Science / Biology Glossary

Brain Stem: The portion of the brain that is continuous with the spinal cord and consists of the medulla oblongata and pons of the hindbrain and the midbrain.

Bronchi: Tubes that carry air from the trachea to the lungs (sing.: bronchus).

Bronchioles: Small tubes in the lungs that are formed by the branching of the bronchi; terminate in the alveoli.

Bronchitis: A respiratory disorder characterized by excess mucus production and swelling of the bronchioles; caused by long-term exposure to irritants such as cigarette smoke and air pollutants.

Brown Algae: Multicellular protistans placed in the Division Phaeophyta, includes kelp.

Brush Border: The collection of microvilli forming a border on the intestinal side of the epithelial cells of the small intestine.

Bryophytes: The nonvascular plants, characterized by life cycles dominated by the gametophyte phase. This group includes the mosses, liverworts, and hornworts, which lack lignified conducting tissues.

Bud Sports: Buds that produce fruit that is different from the rest of the fruit on the tree; vegetatively propagated by grafting cuttings onto another plant.

Budding: 1. Asexual production of new organisms; usually found in yeast; 2. the process by which HIV and similar viruses leave the cell (other than by lysing).

Buffers: Chemicals that maintain pH values within narrow limits by absorbing or releasing hydrogen ions.

Bulbourethral Glands: Glands that secrete a mucus-like substance that is added to sperm and provides lubrication during intercourse.

Bursae: Small sacs lined with synovial membrane and filled with synovial fluid; act as cushions to reduce friction between tendons and bones.

Calcitonin: A hormone produced by the thyroid that plays a role in regulating calcium levels.

Calcium Carbonate: Chemical that also occurs in limestone and marble.

Calvin Cycle: Series of biochemical, enzyme-mediated reactions during which atmospheric carbon dioxide is reduced and incorporated into organic molecules, eventually some of this forms sugars. In eukaryot . . . View Full Definition

Cambium: A lateral meristem in plants. Types of cambiums include vascular, cork, and intercalary.

Cambrian: Geologic period that begins the Paleozoic Era 570 million years ago. Marked in its beginning by a proliferation of animals with hard, preservable parts, such as brachiopods, trilobites, and . . . View Full Definition

Campodactyly: A dominant trait in which a muscle is improperly attached to bones in the little finger, causing the finger to be permanently bent.

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