Definition Primary succession is the orderly and predictable series of events through which a stable ecosystem forms in a previously uninhabited region. Primary succession occurs in regions characterized by the absence of soil and living organisms. Primary Succession Overview Primary succession begins with the appearance of pioneer species – lichen, mosses, and fungi – all … Read more

Lytic Cycle Definition The lytic cycle is named for the process of lysis, which occurs when a virus has infected a cell, replicated new virus particles, and bursts through the cell membrane. This releases the new virions, or virus complexes, so they can infect more cells. The lytic cycle is often accompanied by the lysogenic … Read more

Synapomorphy Definition A synapomorphy is a shared, derived character, common between an ancestor and its descendants. A character, or trait, is anything observable about the organism. It may be the size of the organism, the type of skin covering the organism has, or even things like eye color.  A character may also be considered a … Read more

Operon Definition An operon is a cluster of functionally-related genes that are controlled by a shared operator. Operons consist of multiple genes grouped together with a promoter and an operator. Operons are present in prokaryotes (bacteria and archaea), but are absent in eukaryotes.  In some situations multiple operons are controlled by the same regulatory protein; … Read more

Definition The biceps femoris is a muscle found at the back of the thigh. Part of the biceps femoris belongs to the hamstrings muscle group. The biceps femoris is a two-part spindle-shaped muscle. It has two heads: the long head and the short head. The two heads have different sites of origin and are innervated … Read more

There are approximately 200 different types of cells in the human body, but all cells on Earth fit into just two categories; prokaryotes, and eukaryotes. The Two Types of Cells on Earth All cells on Earth can be classified as either prokaryotic cells or eukaryotic cells. Eukaryotic organisms may be multicellular or unicellular, but prokaryotes … Read more

Stratified Squamous Epithelium Definition Stratified squamous epithelia are tissues formed from multiple layers of cells resting on a basement membrane, with the superficial layer(s) consisting of squamous cells. Underlying cell layers can be made of cuboidal or columnar cells as well. Functions of Stratified Squamous Epithelia Epithelia consisting of multiple cell layers are generally found … Read more

Gluconeogenesis Definition In contrast to glucose that is broken down from the long storage molecule glycogen, glucose is synthesized in the body through glucoseconeogenesis. It occurs primarily in the liver, but also in smaller amounts in the kidneys and small intestines. Glycolysis, the breakdown of glucose molecules into their components, is the opposite process of … Read more

Spongy Bone Definition An animal’s spongy bone, also known as cancellous bone or trabecular bone, is very porous. It contains red bone marrow and is highly vascularized. A spongey bone is usually found at the end of a long bone (the epiphyses), surrounded by a harder, compact bone.  As well as the vertebrae, the ribs, … Read more

Definition A biotic factor is a living thing that has an impact on another population of living things or on the environment. Abiotic factors do the same thing, but they are non-living. Together, biotic and abiotic factors make up an ecosystem.  To survive, biotic factors need abiotic factors. In turn, biotic factors can limit the … Read more