📚 Year 9 SQA Biology: Core Concepts Summary | Year 9 SQA 生物：核心知识点梳理
Year 9 SQA Biology covers a broad range of fundamental biological principles, from the building blocks of life to how entire ecosystems function. This article brings together all the essential topics, providing clear explanations and key facts to support your revision. Each section pairs English and Chinese explanations so you can learn the concepts in both languages and deepen your understanding.
Year 9 SQA 生物课程涵盖了从生命的基石到整个生态系统运作方式的广泛生物学基本原理。这篇文章汇集了所有重要主题，提供清晰的解释和关键事实，帮助您巩固复习内容。每个部分都配有英文和中文解释，让您用两种语言学习概念，加深理解。
1. Cell Structure and Function | 细胞的结构与功能
All living organisms are made of cells. Plant and animal cells share common features such as a cell membrane, cytoplasm, a nucleus and mitochondria. Plant cells also have a rigid cell wall, a large permanent vacuole and chloroplasts, which are not found in animal cells.
所有生物体都由细胞组成。植物细胞和动物细胞有共同的结构，如细胞膜、细胞质、细胞核和线粒体。植物细胞还有坚硬的细胞壁、一个中央大液泡和叶绿体，这些在动物细胞中是不存在的。
The cell membrane controls the movement of substances in and out of the cell. The nucleus contains genetic material (DNA) and controls cell activities. Mitochondria are the sites of aerobic respiration, releasing energy for the cell. In plant cells, chloroplasts absorb light energy for photosynthesis, and the cell wall provides structural support.
细胞膜控制物质进出细胞。细胞核含有遗传物质（DNA）并调控细胞活动。线粒体是有氧呼吸的场所，为细胞释放能量。在植物细胞中，叶绿体吸收光能进行光合作用，细胞壁提供结构支撑。
| Cell structure | Animal cell | Plant cell | Function |
|---|---|---|---|
| Cell membrane | ✓ | ✓ | Controls entry and exit of substances |
| Cytoplasm | ✓ | ✓ | Where chemical reactions occur |
| Nucleus | ✓ | ✓ | Contains DNA, controls the cell |
| Mitochondria | ✓ | ✓ | Site of aerobic respiration |
| Cell wall | ✗ | ✓ | Provides support and shape |
| Chloroplasts | ✗ | ✓ | Absorb light for photosynthesis |
| Permanent vacuole | ✗ | ✓ | Contains cell sap, maintains turgor |
Table: Comparison of animal and plant cell structures | 表：动物细胞与植物细胞结构比较
2. Movement of Substances Across Membranes | 物质跨膜运输
Substances move across cell membranes by diffusion, osmosis and active transport. Diffusion is the net movement of particles from a region of high concentration to a region of low concentration, down a concentration gradient. It is a passive process and does not require energy.
物质通过扩散、渗透和主动运输穿过细胞膜。扩散是粒子从高浓度区域向低浓度区域的净移动，沿着浓度梯度进行。这是一个被动过程，不需要能量。
Osmosis is a special case of diffusion: the movement of water molecules from a dilute solution (high water concentration) to a more concentrated solution (low water concentration) through a selectively permeable membrane. Osmosis is also passive and is crucial for water uptake in plant roots.
渗透是扩散的一种特殊情况：水分子通过选择透性膜从稀溶液（高水浓度）向较浓溶液（低水浓度）的净移动。渗透也是被动的，对植物根部吸收水分至关重要。
Active transport moves substances against the concentration gradient, from low concentration to high concentration. This process requires energy released from respiration. An example is the absorption of mineral ions by root hair cells from the soil, where mineral concentrations are lower than inside the cell.
主动运输使物质逆浓度梯度移动，即从低浓度到高浓度。这个过程需要呼吸作用释放的能量。一个例子是根毛细胞从土壤中吸收矿物质离子，土壤中矿物质浓度低于细胞内部。
| Process | Concentration gradient | Energy needed? | Example |
|---|---|---|---|
| Diffusion | High to low | No | Oxygen entering blood |
| Osmosis | High water to low water potential | No | Water uptake by roots |
| Active transport | Low to high | Yes | Mineral ion uptake |
3. Enzymes | 酶
Enzymes are biological catalysts made of protein. They speed up chemical reactions in living organisms without being used up or changed permanently. Each enzyme has an active site with a specific shape that fits a particular substrate, like a lock and key.
酶是由蛋白质构成的生物催化剂。它们能加速生物体内的化学反应，而自身不被消耗或永久改变。每个酶都有一个形状特异的活性位点，能与特定的底物结合，就像锁和钥匙一样。
The activity of enzymes is affected by temperature and pH. At low temperatures, reactions are slow because molecules have less kinetic energy. As temperature rises, activity increases until the optimum temperature is reached. Beyond this point, the enzyme denatures: the active site loses its shape and the substrate can no longer bind. Each enzyme has an optimum pH; for example, pepsin works best in acidic conditions, while most others prefer neutral or alkaline conditions.
酶的活性受温度和pH值的影响。低温下反应较慢，因为分子动能较低。随着温度升高，活性增强，直到达到最适温度。超过这一温度，酶会变性：活性位点失去形状，底物无法再结合。每种酶有其最适pH值；例如，胃蛋白酶在酸性条件下活性最强，而大多数酶则在中性或碱性条件下工作最佳。
4. Photosynthesis | 光合作用
xygen. The word equation is: carbon dioxide + water → glucose + oxygen. The balanced symbol equation is:
光合作用是绿色植物制造自身养料的过程。它们利用光能将二氧化碳和水转化为葡萄糖和氧气。文字方程式为：二氧化碳 + 水 → 葡萄糖 + 氧气。配平的化学方程式为：
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Light energy is absorbed by chlorophyll in the chloroplasts. The glucose produced is used immediately for respiration, converted into starch for storage, or used to make cellulose for cell walls. Oxygen is released as a by-product.
光能被叶绿体中的叶绿素吸收。产生的葡萄糖可立即用于呼吸作用，转化为淀粉储存，或用于制造细胞壁的纤维素。氧气作为副产品被释放。
Limiting factors of photosynthesis include light intensity, carbon dioxide concentration and temperature. If one of these is in short supply, it limits the rate of photosynthesis, regardless of the other factors.
光合作用的限制因素包括光照强度、二氧化碳浓度和温度。如果其中任何一个供应不足，无论其他因素如何，它都会限制光合作用的速率。
5. Respiration | 呼吸作用
Respiration is the process that releases energy from food, specifically glucose. It occurs in all living cells and is necessary for life processes such as movement, growth and keeping warm. The energy is stored in molecules called ATP.
呼吸作用是从食物（特别是葡萄糖）中释放能量的过程。它发生在所有活细胞中，是维持运动、生长和保暖等生命活动所必需的。能量储存在称为ATP的分子中。
d equation is: glucose + oxygen → carbon dioxide + water. The balanced symbol equation is:
有氧呼吸利用氧气，彻底分解葡萄糖，释放大量能量。文字方程式为：葡萄糖 + 氧气 → 二氧化碳 + 水。配平的化学方程式为：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
Anaerobic respiration occurs without oxygen and releases a much smaller amount of energy. In animal cells, glucose is converted into lactic acid. In plant cells and yeast, it is converted into ethanol and carbon dioxide (fermentation).
无氧呼吸在没有氧气的情况下发生，释放的能量要少得多。在动物细胞中，葡萄糖转化为乳酸。在植物细胞和酵母菌中，葡萄糖转化为乙醇和二氧化碳（发酵）。
- Animals: glucose → lactic acid (+ small amount of ATP)
- Plants / Yeast: glucose → ethanol + carbon dioxide (+ small amount of ATP)
中文:
- 动物：葡萄糖 → 乳酸（+少量ATP）
- 植物/酵母菌：葡萄糖 → 乙醇 + 二氧化碳（+少量ATP）
6. DNA, Genes and Chromosomes | DNA、基因与染色体
DNA is a long molecule that carries the genetic instructions for the development and functioning of living organisms. It is shaped as a double helix and found in the nucleus of cells, organised into structures called chromosomes.
DNA 是一种携带生物体发育和功能遗传指令的长分子。它呈双螺旋结构，存在于细胞核中，组织成称为染色体的结构。
A gene is a short section of DNA that codes for a specific protein, which determines a characteristic, such as eye colour or blood type. Humans have around 20,000–25,000 genes. Different versions of the same gene are called alleles.
基因是 DNA 的一个小片段，编码特定的蛋白质，从而决定某种特征，如眼睛颜色或血型。人类大约有 20,000–25,000 个基因。同一基因的不同版本称为等位基因。
In body cells, chromosomes occur in pairs. Humans have 23 pairs (46 chromosomes in total). Gametes (sperm and egg cells) have only 23 single chromosomes, so that when fertilisation occurs, the zygote restores the full complement of 46 chromosomes.
在体细胞中，染色体成对存在。人类有 23 对染色体（共 46 条）。配子（精子和卵细胞）只有 23 条单倍染色体，因此受精时，合子恢复完整的 46 条染色体。
7. Inheritance | 遗传
Inherited characteristics are passed from parents to offspring through genes. The combination of alleles an organism has is called its genotype; the observable features that result are its phenotype.
遗传特征通过基因由亲代传递给子代。一个生物体所具有的等位基因组合称为基因型；由此产生的可观察特征称为表现型。
Some alleles are dominant and others recessive. A dominant allele (represented by a capital letter, e.g. 'B') will be expressed even if only one copy is present. A recessive allele (lowercase, e.g. 'b') is only expressed if two copies are present. If both alleles are the same, the organism is homozygous; if different, it is heterozygous.
有些等位基因是显性的，有些是隐性的。显性等位基因（用大写字母表示，如 'B'）即使只有一个拷贝也会表达。隐性等位基因（用小写字母表示，如 'b'）只有在有两个拷贝时才会表达。如果两个等位基因相同，则为纯合；如果不同，则为杂合。
uals (Bb × Bb) results in a 3:1 ratio of dominant to recessive phenotype in the offspring.
单基因杂交可用于预测后代的基因型和表现型。例如，两个杂合个体（Bb × Bb）杂交，后代表现型比例为显性：隐性 = 3：1。
8. Ecosystems and Feeding Relationships | 生态系统与摄食关系
An ecosystem is a community of living organisms interacting with each other and their non-living environment. Energy flows through an ecosystem via food chains and webs. A food chain shows a simple linear feeding relationship, always starting with a producer (e.g. grass) that makes its own food by photosynthesis.
生态系统是由生物群落与其非生物环境相互作用形成的统一整体。能量通过食物链和食物网在生态系统中流动。食物链显示简单的直线取食关系，总是以生产者（例如草）开始，它们通过光合作用制造食物。
grass → grasshopper → frog → snake → hawk
草 → 蚱蜢 → 青蛙 → 蛇 → 鹰
In a food web, many interconnected food chains more accurately represent the feeding relationships. Each step in a chain is a trophic level: producers, primary consumers (herbivores), secondary consumers, and tertiary consumers. Decomposers (bacteria and fungi) break down dead matter, recycling nutrients.
食物网中许多相互连接的食物链更准确地代表了摄食关系。链中的每一步都是一个营养级：生产者、初级消费者（草食动物）、次级消费者和三级消费者。分解者（细菌和真菌）分解死去的物质，循环养分。
Only about 10% of the energy is transferred from one trophic level to the next; the rest is lost as heat from respiration, movement and undigested waste. This explains why food chains rarely have more than four or five trophic levels.
只有约 10% 的能量从一个营养级传递到下一个营养级；其余能量以呼吸热、运动和未消化的废物等形式散失。这就解释了为什么食物链很少超过四到五个营养级。
9. Biodiversity and Natural Selection | 生物多样性与自然选择
Biodiversity is the variety of all living things on Earth, including diversity within species, between species and of ecosystems. High biodiversity makes ecosystems more stable and resilient to changes.
生物多样性是指地球上所有生物的多样性，包括物种内部的多样性、物种之间的多样性以及生态系统的多样性。高生物多样性使生态系统更加稳定，更能适应变化。
Natural selection is the process by which organisms with characteristics better suited to their environment are more likely to survive, reproduce and pass on their advantageous alleles. Over many generations, these adaptive traits become more common in the population. This can lead to evolution – the gradual change in the inherited characteristics of a population over time.
自然选择是指具有更适应环境的特征的生物更有可能生存、繁殖并将有利的等位基因传递给后代的过程。经过许多代后，这些适应性性状在种群中变得更加普遍。这可以导致进化——种群遗传特征随时间的逐渐变化。
A classic example is the peppered moth: during the Industrial Revolution, dark-coloured moths became more common because they were better camouflaged on soot-covered trees, avoiding predation. This is a clear demonstration of natural selection.
一个经典例子是桦尺蛾：在工业革命期间，深色蛾变得更常见，因为它们在煤烟覆盖的树上伪装得更好，避免了被捕食。这清楚地展示了自然选择的作用。
10. 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 bloodstream. Enzymes play a key role in chemical digestion.
消化系统将大的、不溶性食物分子分解成小的、可溶性的分子，以便被吸收进入血液。酶在化学消化中起着关键作用。
Carbohydrates (e.g. starch) are broken down by amylase into simple sugars (e.g. maltose, then glucose). Amylase is produced by the salivary glands and the pancreas, and works in the mouth and small intestine. Proteases break down proteins into amino acids; they are produced in the stomach (pepsin), pancreas and small intestine. Lipases break down fats (lipids) into fatty acids and glycerol; they are made in the pancreas and work in the small intestine, aided by bile which emulsifies fats.
碳水化合物（如淀粉）被淀粉酶分解为单糖（如麦芽糖，再变为葡萄糖）。淀粉酶由唾液腺和胰腺产生，在口腔和小肠中起作用。蛋白酶将蛋白质分解为氨基酸；它们在胃（胃蛋白酶）、胰腺和小肠中产生。脂肪酶将脂肪（脂质）分解为脂肪酸和甘油；它们在胰腺中产生并在小肠中起作用，并受胆汁辅助乳化脂肪。
The absorption of digested food mainly occurs in the small intestine. The wall of the small intestine is lined with millions of tiny finger-like projections called villi, which provide a large surface area for efficient absorption into the blood capillaries.
消化后的食物吸收主要在小肠中进行。小肠壁内衬有数百万个指状突起，称为小肠绒毛，它们提供了巨大的表面积，以便高效地吸收进入毛细血管。
11. Circulatory and Respiratory Systems | 循环与呼吸系统
The circulatory system consists of the heart, blood vessels and blood. It transports oxygen, nutrients, hormones and waste products around the body. The heart is a double pump: the right side pumps deoxygenated blood to the lungs, while the left side pumps oxygenated blood to the rest of the body.
循环系统由心脏、血管和血液组成。它向全身输送氧气、营养物质、激素和废物。心脏是一个双泵：右侧将缺氧血泵送到肺部，左侧将含氧血泵送到身体其他部位。
Arteries carry blood away from the heart under high pressure; they have thick, elastic walls. Veins carry blood back to the heart at lower pressure and contain valves to prevent backflow. Capillaries are tiny, thin-walled vessels where exchange of gases and nutrients takes place with tissues.
动脉在高压下将血液从心脏带走；它们有厚而有弹性的壁。静脉在较低的压力下将血液送回心脏，并含有瓣膜以防止回流。毛细血管是与组织进行气体和营养交换的微小薄壁血管。
The respiratory system is where gas exchange occurs. Air passes through the trachea, bronchi and bronchioles to reach the alveoli – tiny air sacs in the lungs. Alveoli have a very large surface area, thin walls and a rich blood capillary supply, making them ideal for the diffusion of oxygen into the blood and carbon dioxide out of the blood.
呼吸系统是发生气体交换的地方。空气通过气管、支气管和细支气管到达肺泡——肺部的微小气囊。肺泡有巨大的表面积、薄壁和丰富的毛细血管供应，使其非常适合氧气扩散进入血液和二氧化碳扩散出血液。
Breathing (ventilation) involves the movement of the diaphragm and intercostal muscles. During inhalation, the diaphragm contracts and flattens, and the ribcage moves up and out, increasing the volume of the chest cavity and lowering pressure, drawing air in.
呼吸（通气）涉及膈肌和肋间肌的运动。吸气时，膈肌收缩变平，胸廓向上向外移动，增加了胸腔容积并降低压力，从而将空气吸入。
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