Science / Biology Glossary

Salivary Amylase: An enzyme secreted by the salivary glands that begins the breakdown of complex sugars and starches.

Salivary Glands: Glands that secrete salvia into the mouth.

Saprophytes: Organisms that obtain their nutrients from decaying plants and animals. Saprophytes are important in recycling organic material.

Sapwood: Layers of secondary xylem that are still functional in older woody plants; visible as the outer lighter areas in the cross section of a tree trunk.

Sarcomeres: The functional units of skeletal muscle; consist of filaments of myosin and actin.

Saturated Fat: A fat with single covalent bonds between the carbons of its fatty acids.

Schwann Cells: Specialized glial cells that form the myelin sheath that coats many axons. Cells surrounding the axons of some neurons, thus forming the myelin sheath.

Scientific Method: Systematic apporach of observation, hypothesis formation, hypothesis testing and hypothesis evaluation that forms the basis for modern science.

Sclereids: Plant cells with thick secondary walls that provide the gritty textures in pears.

Sclerenchyma: One of the three major cell types in plants; have thickened, rigid, secondary walls that are hardened with lignin; provide support for the plant. Sclerenchyma cells include fibers and sclere . . . View Full Definition

Scrotum: In mammals, a pouch of skin located outside the body cavity into which the testes descend; provides proper temperature for the testes.

Second Law Of Thermodynamics (Entropy): The energy available after a chemical reaction is less than that at the beginning of a reaction; energy conversions are not 100% efficient.

Second Messenger: The mechanism by which nonsteroid hormones work on target cells. A hormone binds to receptors on the cells plasma membrane activating a molecule&emdash;the second messenger&emdash;that activ . . . View Full Definition

Secondary (Lateral) Meristems: Plant meristems that produce secondary growth from a cambium.

Secondary Cell Wall: In woody plants, a second wall inside the primary cell wall; contains alternating layers of cellulose and lignin.

Secondary Compounds: Plant products that are not important in metabolism but serve other purposes, such as attracting animals for pollination or killing parasites.

Secondary Extinction: The death of one population due to the extinction of another, often a food species.

Secondary Growth: Cells in a plant that are produced by a cambium. Increase in girth of a plant due to the action of lateral meristems such as the vascular cambium. The main cell produced in secondary growth . . . View Full Definition

Secondary Immunity: Resistance to an antigen the second time it appears. Because of the presence of B and T memory cells produced during the first exposure to the antigen, the second response is faster and more . . . View Full Definition

Secondary Macronutrients: Elements that plants require in relatively small quantities: calcium, magnesium, and sulfur.

Secondary Phloem: Phloem produced by the vascular cambium in a woody plant stem or root.

Secondary Structure: The structure of a protein created by the formation of hydrogen bonds between different amino acids; can be a pleated sheet, alpha helix, or random coil. Shape of a protein caused by attract . . . View Full Definition

Secondary Xylem: Xylem produced by the vascular cambium in a woody plant stem or root; wood.

Secretin: A hormone produced in the duodenum that stimulates alkaline secretions by the pancreas and inhibits gastric emptying.

Secretion: The release of a substance in response to the presence of food or specific neural or hormonal stimulation.

Page: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53