Respiration occurring in the absence of oxygen. In a process not involving oxygen, it ensures that foodstuffs, usually carbohydrates, are partially oxidised, with the release of chemical energy. The energy yield of this type of respiration is lower than that of aerobic respiration. It occurs in bacteria and yeast as well as in muscle tissue …
Category Archives: Uncategorized
Angelman’s syndrome
A genetic disorder dominated by learning disability, ataxia, jerky puppet-like movements, epilepsy, and various behaviour problems, including some autistic features; associated with loss of maternal alleles on chromosome 15q11-13 and other genetic abnormalities (see figure below). Some 75% of those with the syndrome have a similar defect as found in the Prader-Willi syndrome, but occurring …
Anemia
A condition in which there is a low red blood cell count in the blood, usually marked by a decrease in hemoglobin, the pigment in red blood cells that transports oxygen. It can be caused by many different conditions, including iron deficiency. Symptoms may include fatigue, weakness, headache, and dizziness. Common in pregnancy, it is …
Anencephaly
A congenital malformation due to failure of the neural tube to close at the rostral end, which consists of the absence of the cerebral hemispheres in all cases and of the diencephalon and midbrain in most cases (see figure below). Macerated brain stem tissue is visible through a wide defect in the skin and skull …
Androgen
First discovered in 1936, it is a male sex steroid hormone in vertebrates produced by the testes and to a lesser extent by the adrenal cortex, such as testosterone, that controls the development and maintenance of sexual organs and secondary sexual characteristics in males. Also called androgenic hormone and testoid. See Adolescent growth spurt, Adolescent …
Anaphase
Discounting interphase in meiosis, the third stage of cell division in the first division of meiosis (following prophase and the first metaphase). In the first anaphase of meiosis, the paired homologous chromosomes separate and the half chromosomes move to opposite ends of the spindle. In the second anaphase of the second division of meiosis, the …
Analogy (biology)
In 1843, the comparative anatomist Richard Owen (1804-1892) introduced the term into evolutionary biology as he did with homology. It means similarity in function, but not structure, due to convergent evolution. Thus, while the wings of birds and bats do not stem from a common ancestor, they evolved conversantly to have the same function (viz., …
Analysis of variance (ANOVA)
The statistical analysis of mean differences that are traced back to the effects of one or more factors (or independent variables). The simplest ANOVA is a one-way design in which N subjects are (randomly) allocated to a number of different levels of a single factor. Strictly speaking, ANOVA does not analyse variance per se, but …
Analogy (as a trope)
A form of inductive reasoning or logical inference based on the assumption that if two things are alike in some features, then they are probably alike in other respects. Analogous features are those with similar functions, but not necessarily similar structures. A well-worn example is drawing an analogy between the operation of a (digital) computer …
Amygdala
Also called the amygdaloid nucleus, it is a key, almond-shaped, bilateral structure in the limbic system of the forebrain (see figure below), involved in emotion recognition and other social emotional functions such as fear, aggression and defensive behaviours, as well as learning and memory. Connected with the prefrontal cortex, hypothalamus, hippocampus and cingulate gyrus. Many …