📚 Cambridge Lower Secondary Complete Biology SB 2nd: Core Revision Notes | 剑桥初中完整生物学第二版核心复习笔记
This revision guide summarises the core ideas in Cambridge Lower Secondary Complete Biology Student Book Second Edition. It is designed to help learners check their understanding of key biology concepts before end-of-stage tests and progression into IGCSE Biology.
本复习指南总结了《剑桥初中完整生物学学生用书第二版》的核心内容，旨在帮助学习者在阶段测试前检查对关键生物学概念的理解，并为衔接 IGCSE 生物课程打下基础。
1. Characteristics of Living Organisms | 生物的基本特征
All living organisms share seven life processes, often remembered by the letters MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition. Movement can be internal or external; respiration releases energy from food; sensitivity means detecting changes in the environment; growth is a permanent increase in size and mass; reproduction produces new individuals; excretion removes metabolic waste; nutrition involves taking in and using food.
所有生物都具有七大生命活动，常用 MRS GREN 记忆：运动、呼吸作用、感应、生长、生殖、排泄和营养。运动可以是内部或外部的；呼吸作用从食物中释放能量；感应指察觉环境变化；生长是体积和质量的永久性增加；生殖产生新个体；排泄清除代谢废物；营养包括摄取和利用食物。
2. Cell Structure: Plant and Animal Cells | 细胞结构：植物细胞与动物细胞
Both plant and animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. The nucleus controls the cell’s activities, cytoplasm is where many reactions occur, the cell membrane controls what enters and leaves, mitochondria release energy through respiration, and ribosomes make proteins.
植物细胞和动物细胞都含有细胞核、细胞质、细胞膜、线粒体和核糖体。细胞核控制细胞活动，细胞质是许多反应发生的场所，细胞膜控制物质进出，线粒体通过呼吸作用释放能量，核糖体合成蛋白质。
Plant cells also have three structures not found in animal cells: a cellulose cell wall for support, chloroplasts that absorb light for photosynthesis, and a large permanent vacuole containing cell sap. The table below compares the two cell types.
植物细胞还有三种动物细胞没有的结构：由纤维素组成的细胞壁起支撑作用，叶绿体吸收光能进行光合作用，以及含有细胞液的大液泡。下表比较了两种细胞类型。
| Structure | Animal cell | Plant cell |
|---|---|---|
| Nucleus | Present | Present |
| Cytoplasm | Present | Present |
| Cell membrane | Present | Present |
| Mitochondria | Present | Present |
| Ribosomes | Present | Present |
| Cell wall | Absent | Present, made of cellulose |
| Chloroplasts | Absent | Present in green parts |
| Large permanent vacuole | Absent | Present |
3. Levels of Organisation | 组织层次
In multicellular organisms, cells are organised into tissues, organs and organ systems. A tissue is a group of similar cells working together to perform one function, such as muscle tissue. An organ is made of several tissues that work together, such as the heart or leaf. An organ system is a group of organs that work together, such as the digestive system.
在多细胞生物中，细胞组成组织、器官和器官系统。组织是一群相似细胞共同执行某一功能，例如肌肉组织。器官由多种组织共同构成，例如心脏或叶。器官系统是一组协同工作的器官，例如消化系统。
The levels of organisation can be written as: cell → tissue → organ → organ system → organism. Each level has a more complex structure and a wider range of functions.
组织层次可写为：细胞 → 组织 → 器官 → 器官系统 → 生物体。每一层次的结构更复杂，功能范围也更广。
4. Movement in and out of Cells | 物质进出细胞
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. It is a passive process and does not require energy from the cell. Oxygen and carbon dioxide move in and out of cells by diffusion.
扩散是粒子从浓度较高的区域向浓度较低的区域净移动，即沿浓度梯度运动。这是一种被动过程，不需要细胞提供能量。氧气和二氧化碳通过扩散进出细胞。
Osmosis is the diffusion of water molecules through a selectively permeable membrane from a dilute solution to a more concentrated solution. The cell membrane is selectively permeable, so it allows small molecules such as water to pass through but restricts larger solute particles.
渗透是水分子通过选择性透过膜从稀溶液向较浓溶液扩散的过程。细胞膜具有选择性透过性，允许水等小分子通过，但限制较大的溶质颗粒。
In plant cells, water entering by osmosis makes the cell turgid and the cell wall prevents bursting. In animal cells, too much water uptake can cause the cell to burst because there is no cell wall. Active transport is introduced later and uses energy to move substances against the concentration gradient.
在植物细胞中，水通过渗透进入使细胞变得充盈，细胞壁可防止细胞胀破。在动物细胞中，过多吸水会导致细胞破裂，因为没有细胞壁。主动运输在后续学习中引入，它利用能量逆浓度梯度运输物质。
5. Nutrition and Photosynthesis | 营养与光合作用
Green plants make their own food by photosynthesis. The word equation for photosynthesis is: carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll. The balanced chemical equation is shown below.
绿色植物通过光合作用制造自身所需的食物。光合作用的文字方程式为：二氧化碳 + 水 → 葡萄糖 + 氧气，条件是需要光和叶绿素。其配平的化学方程式如下所示。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Glucose produced in photosynthesis is used for respiration to release energy, converted to starch for storage, used to make cellulose for cell walls, and combined with other elements to make amino acids and lipids. Oxygen is released as a by-product and used by most organisms for respiration.
光合作用产生的葡萄糖用于呼吸作用释放能量，转化为淀粉储存，用于制造细胞壁的纤维素，并与其他元素结合生成氨基酸和脂类。氧气作为副产物释放，并被大多数生物用于呼吸作用。
Leaves are adapted for photosynthesis because they are broad and thin, have many chloroplasts in the palisade layer, contain veins for transport, and have stomata for gas exchange. These adaptations increase the rate of photosynthesis.
叶片适应光合作用，因为叶片宽而薄，栅栏组织中含有大量叶绿体，叶脉负责运输，气孔用于气体交换。这些适应性提高了光合作用速率。
6. Human Digestive System | 人体消化系统
The digestive system breaks down large insoluble food molecules into small soluble molecules that can be absorbed into the blood. Mechanical digestion involves chewing in the mouth and churning in the stomach, while chemical digestion uses enzymes to break bonds in food molecules.
消化系统将大分子不溶性食物分解为可被血液吸收的小分子可溶性物质。物理性消化包括口腔中的咀嚼和胃中的搅拌，化学性消化则利用酶破坏食物分子中的化学键。
Key regions of the digestive system include the mouth, oesophagus, stomach, small intestine, large intestine and rectum. The liver and pancreas are accessory organs that produce bile and digestive enzymes. Bile neutralises stomach acid and emulsifies fats.
消化系统的关键部位包括口腔、食管、胃、小肠、大肠和直肠。肝和胰是附属器官，分别产生胆汁和消化酶。胆汁中和胃酸并乳化脂肪。
Amylase breaks down starch into maltose, protease breaks down proteins into amino acids, and lipase breaks down lipids into fatty acids and glycerol. Absorption of digested food occurs mainly in the small intestine through the villi, which increase the surface area.
淀粉酶将淀粉分解为麦芽糖，蛋白酶将蛋白质分解为氨基酸，脂肪酶将脂类分解为脂肪酸和甘油。消化后的食物主要在小肠通过绒毛吸收，绒毛增大了吸收表面积。
7. Gas Exchange and Respiration | 气体交换与呼吸作用
Breathing is the movement of air into and out of the lungs, whereas respiration is the chemical release of energy from food in cells. Aerobic respiration uses oxygen and produces carbon dioxide, water and energy. The word equation is: glucose + oxygen → carbon dioxide + water + energy.
呼吸指空气进出肺部的运动，而呼吸作用是细胞从食物中释放能量的化学过程。有氧呼吸利用氧气并产生二氧化碳、水和能量。文字方程式为：葡萄糖 + 氧气 → 二氧化碳 + 水 + 能量。
Gas exchange in humans takes place in the alveoli, which are tiny air sacs in the lungs. Alveoli have thin walls, a large surface area, a moist lining and a dense network of capillaries. These features allow oxygen to diffuse into the blood and carbon dioxide to diffuse out quickly.
人体的气体交换在肺泡中进行，肺泡是肺部微小的气囊。肺泡壁薄、表面积大、内壁湿润且毛细血管密集。这些特点使氧气能迅速扩散进入血液，二氧化碳迅速扩散出血液。
The balanced equation for aerobic respiration is shown below.
有氧呼吸的配平方程式如下所示。
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
Anaerobic respiration occurs without oxygen and produces less energy. In human muscle cells, glucose is broken down to lactic acid; in yeast, glucose is broken down to ethanol and carbon dioxide. This is why yeast is used in bread making and brewing.
无氧呼吸在无氧条件下进行，产生的能量较少。在人体肌肉细胞中，葡萄糖分解为乳酸；在酵母中，葡萄糖分解为乙醇和二氧化碳。因此酵母被用于制作面包和酿造。
8. Circulatory System | 循环系统
The human circulatory system consists of the heart, blood vessels and blood. It transports oxygen, nutrients, hormones and waste products around the body. Humans have a double circulatory system: the right side of the heart pumps blood to the lungs, and the left side pumps blood to the rest of the body.
人体循环系统由心脏、血管和血液组成。它将氧气、营养物质、激素和废物运输到全身各处。人类具有双循环系统：心脏右侧将血液泵送到肺部，左侧将血液泵送到身体其余部分。
There are three main types of blood vessel: arteries, veins and capillaries. Arteries carry blood away from the heart, veins carry blood back to the heart, and capillaries connect arteries and veins and allow exchange of substances with tissues.
血管主要有三种类型：动脉、静脉和毛细血管。动脉将血液运离心脏，静脉将血液送回心脏，毛细血管连接动脉和静脉并实现与组织的物质交换。
| Feature | Artery | Vein | Capillary |
|---|---|---|---|
| Wall thickness | Thick | Thin | One cell thick |
| Valves | Absent | Present | Absent |
| Blood flow | Away from heart | To heart | From artery to vein |
Blood contains red blood cells, white blood cells, platelets and plasma. Red blood cells carry oxygen using the red pigment haemoglobin. White blood cells defend the body against pathogens. Platelets help blood clot. Plasma transports dissolved substances such as glucose, carbon dioxide and urea.
血液包含红细胞、白细胞、血小板和血浆。红细胞利用红色色素血红蛋白运输氧气。白细胞保护身体免受病原体侵害。血小板帮助血液凝固。血浆运输葡萄糖、二氧化碳和尿素等溶解物质。
9. Reproduction in Plants | 植物的生殖
Flowering plants reproduce sexually. The male gametes are pollen grains produced in the anther, and the female gametes are ovules inside the ovary. Pollination is the transfer of pollen from the anther to the stigma. It can be wind-pollinated or insect-pollinated.
开花植物进行有性生殖。雄配子是花药中产生的花粉粒，雌配子是子房内的胚珠。传粉是花粉从花药转移到柱头的过程，可以是风媒传粉或虫媒传粉。
After pollination, fertilisation occurs when the male nucleus fuses with the female nucleus inside the ovule. The fertilised ovule develops into a seed, and the ovary develops into a fruit. The fruit protects the seeds and helps with dispersal.
传粉后，当雄核与胚珠内的雌核融合时发生受精。受精后的胚珠发育为种子，子房发育为果实。果实保护种子并帮助传播。
Seeds are dispersed by wind, water, animals and explosive mechanisms. For germination, seeds need water, oxygen and a suitable temperature. Water activates enzymes, oxygen is used for respiration, and warmth speeds up reactions.
种子通过风、水、动物和弹射机制传播。种子萌发需要水、氧气和适宜的温度。水激活酶，氧气用于呼吸作用，温暖环境加快反应速率。
10. Ecosystems and Human Impact | 生态系统与人类影响
An ecosystem is made up of all the living organisms in an area interacting with each other and with their non-living environment. Food chains show the transfer of energy from producers to consumers. Producers such as green plants make their own food, primary consumers eat producers, and secondary consumers eat primary consumers.
生态系统由某一区域内所有生物与其非生物环境相互作用组成。食物链显示能量从生产者到消费者的传递。绿色植物等生产者制造自身食物，初级消费者取食生产者，次级消费者取食初级消费者。
In a food chain, energy is lost at each level because organisms use energy for movement, growth and heat. This means food chains rarely have more than four or five trophic levels. Food webs show how several food chains overlap in an ecosystem.
在食物链中，每一营养级都有能量损失，因为生物将能量用于运动、生长和产热。因此食物链通常不超过四到五个营养级。食物网显示生态系统中多条食物链的相互重叠。
Human activities can change ecosystems. Deforestation destroys habitats, reduces biodiversity and increases carbon dioxide in the atmosphere. Pollution from waste, agriculture and industry harms water and air quality. Conservation protects species and their habitats, and sustainable practices help maintain ecosystems for future generations.
人类活动会改变生态系统。砍伐森林破坏栖息地、降低生物多样性并增加大气中的二氧化碳。废物、农业和工业造成的污染损害水和空气质量。保护措施保护物种及其栖息地，可持续实践有助于为后代维持生态系统。
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