Definition A sensory neuron (sometimes referred to as an afferent neuron) is a nerve cell that detects and responds to external signals. Sensory neurons receive information via their receptors, which are part of the peripheral nervous system, and convert this information into electrical impulses. These impulses act as signals and are passed on to the … Read more

Convergent Evolution Definition Convergent evolution is the process in which organisms that are not closely related independently evolve similar features. Adaptions may take the form of similar body forms, colors, organs and other adaptions which make up the organism’s phenotype. Convergent evolution creates analogous structures or ’homoplasies’, those which have similar forms or functions between … Read more

Definition of Sexual Reproduction Sexual reproduction is the process in which new organisms are created, by combining the genetic information from two individuals of different sexes. The genetic information is carried on chromosomes within the nucleus of specialized sex cells called gametes. In males, these gametes are called sperm and in females the gametes are … Read more

Ribosomal RNA Definition Ribosomal ribonucleic acid (rRNA) is the RNA component of ribosomes, the molecular machines that catalyze protein synthesis. Ribosomal RNA constitute over sixty percent of the ribosome by weight and are crucial for all its functions – from binding to mRNA and recruiting tRNA to catalyzing the formation of a peptide bond between … Read more

Fundamental Niche Definition The niche of any organism is the role that it fills within an ecosystem as a response to the amount and distribution of resources, the competition present, and the way that the organism influences those same factors. A fundamental niche is the full range of environmental conditions that a viable population of … Read more

Endocytosis Definition Endocytosis is the process of actively transporting molecules into the cell by engulfing it with its membrane. Endocytosis and exocytosis are used by all cells to transport molecules that cannot pass through the membrane passively. Exocytosis provides the opposite function and pushes molecules out of the cell.  Like all systems in the human … Read more

Transitional Epithelium Definition Transitional epithelium is a stratified tissue made of multiple cell layers, where the cells constituting the tissue can change shape depending on the distention in the organ. When the organ is filled with fluid, cells on the topmost layer of this epithelium can stretch and appear flattened. Alternately, they can also appear … Read more

Fat cells are the basic building blocks of fat tissue. Fat (or adipose) tissue is found throughout the human body and is concentrated beneath the skin, between the muscles, and around the internal organs. The primary functions of fat cells are to store lipids for energy, to produce and secret hormones, and to release heat … Read more

Definition At the base of the mastoid area of the temporal bone, the mastoid process is a smooth conical projection of bone. Among the muscles attached to it are the occipitofrontalis and sternocleidomastoid muscles, as well as the splenius capitis muscle. Mastoid Process Location On the underside of the mastoid portion of the temporal bone, … Read more

Phospholipid Definition A phospholipid is a type of lipid molecule that is the main component of the cell membrane. Lipids are molecules that include fats, waxes, and some vitamins, among others. Each phospholipid is made up of two fatty acids, a phosphate group, and a glycerol molecule. When many phospholipids line up, they form a … Read more