Biology Sub-Disciplines:

Biochemistry
Biophysics
Cell Biology (Cytology)
Biotechnology (many specialty areas)
Histology
Genetics
· Molecular genetics
· Classical genetics
· Genomics
· Population genetics
Anatomy
Physiology
· Animal
· Plant
· Fungal
· Bacterial
· Etc.
Nutrition
Microbiology
· Virology
· Bacteriology
· Protozoology
Mycology
Botany
· Economic botany
· Plant pathology
· Bryology
· Phycology
· Horticulture
· Etc.
Zoology
· Invertebrate zoology
· Entomology
· Parasitology
· Vertebrate zoology
· Icthyology
· Herpetology
· Ornithology
· Mammalogy
· Etc.
Endocrinology
Neurobiology
Cognitive Neuroscience
Immunology
Immunopathology
Developmental Biology (Embryology)
Ethology (Animal Behavior)
Sociobiology
Marine Biology
Systematics / Taxonomy (specializing in certain groups)
Ecology
· Population ecology
· Community ecology
· Terrestrial ecology
· Aquatic ecology
· Physiological ecology
· Behavioral ecology
· Etc.
Environmental Biology
Forestry
Fisheries Biology
Wildlife Biology
Aquaculture
Evolutionary Biology
Paleontology
Medicine (numerous specializations in both human and non-human medicine)
Pharmacology
Pathology
Forensics
Toxicology