The Biology ABC
The Biology Alphabet
Biology is a wonderfully diverse topic that encompasses everything from the tiny world of the cell to how organisms interact with each other. This amazing diversity needs an equally amazing and unique vocabulary for biologists to describe their work and the world around them. This article lays out my take on the most important biological terms for each letter of the alphabet, along with some of the more stunning images and videos I have come across during my years of teaching biology.
A Is for Amino Acid
Two A's for the price of one! Amino acids are the building blocks of proteins. There are 20 different amino acids which are joined together in condensation reactions (water is released) to form polypeptide chains, or proteins. Some amino acids can be made by the human body; others cannot and need to be consumed in our diet—these are known as essential amino acids
B Is for Bacteria
Bacteria are one of the five kingdoms of life and are characterised by their lack of nucleus. They are also called Prokaryotes, a word that means "before nucleus." Bacteria are probably the most successful division of life on the planet. There are more bacterial cells in your body than there are human cells!
C Is for Cell
Cells are the basic unit of life—all living things are made of one or more cells. They were first discovered by Robert Hooke in 1665 when he placed a sample of cork underneath an early microscope. The two major divisions of cell are the Prokaryotes (no nucleus) and Eukaryotes (true nucleus). There are numerous sub-divisions of each group.
D Is for DNA
DNA is a double stranded helix that carries the instructions for building and maintaining an organism. DNA is made up of:
- A phosphate backbone.
- A pentose sugar, deoxyribose.
- One of four organic bases: adenine, thymine, guanine and cytosine.
DNA is the largest molecule in your body, and each of your cells contains around 2 metres of DNA, tightly coiled and packed into the nucleus. This is equivalent to stuffing around 24 miles (40km) of thread into a tennis ball!
It was discovered by Francis Crick, James Watson, and Rosalind Franklin (Franklin died before the Nobel Prize for this discovery was awarded, so her department head, Maurice Wilkins, shared the 1962 Prize with Crick and Watson.)
E Is for Evolution
Evolution is the process by which all of the biodiversity on our planet has arisen, and is credited to Charles Darwin and Alfred Russel Wallace. Evolution is the development of new types of organisms from existing types due to changes in the genetic structure (mutations) that build up over huge expanses of time. Evolution is the framework for modern biology, and links the fields of genetics, molecular biology, ecology, cell biology, and many more.
F Is for Fungi
One of the five kingdoms of life, fungi are eukaryotic (they have a nucleus) and are vital to life on Earth. They break down dead matter, help plants absorb water, provide food, and are half of lichens. Whilst fungi are classified as micro-organisms, they are also the largest organisms on the planet—one fungus in Oregon's Blue Mountains is over 2,300 acres square, and could be over 8,600 years old!
G Is for Gene
A gene is a section of DNA that codes for a specific protein or RNA molecule; it is the basic unit of inheritance. Diploid organisms (like us) carry two alleles (versions) for each gene, which can be dominant, recessive, or co-dominant.
H Is for Histone
Histones are a class of simple protein molecules that help package and condense DNA. Histones + DNA = Nucleosomes. Nucleosomes resemble thread wrapped around cotton spools. Without histones, our DNA would not fit into the nuclei of our cells.
I Is for Immune System
A collection of tissues and cells found in vertebrates that defend the organism from invading pathogens (disease causing micro-organisms, parasites, and debris). The immune system is a learning system once it has been exposed to, and fought off, an infection. It protects the body from reinfection from the same pathogen—the organism is said to be immune.
Vaccinations provide immunity from dangerous diseases by exposing your immune system to dead or inactivated pathogens. The body can then prepare its defences in case of infection by the real thing.
An over-active immune response can cause allergic reactions—a firing up of the immune system in response to a harmless stimulus such as pollen, dust, or nuts.
J Is for Junk DNA
Junk DNA is the term for stretches of DNA that have no immediately obvious structural, maintenance, or coding function. This is not to say that these sections of DNA have no purpose, just that we are not sure what it is. For this reason, junk DNA is currently of great interest to the biological community with a number of projects researching it, such as ENCODE
K Is for Karyotype
An organism's karyotype is simply a photograph of all of their chromosomes, paired up and arranged according to size.
L Is for Lichen
Lichens are symbiotic composite organisms—they are made up of two different organisms that live together in such harmony they are given their own name. They are typically made up of a plant or bacterium and a fungus. They are key indicator species; the species of lichens found in a given area are dependent on levels of air and soil pollution. If the area is polluted, you will only find the hardiest of lichens.
Mitosis and Meiosis Summary
M Is for Mitosis and Meiosis
Mitosis and Meiosis are the two types of cell division seen in all living organisms. Mitosis is used for repair, growth, and maintenance. Meiosis is used to generate sex cells. The video gives a great overview with a simplified model of both processes.
N Is for Nucleus
The nucleus is the largest organelle in most eukaryotic cells. It is where DNA is stored, replicated, and transcribed into mRNA. The presence or absence of a nucleus determines whether a cell is eukaryotic (true nucleus) or prokaryotic (before nucleus.)
O Is for Organs
Multicellular organisms have lots of different cell types (we humans have over 200) that must all work together to help the organism survive. A group of cells that work together for a similar function is known as a tissue; a group of tissues that work together for a similar function is known as an organ.
The skin is the largest organ in the body and is made up of:
- Nervous tissue
- Connective tissue
- Fat tissue
- Vascular tissue (blood vessels)
- Skin tissue
P Is for Plasmid
Plasmids are extra bits of DNA found in bacteria that are not part of the main chromosome. They usually code for things such as antibiotic resistance. Plasmids are important because they are used in genetic engineering.
Plasmids are easily tampered with by scientists. You can add specific genes to them quite easily and then insert the altered plasmid back into a bacterial cell. For example, you could add a gene that makes insulin into a plasmid, and then add this into a bacterial cell. If you then grow this cell and allow it to multiply, the culture of cells will start to excrete insulin—this can then be harvested and purified. This is how most insulin used to treat diabetes is made.
Q Is for Quadrat
A rectangular grid-tool used to examine the plant coverage of a given area.
R Is for RNA
RNA is a large, single-stranded molecule that plays several key roles in the translation of a gene into a protein. It is a genetic material, but differs from DNA in several key ways:
- RNA is single stranded
- RNA contains the pentose sugar ribose (not deoxyribose)
- RNA contains the organic base uracil (not thymine)
It is thought that life started out based on RNA, as RNA can also act as an enzyme and as a protein (so can catalyse reactions). This is still open to debate, however. Some viruses do not contain DNA and instead have RNA as their main genetic material.
S Is for Sex
The evolution of sexual reproduction on Earth had profound consequences. Before sex came along, most organisms reproduced asexually—i.e. they created clones of themselves. This meant that genetic diversity from one individual to another was tremendously low. Without genetic variation created by mixing your genes up during sexual reproduction, asexual species struggled to survive long term (the rotifer being an obvious exception).
Sex mixes up genes and so sexually reproducing organisms are better equipped to handle a changing environment. Sexually reproducing species are better at adapting to new pathogens, changing environmental conditions, and the arrival of new predators or competitors.
T Is for Telomere
Telomeres are structures on the end of each of your chromosomes that protect your genetic material from degradation.
Due to an inherent problem with DNA replication, your chromosomes actually get slightly shorter each time they are copied. To prevent this from eventually eroding your genes, your chromosomes have long repetitive regions of junk that doesn't code for anything. It is thought that the aging process is linked to the shortening of one's telomeres. In some cells, a special enzyme called telomerase repairs the telomeres and prevents them from lengthening. This is usually seen in cells that remain young and in cancer cells.
U Is for Uracil
Uracil is an organic base that substitutes for thymine in RNA, and is one of the key differences between DNA and RNA.
V Is for Virus
Viruses are known as obligate parasites—they need to use another organism in order to reproduce. Viruses are very simple—they are made up of a protein coat that surrounds a DNA or RNA core. The virus injects this into a cell and hi-jacks the cell's machinery to make more viruses. Once the cell is full of a virus, it explodes and releases the virus particles, allowing them to infect more healthy cells and continue to reproduce.
W Is for Watson-Crick Base Pairing
The name given to the standard base-pairing rules of nucleic acids:
- Adenine (A) pairs with thymine (T) (Or uracil (U) in RNA)
- Guanine (G) pairs with cytosine (C)
X Is for Xerophyte
Xerophytes are plants that are adapted to survive in very dry conditions. They often form the basis of desert ecosystems. Xerophytes are not restricted to hot climates—a desert is any place where liquid water is scarce, so plants living in the arctic tundra are also xerophytes.
Y Is for Yeast
Yeast is the name given to a very diverse group of single-celled fungi. Yeasts are used as model organisms in biology and have been instrumental in discovering how the cell cycle is controlled. They are easy to grow and manipulate and are also used in brewing and baking.
Z Is for Zooplankton
Zooplankton are microscopic animals that live in both freshwater and marine environments. They lack any serious mobility and largely drift along in currents. Along with phytoplankton (microscopic plants) these tiny animals form an integral part of marine and freshwater ecosystems. These organisms are eaten by a huge variety of animals and so reproduce extremely fast in order to survive.