FY12CE Biology flashcards

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

Hydrogen bond

Weak attraction between a partially positive hydrogen atom covalently bound to O or N and a lone pair on another electronegative atom; gives water cohesion, high specific heat, and surface tension.

Dehydration synthesis

Reaction joining two monomers by removing a hydroxyl from one and a hydrogen from the other, forming a covalent bond and releasing water; builds polysaccharides, proteins, and nucleic acids.

Enzyme active site

Pocket of the enzyme where substrate binds, lowering activation energy by positioning reactants and straining bonds. Its shape depends on temperature, pH, and ionic conditions.

Competitive inhibition

Inhibitor resembles the substrate and binds the active site reversibly, so it raises apparent Km while Vmax stays the same because more substrate can outcompete it.

Osmosis

Net diffusion of water across a selectively permeable membrane from higher water potential to lower, meaning toward the side with higher solute concentration.

Calvin cycle

Light-independent reactions in the chloroplast stroma where rubisco fixes carbon dioxide into three-carbon compounds, using ATP and NADPH from the light reactions to build sugar.

Glycolysis

First stage of respiration in the cytosol: glucose is split into two pyruvate molecules, with a net gain of two ATP and two NADH, requiring no oxygen.

Law of segregation

Mendel's principle that the two alleles of a gene separate during meiosis so each gamete receives only one allele, restored at fertilization.

Testcross

Cross of an individual with unknown genotype against a homozygous recessive; appearance of recessive offspring proves the unknown parent carried a recessive allele.

Codominance

Condition where both alleles are fully expressed in the heterozygote phenotype, as in AB blood type, distinct from incomplete dominance where the phenotype is intermediate.

Semiconservative replication

Each new DNA molecule contains one original parental strand and one newly synthesized strand, because the helix unwinds and each strand acts as a template.

Frameshift mutation

Insertion or deletion of a number of nucleotides not divisible by three; it shifts the reading frame of every downstream codon, usually producing a nonfunctional protein.

X-linked recessive

Allele on the X chromosome expressed in males who carry only one X; affected fathers pass the allele to daughters as carriers but never to sons.

Hardy-Weinberg equilibrium

Allele frequencies stay constant when there is no mutation, migration, selection, drift, or non-random mating; p + q = 1 and p^2 + 2pq + q^2 = 1.

Genetic drift

Random change in allele frequencies from chance sampling, strongest in small populations; bottleneck and founder effects are examples that reduce variation.

Homologous structures

Body parts with similar underlying anatomy inherited from a common ancestor but possibly differing in function, such as the forelimbs of humans, whales, and bats.

Natural selection

Heritable variation plus differential reproductive success under environmental pressure changes allele frequencies across generations; it acts on phenotypes, not individuals.

Allopatric speciation

Formation of new species after a geographic barrier separates populations, blocking gene flow so mutations and selection diverge until reproductive isolation evolves.

Binomial nomenclature

Two-part scientific name: capitalized genus followed by lowercase species, both italicized, as in Homo sapiens; it is the basic unit of Linnaean classification.

Endosymbiotic theory

Idea that mitochondria and chloroplasts arose from engulfed prokaryotes, supported by their own circular DNA, 70S ribosomes, and double membranes.

Four-chambered heart

Mammal and bird heart with two atria and two ventricles, keeping oxygenated and deoxygenated blood fully separate for efficient oxygen delivery to tissues.

Action potential

Transient reversal of membrane potential: Na+ channels open and depolarize the axon, K+ channels open and repolarize it; the signal propagates and triggers neurotransmitter release.

Negative feedback

Homeostatic loop where the response reduces the original stimulus, such as rising insulin lowering high blood glucose back toward a set point.

Xylem transport

Movement of water and dissolved minerals from roots to leaves, driven by transpiration pull, cohesion between water molecules, and adhesion to vessel walls.

Phloem transport

Pressure-flow movement of sugars from source leaves to sink tissues such as roots and fruits, driven by osmotic pressure differences between loading and unloading sites.

Countercurrent exchange

Blood in fish gills flows opposite to water flow, keeping a concentration gradient along the whole gill so oxygen uptake is maximized.

Carrying capacity

Symbol K, the maximum population size an environment can sustain long term; the logistic growth curve approaches it and growth slows as resources run short.

Ten percent rule

Only about 10 percent of energy at one trophic level is transferred to the next, the rest lost as heat and waste, limiting food chains to four or five levels.

Mark-recapture estimate

Population size estimated as (marked first sample times second sample size) divided by number of marked recaptures, assuming random mixing and no births, deaths, or migration.

Keystone species

Species whose removal causes disproportionate change in community structure, such as a predator controlling herbivore numbers that would otherwise overgraze producers.

Eutrophication

Nutrient runoff, especially nitrate and phosphate, triggers algal blooms; decomposers then deplete dissolved oxygen, harming fish and other aquatic organisms.

Primary succession

Ecological succession starting on newly exposed substrate with no soil, such as bare rock or lava; lichens and mosses are pioneer species that build soil.