Basque PAU Biology flashcards

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

Water cohesion

Attraction between water molecules due to hydrogen bonding; enables surface tension, capillary action and continuous columns in xylem, essential for transport in plants.

Glycosidic bond

Covalent bond formed by condensation between two monosaccharides with loss of a water molecule; joins sugars into disaccharides and polysaccharides such as starch and cellulose.

Phospholipid bilayer

Double layer of amphipathic phospholipids with hydrophilic heads facing water and hydrophobic tails inward; forms the basic structure of all cell membranes.

Enzyme active site

Region of an enzyme where substrate binds; shape is complementary to the substrate (lock-and-key or induced fit), lowering activation energy of the reaction.

DNA base pairing

Adenine pairs with thymine via two hydrogen bonds; guanine pairs with cytosine via three; complementary strands are antiparallel, allowing accurate replication and transcription.

Fluid mosaic model

Description of the plasma membrane as a fluid phospholipid bilayer with embedded proteins, cholesterol and glycoproteins that move laterally, giving selective permeability.

Osmosis

Net movement of water across a selectively permeable membrane from higher to lower water potential; drives turgor in plant cells and lysis or crenation in animal cells.

Mitosis phases

Prophase (chromosomes condense), metaphase (align at equator), anaphase (chromatids separate), telophase (nuclear envelope reforms); produces two genetically identical diploid cells.

Meiosis variation

Reduction division producing four haploid cells; crossing over in prophase I and independent assortment in metaphase I generate genetic variation in gametes.

Active transport

Movement of substances against their concentration gradient using ATP and carrier proteins, for example the sodium-potassium pump moving three sodium ions out and two potassium ions in.

Glycolysis

First stage of respiration in the cytoplasm; glucose is split into two pyruvate molecules, producing net two ATP and two NADH without oxygen.

Oxidative phosphorylation

ATP synthesis driven by the electron transport chain on the inner mitochondrial membrane; NADH and FADH2 donate electrons, oxygen is final acceptor, chemiosmosis makes most ATP.

Calvin cycle

Light-independent reactions in the chloroplast stroma; RuBisCO fixes CO2 onto RuBP, and ATP and NADPH from light reactions reduce products to triose phosphate and glucose.

Km and Vmax

Michaelis constant Km is substrate concentration at half maximum rate; Vmax is maximum velocity at enzyme saturation. Competitive inhibitors raise Km, non-competitive lower Vmax.

Mendel segregation law

During meiosis the two alleles of a gene separate so each gamete receives one; explains 3:1 phenotype ratio in a monohybrid cross of heterozygotes.

Linked genes

Genes located on the same chromosome tend to be inherited together; crossing over produces recombinant gametes, and recombination frequency below 50 percent indicates linkage.

Transcription

Synthesis of mRNA from a DNA template by RNA polymerase in the nucleus; the mRNA carries codons to ribosomes for translation into a polypeptide.

Frameshift mutation

Insertion or deletion of nucleotides not in multiples of three, shifting the reading frame and usually producing a non-functional protein.

Lac operon

Inducible gene system in bacteria; lactose binds the repressor, allowing RNA polymerase to transcribe genes for lactose metabolism only when lactose is present.

Virus structure

Acellular particle with nucleic acid (DNA or RNA) inside a protein capsid, sometimes with a lipid envelope; replicates only inside a host cell and is unaffected by antibiotics.

Humoral immunity

B lymphocytes differentiate into plasma cells that secrete specific antibodies; memory B cells give a faster, stronger secondary response on re-exposure to the same antigen.

Restriction enzymes

Bacterial enzymes that cut DNA at specific recognition sequences, producing sticky ends used in recombinant DNA technology to insert genes into plasmids.

PCR

Polymerase chain reaction amplifies DNA in vitro through repeated cycles of denaturation, primer annealing and extension by DNA polymerase, doubling the target each cycle.

Asexual reproduction

Reproduction without gamete fusion, based on mitosis; offspring are genetically identical clones, as in binary fission, budding and vegetative propagation.

Natural selection

Mechanism of evolution where heritable variation leads to differential survival and reproduction; individuals better adapted to the environment leave more offspring.

Hardy-Weinberg equilibrium

Allele and genotype frequencies remain constant in a large, randomly mating population without mutation, migration or selection; p² + 2pq + q² = 1.

Allopatric speciation

Formation of new species when a geographic barrier separates populations, preventing gene flow; isolated groups accumulate genetic differences and reproductive isolation.

Trophic levels

Feeding positions in a food chain: producers, primary consumers, secondary consumers, decomposers; only about ten percent of energy passes to the next level.

Carrying capacity

Maximum population size an environment can sustain indefinitely; logistic growth levels off at this value due to limited resources.

Eutrophication

Nutrient enrichment of water by nitrates and phosphates causes algal blooms; decomposition depletes oxygen, killing aquatic organisms.

Primary succession

Colonisation of bare substrate such as rock or lava by pioneer species; over time soil forms and communities change until a climax community is reached.

Biodiversity levels

Biological diversity measured at genetic, species and ecosystem levels; maintained by habitat protection, reduced pollution and sustainable resource use.