Polygenic Traits Definition Rather than being controlled by just one gene, polygenic traits are controlled by multiple genes. They may be controlled by genes located near each other or even on different chromosomes. Mendel’s inheritance pattern does not apply to polygenic traits because multiple genes are involved.  As opposed to being measured discretely, they are … Read more

Phloem Definition A vascular plant’s phloem serves as a transport system for soluble organic compounds. The phloem is made up of living tissue, which uses turgor pressure and energy in the form of ATP to actively transport sugars to the plant organs such as the fruits, flowers, buds and roots; xylem, the other component of … Read more

Autotroph Definition Autotrophs are organisms that can produce their own food, using materials from inorganic sources. The word “autotroph” comes from the root words “auto” for “self” and “troph” for “food.” An autotroph is an organism that feeds itself, without the assistance of any other organisms. Autotrophs are extremely important because without them, no other … Read more

Myelin Sheath Definition The myelin sheath is a fatty insulating later that surrounds the nerve cells of jawed vertebrates, or gnathostomes. All extant members of the Gnathostomata, from fish to humans, have a myelin sheath on the axon of their nerve cells.  The oldest known members of the jawed fishes, the exinct placoderms, were armored … Read more

Law of Segregation Definition Gregor Mendel’s law of segregation states that the two alleles for each trait segregate, or separate, during the formation of gametes, and that during the formation of new zygotes, the alleles will combine at random with other alleles.  The law of segregation ensures that a parent, with two copies of each … Read more

Fossil Record Definition A fossil record is a group of fossils which has been analyzed and arranged chronologically and in taxonomic order. Fossils are created when organisms die, are incased in dirt and rock, and are slowly replaced by minerals over time. What is left is a mineral impression of an animal which once existed.  … Read more

Basics of Homeostasis In general, homeostasis refers to the balance within a system that keeps it operating within a range of conditions. Homeostasis helps animals maintain stable internal and external environments with the best conditions for it to operate.  It is a dynamic process that requires constant monitoring of all systems in the body to … Read more

Compact Bone Definition Compact bone, also known as cortical bone, is a denser material used to create much of the hard structure of the skeleton. As seen in the image below, compact bone forms the cortex, or hard outer shell of most bones in the body. The remainder of the bone is formed by cancellous … Read more