On-Line Biology Book: GLOSSARY

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labia majora  The outer folds of skin that cover and protect the genital region in women. PICTURE

labia minora  Thin membranous folds of skin outside the vaginal opening. PICTURE

lactose intolerance  A genetic trait characterized by the absence of the enzyme lactase, which breaks down lactose, the main sugar in milk and other dairy products.

Langerhans' cells  Epidermal cells that participate in the inþammatory response by engulfing microorganisms and releasing chemicals that mobilize immune system cells.

large intestine  Consists of the cecum, appendix, colon, and rectum; absorbs some nutrients, but mainly prepares feces for elimination.

larva  A stage in the development of many insects and other organisms including sea urchins and sponges. In sponges, sexual reproduction results in the production of motile ciliated larvae.

larynx  A hollow structure at the beginning of the trachea. The vocal cords extend across the opening of the larynx.

lateral roots Roots extending away from the main (or taproot) root.

latitudinal diversity gradient  The decrease in species richness that occurs as one moves away from the equator.

latitudinal gradient  As latitude increases, a gradient of cooler, drier conditions occurs.

Laurasia The northern part of the supercontinent of Pangaea, composed of the present-day North America, Europe, and Asia.

Laurentia Name applied to the "core" of North America in the times from the breakup of the precambrian supercontinent Rodinia to the formation of Pangaea.

law of the minimum  Holds that population growth is limited by the resource in shortest supply.

L-dopa  A chemical related to dopamine that is used in the treatment of Parkinson's disease.

leaf primordia Young leaves, recently formed by the shoot apical meristem, located at the tip of a shoot.

leaf veins Vascular tissue in leaves, arranged in a net-like network (reticulate vennation) in dicots, and running parallel (parallel vennation) to each other in monocots.

leaves  The site of photosynthesis; one of the three major organs in plants.

leukocytes  White blood cells; primarily engaged in fighting infection.

lichens  Autotrophic organisms composed of a fungus (sac or club fungus) and a photosynthetic unicellular organism (e.g., a cyanobacterium or alga) in a symbiotic rela