There are lots of jobs to do with biology and it depends which parts of biology you like which way you may want to go. On a weekly basis, I do the following types of biology:
Molecular biology: This is manipulating DNA – I clone genes and in fact will do some of this later today.
Protein biology: Making proteins and then doing experiments on them (this is part of biochemistry).
Structural biology: Using techniques like X-ray diffraction to find of the 3D structure of proteins (or DNA/RNA).
I also collaborate with people who are cell biologists and systems biologists.
Cell biology: Looking at how cells work which could be human, animal or plant cells.
Systems biology: This is an integrated approach to looking at complex biological systems. For instance someone may be interested in metabolism and so looks at the network of protein/DNA/events which are part of this system.
Plant biology: I have worked with some people looking at plant parasites who not only look at proteins from the insects but also the plant proteins these interact with.
As you can see, I’m more at the molecular end of the biology scale rather than the whole animal/plant part.
There is a whole field out there and lots of interesting subject some of which are on the boundaries between biology and chemistry or physics as well as engineering.