MTEL Biology key terms

A phospholipid bilayer studded with proteins and cholesterol that surrounds every cell, controlling which substances enter and leave and helping cells recognize and communicate with one another.

The net movement of particles from an area of higher concentration to one 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 a region of higher water concentration (lower solute concentration) to one of lower water concentration (higher solute concentration).

Movement of solutes across a membrane against their concentration gradient using carrier proteins and energy from ATP, as in the sodium-potassium pump.

A difference in the amount of a substance between two adjacent regions; this difference stores potential energy and determines the direction of diffusion and osmosis.

A solution with a higher solute concentration than the cell placed in it, causing water to leave the cell and the cell to shrink or shrivel.

A solution with a lower solute concentration than the cell placed in it, causing water to enter the cell and the cell to swell, potentially bursting.

A protein that speeds up a specific biochemical reaction by lowering its activation energy; its active site binds particular substrates and its shape determines specificity.

The minimum energy that reactant molecules must possess for a chemical reaction to proceed; enzymes reduce this barrier without being consumed by the reaction.

Loss of a protein's functional three-dimensional shape caused by heat, extreme pH, or chemicals, usually disrupting hydrogen bonds and permanently destroying the protein's activity.

Adenosine triphosphate, the cell's main energy currency; releasing its terminal phosphate group yields energy that powers cellular work such as active transport and synthesis.

The first stage of cellular respiration, occurring in the cytoplasm, in which one glucose molecule is split and oxidized to yield two pyruvate molecules and a small net gain of ATP.

A series of reactions in the mitochondrial matrix that oxidizes acetyl-CoA derived from pyruvate, releasing carbon dioxide and transferring electrons to NADH and FADH2.

A series of membrane-embedded protein complexes that pass electrons from NADH and FADH2 to oxygen, pumping protons to drive most ATP production in aerobic respiration.

ATP production driven by protons flowing back across a membrane through ATP synthase, down the gradient established by electron transport.

The process by which chloroplast-containing organisms convert light energy, carbon dioxide, and water into glucose and oxygen, using light-dependent reactions and the Calvin cycle.

The light-independent stage of photosynthesis in the chloroplast stroma, in which ATP and NADPH are used to fix carbon dioxide into sugar.

The green pigment in chloroplasts that absorbs mainly red and blue-violet light and reflects green, donating excited electrons to begin the light-dependent reactions.

Nuclear division producing two genetically identical daughter nuclei, used for growth, repair, and asexual reproduction; conventionally described in prophase, metaphase, anaphase, and telophase.

Two successive nuclear divisions that produce four haploid gametes from one diploid cell, with crossing over and independent assortment generating genetic variation.

Exchange of corresponding segments between homologous chromosomes during prophase I of meiosis, creating new combinations of alleles on the resulting chromosomes.

The random orientation of homologous chromosome pairs at metaphase I of meiosis, so that alleles of different genes are distributed to gametes independently of one another.

One of two or more alternative forms of a gene, occupying the same locus on homologous chromosomes and producing different versions of the same trait.

The particular combination of alleles an organism carries for a gene or set of genes, which together with environmental influences helps determine the observable phenotype.

The observable characteristics of an organism, resulting from the interaction of its genotype with the environment.

An allele whose trait appears in the phenotype whenever it is present, masking the expression of a recessive allele in a heterozygote.

An allele whose trait is expressed only when two copies are present, because its effect is hidden by a dominant allele in a heterozygote.

A grid used to predict the possible genotypes of offspring by combining the possible gametes of two parents.

Semiconservative copying of DNA before cell division, in which helicase unwinds the double helix and DNA polymerase builds each new strand using the original strand as a template.

An enzyme that adds nucleotides to a growing DNA strand in the 5' to 3' direction during replication and also proofreads and corrects mismatched bases.

Synthesis of an RNA molecule from a DNA template, carried out by RNA polymerase in the nucleus of eukaryotes and serving as the first step of gene expression.

The process in which ribosomes read mRNA codons and assemble the corresponding amino acids into a polypeptide chain, using tRNA to deliver amino acids.

A sequence of three mRNA nucleotides that specifies one amino acid or a stop signal during translation, read in order by the ribosome.

A change in the nucleotide sequence of DNA, such as a substitution, insertion, or deletion, which may alter protein structure and can be inherited if present in gametes.

The process by which individuals with inherited traits better suited to their environment tend to survive and reproduce more, increasing those traits in later generations.

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

An organism's relative contribution of offspring to the next generation, used as the measure of how well a phenotype performs in a given environment.

A close, long-term relationship between organisms of different species, including mutualism, commensalism, and parasitism, in which at least one participant benefits.

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

The maximum population size of a species that an environment can sustain indefinitely given the resources available.