If you are studying details of cells and tissues using a microscope.Then which of the following branch of biology are you studying ?
histology
Histology is the scientific study of the fine detail of biological cells and tissues using microscopes to look at specimens of tissues that have been carefully prepared using special processes called "histological techniques".
Oncology is a branch of medicine that deals with the prevention, diagnosis and treatment of cancer.
Embryology is the branch of biology which deals with the study of embryos and their development.
Microbiology deals with the study of microorganisms.