Science / Biology Glossary

Amniocentesis: A method of prenatal testing in which amniotic fluid is withdrawn from the uterus through a needle. The fluid and the fetal cells it contains are analyzed to detect biochemical or chromosoma . . . View Full Definition

Amniote Egg: An egg with compartmentalized sacs (a liquid-filled sac in which the embryo develops, a food sac, and a waste sac) that allowed vertebrates to reproduce on land.

Amoebocytes: Amoeboid cells in sponges that occur in the matrix between the epidermal and collar cells. They transport nutrients.

Amphibians: Class of terrestrial vertebrates which lay their eggs (and also mate) in water but live on land as adults following a juvenile stage where they live in water and breathe through gills. Amphi . . . View Full Definition

Anabolic Reactions: Reactions in cells in which new chemical bonds are formed and new molecules are made; generally require energy, involve reduction, and lead to an increase in atomic order.

Anaerobic: Refers to organisms that are not dependent on oxygen for respiration.

Analogous Structures: Body parts that serve the same function in different organisms, but differ in structure and embryological development; e. g., the wings of insects and birds.

Anaphase: Phase of mitosis in which the chromosomes begin to separate.

Anaphylaxis: A severe allergic reaction in which histamine is released into the circulatory system; occurs upon subsequent exposure to a particular antigen; also called anaphylactic shock.

Androecium: Collective term applied to all of the male (stamen) parts of the flower.

Aneuploidy: Variation in chromosome number involving one or a small number of chromosomes; commonly involves the gain or loss of a single chromosome.

Angina: Chest pain, especially during physical exertion or emotional stress, that is caused by gradual blockage of the coronary arteries.

Angiosperms: Flowering plants. First appearing at least 110 million years ago from an unknown gymnosperm ancestor, flowering planbts have risen to dominance in most of the worlds floras. The male gametop . . . View Full Definition

Animalia: Animal Kingdom. Multicellular eukaryotic group characterized by heterotrophic nutritional mode, usually organ and tissue development, and motility sometime during the organisms life history.

Annuals: Plants that grow and reproduce sexually during one year.

Antagonistic Muscles: A pair of muscles that work to produce opposite effects&emdash;one contracts as the other relaxes: for example, the bicep and tricep muscles on opposite sides of your upper arm.

Anther: The top of a stamens filament; divided into pollen sacs in which the pollen grains form.

Antibiotic Resistance: Tendency of certain bacteria to develop a resistance to commonly over-used antibiotics.

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