BW Abitur Biology Bilingual EN flashcards

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

Fluid-mosaic model

Description of the plasma membrane as a fluid phospholipid bilayer in which integral and peripheral proteins, cholesterol and glycolipids are embedded and can move laterally, giving selective permeability.

Osmosis

Net movement of water across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration, driven by the water potential gradient.

Active transport

Carrier-mediated movement of a solute against its concentration gradient using energy, typically ATP hydrolysis, as in the Na+/K+-ATPase that exports three sodium ions and imports two potassium ions.

Competitive inhibition

An inhibitor resembling the substrate binds the enzyme's active site, so increasing substrate concentration can overcome it; apparent Km rises while Vmax stays unchanged.

Chemiosmosis

ATP synthesis driven by a proton gradient across a membrane: electron transport pumps H+ ions, and ATP synthase lets them flow back, coupling the flow to phosphorylation of ADP.

Calvin cycle

Light-independent reactions in the chloroplast stroma: RuBisCO fixes CO2 onto RuBP, ATP and NADPH reduce the products to triose phosphate, and RuBP is regenerated.

Fermentation

Anaerobic pathway that regenerates NAD+ from NADH so glycolysis can continue; pyruvate is converted to lactate in muscle or to ethanol and CO2 in yeast.

Semi-conservative replication

DNA replication in which each parental strand serves as a template, so every new double helix contains one original and one newly synthesised strand.

Frameshift mutation

Insertion or deletion of a number of bases not divisible by three, shifting the reading frame and usually altering all downstream amino acids.

PCR

In vitro amplification of DNA using repeated cycles of denaturation, primer annealing and extension by a thermostable polymerase, doubling the target sequence each cycle.

Test cross

Cross of an individual showing a dominant phenotype with a homozygous recessive partner; offspring ratios reveal whether the tested individual is homozygous or heterozygous.

Restriction enzyme

Bacterial enzyme that recognises a specific palindromic DNA sequence and cuts it, often leaving sticky ends, and is a key tool for cloning and genetic engineering.

Action potential

All-or-none electrical signal along an axon: voltage-gated Na+ channels open at threshold, depolarising the membrane, then K+ efflux repolarises it before the refractory period.

Saltatory conduction

Rapid propagation of an action potential in myelinated axons, where depolarisation jumps between nodes of Ranvier instead of travelling continuously along the membrane.

Synaptic cleft

Narrow gap between presynaptic terminal and postsynaptic membrane into which neurotransmitters are released by exocytosis and diffuse to bind receptors.

Summation

Temporal or spatial addition of excitatory and inhibitory postsynaptic potentials at the axon hillock, determining whether threshold is reached and an action potential fires.

Hardy-Weinberg principle

In an ideal population without mutation, migration, selection or drift and with random mating, allele and genotype frequencies remain constant across generations.

Allopatric speciation

Formation of new species after a geographic barrier separates populations, which then diverge genetically and become reproductively isolated over time.

Homologous structures

Body structures in different species sharing common ancestry and similar basic layout, such as forelimbs of vertebrates, even when their functions differ.

Genetic drift

Random change in allele frequencies between generations, strongest in small populations, where chance events such as bottlenecks or founder effects reduce genetic variation.

Carrying capacity

Maximum population size an environment can sustain indefinitely given available resources; in logistic growth the population levels off at this value K.

Eutrophication

Nutrient enrichment of water, mainly by nitrate and phosphate, causing algal blooms whose decomposition depletes oxygen and can kill aquatic animals.

Keystone species

Species whose influence on community structure is disproportionately large relative to its abundance; its removal causes major changes in the ecosystem.

Trophic level

Position of an organism in a food chain, such as producer, primary consumer or secondary consumer; only about ten percent of energy passes to the next level.

Clonal selection

Antigen-driven activation of lymphocytes whose receptors match that antigen; they proliferate and differentiate into effector cells and long-lived memory cells.

Antibody

Y-shaped protein produced by plasma cells with two heavy and two light chains; its variable regions bind a specific antigen and mark it for destruction.

Allergy

Type I hypersensitivity in which IgE antibodies bound to mast cells trigger histamine release on allergen contact, causing rapid inflammation, sneezing or anaphylaxis.

Herd immunity

Indirect protection of unvaccinated individuals when a high proportion of a population is immune, reducing pathogen transmission and outbreak risk.

Memory cells

Long-lived B or T lymphocytes generated after an infection or vaccination that respond rapidly and strongly on renewed contact with the same antigen.

Controlled variable

Factor kept constant across experimental groups so that observed differences in the dependent variable can be attributed to the manipulated independent variable.

Correlation versus causation

Two variables changing together does not prove one causes the other; a causal claim requires controlled experiments or exclusion of confounding variables.

Reliability

Consistency of repeated measurements; increased by larger sample sizes, repetition and standardised procedures, and often reported as standard deviation or error bars.

Scientific model

Simplified representation of a real system, such as a membrane or population model, whose assumptions and limits must be stated when interpreting its predictions.