📚 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 life on Earth, providing food and oxygen for living organisms.
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，为生物提供食物和氧气。
1. What is Photosynthesis? | 什么是光合作用？
Photosynthesis is a series of chemical reactions that take place in the chloroplasts of plant cells. During this process, carbon dioxide and water are turned into glucose and oxygen, using energy from sunlight.
光合作用是发生在植物细胞叶绿体中的一系列化学反应。在这个过程中，二氧化碳和水在阳光能量作用下转化为葡萄糖和氧气。
The overall process can be summarised as a simple equation, but it actually involves many small steps. The rate of photosynthesis depends on environmental conditions.
整个过程可以用一个简单的方程概括，但实际上包含许多小步骤。光合作用的速率取决于环境条件。
2. The Word Equation and Chemical Equation | 文字方程和化学方程
The word equation for photosynthesis is: carbon dioxide + water → glucose + oxygen.
光合作用的文字方程是：二氧化碳 + 水 → 葡萄糖 + 氧气。
The balanced chemical equation for photosynthesis is:
光合作用的平衡化学方程是：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
This equation 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。
3. The Reactants: Water and Carbon Dioxide | 反应物：水和二氧化碳
Water is absorbed by the roots from the soil and transported to the leaves through the xylem vessels. It provides the hydrogen atoms needed to build glucose.
水分通过根从土壤中吸收，并通过木质部导管运输到叶片。它提供构建葡萄糖所需的氢原子。
Carbon dioxide enters the leaf through small pores called stomata. It provides the carbon and oxygen atoms that make up glucose.
二氧化碳通过称为气孔的小孔进入叶片。它提供构成葡萄糖的碳和氧原子。
Both reactants must be available in sufficient amounts for photosynthesis to occur at a high rate.
两种反应物都必须以足够的量供应，光合作用才能以高速率进行。
4. The Products: Glucose and Oxygen | 产物：葡萄糖和氧气
Glucose is a simple sugar that stores chemical energy. It can be used immediately for respiration, converted into starch for storage, or used to build other substances such as cellulose and proteins.
葡萄糖是一种储存化学能的单糖。它可以立即用于呼吸作用，转化为淀粉储存，或用于构建其他物质，如纤维素和蛋白质。
Oxygen is a waste product of photosynthesis. It is released into the atmosphere through the stomata, and most living organisms, including humans, depend on this oxygen for respiration.
氧气是光合作用的废物。它通过气孔释放到大气中，包括人类在内的大多数生物都依赖这种氧气进行呼吸。
5. The Role of Chlorophyll and Light | 叶绿素和光的作用
Chlorophyll is a green pigment located in the chloroplasts. It absorbs light energy, mainly in the blue and red regions of the spectrum, and uses it to drive the photosynthetic reactions.
叶绿素是位于叶绿体中的绿色色素。它吸收光能，主要吸收光谱中的蓝光和红光区域，并利用它驱动光合反应。
Light provides the energy needed to split water molecules into hydrogen and oxygen during the light-dependent stage. Without light, photosynthesis cannot occur.
光提供能量，在光依赖阶段将水分子分解为氢和氧。没有光，光合作用无法进行。
The intensity, colour, and duration of light all affect the rate of photosynthesis.
光的强度、颜色和持续时间都会影响光合作用的速率。
6. The Structure of a Leaf Adapted for Photosynthesis | 叶片结构对光合作用的适应
Leaves are highly adapted to capture light and exchange gases. The broad, flat shape provides a large surface area for light absorption.
叶片高度适应于捕捉光能以及交换气体。宽而扁平的形状提供了吸收光能的大表面积。
The upper epidermis is transparent, allowing light to pass through to the palisade layer, which contains many chloroplasts. The spongy mesophyll has air spaces that allow carbon dioxide to diffuse to the cells.
上表皮是透明的，允许光通过到达栅栏层，该层含有大量叶绿体。海绵状叶肉具有气隙，使二氧化碳扩散到细胞中。
Stomata, mainly found on the lower surface, open to allow carbon dioxide in and oxygen out. Guard cells control the opening and closing of stomata.
主要位于下表皮的气孔打开允许二氧化碳进入，氧气排出。保卫细胞控制气孔的开闭。
7. Factors Affecting Photosynthesis | 影响光合作用的因素
Three main environmental factors affect the rate of photosynthesis: light intensity, carbon dioxide concentration, and temperature.
影响光合作用速率的主要环境因素有三个：光强度、二氧化碳浓度和温度。
As light intensity increases, the rate of photosynthesis increases until a maximum level is reached. At this point, light is no longer the limiting factor.
随着光强度的增加，光合作用速率增加，直到达到最大值。此时，光不再是限制因素。
Similarly, increasing carbon dioxide concentration generally boosts photosynthesis until a saturation point. Temperature affects the enzymes involved; if it is too high, enzymes denature and the rate declines.
类似地，增加二氧化碳浓度通常会促进光合作用，直到饱和点。温度影响参与的酶；如果温度过高，酶会变性，速率下降。
8. Limiting Factors | 限制因素
A limiting factor is the factor that is closest to its minimum level and therefore restricts the rate of a reaction. For photosynthesis, the limiting factor at any moment is the one in shortest supply relative to the plant’s needs.
限制因素是最接近其最低水平、因此限制反应速率的因素。对于光合作用，任一时刻的限制因素是相对于植物需求供应最短缺的那个因素。
For example, on a sunny day, carbon dioxide concentration might be the limiting factor. On a cloudy day, light intensity might be limiting. If temperature is very low, it could also be limiting because enzymes work slowly.
例如，在晴天，二氧化碳浓度可能是限制因素。在阴天，光强度可能是限制因素。如果温度很低，也可能成为限制因素，因为酶工作缓慢。
Understanding limiting factors is important in agriculture and horticulture for maximising crop yields in greenhouses.
了解限制因素在农业和园艺中对于最大化温室作物产量很重要。
9. How Plants Use Glucose | 植物如何使用葡萄糖
Glucose produced during photosynthesis is used in several ways. It is broken down during respiration to release energy for cell activities.
光合作用产生的葡萄糖有几种用途。它在呼吸作用中被分解，为细胞活动释放能量。
Excess glucose can be converted into starch and stored in leaves, roots, or seeds. It is also used to make cellulose for cell walls, and combined with nitrates to form amino acids, which build proteins.
多余的葡萄糖可以转化为淀粉并储存在叶片、根或种子中。它还用于制造细胞壁的纤维素，并与硝酸盐结合形成氨基酸，从而构建蛋白质。
Some glucose is converted into lipids (fats) for storage, especially in seeds.
一些葡萄糖转化为用于储存的脂质（脂肪），尤其是在种子中。
10. Photosynthesis and the Environment | 光合作用与环境
Photosynthesis plays a vital role in the carbon cycle and the oxygen cycle. It removes carbon dioxide from the atmosphere and releases oxygen, helping to regulate global gas levels.
光合作用在碳循环和氧循环中起着至关重要的作用。它从大气中去除二氧化碳并释放氧气，有助于调节全球气体水平。
Forests and oceans act as carbon sinks, storing carbon absorbed through photosynthesis. This has major implications for climate change and the preservation of ecosystems.
森林和海洋作为碳汇，储存通过光合作用吸收的碳。这对气候变化和生态系统保护具有重要意义。
11. Investigating Photosynthesis | 实验研究光合作用
One common way to measure the rate of photosynthesis is by counting oxygen bubbles produced by an aquatic plant, such as elodea, in a beaker of water.
一种常见的测量光合作用速率的方法是计数水生植物（如水蕴草）在烧杯水中产生的氧气气泡数。
The distance from a lamp can be varied to change light intensity, and the number of bubbles per minute is recorded. Alternatively, the volume of oxygen collected in a gas syringe can be measured.
可以改变灯的距离以改变光强度，并记录每分钟的气泡数。或者，可以测量在气体注射器中收集的氧气体积。
To test the effect of carbon dioxide concentration, sodium hydrogencarbonate can be added to release CO₂. The effect of temperature can be investigated by heating the water bath around the plant.
为了测试二氧化碳浓度的影响，可以添加碳酸氢钠释放CO₂。温度的影响可以通过加热植物周围的水浴来研究。
12. Importance of Photosynthesis | 光合作用的重要性
Photosynthesis is the primary source of energy for almost all ecosystems. Plants convert solar energy into chemical energy, which is then passed along food chains.
光合作用是几乎所有生态系统的主要能量来源。植物将太阳能转化为化学能，然后沿着食物链传递。
Without photosynthesis, there would be no oxygen in the atmosphere and no organic matter to sustain heterotrophic organisms, including humans. It is essential for life on Earth.
没有光合作用，大气中将没有氧气，也没有有机物来维持包括人类在内的异养生物。它对于地球上的生命至关重要。
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