The method of explaining complex research objects with models is called model method.

1. physical model: This model is a physical model that intuitively expresses the characteristics of cognitive objects in the form of objects or pictures. For example, Watson and Crick's DNA double helix structure model, animal and plant cell pattern diagram, bacterial structure pattern diagram, secretory protein synthesis and transportation schematic diagram (note that words are conceptual models) and so on.

2. Conceptual model: through the analysis of a large number of concrete images, the same essence is revealed by classification, and its essence is condensed in concepts, and the relationship between various objects is expressed by the relationship between concepts, and the main characteristics and connections of objects are highlighted by words and symbols. For example, the main reaction process of photosynthesis, the graded regulation of thyroid hormone, is described graphically by photosynthesis.

3. Mathematical model: A mathematical model is a mathematical form used to describe a system or its attributes. The life essence and movement law of the research object are analyzed and synthesized in detail, and expressed in appropriate mathematical forms, such as mathematical equations, relationships, charts, tables, etc., so as to make judgments and predictions according to phenomena. For example, the number of bacteria after N generation Nn=2n, Mendel hybridization experiment "tall stem: short stem = 3: 1", the schematic diagram of enzyme activity affected by temperature, etc.