The Structure of Life
Molecular biology is the study of biology at a molecular level.
The field overlaps with other areas of biology, particularly
genetics and biochemistry. Molecular biology chiefly concerns
itself with understanding the interactions between the various
systems of a cell, including the interrelationship of DNA, RNA
and protein synthesis and learning how these interactions are
Cell biology studies the physiological properties of cells, as
well as their behaviors, interactions, and environment; this is
done both on a microscopic and molecular level. Cell biology researches
both single-celled organisms like bacteria and specialized cells
in multicellular organisms like humans.
Understanding the composition of cells and how cells works is
fundamental to all of the biological sciences. Appreciating the
similarities and differences between cell types is particularly
important to the fields of cell and molecular biology. These fundamental
similarities and differences provide a unifying theme, allowing
the principles learned from studying one cell type to be extrapolated
and generalized to other cell types.
Genetics is the science of genes, heredity, and the variation
of organisms. In modern research, genetics provides important tools
in the investigation of the function of a particular gene, e.g.
analysis of genetic interactions. Within organisms, genetic information
generally is carried in chromosomes, where it is represented in
the chemical structure of particular DNA molecules.
Genes encode the information necessary for synthesizing proteins,
which, in turn play a large role in influencing, although, in many
instances, do not completely determine, the final phenotype of
Developmental biology studies the process by which
organisms grow and develop. Originating in embryology, today
studies the genetic control of cell growth, differentiation and "morphogenesis," which
is the process that gives rise to tissues, organs and anatomy.
Model organisms for developmental biology include the round worm
Caenorhabditis elegans, the fruit fly Drosophila melanogaster,
the zebrafish Brachydanio rerio, the mouse Mus musculus, and the
weed Arabidopsis thaliana.
Physiology of Organisms
Physiology studies the mechanical, physical, and biochemical processes
of living organisms, by attempting to understand how all the
structures function as a whole. It has traditionally been divided
into plant physiology and animal physiology but the principles
of physiology are universal, no matter what particular organism
is being studied. For example, what is learned about the physiology
of yeast cell can also apply to human cells. The field of animal
physiology extends the tools and methods of human physiology
to non-human animal species. Plant physiology also borrows techniques
from both fields.
Anatomy is an important part of physiology and considers how organ
systems in animals such as the nervous, immune, endocrine, respiratory
and circulatory systems function and interact. The study of these
systems is shared with the medically oriented disciplines of neurology,
immunology and the like.
Diversity and Evolution of Organisms
In population genetics the evolution of a population of organisms
is sometimes depicted as if traveling on a fitness landscape.
The arrows indicate the preferred flow of a population on the
landscape, and the points A, B, and C are local optima. The red
ball indicates a population that moves from a very low fitness
value to the top of a peak.
Evolutionary biology is concerned with the origin and descent
of species, as well as their change over time, i.e. their evolution.
Evolutionary biology is an inclusive field because it includes
scientists from many traditional taxonomically-oriented disciplines.
For example, it generally includes scientists who may have a specialist
training in particular organisms such as mammalogy, ornithology,
or herpetology but use those organisms as systems to answer general
questions in evolution. It also generally includes paleontologists
who use fossils to answer questions about the mode and tempo of
evolution, as well as theoreticians in areas such as population
genetics and evolutionary theory. In the 1990s developmental biology
made a re-entry into evolutionary biology from its initial exclusion
from the modern synthesis through the study of evolutionary developmental
biology. Related fields which are often considered part of evolutionary
biology are phylogenetics, systematics and taxonomy.
The two major traditional taxonomically-oriented disciplines are
botany and zoology. Botany is the scientific study of plants. Botany
covers a wide range of scientific disciplines that study the growth,
reproduction, metabolism, development, diseases, and evolution
of plant life. Zoology is the discipline which involves the study
of animals, which includes the physiology of animals is studied
under various fields including anatomy and embryology. The common
genetic and developmental mechanisms of animals and plants is studied
in molecular biology, molecular genetics and developmental biology.
The ecology of animals is covered under behavioral ecology and
Classification of Life
The dominant classification system is called Linnaean taxonomy,
which includes ranks and binomial nomenclature. How organisms
are named is governed by international agreements such as the
International Code of Botanical Nomenclature (ICBN), the International
Code of Zoological Nomenclature (ICZN), and the International
Code of Nomenclature of Bacteria (ICNB). A fourth Draft BioCode
was published in 1997 in an attempt to standardize naming in
the three areas, but it does not appear to have yet been formally
adopted. The International Code of Virus Classification and Nomenclature
(ICVCN) remains outside the BioCode.
Interactions of Organisms
Ecology studies the distribution and abundance of living organisms,
and the interactions between organisms and their environment.
The environment of an organism includes both its habitat, which
can be described as the sum of local abiotic factors like climate
and geology, as well as the other organisms which share its habitat.
Ecological systems are studied at several different levels from
individuals and populations to ecosystems and biosphere level.
Ecology is a multi-disciplinary science, drawing on many other
branches of science.
Ethology studies animal behavior (particularly of social animals
such as primates and canids), and is sometimes considered as a
branch of zoology. Ethologists have been particularly concerned
with the evolution of behavior and the understanding of behavior
in terms of the theory of natural selection. In one sense the first
modern ethologist was Charles Darwin, whose book The Expression
of the Emotions in Animals and Men influenced many ethologists.