与六个水分子结合，形成一个葡萄糖分子和六个氧分子。

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3. Site of Photosynthesis | 光合作用的场所

Photosynthesis takes place mainly in the mesophyll cells of leaves, especially in the chloroplasts. Each chloroplast contains chlorophyll pigments that absorb light energy.

光合作用主要发生在叶片的叶肉细胞中，尤其是叶绿体中。每个叶绿体都含有吸收光能的叶绿素色素。

• Chlorophyll absorbs red and blue light most efficiently, reflecting green light | 叶绿素最有效吸收红光和蓝光，反射绿光

• Chloroplasts are surrounded by a double membrane and contain thylakoids stacked into grana | 叶绿体由双层膜包围，含有堆叠成基粒的类囊体

• The fluid surrounding the grana is called the stroma | 基粒周围的流体称为基质

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4. Light-Dependent Stage | 光依赖阶段

The light-dependent stage occurs in the thylakoid membranes. It requires light energy to split water and produce ATP and reduced NADP.

光依赖阶段发生在类囊体膜上。它需要光能来分解水并产生ATP和还原型NADP。

Splitting water is called photolysis. The oxygen released during photosynthesis comes from this water splitting.

分解水称为光解。光合作用释放的氧气来自这种水的分解。

2H₂O → 4H⁺ + 4e⁻ + O₂

The hydrogen ions are taken up by the carrier molecule NADP, forming reduced NADP. Light energy also converts ADP and phosphate into ATP.

氢离子被载体分子NADP吸收，形成还原型NADP。光能还将ADP和磷酸转化为ATP。

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5. Light-Independent Stage (Calvin Cycle) | 光不依赖阶段（卡尔文循环）

The light-independent stage occurs in the stroma. It uses the ATP and reduced NADP produced in the light-dependent stage to convert carbon dioxide into glucose.

光不依赖阶段发生在基质中。它利用光依赖阶段产生的ATP和还原型NADP将二氧化碳转化为葡萄糖。

• Carbon dioxide combines with a five-carbon compound (RuBP) | 二氧化碳与五碳化合物（RuBP）结合

• This forms an unstable six-carbon compound, which quickly splits into two molecules of GP (glycerate 3-phosphate) | 这形成不稳定的六碳化合物，迅速分裂成两个甘油酸-3-磷酸（GP）分子

• GP is reduced to TP (triose phosphate) using ATP and reduced NADP | GP在ATP和还原型NADP的作用下被还原为磷酸丙糖（TP）

• Most TP molecules regenerate RuBP; some are used to produce glucose and other organic compounds | 大多数TP分子再生RuBP，部分用于产生葡萄糖和其他有机物

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

The three main factors that affect photosynthesis are light intensity, carbon dioxide concentration and temperature. Each of these can be a limiting factor.

影响光合作用的三个主要因素是光照强度、二氧化碳浓度和温度。这些因素中的每一个都可以成为限制因子。

Factor | 因素	Effect | 效应
Light intensity | 光照强度	As light intensity increases, rate increases until another factor becomes limiting | 光强增加，速率增加，直到另一个因素成为限制因子
CO₂ concentration | 二氧化碳浓度	Higher CO₂ levels speed up the Calvin cycle | 较高的CO₂水平加速卡尔文循环
Temperature | 温度	Enzymes work best at optimum temperature; above this, rate drops sharply | 酶在最适温度下效率最高；超过此温度，速率急剧下降

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7. Limiting Factors | 限制因子

A limiting factor is the factor that is in shortest supply and therefore slows down the rate of photosynthesis. If this factor is increased, the rate will increase until another factor becomes limiting.

限制因子是指供应最短缺从而减慢光合作用速率的因素。如果增加该因素，速率会增加，直到另一个因素成为限制因子。

In agriculture, farmers and greenhouse growers manipulate these factors to maximise crop yield. They may add artificial lighting, CO₂ generators or heating systems.

在农业中，农民和温室种植者通过调节这些因素来最大化作物产量。他们可以添加人工照明、CO₂发生器或加热系统。

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8. Investigating Photosynthesis | 探究光合作用

A common experiment uses pondweed (Elodea) to measure the volume of oxygen produced in a fixed time. The number of bubbles or the gas volume collected is an indicator of the rate.

一个常见实验使用金鱼藻（Elodea）来测量固定时间内产生的氧气体积。气泡数量或收集的气体体积可作为速率的指标。

• Place pondweed in a beaker with sodium hydrogen carbonate solution | 将金鱼藻放入装有碳酸氢钠溶液的烧杯中

• Vary the distance from a lamp to change light intensity | 改变与灯泡的距离以改变光照强度

• Count bubbles per minute or collect gas in a capillary tube | 每分钟计数气泡或在毛细管中收集气体

• Control temperature by keeping the water bath constant | 通过保持水浴恒温来控制温度

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9. Uses of Glucose | 葡萄糖的用途

Glucose produced in photosynthesis is used by the plant in several ways. It is converted into starch for storage, used in respiration for energy, or transformed into other molecules.

光合作用产生的葡萄糖在植物体内有多种用途。它转化为淀粉进行储存，用于呼吸作用提供能量，或转化为其他分子。

• Starch for storage | 淀粉用于储存

• Sucrose for transport in the phloem | 蔗糖用于韧皮部运输

• Cellulose for cell walls | 纤维素用于细胞壁

• Proteins and lipids for growth | 蛋白质和脂质用于生长

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10. Leaf Adaptations for Photosynthesis | 叶片对光合作用的适应

Leaves are well adapted to maximise light capture and gas exchange. Their broad, flat shape gives a large surface area.

叶片非常适合最大化吸收光能并进行气体交换。其宽阔扁平的形状提供了大的表面积。

• Palisade cells are packed with chloroplasts near the upper surface | 栅栏细胞在近上表面充满叶绿体

• Thin structure allows rapid diffusion of CO₂ to mesophyll cells | 薄的结构使CO₂能快速扩散到叶肉细胞

• Stomata allow gas exchange with the atmosphere | 气孔允许与大气进行气体交换

• Transparent epidermis lets light reach photosynthetic cells | 透明表皮让光到达光合细胞

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Published by TutorHao | Biology Revision Series | aleveler.com

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