Photosynthesis and Plant Nutrition | 光合作用与植物营养

📚 Photosynthesis and Plant Nutrition | 光合作用与植物营养

Photosynthesis is the fundamental process by which green plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water. This topic is central to IGCSE Science, covering the word equation, limiting factors, leaf structure, and the importance of photosynthesis to ecosystems.

光合作用是绿色植物、藻类和某些细菌利用光能将二氧化碳和水转化为葡萄糖和氧气，从而将光能转变为化学能的基本过程。这一主题是 IGCSE 科学的核心，涉及文字方程式、限制因子、叶片结构以及光合作用对生态系统的重要性。

1. The Word Equation for Photosynthesis | 光合作用的文字方程式

During photosynthesis, plants take in carbon dioxide from the air and water from the soil. Using energy from sunlight and the green pigment chlorophyll, they produce glucose and oxygen. The overall process can be summarised by the following word equation:

在光合作用过程中，植物从空气中吸收二氧化碳，从土壤中吸收水分。植物利用阳光中的能量和绿色色素叶绿素，生成葡萄糖和氧气。整个过程可用下列文字方程式概括：

Carbon dioxide + Water → Glucose + Oxygen

二氧化碳 + 水 → 葡萄糖 + 氧气

In chemical terms, the reactants are CO₂ and H₂O, while the products are C₆H₁₂O₆ and O₂. The reaction requires light energy and chlorophyll, so it is an endothermic reaction.

用化学式表示，反应物是 CO₂ 和 H₂O，产物是 C₆H₁₂O₆ 和 O₂。该反应需要光能和叶绿素，因此是一个吸热反应。

2. The Balanced Chemical Symbol Equation | 配平的化学符号方程式

For IGCSE, you should be able to write and balance the full symbol equation for photosynthesis. The balanced equation shows the exact number of molecules involved:

对于 IGCSE，你需要能够写出并配平光合作用的完整符号方程式。配平后的方程式显示了参与反应的精确分子数目：

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

6二氧化碳 + 6水 → 葡萄糖 + 6氧气

Note that six carbon dioxide molecules react with six water molecules to produce one glucose molecule and six oxygen molecules. The numbers in front of the formulas are called coefficients, and they must balance on both sides.

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。化学式前面的数字称为化学计量数，两侧必须相等。

3. The Role of Chlorophyll and Light | 叶绿素与光的作用

Chlorophyll is a green pigment found in chloroplasts, mainly in the palisade mesophyll cells of leaves. It absorbs light energy, particularly red and blue-violet light, and transfers it to the chemical reactions of photosynthesis. Without chlorophyll, photosynthesis cannot occur.

叶绿素是叶肉栅栏细胞中叶绿体内的一种绿色色素。它吸收光能，尤其是红光和蓝紫光，并将光能传递给光合作用的化学反应。没有叶绿素，光合作用就无法进行。

Light provides the energy needed to split water into hydrogen and oxygen during the light-dependent stage. The hydrogen is then used to reduce carbon dioxide to glucose. Therefore, light intensity directly affects the rate of photosynthesis.

在光反应阶段，光提供分解水所需的能量，使水分解为氢和氧。随后氢用于将二氧化碳还原为葡萄糖。因此，光照强度直接影响光合作用速率。

4. Leaf Structure and Function | 叶片结构与功能

Leaves are specialised organs for photosynthesis. Their structure is closely adapted to maximise light absorption, gas exchange, and water supply. Key parts include the waxy cuticle, upper and lower epidermis, palisade mesophyll, spongy mesophyll, stomata, and vascular bundles.

叶片是光合作用特化的器官。它们的结构与最大限度地吸收光、进行气体交换和供水密切相关。主要部分包括角质层、上表皮和下表皮、栅栏组织、海绵组织、气孔和维管束。

Cuticle: a waxy layer that reduces water loss.

角质层：减少水分蒸发的蜡质层。
Palisade mesophyll: tightly packed cells with many chloroplasts, located near the upper surface.

栅栏组织：排列紧密、富含叶绿体的细胞，靠近上表面。
Spongy mesophyll: loosely packed cells with air spaces to allow gas circulation.

海绵组织：排列疏松、具有细胞间隙，利于气体流通。
Stomata: pores, usually on the lower epidermis, controlling gas exchange and water loss.

气孔：通常位于下表皮的小孔，控制气体交换和水分蒸腾。

5. Investigation: Testing a Leaf for Starch | 实验：检测叶片中的淀粉

To prove that photosynthesis has occurred, you can test a leaf for starch. Starch is stored glucose. The test involves several steps: boiling the leaf in water to kill cells, boiling in ethanol to remove chlorophyll, washing with water, and then adding iodine solution.

为了证明光合作用已经发生，可以检测叶片中的淀粉。淀粉是葡萄糖的储存形式。该实验包括以下步骤：将叶片在沸水中煮以杀死细胞，用乙醇煮沸以去除叶绿素，用水冲洗，然后滴加碘液。

If starch is present, the leaf turns blue-black. A leaf that was kept in the dark before the test should remain orange-brown, because no photosynthesis took place and any stored starch would have been used up.

如果存在淀粉，叶片会变成蓝黑色。测试前置于黑暗中的叶片应保持黄褐色，因为没有发生光合作用，且储存的淀粉已被消耗殆尽。

6. Rate of Photosynthesis and Its Measurement | 光合作用速率及其测量

The rate of photosynthesis can be measured by the volume of oxygen produced per unit time, the amount of carbon dioxide absorbed, or the increase in biomass of the plant. In pondweed experiments, oxygen bubbles are counted or collected in a gas syringe.

光合作用速率可以通过单位时间内氧气的产生量、二氧化碳的吸收量或植物生物量的增加来测量。在伊乐藻实验中，可以计数氧气泡或用量气管收集气体。

For accurate results, you should control temperature, light intensity and carbon dioxide concentration. The rate can be calculated using the formula:

为了获得准确结果，应控制温度、光照强度和二氧化碳浓度。速率可用公式计算：

Rate = Amount of product produced ÷ Time taken

速率 = 产生的产物量 ÷ 所用时间

7. Limiting Factors: Light Intensity | 限制因子：光照强度

A limiting factor is something that stops the rate of reaction from increasing even if other conditions are favourable. Light intensity is one such factor. As light intensity increases, the rate of photosynthesis initially increases proportionally, but eventually plateaus because another factor becomes limiting.

限制因子是指即使其他条件适宜，也会阻止反应速率增加的因素。光照强度就是这样一个因子。当光照强度增加时，光合作用速率起初按比例增加，但最终会趋于平缓，因为另一个因子成为限制因素。

The relationship between light intensity and rate is not linear at high intensities. You can change light intensity by moving a lamp closer or further away. Remember that light intensity follows the inverse square law:

在较高光照强度下，光照强度与速率之间的关系不再是线性。你可以通过将灯移近或移远来改变光照强度。请记住，光照强度遵循平方反比定律：

Light intensity ∝ 1 ÷ (distance)²

光照强度 ∝ 1 ÷（距离）²

8. Limiting Factors: Carbon Dioxide and Temperature | 限制因子：二氧化碳与温度

Carbon dioxide concentration is another limiting factor. If there is not enough CO₂, the rate of photosynthesis slows down, even if light and water are plentiful. Increasing CO₂ concentration usually raises the rate until the enzyme-controlled reactions become saturated.

二氧化碳浓度是另一个限制因子。如果 CO₂ 不足，即使光照和水分充足，光合作用速率也会减慢。增加 CO₂ 浓度通常能提高速率，直到酶促反应达到饱和。

Temperature affects photosynthesis because enzymes like Rubisco are involved in the Calvin cycle. As temperature rises, the rate increases until the optimum temperature, but if it becomes too high (above about 40°C), enzymes denature and the rate drops sharply.

温度通过影响光合作用中的酶（如 RuBisCO）来影响速率，RuBisCO 参与卡尔文循环。温度升高时速率增加，直到最适温度；但如果温度过高（超过约 40°C），酶会变性，速率急剧下降。

9. Uses of Glucose Produced by Photosynthesis | 光合作用产生葡萄糖的用途

Glucose produced during photosynthesis is used by the plant for several purposes. It can be converted into starch for storage, used in respiration to release energy, converted into sucrose for transport, or used to make cellulose for cell walls and proteins for growth.

光合作用产生的葡萄糖被植物用于多种用途。它可以转化为淀粉进行储存，用于呼吸作用释放能量，转化为蔗糖用于运输，或用于制造构成细胞壁的纤维素以及供生长所需的蛋白质。

Respiration: glucose is broken down to release ATP for cellular work.

呼吸作用：葡萄糖被分解以释放 ATP 供细胞活动。
Storage: glucose is stored as starch in roots, stems and leaves.

储存：葡萄糖以淀粉形式储存在根、茎和叶中。
Cellulose: glucose units form cellulose for strong plant cell walls.

纤维素：葡萄糖单元构成纤维素，形成坚固的植物细胞壁。
Amino acids: glucose combined with nitrate ions makes amino acids and proteins.

氨基酸：葡萄糖与硝酸根离子结合生成氨基酸和蛋白质。

10. The Importance of Photosynthesis to Life | 光合作用对生命的重要意义

Photosynthesis is essential for almost all life on Earth. It provides the oxygen we breathe and produces the organic molecules that form the base of most food chains. It also removes carbon dioxide from the atmosphere, helping to regulate the global carbon cycle.

光合作用对地球上几乎所有生命都至关重要。它提供我们呼吸的氧气，并产生构成大多数食物链基础的有机物。它还从大气中去除二氧化碳，有助于调节全球碳循环。

Fossil fuels such as coal, oil and natural gas are formed from the remains of ancient plants and algae that originally stored energy through photosynthesis. Therefore, the energy we use today is ultimately derived from the sun captured by this process millions of years ago.

煤炭、石油和天然气等化石燃料是由古代植物和藻类的残骸形成的，这些生物最初通过光合作用储存能量。因此，我们今天使用的能量最终源自数百万年前这一过程捕获的太阳能。

11. Comparing Photosynthesis with Respiration | 光合作用与呼吸作用比较

Photosynthesis and respiration are opposite processes in terms of overall equations, but they are linked through the cycling of oxygen and carbon dioxide. Photosynthesis stores energy, while respiration releases energy.

光合作用和呼吸作用在总方程式上是相反的过程，但通过氧气和二氧化碳的循环相互联系。光合作用储存能量，而呼吸作用释放能量。

Feature	Photosynthesis	Respiration
Energy	Stores energy	Releases energy
Reactants	CO₂ and H₂O	Glucose and O₂
Products	Glucose and O₂	CO₂ and H₂O
Location	Chloroplasts	Cytoplasm and mitochondria
Light requirement	Requires light	Occurs all the time

In daytime, plants photosynthesise and respire simultaneously, but the rate of photosynthesis is usually higher. At night, only respiration occurs, so plants take in oxygen and release carbon dioxide.

白天，植物同时进行光合作用和呼吸作用，但光合作用速率通常更高。夜间只进行呼吸作用，因此植物吸收氧气并释放二氧化碳。

12. Common Exam Questions and Key Skills | 常见考点与关键技能

In Edexcel IGCSE Science exams, you may be asked to describe the process, interpret graphs of limiting factors, design experiments to investigate the rate, or explain why photosynthesis is important. You should also be able to use the key terms: chlorophyll, chloroplast, stomata, guard cells, and limiting factor.

在 Edexcel IGCSE 科学考试中，你可能会被要求描述过程、解读限制因子曲线图、设计实验研究速率，或解释光合作用的重要性。你还应能够使用这些关键术语：叶绿素、叶绿体、气孔、保卫细胞和限制因子。

Practice balancing the equation, recall the starch test, and understand how to measure oxygen production using pondweed. Always state that photosynthesis is endothermic as it requires energy from the environment.

练习配平方程式，记住淀粉检测方法，并理解如何用伊乐藻测量氧气产量。始终说明光合作用是吸热反应，因为它需要从环境中获取能量。

Published by TutorHao | Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Photosynthesis and Plant Nutrition | 光合作用与植物营养