📚 Photosynthesis | 光合作用
Photosynthesis is the process by which green plants, algae and some bacteria use sunlight to synthesise glucose from carbon dioxide and water. This process releases oxygen as a by-product and stores energy in the form of chemical bonds. It is the ultimate source of food and oxygen for almost all living organisms on Earth.
光合作用是绿色植物、藻类和某些细菌利用阳光，将二氧化碳和水合成葡萄糖的过程。该过程会释放氧气作为副产物，并以化学键的形式储存能量。它是地球上几乎所有生物获得食物和氧气的最终来源。
1. What Is Photosynthesis? | 什么是光合作用？
Photosynthesis is an endothermic reaction, meaning it takes in energy from the surroundings. The energy comes from sunlight and is captured by a green pigment called chlorophyll. The word ‘photosynthesis’ comes from ‘photo’ meaning light and ‘synthesis’ meaning to make.
光合作用是一种吸热反应（endothermic reaction），即从周围环境吸收能量。能量来自阳光，由称为叶绿素（chlorophyll）的绿色色素捕获。”photosynthesis”一词源自”photo”（光）和”synthesis”（合成）。
During photosynthesis, plants convert low-energy inorganic molecules, carbon dioxide and water, into a high-energy organic molecule, glucose. This glucose can then be used as a respiratory substrate or converted into other substances such as starch, cellulose and amino acids.
在光合作用过程中，植物将低能量的无机分子（二氧化碳和水）转化为高能量的有机分子（葡萄糖）。葡萄糖随后可用作呼吸作用的底物，或转化为淀粉、纤维素和氨基酸等其他物质。
Photosynthesis occurs mainly in the leaves of plants, but any green part of the plant, including green stems, can photosynthesise. The overall reaction is a reduction-oxidation process in which water is oxidised and carbon dioxide is reduced.
光合作用主要发生在植物的叶片中，但植物的任何绿色部分，包括绿色的茎，都可以进行光合作用。整体反应是一个氧化还原过程，其中水被氧化，二氧化碳被还原。
2. The Balanced Chemical Equation | 化学方程式
For IGCSE Edexcel Science, you must be able to recall both the word equation and the balanced chemical symbol equation for photosynthesis. The reactions occur in the chloroplasts of plant cells.
对于 IGCSE Edexcel 科学考试，你必须能够记住光合作用的文字方程式和配平的化学符号方程式。反应发生在植物细胞的叶绿体中。
Carbon dioxide + Water → Glucose + Oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
The balanced symbol equation is:
配平的符号方程式为：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Notice that six carbon dioxide molecules react with six water molecules to produce one glucose molecule and six oxygen molecules. The oxygen produced comes from the water molecules, not from carbon dioxide. This is a common exam question.
注意：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。产生的氧气来自水分子，而不是二氧化碳分子。这是一个常见的考试考点。
When writing the equation, remember to include the conditions: sunlight energy and chlorophyll. These are often written above and below the arrow. Energy is not a substance, so it must not be written as a reactant or product.
书写方程式时，记得包含条件：光能和叶绿素。这些通常写在箭头的上下方。能量不是物质，所以不能作为反应物或产物写出。
3. Leaf Structure and Adaptations | 叶片结构与适应性
Leaves are the main photosynthetic organs of most plants. Their structure is highly adapted to maximise the rate of photosynthesis. You should be able to label a cross-section of a leaf and explain how each part is adapted.
叶片是大多数植物进行光合作用的主要器官。它们的结构高度适应于最大化光合作用速率。你应该能够标注叶片横截面，并解释每个部分的适应性。
| Structure | 结构 | Function | 功能 |
| Waxy cuticle | 蜡质角质层 | Prevents water loss | 防止水分蒸发 |
| Upper epidermis | 上表皮 | Transparent, lets light through | 透明，让光透过 |
| Palisade mesophyll | 栅栏组织 | Contains many chloroplasts for photosynthesis | 含大量叶绿体进行光合作用 |
| Spongy mesophyll | 海绵组织 | Air spaces for gas diffusion | 气室供气体扩散 |
| Stomata | 气孔 | Allow gas exchange (CO₂ in, O₂ out) | 允许气体交换（CO₂进入，O₂排出） |
The palisade mesophyll cells are found near the top of the leaf where light intensity is highest. They are packed with chloroplasts to absorb maximum light. The spongy mesophyll has large air spaces, which allow carbon dioxide to diffuse rapidly to the photosynthetic cells.
栅栏组织细胞位于叶片靠近顶部的位置，此处光强度最高。它们充满叶绿体以吸收最多光线。海绵组织具有大的气室，使二氧化碳能迅速扩散到光合作用细胞。
Stomata are tiny pores, mostly on the lower epidermis, surrounded by guard cells. They open during the day to allow carbon dioxide entry but lose water vapour in the process. The internal leaf environment is kept moist to allow gases to dissolve before diffusing into cells.
气孔是微小的孔隙，大多位于下表皮，由保卫细胞包围。它们在白天张开以允许二氧化碳进入，但过程中会损失水蒸气。叶片内部环境保持湿润，使气体在扩散进入细胞之前先溶解。
4. Chloroplasts and Chlorophyll | 叶绿体与叶绿素
Chloroplasts are organelles found mainly in the palisade mesophyll cells. Each chloroplast contains stacks of membranes called thylakoids, where chlorophyll is located. Chlorophyll absorbs red and blue-violet light most strongly and reflects green light, which is why leaves appear green.
叶绿体是主要存在于栅栏组织细胞中的细胞器。每个叶绿体含有称为类囊体（thylakoids）的膜堆叠，叶绿素就位于其中。叶绿素最强烈地吸收红光和蓝紫光，反射绿光，这就是叶片呈现绿色的原因。
Chlorophyll is essential for photosynthesis because it absorbs light energy and transfers it into chemical energy. Without chlorophyll, plants cannot photosynthesise. Plants with variegated leaves (green and white areas) can photosynthesise only in the green areas, which is used in the classic iodine-starch experiment.
叶绿素对光合作用至关重要，因为它吸收光能并将其转化为化学能。没有叶绿素，植物无法进行光合作用。斑叶植物（绿白相间的叶片）只能在绿色区域进行光合作用，这被用于经典的碘-淀粉实验中。
Chlorophyll molecules are
Published by TutorHao | IGCSE Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导