Photosynthesis Revision for IGCSE AQA Biology | IGCSE AQA 生物：光合作用 考点精讲

📚 Photosynthesis Revision for IGCSE AQA Biology | IGCSE AQA 生物：光合作用 考点精讲

Photosynthesis is the fundamental process by which green plants, algae and some bacteria convert light energy into chemical energy stored in glucose. For IGCSE AQA Biology, you need to understand the word and chemical equations, the conditions required, the products and their fates, leaf structure, limiting factors, and the key practical investigations. This article provides a comprehensive revision of all these aspects.

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基本过程。针对 IGCSE AQA 生物考试，你需要掌握文字方程和化学方程、所需条件、产物及其去向、叶片结构、限制因素以及重要的实验探究。本文对这些内容进行全面梳理。

1. What is Photosynthesis? | 什么是光合作用？

Photosynthesis is an endothermic reaction in which light energy is absorbed and used to convert carbon dioxide and water into glucose and oxygen. It takes place in the chloroplasts of plant cells, which contain the green pigment chlorophyll that captures light energy. The process is vital for life on Earth because it produces oxygen and forms the base of most food chains.

光合作用是一种吸热反应，吸收光能并将其用于将二氧化碳和水转化为葡萄糖和氧气。该过程发生在植物细胞的叶绿体中，叶绿体含有能捕获光能的绿色色素——叶绿素。这一过程对地球生命至关重要，因为它产生氧气并构成了大多数食物链的基础。

The overall word equation for photosynthesis is: Carbon dioxide + Water → Glucose + Oxygen, in the presence of light and chlorophyll.

光合作用的文字方程式为：二氧化碳 + 水 → 葡萄糖 + 氧气，需要光和叶绿素的参与。

---

2. The Chemical Equation | 化学方程式

The balanced chemical equation must be remembered. It shows that six molecules of carbon dioxide combine with six molecules of water to produce one molecule of glucose and six molecules of oxygen.

必须记住配平的化学方程式。它表示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

Light energy and chlorophyll are essential for this reaction; they are written above the arrow but are not reactants. The glucose produced is a simple sugar, which is a carbohydrate.

光能和叶绿素是这一反应所必需的；它们写在箭头之上，但不是反应物。生成的葡萄糖是一种单糖，属于碳水化合物。

---

3. Conditions Required for Photosynthesis | 光合作用所需条件

For photosynthesis to occur, a plant needs three main factors: light energy, carbon dioxide, and water. Additionally, chlorophyll must be present to absorb light. Without any one of these, the rate of photosynthesis will be zero.

要进行光合作用，植物需要三个主要因素：光能、二氧化碳和水。此外，必须有叶绿素来吸收光能。缺少任何一个，光合作用速率都将为零。

Light provides the energy to drive the reaction. Carbon dioxide enters the leaf through stomata and diffuses into the cells. Water is absorbed from the soil by roots and transported up the stem via xylem vessels.

光提供驱动反应的能量。二氧化碳通过气孔进入叶片并扩散到细胞中。水由根从土壤吸收，并通过木质部导管向上运输到茎。

A suitable temperature is also important because the enzymes involved in the light-independent stage (Calvin cycle) work best within an optimum range. If the temperature is too low, enzyme activity slows; if too high, enzymes denature.

适宜的温度也很重要，因为参与暗反应（卡尔文循环）的酶在最佳温度范围内活性最高。温度过低，酶活性降低；过高则酶会变性。

---

4. Products of Photosynthesis and Their Uses | 光合作用的产物及其用途

The immediate products are glucose and oxygen. Oxygen is released as a by-product and diffuses out of the leaf into the atmosphere. Some oxygen is used by the plant for its own aerobic respiration, but during daylight, the rate of photosynthesis usually exceeds respiration, so there is a net release of oxygen.

直接产物是葡萄糖和氧气。氧气作为副产品释放，从叶片扩散到大气中。一部分氧气被植物自身用于有氧呼吸，但在白天，光合作用速率通常超过呼吸作用，因此有净氧气释放。

Glucose is an energy-rich molecule and can be used by the plant in several ways:

• Converted into starch for storage – this is insoluble and does not affect the water potential of cells.
• Used in respiration to release energy for growth and metabolism.
• Converted into cellulose to build cell walls.
• Combined with nitrogen and other minerals to synthesise amino acids and proteins.
• Converted into lipids (fats and oils) for storage in seeds.

葡萄糖是一种高能分子，植物可以通过多种方式利用它：

• 转化为淀粉储存——淀粉不溶于水，不影响细胞水势。
• 用于呼吸作用，释放能量供生长和代谢。
• 转化为纤维素构建细胞壁。
• 与氮和其他矿物质结合合成氨基酸和蛋白质。
• 转化为脂质（脂肪和油）储存在种子中。

---

5. Structure of a Leaf | 叶片结构

The leaf is an organ perfectly adapted for photosynthesis. Its internal structure can be seen in a cross-section and consists of several layers: upper epidermis, palisade mesophyll, spongy mesophyll, vascular bundles, and lower epidermis with stomata.

叶片是极为适合光合作用的器官。从横截面可看到其内部结构，包括：上表皮、栅栏组织、海绵组织、维管束以及带有气孔的下表皮。

The upper epidermis is transparent and covered by a waxy cuticle that reduces water loss. Palisade mesophyll cells are column-shaped, tightly packed, and contain many chloroplasts – they are the main photosynthetic tissue.

上表皮是透明的，并覆盖有蜡质角质层以减少水分流失。栅栏组织细胞呈柱状、排列紧密，含有大量叶绿体——它们是主要的光合组织。

Spongy mesophyll cells are more loosely arranged with air spaces to allow efficient gas exchange. Vascular bundles contain xylem (to transport water and minerals) and phloem (to carry away sucrose produced during photosynthesis).

海绵组织细胞排列较松散，有许多气隙以利于气体交换。维管束包含木质部（运输水和矿物质）和韧皮部（运走光合作用产生的蔗糖）。

Stomata are pores usually found on the lower epidermis; they open and close to regulate gas exchange and water loss.

气孔是通常位于下表皮的孔隙；它们开闭以调节气体交换和水分流失。

---

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

Leaves have several adaptations to maximise the rate of photosynthesis:

叶片具有多种适应性以最大化光合作用速率：

• Large surface area to capture as much light as possible.
• Thin structure so that carbon dioxide diffuses quickly into the cells and oxygen diffuses out.
• Numerous chloroplasts, especially in palisade cells, to absorb light.
• Stomata allow carbon dioxide to enter from the atmosphere.
• Xylem delivers water constantly; phloem removes sugars so that end-product inhibition is avoided.
• Many leaves are arranged on the plant to avoid shading each other.

• 宽大的表面积，以捕获尽可能多的光。
• 薄的结构，使二氧化碳能快速扩散进入细胞，氧气扩散出去。
• 大量叶绿体，尤其在栅栏细胞中，用于吸收光。
• 气孔让大气中的二氧化碳进入。
• 木质部持续输送水分；韧皮部移除糖类，以免发生产物抑制。
• 许多叶片在植株上的排列方式可避免相互遮挡。

---

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

The rate of photosynthesis can be limited by light intensity, carbon dioxide concentration, and temperature. A limiting factor is one that is in shortest supply and therefore restricts the rate of the whole

Published by TutorHao | IGCSE Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）