Mastering Cambridge Lower Secondary Science 7: Core Topics | 掌握剑桥初中科学7：核心主题

📚 Mastering Cambridge Lower Secondary Science 7: Core Topics | 掌握剑桥初中科学7：核心主题

Cambridge Lower Secondary Science 7, based on the second edition by Mary Jones and co-authors, builds a strong foundation in biology, chemistry and physics. This revision guide covers the core topics you need to understand, from cells and particle theory to forces, energy and scientific enquiry.

剑桥初中科学7基于 Mary Jones 及其合著者的第二版教材，为生物、化学和物理打下坚实基础。本复习指南涵盖你需要掌握的核心主题，从细胞、粒子理论到力、能量和科学探究。

Each section below pairs an English explanation with a Chinese translation. Use the headings to focus your revision and the examples to check your understanding before assessments.

以下每一节都提供英文解释与中文翻译配对。复习时可根据标题聚焦重点，并在评估前用示例检验自己的理解。

---

1. Cells: Building Blocks of Life | 细胞：生命的基本单位

All living organisms are made of cells. A cell is the smallest unit that can carry out the seven life processes: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.

所有生物都由细胞组成。细胞是能够进行七种生命活动的最小单位：运动、呼吸、感应、生长、繁殖、排泄和营养。

In the Cambridge Lower Secondary Science 7 course, students learn to use a light microscope, prepare a simple wet mount slide, and identify the nucleus, cytoplasm, cell membrane and, in plant cells, the cell wall, chloroplasts and permanent vacuole.

在剑桥初中科学7课程中，学生学会使用光学显微镜、制作简单的临时装片，并识别细胞核、细胞质、细胞膜，以及植物细胞中的细胞壁、叶绿体和中央液泡。

Plant cells are usually more regular in shape than animal cells because of the cellulose cell wall. Chloroplasts absorb light energy for photosynthesis, while the permanent vacuole stores cell sap and helps maintain turgor pressure.

由于有纤维素细胞壁，植物细胞通常比动物细胞形状更规则。叶绿体吸收光能进行光合作用，而中央液泡储存细胞液并帮助维持膨压。

When preparing a microscope slide, a stain such as iodine is often used to make cell structures more visible. The total magnification is calculated by multiplying the eyepiece lens magnification by the objective lens magnification.

制作显微镜装片时，常使用碘液等染色剂使细胞结构更清晰。总放大倍数的计算方法是目镜放大倍数乘以物镜放大倍数。

---

2. Materials and Their Particle Structure | 材料及其粒子结构

The particle model explains why solids, liquids and gases behave differently. Particles in a solid are closely packed and only vibrate in fixed positions. Particles in a liquid are close together but can move past one another. Particles in a gas are far apart and move rapidly in all directions.

粒子模型解释了为什么固体、液体和气体的表现不同。固体中的粒子紧密排列，只能在固定位置振动。液体中的粒子靠得很近，但能相互滑动。气体中的粒子相距很远，向各个方向快速运动。

When a substance is heated, its particles gain kinetic energy. This explains expansion, melting and boiling. When a substance is cooled, particles lose kinetic energy, so the substance contracts, freezes or condenses.

当物质受热时，其粒子获得动能。这解释了膨胀、熔化和沸腾。当物质冷却时，粒子失去动能，因此物质收缩、凝固或凝结。

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. It occurs fastest in gases, more slowly in liquids and extremely slowly in solids because of the different spacing and movement of particles.

扩散是粒子从高浓度区域向低浓度区域的净运动。扩散在气体中最快，在液体中较慢，在固体中极慢，这是因为粒子的间距和运动方式不同。

Brownian motion provides evidence for the particle model. When smoke particles in air are viewed under a microscope, they move in random zigzag paths because they are being hit by fast-moving air particles.

布朗运动为粒子模型提供了证据。在显微镜下观察空气中的烟雾颗粒时，它们会做无规则的锯齿形运动，这是因为它们受到快速运动的空气粒子的撞击。

---

3. Forces and Motion | 力与运动

A force is a push or a pull. Forces can change the speed of an object, change its direction, or change its shape. Force is measured in newtons, symbol N, using a force meter or spring balance.

力是推或拉。力可以改变物体的速度、方向或形状。力用测力计或弹簧秤测量，单位是牛顿，符号为 N。

Forces acting in the same direction are added together, while forces acting in opposite directions are subtracted. The single force that represents the combined effect of all forces is called the resultant force.

方向相同的力相加，方向相反的力相减。代表所有力共同作用的单一力称为合力。

If the resultant force on an object is zero, the object remains at rest or continues to move at a constant speed in a straight line. If the resultant force is not zero, the object accelerates in the direction of the resultant force.

如果作用在物体上的合力为零，物体保持静止或沿直线匀速运动。如果合力不为零，物体沿合力方向加速。

The relationship between resultant force, mass and acceleration is given by Newton’s second law:

合力、质量和加速度之间的关系由牛顿第二定律给出：

F = m × a

where F is force in newtons, m is mass in kilograms and a is acceleration in metres per second squared (m/s²).

其中 F 是力，单位为牛顿；m 是质量，单位为千克；a 是加速度，单位为米每二次方秒（m/s²）。

Friction is a force that opposes motion. It can be useful, for example when it allows tyres to grip a road, but it can also be a problem because it wears away surfaces and wastes energy as heat.

摩擦力是阻碍运动的力。它有时很有用，例如使轮胎抓住路面，但也可能带来问题，因为它会磨损表面并以热的形式浪费能量。

---

4. Energy and Energy Transfers | 能量与能量传递

Energy is the ability to do work. It is measured in joules, symbol J. Energy can be stored in different ways, including kinetic energy, gravitational potential energy, chemical energy, thermal energy, elastic potential energy and nuclear energy.

能量是做功的能力。能量的单位是焦耳，符号为 J。能量可以以不同方式储存，包括动能、重力势能、化学能、热能、弹性势能和核能。

Energy can be transferred from one store to another. For example, a falling object transfers energy from its gravitational potential energy store to its kinetic energy store.

能量可以从一种储存形式转移到另一种储存形式。例如，下落的物体会将其重力势能储存转移到动能储存。

The principle of conservation of energy states that energy cannot be created or destroyed. It can only be transferred from one store to another or dissipated to the surroundings.

能量守恒定律指出，能量既不能凭空产生也不能凭空消失。它只能从一种储存形式转移到另一种储存形式，或耗散到周围环境中。

The gravitational potential energy store of an object can be calculated using the equation:

物体的重力势能储存可以用以下公式计算：

E = m × g × h

where E is gravitational potential energy in joules, m is mass in kilograms, g is gravitational field strength in newtons per kilogram and h is height in metres. On Earth, g is approximately 10 N/kg.

其中 E 是重力势能，单位为焦耳；m 是质量，单位为千克；g 是引力场强度，单位为牛顿每千克；h 是高度，单位为米。在地球上，g 约为 10 N/kg。

Energy transfers are often shown using a flow diagram. For a battery-powered torch, chemical energy in the battery is transferred to electrical energy and then to light and thermal energy.

能量转移通常用流程图表示。对于电池供电的手电筒，电池中的化学能先转化为电能，再转化为光能和热能。

---

5. Classification of Living Organisms | 生物的分类

Scientists classify living organisms into groups based on shared features. The broadest groups are the kingdoms: animals, plants, fungi, protoctists and bacteria.

科学家根据共同特征将生物分类。最广泛的类群是界：动物界、植物界、真菌界、原生生物界和细菌界。

Animals are further divided into vertebrates and invertebrates. Vertebrates have a backbone made of vertebrae; invertebrates do not have a backbone.

动物可进一步分为脊椎动物和无脊椎动物。脊椎动物有由椎骨组成的脊柱；无脊椎动物没有脊柱。

Vertebrate group | 脊椎动物类群	Key features | 主要特征	Example | 示例
Mammals | 哺乳动物	Hair, mammary glands, warm-blooded | 有毛发、乳腺、恒温	Human | 人类
Birds | 鸟类	Feathers, beak, lay eggs | 有羽毛、喙、产卵	Eagle | 鹰
Fish | 鱼类	Scales, gills, fins | 有鳞片、鳃、鳍	Salmon | 鲑鱼
Amphibians | 两栖动物	Moist skin, lay eggs in water | 皮肤湿润、在水中产卵	Frog | 青蛙
Reptiles | 爬行动物	Dry scaly skin, lay leathery eggs | 干燥鳞状皮肤、产革质卵	Snake | 蛇

A dichotomous key is a tool used to identify organisms by answering a series of questions with two possible choices. Each answer leads to another question until the organism is identified.

二歧检索表是一种通过回答一系列只有两个选项的问题来鉴定生物的工具。每个答案会导向下一个问题，直到鉴定出该生物。

---

6. Properties of Materials | 材料的性质

Materials can be described by their properties, such as hardness, strength, flexibility, conductivity, transparency, brittleness and density. Engineers choose materials based on the properties needed for a specific use.

材料可以通过其性质来描述，如硬度、强度、柔韧性、导电性、透明度、脆性和密度。工程师根据特定用途所需的性质来选择材料。

Thermal conductors allow heat to pass through them easily. Metals such as copper and aluminium are good thermal conductors. Thermal insulators reduce heat transfer; examples include wood, plastic, wool and trapped air.

热导体容易让热量通过。铜和铝等金属是良好的热导体。热绝缘体减少热量传递；例子包括木材、塑料、羊毛和静止空气。

Electrical conductors allow electric current to flow easily. Most metals are good electrical conductors. Electrical insulators, such as rubber and plastic, do not allow current to flow easily and are used for safety coatings.

电导体容易让电流通过。大多数金属是良好的电导体。橡胶和塑料等电绝缘体不易让电流通过，因此用于安全外皮。

The density of a material is its mass per unit volume. A dense material feels heavy for its size. Density is calculated using:

材料的密度是单位体积的质量。密度大的材料按体积来说感觉更重。密度计算公式为：

density = mass ÷ volume

Density is usually measured in grams per cubic centimetre (g/cm³) for solids and liquids, or kilograms per cubic metre (kg/m³) for larger samples.

固液体的密度通常以克每立方厘米（g/cm³）计量，较大样本的密度可用千克每立方米（kg/m³）计量。

---

7. Earth and Space Physics | 地球与空间物理

The Earth rotates on its axis once every 24 hours. This rotation causes day and night because different parts of the Earth face the Sun at different times.

地球每 24 小时绕地轴自转一次。这种自转形成昼夜交替，因为地球的不同部分在不同时间面向太阳。

The Earth orbits the Sun once every 365.25 days. The tilt of the Earth’s axis causes the seasons as different hemispheres receive different amounts of sunlight during the year.

地球每 365.25 天绕太阳公转一次。地轴的倾斜导致四季变化，因为一年中不同半球获得的光照量不同。

The Moon orbits the Earth and reflects light from the Sun. The changing appearance of the Moon is called its phases. A full moon occurs when the whole visible face of the Moon is lit by the Sun.

月球围绕地球运行并反射太阳

Published by TutorHao | IB Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）