Cells 细 胞 xì bāo are the basic units of living things. Groups of similar cells 细 胞 xì bāo form tissues 组织 zǔ zhī. Tissues 组织 zǔ zhī make up organs 器官 qì guān and a group of organs that have associated or connected functions make up a system . An organism, such as a human being, is composed of many different systems 系统 xì tǒng:

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Nervous System 神经系统 shén jīng xì tǒng:

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Respiratory System 呼 吸系统 hū xī xì tǒng

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Digestive System 消 化系统 xiāo huà xì tǒng

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Skeletal System 骨骼系统 gǔ gé xì tǒng

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Muscular System 肌肉系统 jī ròu xì tǒng

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Blood Circulatory System 血液循环系统 xiě yè xún huán xì tǒng

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Endocrine System 内分泌系统 nèi fēn mì xì tǒng

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Excretory System 排泄系统 pái xiè xì tǒng

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Reproductive System 生殖系统 shēng zhí xì tǒng

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