Dr. Paul's Virtually Biology Show.

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S

Saccharide. A saccharide is a simple sugar or compounds built from simple sugars. Saccharides consisting of one simple sugar unit are called monosaccharides. Those built from two sugar units are disaccharides. Those from more than two but not a whole bunch are oligosaccharides, and those saccharides built from many sugar units are called polysaccharides. Glucose and fructose are common monosaccharides. Linking these two together yield the common disaccharide, sucrose. Starch. Pectin and cellulose are common polysaccharides produced by plants. Glycogen is a polysaccharide produced by animals. All of these polysaccharides are polymers of glucose.
Saprophyte(saprobe). A fungus or bacteria that feeds on the remains of other organisms. Decomposer.
Saturated and Unsaturated. These terms refer to the number of available bonds for more hydrogens in a hydrocarbon or other organic compound. If the compound is saturated then all the available bonds are taken up by hydrogens and other atoms and there are only single bonds between the carbons. In unsaturated compounds, there are double bonds between at least two of the carbons which could be broken to add more hydrogens. Fats are typically saturated while oils are unsaturated.

Science. Science is the systematic study of the natural world. Science involves the use of a systematic method called the Scientific method which has the following basic steps: Observation; question; hypothesis; prediction based on hypothesis; test(may involve experiment or more observations); conclusion(a judgment of the likelihood that the hypothesis is correct); communication to the outside world sufficient to allow others to repeat the test or build on the scientist's results This latter aspect allows for repeatability and gives science its relative objectivity.
Secondary structure. For proteins refers to that aspect of a proteins three dimensional structure which is due to the geometry of amino acid bonding between adjacent amino acids and short range hydrogen bonding. Typical secondary structures are pleated plates and alpha helices.
Second Law of Thermodynamics. The second law says that no process is 100% efficient because heat is always produced. Another way of stating this is that any process that does work produces heat. Still another way of stating this law is that in a closed system entropy tends to increase.

Segmentation. An animal body plan in which the organism is subdivided into serially arranged units. Think of your back bone or even the bones in your hands as examples of segmentation.
Self assembly. The concept that certain molecules can organize themselves spontaneously into more complex forms. The organization of protein folding and the phospholipid bi-layer are prime examples.

Selfish behavior. Behavior that increases the organism's ability to survive and leave offspring while at best only incidentally benefiting other members of the same species.

Semi-conservative replication. Refers to the fact that each daughter molecule produced when DNA replicates has one of the original parent strands and one newly constructed strand.

Semi-permeable(selectively permeable). refers to a membrane that will let some material through and other other material.
Sensory neuron. A neuron leading from a sensory receptor to the central nervous system and sending information from the receptor to the central nervous system. Sensory neurons may either link to a receptor or itself be a receptor at one end, as in some pain receptors.
Sex limited. An aspect of the organism's phenotype that is only or usually expressed by one sex. For example pattern baldness runs in families but the women usually will not express it even if they have the correct genotype. Its typically only expressed in the males. Contrast sex linked.
Sex linked. Sex linked traits are traits that are due to alleles found on the X chromosome. Thus color blindness is a recessive sex linked trait because if the male has an allele for color blindness it will be expressed in that male since he does not have another X chromosome potentially carried the dominant allele for normal vision. Note carefully that females can be color blind if they are homozygous recessive. If color blindness was really sex limited, it would restricted, say to males, regardless of the female's genotype with respect to color blindness.
Shell. With reference to electrons the shell is an energy level. Roughly, the further the electrons are from the nucleus of the atom the more energy they have. Chemical properties of an atom are determined by the number of electrons in the outermost shell.

Sign stimulus. A stimulus from the environment, especially from another organism, that causes an organism to exhibit a stereotyped set of instinctive behaviors. Often called a releaser.

Siphonophora. These creatures are a group of organisms related to jellyfish, coral and sea anemones. While they superficially resemble jellyfish, each apparent organism is really a complex colony of multicellular organisms called polyps. The polyps each have their own specific function in the colony but are genetically identical to each other.

Smooth endoplasmic reticulum(Smooth ER). A series of membranous networks involved in the final modification of proteins and the synthesis of lipids. Contrast rough ER.
Social behavior. Behavior involving interactions with other members of the same species. There are different degrees of such interaction, thus even "solitary" animals such as tigers will exhibit at least some degree of social behavior, if only during mating.

Sociobiology. The branch of biology that studies the evolutionary basis of social behavior.

Sol. A mixture involving a solvent such as water and very large molecules or groups of molecules that are mixed into the solvent. The large groups of molecules are prevented from settling out by a combination of hydration shells and kinetic energy from the water molecules. A change in pH can cause these large molecules to settle out and not be available to the cell. A gel is similar but the molecules are in a mesh work which holds the solvent molecules in place. Think "Jello".
Somatic. Refers to body. For instance, somatic cells refers to all the cells in the body except for the germ cells.
Somatic nervous system. That part of the peripheral nervous system which is under voluntary control..ok more or less under voluntary control. Contrast autonomic nervous system.

Solvent. A substance, usually a liquid or gas into which another substance will dissolve. The substance being dissolved is the solute and the two substances together is the solution. Obviously, such as in the cell solutions may be a mixture of many solutes in the solvent water. We are interested in these three terms because cells often operate at particular concentrations of solutes and water.

Spatial learning. The ability of organisms learn relationships and perhaps solve problems in two or three dimensional space. Examples of this type of learning involve the navigational abilities of bees and birds as well as our abilities to get around in large cities.
Speciation. The evolutionary processes by which new kinds of organisms evolve from preexisting kinds or evolve from currently existing kinds.

Species. In biology a species generally taken to be either the lowest level of taxonomic classification or a group of interbreeding individuals that are reproductively isolated from other organisms. A species in biology is not a "kind" in Plato's sense of the word.

Species isolating mechanisms. Diverging behaviors, physical attributes, or habitat preferences found in closely related species that have the effect of preventing mating and or the production of offspring. Species isolating mechanism may be prezygotic or post zygotic. Pre-mating or post mating.
Sphincter. A ring of smooth muscle that can close off a tubular structure such as an arteriole or part of the colon.
Spindle. In mitosis and meiosis the microtubule assembly to which the chromosomes become attached.
Spore. A resistant single cell. In plants the spores are products of meiosis produced on special leaves called sporophylls. The plant bearing the sporophylls is called the sporophyte. Spores that land in suitable habitat germinate and develop in Haploid plants called gametophytes.
Sporophyte. In plants, a multicellular stage that produces haploid spores by meiosis. What we think of as a plant in everyday speech refers to the sporophyte stage of the plant life cycle.
Stamen. The part of the flower that produces pollen. Basically a micro (or small) sporophyll. The stamen part where the pollen. grains develop is the anther. The narrow stalk supporting the anther is the filament.
Starch. Any one of a number of polysaccharides produced by plants and other photosynthetic organisms as a means of storing excess carbohydrate. For example the white part of a potato consists of grains of starch stored in a specialized ground tissue. When the energy in the starch is needed by the plant, it is broken down to sucrose for transport and when the sucrose reaches the cells where it is needed it is converted to glucose and or fructose.
cholesterol moleculeSteroid. A class of lipids characterized by a four carbon ring structure. Male hormones(androgens) and female hormones(estrogens) are steroids as is cholesterol. Cholesterol is an important component in cell membranes, increasing the flexibility of the membrane.
Stigma. The part of the pistil that receives the pollen grain.
Stoma. In plants, the small pores located usually on the lower surface of leaves through which gas exchange and transpiration takes place.
Stroma. The region inside the chloroplast, outside the grana, where the Calvin-Benson cycle of photosynthesis takes place.
Style. The elongated part of the pistil just below the stigma.
Substrate. In biochemistry, the substances being acted up by an enzyme.
Surface tension. The tendency of water to behave is if it is covered by a semi-rigid film.
Suspension. A mixture of a liquid and small particles that stay in the liquid rather than settling out because of kinetic energy of the solvent's molecules. Milk is a good example of a suspension. The cytoplasm of the cell is, at least in part, a suspension of various particles.
Symbiosis. The living together in close association of two or more species. In some parts of the world symbiosis is used solely referring to a beneficial relationship, but the modern meaning is much broader.
Sympatric speciation. The process by which new species evolve within the range of its parent species without any sort of geographical isolation. This type of speciation is well documented in plants where it typically involves polyploidy. Circumstantial evidence suggests that this mode of speciation may be important in certain groups of animals as well.