1. Explain the concept of hierarchical homework design: hierarchical homework design refers to designing homework with different levels and difficulties according to the differences of students' learning level, ability and interest, so as to meet the needs of students at different levels and promote their personalized development.

2. Clarify the research scope: When studying the hierarchical design of junior high school biology homework, it is necessary to clarify the research scope, including research objectives, research contents and research objects.

3. Determine the research methods: When studying the hierarchical design of junior high school biology homework, we need to adopt appropriate research methods, such as literature research, questionnaire survey and interview.

4. Explain the research purpose: When studying the hierarchical design of junior high school biology homework, we should make clear the research purpose, such as improving students' academic performance, cultivating students' innovative ability and promoting students' personalized development.

5. Summarize the research results: When studying the hierarchical design of junior high school biology homework, it is necessary to summarize the research results, including conclusions, findings and suggestions.

Through the above steps, we can write the definition of the hierarchical design topic of junior high school biology homework.