OSAT Biological Sciences (110) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Emergent properties

Characteristics that arise at each higher level of biological organization and cannot be predicted from the properties of the component parts alone.

Independent variable

The factor the researcher deliberately manipulates or changes in an experiment, as opposed to the dependent variable, which is measured as the response.

Hydrogen bonding in water

Attraction between the partially positive hydrogen of one water molecule and the partially negative oxygen of another; explains cohesion, high specific heat, and solvent ability.

pH scale

A logarithmic scale defined as pH = −log[H+]; each one-unit change represents a tenfold change in hydrogen ion concentration, with 7 neutral at 25 °C.

Biological magnification

The increasing concentration of fat-soluble toxins in organisms at successively higher trophic levels, because the toxin is retained rather than excreted.

Buffer

A substance that resists large changes in pH by absorbing excess hydrogen ions or releasing them when the solution becomes too basic.

Endosymbiotic theory

The proposal that mitochondria and chloroplasts originated from bacteria engulfed by ancestral eukaryotic cells, supported by their double membranes, circular DNA, and 70S ribosomes.

Fluid mosaic model

The description of membranes as a phospholipid bilayer studded with movable proteins, cholesterol, and glycoproteins, giving the membrane a fluid, patchwork character.

Facilitated diffusion

Passive movement of polar molecules or ions across a membrane through channel or carrier proteins, down their concentration gradient and without ATP expenditure.

Active transport

Movement of substances against their concentration gradient using membrane proteins and cellular energy, usually ATP, as in the sodium-potassium pump.

Osmosis

The diffusion of water across a selectively permeable membrane from a region of higher water concentration to one of lower water concentration, that is, toward higher solute.

Competitive inhibitor

A molecule that binds the enzyme's active site and blocks substrate access; its effect can be reduced by increasing substrate concentration.

Glycolysis

The first stage of cellular respiration, occurring in the cytoplasm, which splits glucose into two pyruvate molecules and yields a net two ATP and two NADH.

Calvin cycle

The light-independent reactions in the chloroplast stroma in which rubisco fixes carbon dioxide into G3P, using ATP and NADPH produced by the light reactions.

Semiconservative replication

DNA replication in which each new double helix contains one original parental strand and one newly synthesized strand, as demonstrated by the Meselson-Stahl experiment.

Central dogma

The flow of genetic information from DNA to RNA through transcription, and from RNA to protein through translation at the ribosome.

Law of segregation

Mendel's principle that the two alleles of a gene separate during meiosis, so each gamete carries only one allele for each gene.

Incomplete dominance

A pattern in which the heterozygous phenotype is intermediate between the two homozygous phenotypes, as when red and white flowers produce pink offspring.

Codominance

A pattern in which both alleles are fully expressed in the heterozygote, as in AB blood type, where both A and B antigens appear on red blood cells.

Sex-linked trait

A trait controlled by a gene on a sex chromosome, usually the X; recessive X-linked disorders appear more often in males because they are hemizygous.

Genetic drift

Random change in allele frequencies in a population, especially strong in small populations; bottleneck and founder effects are examples.

Hardy-Weinberg equilibrium

A null model in which allele frequencies stay constant across generations given no mutation, no migration, no selection, infinite population size, and random mating.

Allopatric speciation

Speciation that occurs when a geographic barrier separates populations, preventing gene flow and allowing reproductive isolation to evolve independently.

Homologous structures

Body parts in different species that share a common evolutionary origin and similar underlying anatomy, though they may differ in function, such as the forelimbs of mammals.

Xylem and phloem

The two vascular tissues of plants: xylem carries water and dissolved minerals upward from roots, while phloem transports sugars bidirectionally between sources and sinks.

Transpiration-cohesion-tension

The mechanism of water ascent in plants: evaporation at stomata pulls water upward through xylem, aided by cohesion between water molecules and adhesion to vessel walls.

Negative feedback

A homeostatic mechanism in which a change triggers a response that reverses the original deviation, as when rising blood glucose stimulates insulin release.

Carrying capacity

The maximum population size an environment can sustain indefinitely given available resources; symbolized K in the logistic growth equation.

Logistic growth

Population growth that slows as the population approaches carrying capacity, following dN/dt = rN(K−N)/K and producing an S-shaped curve.

Mutualism

A species interaction in which both participants benefit, such as mycorrhizal fungi supplying nutrients to plants in exchange for sugars.

Primary succession

Ecological succession beginning on bare substrate with no soil, such as new volcanic rock, where lichens and mosses act as pioneer species.

Nitrogen fixation

Conversion of atmospheric nitrogen gas into ammonia by bacteria such as Rhizobium in root nodules, making nitrogen available for building amino acids and nucleic acids.