Category: Biology Dictionary A

Definition Artificial selection or selective breeding describes the human selection of breeding pairs to produce favorable offspring. This applies to all organisms – from virus to four-footer, and from pet to food source. Artificial selection aims to increase the productive or esthetic value of an organism to our advantage. Artificial Selection Examples In the field…

Definition Articular cartilage is found only in diarthroidal joints (synovial joints), and is comprised of hyaline cartilage – a particularly smooth type of cartilage which allows for easy articulation, increased weight distribution, and shock absorption. Articular Cartilage Explained Articular cartilage’s role is often better understood in patients in which it has degenerated (usually due to…

Arthropods Definition An “arthropod” is an invertebrate animal that has an exoskeleton, a segmented body, and jointed appendages. The following families of organisms are all examples of arthropods: It may help to remember that the term “arthropod” comes from the Greek words for “jointed foot.” If the organism has an exoskeleton with joints between its…

Archaebacteria Definition Archaebacteria are a type of single-cell organism which are so different from other modern life-forms that they have challenged the way scientists classify life. Until the advent of sophisticated genetic and molecular biology studies allowed scientists to see the major biochemical differences between archaebacteria and “normal” bacteria, both were considered to be part…

Apoptosis Definition Apoptosis is a process that occurs in multicellular when a cell intentionally “decides” to die. This often occurs for the greater good of the whole organism, such as when the cell’s DNA has become damaged and it may become cancerous. Apoptosis is referred to as “programmed” cell death because it happens due to…

Apoplexy Definition and Explanation Apoplexy is a term used to describe internal bleeding and the accompanying symptoms. Historically, the term originated in the medical profession to describe the phenomenon of patients becoming suddenly weak and becoming unconscious. It was not well understood why an apoplexy would occur until the mid to late 1800s. Patients could…

Apical Meristem Definition The apical meristem is the growth region in plants found within the root tips and the tips of the new shoots and leaves. Apical meristem is one of three types of meristem, or tissue which can differentiate into different cell types. Meristem is the tissue in which growth occurs in plants. Apical is…

Antioxidant Definition Antioxidants are molecules that prevent the oxidation of other molecules. Oxidation is a chemical reaction in which electrons are lost. In living things, this process can be harmful, leading to the breakdown of organic molecules. One challenge of life on Earth is that the same thing that makes oxygen a great electron acceptor,…

Anticodon Definition Anticodons are sequences of nucleotides that are complementary to codons. They are found in tRNAs, and allow the tRNAs to bring the correct amino acid in line with an mRNA during protein production. During protein production, amino acids are bound together into a string, much like beads on a necklace. It’s important that…

Antibody Definition An antibody is a specialized defense protein synthesized by the vertebrate immune system. These small structures are actually made of 4 different protein units. The ends of the molecule are variable, and can be adapted to bind to any molecule. The shape is determined by the antigens in the system which are causing damage. Special…