Lebanese Baccalaureate - Life Sciences (LS) flashcards

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

Osmosis

Movement of water across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration, without requiring energy.

Resting membrane potential

The electrical difference across a neuron membrane at rest, about -70 mV, maintained mainly by the Na+/K+ pump and K+ leak channels.

Michaelis constant Km

The substrate concentration at which an enzyme works at half its maximum velocity; a low Km indicates high enzyme affinity for substrate.

Semiconservative replication

DNA replication in which each new double helix contains one original parental strand and one newly synthesized complementary strand.

Start codon

The mRNA triplet AUG, which signals the beginning of translation and codes for the amino acid methionine.

Test cross

Crossing an individual showing a dominant phenotype with a homozygous recessive individual to reveal whether the dominant individual is homozygous or heterozygous.

Hardy-Weinberg equilibrium

Condition in which allele and genotype frequencies stay constant across generations; requires no mutation, migration, selection, or drift and random mating.

Negative feedback

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

Insulin

A hormone from pancreatic beta cells that lowers blood glucose by promoting cellular uptake and glycogen storage.

Action potential

A rapid electrical change in a neuron caused by ion channel opening: depolarization by Na+ entry followed by repolarization by K+ exit.

Synaptic cleft

The narrow gap between two neurons across which neurotransmitters diffuse to carry the signal from the presynaptic to the postsynaptic cell.

Reflex arc

The pathway of a reflex: receptor, sensory neuron, integration center, motor neuron, and effector, producing a rapid involuntary response.

Antibody

A Y-shaped protein made by B lymphocytes that binds specifically to an antigen, neutralizing it or marking it for destruction.

Memory cells

Long-lived lymphocytes that remain after an infection and allow a faster, stronger secondary immune response on later exposure.

Vaccination

Introducing a harmless form of an antigen to stimulate an immune response and produce memory cells without causing disease.

Carrying capacity

The maximum population size that an environment can support indefinitely with the resources available.

Trophic level

A feeding position in a food chain, such as producer, primary consumer, or secondary consumer, with energy decreasing at each higher level.

Eutrophication

Nutrient enrichment of water that causes excessive algal growth, followed by oxygen depletion and death of aquatic organisms.

Natural selection

The process by which individuals with heritable traits that improve survival and reproduction leave more offspring, changing allele frequencies over generations.

Homologous structures

Body parts in different species that share a common evolutionary origin, though they may differ in function, such as the forelimbs of mammals.

Speciation

The formation of new species, often when populations become reproductively isolated through geographic separation or other barriers.

Independent variable

The factor deliberately changed or manipulated by the experimenter to test its effect on the dependent variable.

Control group

A comparison group that receives no treatment or a placebo, used to isolate the effect of the independent variable.

Standard deviation

A statistical measure of how widely values in a data set spread around their mean; a small value indicates values cluster near the mean.

Hypothalamus-pituitary axis

A control system in which hypothalamic releasing hormones stimulate the anterior pituitary, which secretes hormones controlling other endocrine glands.

LH surge

A sharp mid-cycle rise in luteinizing hormone that triggers ovulation and formation of the corpus luteum.

Progesterone

A hormone from the corpus luteum and placenta that prepares and maintains the uterine lining for pregnancy.

Phagocytosis

A process in which cells such as macrophages engulf and digest pathogens or particles, an important part of innate immunity.

Clonal selection

The process by which an antigen stimulates the specific lymphocytes with matching receptors to multiply into effector and memory cells.

Primary succession

Ecological succession that begins in a lifeless area without soil, starting with pioneer species such as lichens and mosses.

Genetic drift

Random change in allele frequencies in a population, especially strong in small populations, independent of natural selection.

Binomial nomenclature

The two-part naming system for species: capitalized genus followed by lowercase species epithet, both italicized.