MTTC Biology (017) key terms

A thin double layer of phospholipids with embedded proteins that surrounds every cell and controls which substances enter or leave, while also helping cells recognize and attach to one another.

The property of a membrane that lets some molecules pass through easily while blocking or slowing others, allowing a cell to keep a stable internal environment different from its surroundings.

The net movement of particles from a region of higher concentration to a region of lower concentration, driven by random molecular motion and requiring no energy input from the cell.

The diffusion of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration, which can cause cells to swell or shrink.

A solution with a higher solute concentration than the fluid inside a cell, causing water to leave the cell and leading to shrinkage or wilting.

A solution with a lower solute concentration than the fluid inside a cell, causing water to enter the cell and potentially making it swell or burst.

The outward push of water against a plant cell wall, keeping nonwoody plant parts firm; loss of this pressure produces wilting.

Movement of substances across a membrane against their concentration gradient using energy from ATP, typically carried out by pump proteins such as the sodium-potassium pump.

Passive movement of molecules through membrane channel or carrier proteins down their concentration gradient, used for substances like glucose that cannot cross the lipid bilayer directly.

A difference in the amount of a substance between two neighboring regions; particles tend to spread from the higher-concentration side toward the lower, and cells use such differences to store energy.

A protein that speeds up a specific chemical reaction by lowering its activation energy, binding substrates at an active site whose shape determines which reactions it can catalyze.

The small region of an enzyme where substrate molecules bind and are converted to products; its shape is complementary to the substrate, giving enzymes their specificity.

The reactant molecule that an enzyme binds and chemically changes during a reaction; each enzyme typically acts on one or a few closely related substrates.

Loss of a protein's functional three-dimensional shape caused by heat, extreme pH, or other stress, which destroys enzyme activity and is usually irreversible.

Adenosine triphosphate, the cell's main energy-carrying molecule; breaking its terminal phosphate bond releases energy that powers reactions, transport, and movement.

The first stage of cellular respiration, in which glucose is split into two pyruvate molecules in the cytoplasm, producing a small amount of ATP and NADH without requiring oxygen.

A series of reactions in the mitochondrial matrix that oxidize acetyl groups from pyruvate, releasing carbon dioxide and transferring electrons to NADH and FADH2.

A set of protein complexes in the inner mitochondrial membrane that pass electrons along, pumping protons to build a gradient that drives most ATP production.

The oxygen-requiring breakdown of glucose through glycolysis, the Krebs cycle, and the electron transport chain to capture energy as ATP, releasing carbon dioxide and water.

The process by which plants, algae, and some bacteria use light energy to convert carbon dioxide and water into glucose, releasing oxygen as a byproduct.

The green pigment in chloroplasts that absorbs light energy, mainly in the blue and red parts of the spectrum, to drive the light reactions of photosynthesis.

The light-independent stage of photosynthesis in the chloroplast stroma, where carbon dioxide is fixed and, using ATP and NADPH, reduced into sugar.

Nuclear division that produces two daughter nuclei with the same chromosome number as the parent cell, underlying growth, repair, and asexual reproduction in many organisms.

A two-round division of germ cells that halves the chromosome number and shuffles alleles through crossing over and independent assortment, producing genetically varied gametes.

Exchange of corresponding chromosome segments between homologous chromosomes during prophase I of meiosis, creating new combinations of alleles on a single chromosome.

The ordered sequence of growth, DNA replication, and division a cell passes through, including interphase and the mitotic phase, controlled by checkpoint proteins.

One of the alternative forms of a gene at a given locus, such as a dominant or recessive version, which together determine an organism's genotype and often its phenotype.

The combination of alleles an organism carries for a trait or set of traits, written as pairs of letters such as AA, Aa, or aa.

The observable traits of an organism, such as height or flower color, resulting from the interaction of its genotype with the environment.

An allele whose effect appears in the phenotype even when only one copy is present, masking the expression of a recessive allele paired with it.

An allele that affects the phenotype only when two copies are present, because its effect is hidden by a dominant allele in heterozygotes.

Describing an organism that carries two identical alleles for a particular gene, whether both dominant or both recessive.

Describing an organism that carries two different alleles for a particular gene, so its phenotype reflects the dominant allele or an intermediate blend.

A grid used to predict the possible genotypes of offspring by combining the alleles each parent can contribute for a trait.

The process by which individuals with inherited traits better suited to their environment tend to survive and reproduce more, gradually changing allele frequencies in a population.

An inherited characteristic that improves an organism's ability to survive and reproduce in its particular environment, arising over generations through natural selection.

Random change in allele frequencies in a population, especially strong in small populations, occurring by chance rather than because of natural selection.

Movement of alleles between populations when individuals migrate and interbreed, which tends to reduce genetic differences among populations.

A group of organisms that can interbreed under natural conditions to produce fertile offspring, generally sharing a common gene pool.

A community of living organisms together with the nonliving components of their environment, interacting as a system through energy flow and nutrient cycling.

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

A network of interconnected food chains showing the many feeding relationships among organisms in an ecosystem and how energy and matter move through them.

The maximum population size of a species that a given environment can support indefinitely, set by resources such as food, water, and space.

A group of individuals of the same species living in the same area at the same time and capable of interbreeding.

The process by which living systems maintain relatively stable internal conditions, such as temperature or blood glucose, through feedback mechanisms.

A control mechanism in which a change in a variable triggers a response that counteracts the change, helping keep conditions near a set point.

A single-celled organism lacking a membrane-bound nucleus and organelles, with DNA in a nucleoid region; includes bacteria and archaea.

An organism whose cells contain a membrane-bound nucleus and other organelles, including protists, fungi, plants, and animals.

A membrane-bound organelle in eukaryotic cells where the later stages of cellular respiration occur, producing most of the cell's ATP.

A structure of DNA and associated proteins that carries a cell's genes; eukaryotic chromosomes are linear and occur in pairs in diploid cells.