The three major themes in the study of biology are diversity, interdependence, and evolution.
One could also find good research topics related to traditional biology subfields like plant and animal biology, ecology (current global problems warrant a number of hot topics), or topics related to humans: neurobiology (and determinants of human behavior), recent discoveries on diseases and the immune system, etc.
Themes and Concepts of Biology
Order.
Sensitivity or Response to Stimuli.
Reproduction.
Growth and Development.
Regulation.
Homeostasis.
Energy Processing.