Biology
Defaults: IQ-6 or Naturalist-6.
This is the scientific study of the structure, behavior, and habitats of living organisms. You must specialize in the life of a particular planet type (see below). If you do not specify a planet type, your native planet type is assumed. The IQ default applies only to the planet type you grew up on. The default between different planet-type specialties is -4.
At TL6+, most biologists have an optional specialty as well. The most common options are biochemistry (the study of the chemical reactions that sustain life), botany (the study of plants), ecology (the study of environments), genetics (the study of heredity and genomes), marine biology (the study of ocean life), microbiology (the study of microscopic organisms), and zoology (the study of animals), but more obscure specialties are possible.
Planet Types
Biology, Geology, and Meteorology require you to specialize by "planet type," as does the "Physical" specialty of Geography. If you do not specify a planet type, your native planet type is assumed – so if the campaign will never leave your home world, save space and just write "Geology," "Biology," etc. GURPS sorts planets into six broad categories for these purposes.
Earthlike: Essentially, all habitable worlds.
Gas Giants: Jupiter/Uranus types.
Hostile Terrestrial: Venus types.
Ice Dwarfs: Comets and small moons composed almost entirely of snow or ice.
Ice Worlds: Rock worlds covered by a frozen "ocean."
Rock Worlds: Most moons, asteroids, etc.
Unless otherwise specified, all planet-type specialties for a given skill default to one another at -4.