Bagrut Biology 5 Units flashcards

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

Nucleoid

Region of a prokaryotic cell containing the circular DNA chromosome, not enclosed by a membrane; distinguishes prokaryotes from eukaryotes with a true nucleus.

Endosymbiotic theory

Explanation that mitochondria and chloroplasts originated from engulfed bacteria; supported by their double membranes, circular DNA, and 70S ribosomes.

Osmosis

Passive movement of water across a semipermeable membrane from higher water potential to lower water potential, driven by solute concentration differences without ATP.

Na⁺/K⁺ pump

Active transport protein that moves three sodium ions out and two potassium ions in per ATP hydrolyzed, maintaining the resting membrane potential of cells.

Peptide bond

Covalent bond formed by a condensation reaction between the carboxyl group of one amino acid and the amino group of another, releasing water.

Enzyme active site

Specific region of an enzyme where substrate binds, lowering activation energy; its shape depends on temperature and pH and determines substrate specificity.

Competitive inhibition

Inhibitor binds the enzyme active site, blocking substrate access; effect is reduced by increasing substrate concentration, and maximum rate can still be reached.

Denaturation

Loss of a protein's three-dimensional shape by heat, extreme pH, or chemicals, disrupting hydrogen bonds and hydrophobic interactions while peptide bonds remain intact.

Semi-conservative replication

DNA replication in which each new double helix contains one original parental strand and one newly synthesized strand, conserving half the original molecule.

Codon

Sequence of three mRNA nucleotides specifying one amino acid or a stop signal; the code is degenerate and read in the 5' to 3' direction.

Test cross

Cross between an individual showing a dominant phenotype and a homozygous recessive individual to reveal whether the dominant individual is heterozygous or homozygous.

Restriction enzyme

Bacterial enzyme that cuts DNA at a specific palindromic sequence, producing sticky or blunt ends used in genetic engineering and cloning.

Polymerase chain reaction

Technique amplifying DNA through repeated cycles of denaturation, primer annealing, and extension by heat-stable Taq polymerase, doubling DNA each cycle.

Hardy-Weinberg equilibrium

Condition in which allele and genotype frequencies remain constant across generations; genotype frequencies follow p² + 2pq + q² = 1 for two alleles.

Genetic drift

Random change in allele frequencies between generations, strongest in small populations; reduces genetic diversity and can fix alleles by chance.

Directional selection

Natural selection favoring individuals at one extreme of a trait's range, shifting the population mean in that direction over generations.

Reproductive isolation

Condition in which populations cannot interbreed to produce fertile offspring, preventing gene flow and allowing speciation to proceed.

Negative feedback

Homeostatic mechanism in which a deviation from a set point triggers a response that reverses the change, restoring stability.

Action potential

Rapid electrical change along a neuron caused by sodium influx and potassium efflux, propagating a signal with a fixed threshold and refractory period.

ADH

Antidiuretic hormone released by the pituitary that increases water reabsorption in kidney collecting ducts, concentrating urine and raising blood water potential.

Hemoglobin

Iron-containing respiratory pigment in red blood cells that binds oxygen cooperatively, producing a sigmoid dissociation curve and releasing oxygen in tissues.

Meiosis

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

Corpus luteum

Structure formed from the ruptured follicle after ovulation; secretes progesterone to maintain the endometrium and is sustained by hCG in pregnancy.

Memory cells

Long-lived lymphocytes formed after exposure to an antigen that enable a faster, stronger secondary immune response upon re-exposure.

Antibody

Protein produced by plasma cells with variable antigen-binding sites that binds specifically to antigens, marking pathogens for destruction.

Carrying capacity

Maximum population size an environment can sustain indefinitely, denoted K; logistic growth slows as population approaches this limit.

Keystone species

Species whose influence on community structure exceeds its abundance; its removal can trigger trophic cascades and alter ecosystem composition.

Eutrophication

Nutrient enrichment of water by runoff, causing algal blooms, oxygen depletion, and death of aquatic organisms.

Controlled variables

Factors held constant across experimental groups to prevent confounding effects and ensure observed differences result from the independent variable.

Standard deviation

Measure of the spread of data around the mean; a small value indicates data clustered near the mean, reflecting greater precision.

CRISPR-Cas9

Gene-editing system in which a guide RNA directs the Cas9 nuclease to a specific DNA sequence to create a targeted double-strand break.

Monoclonal antibodies

Identical antibodies produced by a hybridoma clone, binding a single specific epitope and used in diagnostics and targeted therapy.