Z: Zooplankton

Zooplankton: A collective term for the nonphotosynthetic organisms present in plankton.

Y: Yeast

Yeast: A unicellular fungus that lives in liquid or moist habitats, primarily reproducing asexually by simple cell division or by budding of a parent cell.

X: Xylem

Xylem: The tube-shaped, nonliving portion of the vascular system in plants that carries water and minerals from the roots to the rest of the plant.

W: Wild Type

Wild Type: An individual with the normal phenotype.

V: Ventricle

Ventricle: A muscular chamber of the heart that receives blood from an atrium and pumps blood out of the heart, either to the lungs or to the body tissues.

U: Urethra

Urethra: A tube that releases urine from the body near the vagina in females or through the penis in males; also serves in males as the exit tube for the reproductive system.

T: T-cell

T cell: A type of lymphocyte responsible for cell-mediated immunity that differentiates under the influence of the thymus.

S: Secondary Consumer

Secondary Consumer: A member of the trophic level of an ecosystem consisting of carnivores that eat herbivores.

R: Reptilia

Reptilia: The vertebrate class of reptiles, represented by lizards, snakes, turtles, and crocodilians.

P: Placenta

Placenta: A structure in the pregnant uterus for nourishing a fetus with the mother's blood supply; formed from the uterine lining and embryonic membranes.

O: Oogenesis

Oogenesis: The process in the ovary that results in the production of female gametes.

N: Null Hypothesis

Null Hypothesis: In statistical analysis, a hypothesis proposing that there is no statistically significant difference between the observed results of an experiment and the expected results.

M: Macrophage

Macrophage: An amoeboid cell that moves through tissue fibers, engulfing bacteria and dead cells by phagocytosis.

L: Law of Segregation

Law of Segregation: Mendel's first law, stating that allele pairs separate during gamete formation, and then randomly re-form pairs during the fusion of gametes at fertilization.

K: Kinesis

Kinesis: A change in activity rate in response to a stimulus.

J: Joule

Joule (J): A unit of energy: 1 J = 0.239 cal; 1 cal = 4.184 J.

I: Imprinting

Imprinting: A type of learned behavior with a significant innate component, acquired during a limited critical period.

H: Habituation

Habituation: A simple kind of learning involving a loss of sensitivity to unimportant stimuli, allowing an animal to conserve time and energy.

G: Gamete

Gamete: A haploid egg or sperm cell; gametes unite during sexual reproduction to produce a diploid zygote.

F: Fixed Action Pattern

Fixed Action Pattern: A highly stereotypical behavior that is innate and must be carried to completion once initiated.

E: Endoskeleton

Endoskeleton: A hard skeleton buried within the soft tissues of an animal, such as the spicules of sponges, the plates of echinoderms, and the bony skeletons of vertebrates.

D: Darwinian Fitness

Darwinian fitness: A measure of the relative contribution of an individual to the gene pool of the next generation.

C: Catalyst

Catalyst: A substance that lowers the activation energy of a chemical reaction by forming a temporary association with the reacting molecules; as a result, the rate of the reaction is accelerated. Enzymes are catalysts.

B: Bacteriophage

Bacteriophage: A virus that parasitizes a bacterial cell.

A: Anticodon

Anticodon: A nucleotide base triplet in a transfer RNA molecule that pairs with a complementary base triplet, or codon, in a messenger RNA molecule.