F Biological TERMS 
facilitated diffusion The passage of materials through the cell's plasma membrane aided by a concentration gradient and a transport protein.
facilitation In primary succession, the actions or qualities of earlier species that in some way assist growth of later species.
Fallopian tube The tube that transports the ovulated egg from the ovary to the uterus in humans. Fertilization occurs inside this tube.
family A taxonomic grouping of related genera. This category lies below order and above genus. Humans are in the family Hominidae.
fatty acid A long chain of carbon and hydrogen atoms punctuated at the end with an acid carboxyl (COOH) group. Fatty acids are found in glycerides (common lipids) attached to the alcohol "head."
fertilization The fusion of two gametes to form a zygote. In humans (and most other organisms), the haploid sperm and egg fuse, and the resulting zygote is diploid.
fetus An organism at a later stage of development. In humans, the developing organism from the start of the ninth week of development to the moment of birth.
fever A sustained, elevated body temperature which speeds up the activities of the immune system and may therefore more quickly rid the body of an infection. In humans, fever is defined as a continued body temperature greater than 37.2 oC (99 oF).
fiber In skeletal muscle, a single elongated muscle cell, containing hundreds of long, thin myofibrils that run the length of the cell.
fibrinogen A type of protein in blood plasma that, under certain conditions, forms into long strands of fibrin, the framework molecule of a blood clot.
fibrous root system A plant root system that consists of many roots all about the same size.
filament The part of a stamen (male reproductive part of a flower) that is shaped like and functions as a stalk, and has an anther at the top.
filtrate The fluid that is passed from the blood in the glomerulus into Bowman's capsule of the nephron in the first stage of urine formation in the kidney.
filtration The process of passing fluid from the blood into the kidney at Bowman's capsule. Materials such as red blood cells, proteins, and lipids are too large to pass out of the capillaries of the glomerulus, and these remain in the blood.
first filial generation The offspring of the parental generation in an experimental cross.
first law of thermodynamics Energy cannot be created or destroyed, but only transformed from one form to another. The process of transformation of energy is never totally efficient, and some energy is always converted into heat.
fitness The success of an organism, relative to other members of its population, in passing on its genes to offspring. Fitness is a relative concept only; some organisms are better than others at passing on their genes in a given environment at a given point in time.
fixation The process of a gas being incorporated into an organic molecule.
flagella(singular, flagellum) Long, whip-like cell extensions, made of microtubules, that help the cell move. Only one or a few flagella will occur on any given cell. The tail of a sperm cell is a flagellum that enables it to swim to an unfertilized egg.
fluid-mosaic model The widely accepted view of the cell membrane as a mosaic of proteins moving within the fluid that is the phospholipid bilayer.
follicle In the vertebrate ovary, the complex of the oocyte (developing egg) and the cells and fluids that surround and nourish the oocyte.
follicle stimulating hormone (FSH) A hormone, secreted by the anterior pituitary, that promotes egg development and stimulates secretion of estrogens in women, and supports sperm production and testosterone secretion in men.
forensic DNA typing Popularly known as genetic fingerprinting, this technique compares the number of copies of short, repeated stretches of DNA between DNA samples. These DNA patterns are highly variable among individuals, so a sample can be matched to a suspect.
formed elements Cells and cell fragments that form the non-fluid portion of blood. Formed elements include red blood cells, white blood cells, and platelets. Contrast with plasma, the fluid portion of blood, consisting mostly of water.
founder effect The effect on the genetic makeup of a small subpopulation migrating to a new area and starting a new population. The genetic makeup of the few founder individuals defines the gene pool for the new population.
