Common Misconceptions in Year 7 Biology and How to Correct Them | Year 7 生物学常见误区与纠正方法

📚 Common Misconceptions in Year 7 Biology and How to Correct Them | Year 7 生物学常见误区与纠正方法

In Year 7 Biology, students encounter many new concepts about living organisms, cells, and body systems. Along the way, certain misunderstandings can form and become persistent if not addressed early. This article identifies some of the most common misconceptions in the CAIE Year 7 Biology syllabus and provides clear corrections to help you build accurate scientific knowledge.

在七年级生物学中，学生会接触到许多关于生命体、细胞和身体系统的新概念。在这个过程中，如果未能及早纠正，某些误解可能会形成并持续存在。本文梳理了 CAIE 七年级生物学大纲中最常见的一些误区，并提供清晰的纠正方法，帮助你建立准确的科学知识。

1. All Bacteria Are Harmful | 所有细菌都是有害的

Many students believe that bacteria are germs that always cause illness and should be eliminated.

许多学生认为细菌就是会致病的病菌，应当被彻底消灭。

In reality, the vast majority of bacteria are harmless, and many are essential for our health and the environment.

实际上，绝大多数细菌是无害的，许多细菌对我们的健康和环境至关重要。

For example, bacteria in our intestines help digest food, produce vitamins such as vitamin K, and protect against harmful microbes.

例如，我们肠道中的细菌有助于消化食物、产生维生素 K 等维生素，并抵御有害微生物。

Bacteria are also used in making yogurt, cheese, and in decomposing dead matter to recycle nutrients.

细菌还被用于制作酸奶、奶酪，以及分解死去的生物以循环养分。

Only a small fraction of bacteria are pathogenic, meaning they can cause diseases like cholera or tuberculosis.

只有一小部分细菌是致病菌，它们能引发霍乱、结核病等疾病。

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2. Plants Only Respire at Night | 植物只在夜间呼吸

A widespread misconception is that plants perform respiration only in the dark, while photosynthesis occurs in the light.

一个普遍的误解是，植物只在黑暗中才进行呼吸，而光合作用只在有光时进行。

The truth is that plants respire all the time — day and night — to release energy from glucose for their cells.

事实是，植物无时无刻不在进行呼吸——无论是白天还是夜晚——从葡萄糖中释放能量供细胞使用。

Photosynthesis, however, requires light and only happens during the day. During the day, the rate of photosynthesis is usually higher than respiration, so plants produce more oxygen than they consume.

然而，光合作用需要光，只在白天进行。在白天，光合作用的速率通常高于呼吸速率，因此植物产生的氧气多于消耗的氧气。

At night, without light, photosynthesis stops, but respiration continues, taking in oxygen and releasing carbon dioxide.

到了夜晚，没有光，光合作用停止，但呼吸作用仍在继续，吸收氧气并释放二氧化碳。

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3. Arteries Always Carry Oxygenated Blood, and Veins Carry Deoxygenated Blood | 动脉总是输送含氧血，静脉总是输送缺氧血

Many students learn that arteries carry blood away from the heart and veins carry blood back, and then assume that arteries always carry oxygen-rich blood.

许多学生学习到动脉将血液带离心脏，静脉将血液送回心脏，然后就认为动脉总是输送富含氧气的血液。

While this is true for most arteries in the systemic circulation, there is an important exception: the pulmonary artery carries deoxygenated blood from the heart to the lungs.

尽管这对体循环中的大多数动脉是正确的，但有一个重要的例外：肺动脉将缺氧的血液从心脏输送到肺部。

Similarly, the pulmonary vein carries oxygenated blood from the lungs back to the heart.

同样，肺静脉将含氧的血液从肺部送回心脏。

Therefore, the defining feature of an artery is the direction of blood flow relative to the heart, not the oxygen content.

因此，动脉的定义特征是与心脏相关的血流方向，而不是氧气含量。

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4. Breathing and Respiration Are the Same Thing | 呼吸（Breathing）和呼吸作用（Respiration）是同一回事

It is very common for students to use the terms ‘breathing’ and ‘respiration’ interchangeably, but they refer to different processes.

学生们常常互换使用“呼吸”和“呼吸作用”这两个术语，但它们指的是不同的过程。

Breathing (ventilation) is the physical act of moving air in and out of the lungs — inhaling and exhaling.

呼吸（通气）是指空气进出肺部的物理动作——吸气和呼气。

Respiration is a chemical reaction that occurs inside cells, where glucose reacts with oxygen to release energy. The word equation for aerobic respiration is:

呼吸作用是在细胞内发生的一种化学反应，葡萄糖与氧气反应释放能量。有氧呼吸的文字方程式为：

glucose + oxygen → carbon dioxide + water + energy

葡萄糖 + 氧气 → 二氧化碳 + 水 + 能量

In symbols: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

用符号表示：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量

Breathing brings oxygen into the body for respiration and removes the carbon dioxide produced.

呼吸将氧气带入体内用于呼吸作用，并排出产生的二氧化碳。

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5. The Heart Is Located on the Left Side of the Chest | 心脏位于胸腔左侧

Many diagrams depict the heart slightly tilted, and students often think the heart is entirely on the left side of the chest.

许多示意图显示心脏稍微倾斜，学生常认为心脏完全位于胸腔左侧。

In fact, the heart is located in the center of the chest, behind the sternum (breastbone), between the lungs.

事实上，心脏位于胸腔中央，胸骨后方，两肺之间。

The bottom tip of the heart (the apex) points slightly to the left, which is why we feel the heartbeat more strongly on the left side.

心脏的底部尖端（心尖）略微指向左侧，这就是为什么我们在左侧能更强烈地感受到心跳。

This central position allows the heart to pump blood efficiently to both the lungs and the rest of the body.

这种中央位置使得心脏能够有效地将血液泵送到肺部和身体其他部位。

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6. Seeds Need Sunlight to Germinate | 种子萌发需要阳光

Many students think that a seed must have sunlight to start growing into a seedling.

许多学生认为种子必须要有阳光才能开始长成幼苗。

In reality, most seeds require three main conditions for germination: water, warmth (suitable temperature), and oxygen. Sunlight is not necessary for germination.

实际上，大多数种子萌发需要三个主要条件：水分、温暖（适宜的温度）和氧气。阳光并非萌发所必需。

Water activates enzymes, warmth speeds up metabolic reactions, and oxygen is needed for aerobic respiration to provide energy for growth.

水分能激活酶，温暖加速代谢反应，氧气则需要用于有氧呼吸，为生长提供能量。

Once the seedling emerges above the soil, light becomes essential for photosynthesis to produce food.

一旦幼苗出土，光对于进行光合作用制造养分就变得至关重要。

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7. Classification of Organisms Is Based Only on Size | 生物分类只基于大小

When first learning about classification, some students mistakenly think organisms are grouped simply by their size or where they live.

刚开始学习分类时，一些学生错误地认为生物只是根据大小或生活环境来分组。

In biology, organisms are classified based on shared characteristics, such as cell structure, method of reproduction, and nutrition.

在生物学中，生物是根据共同的特征进行分类的，例如细胞结构、繁殖方式和营养方式。

For example, whales are large and live in water, but they are mammals because they have lungs, give birth to live young, and produce milk.

例如，鲸鱼体型巨大且生活在水中，但它们属于哺乳动物，因为它们有肺、胎生并分泌乳汁。

Classification follows a hierarchical system: Kingdom, Phylum, Class, Order, Family, Genus, Species.

分类遵循一个层级系统：界、门、纲、目、科、属、种。

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8. Humans Get Energy Only from Food, Not Water | 人类只从食物中获取能量，不需要水提供能量

Some students think that because water has no calories, it does not contribute to energy levels.

一些学生认为，由于水没有热量，所以它对能量水平没有贡献。

While water itself does not provide metabolic energy (calories), it is essential for all energy-releasing processes.

尽管水本身不提供代谢能量（卡路里），但它对所有释放能量的过程都至关重要。

Water is needed for digestion, absorption, and transport of nutrients, as well as for chemical reactions like respiration. Without water, cells cannot release energy from glucose efficiently.

水是消化、吸收和运输营养物质所必需的，也是呼吸等化学反应所必需的。没有水，细胞就无法高效地从葡萄糖中释放能量。

Dehydration quickly leads to fatigue and a drop in physical and mental performance.

脱水会迅速导致疲劳以及身体和精神表现的下降。

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9. Plants Eat Soil to Obtain Food | 植物从土壤中“吃”取食物

A common early misconception is that plants take in their food from the soil through their roots, much like animals eat.

一个常见的早期误解是，植物像动物进食一样，从土壤中通过根部获取食物。

In fact, plants make their own food through photosynthesis using sunlight, carbon dioxide from the air, and water from the soil.

事实上，植物通过光合作用自己制造食物，利用阳光、空气中的二氧化碳和来自土壤的水。

The glucose produced is the plant’s food, providing energy and building material.

产生的葡萄糖就是植物的食物，提供能量和构建物质。

What roots absorb from the soil are mainly water and dissolved mineral ions (such as nitrates and magnesium), which are needed for growth but are not the main energy source.

根部从土壤中吸收的主要是水和溶解的矿物质离子（如硝酸盐和镁），它们是生长所必需的，但不是主要的能量来源。

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10. Every Cell Has a Nucleus | 每个细胞都有细胞核

After learning about animal and plant cells, students may assume that all cells contain a nucleus.

学完动物和植物细胞后，学生可能会认为所有细胞都含有细胞核。

While it is true that typical plant and animal cells are eukaryotic and have a nucleus, there are important exceptions.

虽然典型的动植物细胞是真核细胞且具有细胞核，但存在重要的例外。

For example, mature red blood cells in mammals have no nucleus — they lose it during development to make more space for hemoglobin.

例如，哺乳动物的成熟红细胞没有细胞核——它们在发育过程中失去细胞核，以便为血红蛋白留出更多空间。

Another example is bacterial cells, which are prokaryotic; they have no true nucleus, just a single circular strand of DNA floating in the cytoplasm.

另一个例子是细菌细胞，它们是原核生物；它们没有真正的细胞核，只有一条环状DNA链漂浮在细胞质中。

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