How database buffer pool work?

For example we have 2 Scenarios:

Scenario 1:- We have very small buffer pool like 100 mb .But my query data is 500 mb .Does system will allow to keep 500mb query data in RAM .So new query will access from RAM?

Scenario 2:- Buffer pool size is 1 GB .In this situation Will system always keep 1GB free(in RAM) for mySQL query processing. For example ,system will/will not allow to use 1 GB for other resources