1. Cell is the basic unit of structure and function.

2. Tissue: Many cell groups with different shapes, structures and functions are formed by cell differentiation, and the cell groups with similar shapes, structures and functions are called tissues.

3. Organs: Organisms' organs are composed of several different tissues, which are combined in a certain order to form a structure with certain functions.

4. System: In most animals and human bodies, some organs are further connected in an orderly way, and together with one or several physiological activities, a system is formed.

connection: the structure of human body (animal):

cell (tissue formed by differentiation)-tissue-organ-system-organism? From simple to complex, the structure in which various organs are arranged together in a certain order to complete one or more physiological activities is called a system.

Extended information:

Eight systems of the human body:

Many organs in a multicellular organism are linked together, and * * * perform some continuous basic physiological functions, and these organs form a system. Humans and higher animals have eight systems, namely digestive system, respiratory system, circulatory system, urinary system, exercise system, reproductive system, endocrine system and nervous system.

The above systems constitute the human body and the animal body, and under the regulation of the nervous and endocrine systems, they are interrelated and mutually restricted, and * * * together complete all the life activities of the whole organism to ensure the individual survival and ethnic continuity of the organism.

Baidu Encyclopedia-Eight Systems of Human Body