user6: Biology is an extremely wide field, questions ranging from zoology, botany to biochemistry are all on-topic here. A mechanism for users to get a rough selection of questions they are actually interested in and capable of answering would be useful.
I suggest that we try to tag questions with at least on general biological category, in addition to any more specific tags that might apply. This would allow users to favorite the category they have experience in and take a closer look there.
The division in biology are not necessarily well-defined, we would have to come up with some reasonable schema. This would not replace more specific tags, but just provide a rough division into the different biology fields.
Does this generally make sense? And what should the categories be?

user3340: Addition to previous answers:
Each tag should point to a topic that has uniqueness of principle or of techniques used to study those.
For example genetics is an appropriate tag. Human genetics is an unnecessary tag. There is nothing unique about human genetics. 

user25: Drawing parallels to SO, I might compare the field tags (zoology, biochemistry, et. al.) to programming languages and some of the more technique-oriented tags (cell-culture) to features of them (object-oriented, strings, etc).  One zoologist would be more likely than not to know something about a zoology question, and likewise for someone who's done cell culture in any respect.

user66: The problem I see now with the questions is not that those are extremely broad, but also the level of requested answer may vary greatly: some are questions from experts to experts, others are more like a questions from biology students or just people interested in biology. Some question target well known facts one can find even in Wikipedia, some require knowledge from cutting edge research papers and others just ask for practical tips how to perform certain experiment etc.
So, we need a sort of two-dimensional tagging: both the area and the level of the requested information, in my opinion.
For categories I would use Wikipedia article on biology and introduce:
I. Major tags:

History of biology
Structural biology

Molecular biology
Cell biology // Histology 
Genetics
Developmental biology

Physiology
Medical biology
Systematics // Zoology // Botanics // Mycology.
Computational biology
Ecology
Biochemistry // Pharmacology
Biophysics // Bionics.

II. Minor tags
(look the list in Wikipedia!)
III. Level tag

Known or established concept (textbook fact).
Research topic.
Lab tip // Preparation // Methodology.


user73: Yes we should. It seems a no-brainer that people would want to search via the main established branches of biology.
So far the beta seems to be dominated by questions on biochemistry, which I'm not especially interested in on this Q&A site, but that tag has only been used twice.
I would like to be able to search for questions pertaining to, for instance, ecology or botany or genetics tags, which are my primary interests here, even though those categories themselves are incredibly broad.
Wikipedia has a useful listing from which we could derive broad topic tags:
Aerobiology — the study of airborne organic particles
Agriculture — the study of producing crops from the land, with an emphasis on practical applications
Anatomy — the study of form and function, in plants, animals, and other organisms, or specifically in humans
Arachnology — the study of arachnids
Astrobiology — the study of evolution, distribution, and future of life in the universe—also known as exobiology, exopaleontology, and bioastronomy
Biochemistry — the study of the chemical reactions required for life to exist and function, usually a focus on the cellular level
Bioengineering — the study of biology through the means of engineering with an emphasis on applied knowledge and especially related to biotechnology
Biogeography — the study of the distribution of species spatially and temporally
Bioinformatics — the use of information technology for the study, collection, and storage of genomic and other biological data
Biomathematics or Mathematical Biology — the quantitative or mathematical study of biological processes, with an emphasis on modeling
Biomechanics — often considered a branch of medicine, the study of the mechanics of living beings, with an emphasis on applied use through prosthetics or orthotics
Biomedical research — the study of the human body in health and disease
Biophysics — the study of biological processes through physics, by applying the theories and methods traditionally used in the physical sciences
Biotechnology — a new and sometimes controversial branch of biology that studies the manipulation of living matter, including genetic modification and synthetic biology
Building biology — the study of the indoor living environment
Botany — the study of plants
Cell biology — the study of the cell as a complete unit, and the molecular and chemical interactions that occur within a living cell
Conservation Biology — the study of the preservation, protection, or restoration of the natural environment, natural ecosystems, vegetation, and wildlife
Cryobiology — the study of the effects of lower than normally preferred temperatures on living beings.
Developmental biology — the study of the processes through which an organism forms, from zygote to full structure
Ecology — the study of the interactions of living organisms with one another and with the non-living elements of their environment
Embryology — the study of the development of embryo (from fecundation to birth). See also topobiology.
Entomology — the study of insects
Environmental Biology — the study of the natural world, as a whole or in a particular area, especially as affected by human activity
Epidemiology — a major component of public health research, studying factors affecting the health of populations
Ethology — the study of animal behavior
Evolutionary Biology — the study of the origin and descent of species over time
Genetics — the study of genes and heredity
Herpetology — the study of reptiles and amphibians
Histology — the study of cells and tissues, a microscopic branch of anatomy
Ichthyology — the study of fish
Integrative biology — the study of whole organisms
Limnology — the study of inland waters
Mammalogy — the study of mammals
Marine Biology — the study of ocean ecosystems, plants, animals, and other living beings
Microbiology — the study of microscopic organisms (microorganisms) and their interactions with other living things
Molecular Biology — the study of biology and biological functions at the molecular level, some cross over with biochemistry
Mycology — the study of fungi
Neurobiology — the study of the nervous system, including anatomy, physiology and pathology
Oceanography — the study of the ocean, including ocean life, environment, geography, weather, and other aspects influencing the ocean
Oncology — the study of cancer processes, including virus or mutation oncogenesis, angiogenesis and tissues remoldings
Ornithology — the study of birds
Population biology — the study of groups of conspecific organisms, including
    Population ecology — the study of how population dynamics and extinction
    Population genetics — the study of changes in gene frequencies in populations of organisms
Paleontology — the study of fossils and sometimes geographic evidence of prehistoric life
Pathobiology or pathology — the study of diseases, and the causes, processes, nature, and development of disease
Parasitology — the study of parasites and parasitism
Pharmacology — the study and practical application of preparation, use, and effects of drugs and synthetic medicines
Physiology — the study of the functioning of living organisms and the organs and parts of living organisms
Phytopathology — the study of plant diseases (also called Plant Pathology)
Psychobiology — the study of the biological bases of psychology
Sociobiology — the study of the biological bases of sociology
Structural biology — a branch of molecular biology, biochemistry, and biophysics concerned with the molecular structure of biological macromolecules
Virology — the study of viruses and some other virus-like agents
Zoology — the study of animals, including classification, physiology, development, and behavior (See also Entomology, Ethology, Herpetology, Ichthyology, Mammalogy, and Ornithology)


6: <p>Biology is an extremely wide field, questions ranging from zoology, botany to biochemistry are all on-topic here. A mechanism for users to get a rough selection of questions they are actually interested in and capable of answering would be useful.</p>

<p>I suggest that we try to tag questions with at least on general biological category, in addition to any more specific tags that might apply. This would allow users to favorite the category they have experience in and take a closer look there.</p>

<p>The division in biology are not necessarily well-defined, we would have to come up with some reasonable schema. This would not replace more specific tags, but just provide a rough division into the different biology fields.</p>

<p>Does this generally make sense? And what should the categories be?</p>
 3340: <p>Addition to previous answers:</p>

<p>Each tag should point to a topic that has uniqueness of principle or of techniques used to study those.</p>

<p>For example genetics is an appropriate tag. Human genetics is an unnecessary tag. There is nothing unique about human genetics. </p>
 25: <p>Drawing parallels to SO, I might compare the field tags (zoology, biochemistry, et. al.) to programming languages and some of the more technique-oriented tags (cell-culture) to features of them (object-oriented, strings, etc).  One zoologist would be more likely than not to know something about a zoology question, and likewise for someone who's done cell culture in any respect.</p>
 66: <p>The problem I see now with the questions is not that those are extremely broad, but also the level of requested answer may vary greatly: some are questions from experts to experts, others are more like a questions from biology students or just people interested in biology. Some question target well known facts one can find even in Wikipedia, some require knowledge from cutting edge research papers and others just ask for practical tips how to perform certain experiment etc.
So, we need a sort of two-dimensional tagging: both the area and the level of the requested information, in my opinion.</p>

<p>For categories I would use <a href="http://en.wikipedia.org/wiki/Biology" rel="nofollow">Wikipedia article on biology</a> and introduce:</p>

<p>I. Major tags:</p>

<ol>
<li>History of biology</li>
<li><p>Structural biology</p>

<ul>
<li>Molecular biology</li>
<li>Cell biology // Histology </li>
<li>Genetics</li>
<li>Developmental biology</li>
</ul></li>
<li><p>Physiology</p></li>
<li>Medical biology</li>
<li>Systematics // Zoology // Botanics // Mycology.</li>
<li>Computational biology</li>
<li>Ecology</li>
<li>Biochemistry // Pharmacology</li>
<li>Biophysics // Bionics.</li>
</ol>

<p>II. Minor tags</p>

<p>(look the list in Wikipedia!)</p>

<p>III. Level tag</p>

<ol>
<li>Known or established concept (textbook fact).</li>
<li>Research topic.</li>
<li>Lab tip // Preparation // Methodology.</li>
</ol>
 73: <p>Yes we should. It seems a no-brainer that people would want to search via the main established branches of biology.</p>

<p>So far the beta seems to be dominated by questions on <a href="https://biology.stackexchange.com/questions/tagged/biochemistry" class="post-tag" title="show questions tagged &#39;biochemistry&#39;" rel="tag">biochemistry</a>, which I'm not especially interested in on this Q&amp;A site, but that tag has only been used twice.</p>

<p>I would like to be able to search for questions pertaining to, for instance, <a href="https://biology.stackexchange.com/questions/tagged/ecology" class="post-tag" title="show questions tagged &#39;ecology&#39;" rel="tag">ecology</a> or <a href="https://biology.stackexchange.com/questions/tagged/botany" class="post-tag" title="show questions tagged &#39;botany&#39;" rel="tag">botany</a> or <a href="https://biology.stackexchange.com/questions/tagged/genetics" class="post-tag" title="show questions tagged &#39;genetics&#39;" rel="tag">genetics</a> tags, which are my primary interests here, even though those categories themselves are incredibly broad.</p>

<p>Wikipedia has a <a href="http://en.wikipedia.org/wiki/Biology#Branches_of_biology" rel="nofollow noreferrer">useful listing</a> from which we could derive broad topic tags:</p>

<pre><code>Aerobiology — the study of airborne organic particles
Agriculture — the study of producing crops from the land, with an emphasis on practical applications
Anatomy — the study of form and function, in plants, animals, and other organisms, or specifically in humans
Arachnology — the study of arachnids
Astrobiology — the study of evolution, distribution, and future of life in the universe—also known as exobiology, exopaleontology, and bioastronomy
Biochemistry — the study of the chemical reactions required for life to exist and function, usually a focus on the cellular level
Bioengineering — the study of biology through the means of engineering with an emphasis on applied knowledge and especially related to biotechnology
Biogeography — the study of the distribution of species spatially and temporally
Bioinformatics — the use of information technology for the study, collection, and storage of genomic and other biological data
Biomathematics or Mathematical Biology — the quantitative or mathematical study of biological processes, with an emphasis on modeling
Biomechanics — often considered a branch of medicine, the study of the mechanics of living beings, with an emphasis on applied use through prosthetics or orthotics
Biomedical research — the study of the human body in health and disease
Biophysics — the study of biological processes through physics, by applying the theories and methods traditionally used in the physical sciences
Biotechnology — a new and sometimes controversial branch of biology that studies the manipulation of living matter, including genetic modification and synthetic biology
Building biology — the study of the indoor living environment
Botany — the study of plants
Cell biology — the study of the cell as a complete unit, and the molecular and chemical interactions that occur within a living cell
Conservation Biology — the study of the preservation, protection, or restoration of the natural environment, natural ecosystems, vegetation, and wildlife
Cryobiology — the study of the effects of lower than normally preferred temperatures on living beings.
Developmental biology — the study of the processes through which an organism forms, from zygote to full structure
Ecology — the study of the interactions of living organisms with one another and with the non-living elements of their environment
Embryology — the study of the development of embryo (from fecundation to birth). See also topobiology.
Entomology — the study of insects
Environmental Biology — the study of the natural world, as a whole or in a particular area, especially as affected by human activity
Epidemiology — a major component of public health research, studying factors affecting the health of populations
Ethology — the study of animal behavior
Evolutionary Biology — the study of the origin and descent of species over time
Genetics — the study of genes and heredity
Herpetology — the study of reptiles and amphibians
Histology — the study of cells and tissues, a microscopic branch of anatomy
Ichthyology — the study of fish
Integrative biology — the study of whole organisms
Limnology — the study of inland waters
Mammalogy — the study of mammals
Marine Biology — the study of ocean ecosystems, plants, animals, and other living beings
Microbiology — the study of microscopic organisms (microorganisms) and their interactions with other living things
Molecular Biology — the study of biology and biological functions at the molecular level, some cross over with biochemistry
Mycology — the study of fungi
Neurobiology — the study of the nervous system, including anatomy, physiology and pathology
Oceanography — the study of the ocean, including ocean life, environment, geography, weather, and other aspects influencing the ocean
Oncology — the study of cancer processes, including virus or mutation oncogenesis, angiogenesis and tissues remoldings
Ornithology — the study of birds
Population biology — the study of groups of conspecific organisms, including
    Population ecology — the study of how population dynamics and extinction
    Population genetics — the study of changes in gene frequencies in populations of organisms
Paleontology — the study of fossils and sometimes geographic evidence of prehistoric life
Pathobiology or pathology — the study of diseases, and the causes, processes, nature, and development of disease
Parasitology — the study of parasites and parasitism
Pharmacology — the study and practical application of preparation, use, and effects of drugs and synthetic medicines
Physiology — the study of the functioning of living organisms and the organs and parts of living organisms
Phytopathology — the study of plant diseases (also called Plant Pathology)
Psychobiology — the study of the biological bases of psychology
Sociobiology — the study of the biological bases of sociology
Structural biology — a branch of molecular biology, biochemistry, and biophysics concerned with the molecular structure of biological macromolecules
Virology — the study of viruses and some other virus-like agents
Zoology — the study of animals, including classification, physiology, development, and behavior (See also Entomology, Ethology, Herpetology, Ichthyology, Mammalogy, and Ornithology)
</code></pre>
