ORT Biology flashcards

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

Fluid mosaic model

Model of the plasma membrane describing a phospholipid bilayer with embedded proteins, cholesterol, and glycolipids that can move laterally, giving the membrane a mosaic and fluid character.

Competitive inhibition

An inhibitor that resembles the substrate and binds to the enzyme's active site, raising Km but leaving Vmax unchanged because higher substrate concentration can outcompete the inhibitor.

Oxidative phosphorylation

The final stage of aerobic respiration on the inner mitochondrial membrane, where the electron transport chain creates a proton gradient that ATP synthase uses to produce most of the cell's ATP.

Semiconservative replication

DNA replication in which each new double helix contains one original parental strand and one newly synthesized strand, as demonstrated by the Meselson–Stahl experiment.

Codon

A sequence of three nucleotides in mRNA that specifies a particular amino acid or a stop signal during translation; the genetic code is degenerate, so several codons can code for one amino acid.

Test cross

A cross between an individual of unknown genotype and a homozygous recessive individual; the offspring phenotypes reveal whether the unknown parent was homozygous dominant or heterozygous.

Lac operon

An inducible gene system in E. coli in which lactose binds the repressor protein, allowing RNA polymerase to transcribe genes for lactose metabolism when glucose is scarce.

Hardy–Weinberg principle

The principle that allele and genotype frequencies in a large, randomly mating population remain constant across generations in the absence of mutation, migration, selection, and genetic drift.

Homologous structures

Body parts in different species that share a common evolutionary origin but may have different functions, such as the human arm, bat wing, and whale flipper; they provide evidence for evolution.

Allopatric speciation

The formation of new species when a population is divided by a geographic barrier, preventing gene flow and allowing reproductive isolation to evolve over time.

Natural selection

The process by which individuals with inherited traits better suited to their environment survive and reproduce more successfully, increasing the frequency of those advantageous alleles in later generations.

Binomial nomenclature

The two-part scientific naming system for species, consisting of the genus name (capitalized) followed by the species epithet (lowercase), both usually italicized, for example Homo sapiens.

Cardiac cycle

The sequence of contraction (systole) and relaxation (diastole) of the heart chambers that pumps blood through the pulmonary and systemic circulations, initiated by the sinoatrial node.

Nephron

The functional unit of the kidney that filters blood in the glomerulus and reabsorbs useful substances such as glucose and water along the tubule to produce urine.

Negative feedback

A homeostatic control mechanism in which a change in a variable is detected by receptors and an effector response reverses the change, restoring the variable toward its set point.

Sliding filament model

Explanation of muscle contraction in which myosin heads bind actin filaments and pull them toward the centre of the sarcomere, shortening it; ATP and calcium ions are required.

Alveoli

Tiny air sacs in the lungs where gas exchange occurs by diffusion; their large surface area, thin walls, and rich blood supply maximise oxygen uptake and carbon dioxide removal.

Carrying capacity

The maximum population size of a species that an environment can sustain indefinitely given available food, water, habitat, and other resources; logistic growth levels off at this value.

Biomagnification

The increasing concentration of a persistent, fat-soluble pollutant in organisms at successively higher trophic levels of a food chain, such as DDT and mercury.

Primary succession

Ecological succession that begins on bare rock or newly formed land with no existing soil, starting with pioneer species such as lichens and mosses that help create soil.

Trophic level

A feeding position in a food chain, such as producer, primary consumer, or secondary consumer; only about 10% of energy passes from one level to the next.

Greenhouse effect

The warming of Earth's surface as atmospheric gases such as carbon dioxide, methane, and water vapour absorb and re-emit infrared radiation, trapping heat in the atmosphere.

Transpiration

The loss of water vapour from plant leaves through stomata; it creates a pulling force that draws water and dissolved minerals up the xylem from the roots.

Calvin cycle

The light-independent stage of photosynthesis in the chloroplast stroma, where ATP and NADPH are used to fix carbon dioxide into glucose via enzyme-controlled reactions.

Guard cells

Pairs of specialised epidermal cells surrounding a stoma; they swell when turgid to open the pore for gas exchange and lose water to close it and reduce transpiration.

Auxin

A plant hormone that promotes cell elongation and is involved in phototropism and gravitropism; it accumulates on the shaded side of a shoot, causing bending toward light.

Meiosis

A type of cell division that produces four genetically varied haploid gametes from one diploid cell through two divisions, including crossing over and independent assortment.

Ovulation

The release of a mature egg from an ovarian follicle into the fallopian tube, triggered by a surge in luteinising hormone (LH) around the middle of the menstrual cycle.

Placenta

The organ that develops in the uterus during pregnancy, allowing exchange of nutrients, gases, and wastes between maternal and fetal blood and secreting hormones such as progesterone.

Apical meristem

A region of actively dividing cells at the tips of roots and shoots that produces primary growth, increasing the length of the plant and forming new leaves and flowers.

Polymerase chain reaction

A laboratory technique that amplifies a specific DNA sequence through repeated cycles of denaturation, primer annealing, and extension by a heat-stable DNA polymerase such as Taq.

Restriction enzyme

A bacterial enzyme that cuts DNA at specific palindromic recognition sequences, often producing sticky ends; it is used in genetic engineering to insert genes into vectors.