Biology flashcards

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

Endosymbiotic theory

Explanation that mitochondria and chloroplasts descended from free-living bacteria engulfed by ancestral eukaryotes, supported by their double membranes, circular DNA, and bacteria-like ribosomes.

Michaelis constant Km

Substrate concentration at which an enzyme works at half its maximum velocity; a low Km indicates high substrate affinity, while a high Km indicates weak binding.

Competitive inhibition

Inhibitor binds the enzyme active site, competing with substrate; it raises apparent Km but leaves Vmax unchanged because high substrate can outcompete the inhibitor.

Facilitated diffusion

Passive movement of polar or charged solutes down their concentration gradient through membrane proteins; requires no ATP and cannot move substances against the gradient.

Cell cycle checkpoints

Quality-control points at G1/S and G2/M that verify DNA integrity and replication before division; failure allows mutations to accumulate and can promote cancer.

Semiconservative replication

Each new DNA molecule contains one original template strand and one newly synthesized strand, confirmed by the Meselson-Stahl density gradient experiment.

Hardy-Weinberg equilibrium

Null model in which allele and genotype frequencies stay constant across generations absent mutation, migration, selection, drift, and nonrandom mating; p2 plus 2pq plus q2 equals one.

Genetic drift

Random fluctuation of allele frequencies across generations, strongest in small populations; it can fix or eliminate alleles regardless of their effect on fitness.

Testcross

Cross of an individual with unknown genotype to a homozygous recessive partner; offspring phenotypes reveal whether the unknown carried a recessive allele.

Incomplete dominance

Heterozygote displays an intermediate phenotype between the two homozygotes, such as pink flowers from red and white parents, rather than one trait masking the other.

Biological species concept

Species are groups of populations that interbreed and produce fertile offspring; reproductive isolation, not appearance alone, marks the boundary between species.

Allopatric speciation

Speciation following geographic separation of populations; isolation blocks gene flow, and mutation, drift, and selection then diverge the populations until reproductive isolation develops.

Bohr effect

Rightward shift of the hemoglobin oxygen dissociation curve when carbon dioxide rises or pH falls, promoting oxygen release in metabolically active tissues.

Negative feedback

Homeostatic mechanism in which a detected deviation from a set point triggers an effector response that reverses the deviation and restores the internal condition.

Transpiration

Evaporation of water from leaf stomata that pulls water upward through xylem under tension, driven by cohesion between water molecules and adhesion to vessel walls.

Surface area to volume ratio

Ratio that falls as an object grows larger, limiting diffusion-based exchange and requiring specialized respiratory, circulatory, or digestive structures in large organisms.

Action potential

Rapid electrical signal in neurons created by voltage-gated sodium influx during depolarization and potassium efflux during repolarization, followed by a refractory period.

Stomatal regulation

Guard cells open stomata by taking up potassium and water to become turgid; abscisic acid triggers water loss and closure during drought, reducing transpiration.

Logistic growth

Population growth that slows as density rises toward carrying capacity K; growth rate peaks at half of K and approaches zero as the population reaches K.

Carrying capacity

Maximum population size an environment can sustain indefinitely given available resources, represented by K in the logistic growth equation.

Keystone species

Species whose effect on community structure far exceeds its abundance; its removal causes cascading changes, such as sea otter loss leading to kelp forest decline.

Secondary succession

Ecological recovery after disturbance that leaves soil and seeds intact; it proceeds faster than primary succession because nutrients and propagules are already present.

Shannon diversity index

Metric combining species richness and evenness, calculated as the negative sum of each species proportion times its natural logarithm; higher values indicate greater diversity.

Trophic energy transfer

Only about ten percent of energy at one trophic level passes to the next; the rest is lost mainly as heat through respiration, limiting food chain length.

Nitrogen fixation

Conversion of atmospheric nitrogen gas into ammonia by bacteria such as Rhizobium and cyanobacteria, making nitrogen available for incorporation into amino acids and nucleic acids.

Independent variable

The factor deliberately manipulated by the researcher in an experiment, whose effect on the measured dependent variable is being tested.

Control group

Comparison group that receives no treatment or a placebo, held under identical conditions, so that treatment effects can be isolated from other influences.

Accuracy versus precision

Accuracy is closeness of a measurement to the true value; precision is how closely repeated measurements agree with each other, regardless of the true value.

Standard deviation

Measure of the spread of data points around the mean; a small value indicates tightly clustered data, while a large value indicates wide variability.

Percent error

Difference between measured and accepted value, divided by the accepted value and multiplied by one hundred, expressing experimental deviation as a percentage.

p-value

Probability of obtaining results at least as extreme as those observed if the null hypothesis were true; below alpha, usually 0.05, the null is rejected.

Confounding variable

Uncontrolled factor that varies alongside the independent variable and can produce or mask the observed effect, threatening the internal validity of an experiment.