NSEB key terms

The active maintenance of a stable internal environment, such as temperature, pH, and glucose level, despite changes outside the body. It relies on feedback loops involving sensors, control centres, and effectors.

A control mechanism in which the output of a process reduces the stimulus that triggered it, bringing a variable back toward a set point. Most physiological regulation, including insulin action on blood glucose, works this way.

The net movement of water across a selectively permeable membrane from a region of lower solute concentration to one of higher solute concentration. It is passive and driven by a water potential gradient.

The tendency of water to move from one place to another, expressed in pressure units. Pure water at standard conditions has a potential of zero; adding solutes or tension lowers it, so water flows toward lower potential.

The shrinking of a plant cell's protoplast away from its cell wall when the cell loses water in a hypertonic solution. It demonstrates that the plasma membrane is selectively permeable and that the wall is relatively rigid.

A biological catalyst, usually a protein, that speeds up a reaction by lowering its activation energy without being consumed. Its activity depends on shape, temperature, pH, and substrate concentration.

The specific pocket or cleft on an enzyme surface where substrate binds and catalysis occurs. Its shape and chemical groups determine substrate specificity and can be altered by inhibitors or denaturation.

Loss of a protein's functional three-dimensional shape caused by heat, extremes of pH, or chemicals. Because structure determines function, denatured enzymes lose catalytic activity, often irreversibly.

A form of enzyme inhibition in which a molecule resembling the substrate binds the active site, blocking substrate access. It can be overcome by raising substrate concentration and raises the apparent Michaelis constant.

The sequence of reactions in the cytoplasm that splits one glucose molecule into two pyruvate molecules, yielding a small amount of ATP and NADH. It occurs with or without oxygen and is the first stage of respiration.

A cyclic series of reactions in the mitochondrial matrix that oxidises acetyl coenzyme A, releasing carbon dioxide and reducing NAD and FAD. It also generates a small amount of ATP by substrate-level phosphorylation.

ATP production driven by a proton gradient across the inner mitochondrial membrane. Electrons passed along the electron transport chain pump protons, and their return through ATP synthase phosphorylates ADP.

The movement of protons down an electrochemical gradient across a membrane to drive ATP synthesis. It links electron transport to phosphorylation in mitochondria and chloroplasts.

The light-dependent stage of photosynthesis in the thylakoid membranes, where water is split, oxygen is released, and light energy is captured to produce ATP and NADPH for carbon fixation.

The light-independent stage of photosynthesis in the stroma, in which carbon dioxide is fixed by the enzyme RuBisCO and reduced to carbohydrate using ATP and NADPH from the light reactions.

Ribulose bisphosphate carboxylase/oxygenase, the enzyme that catalyses carbon fixation in the Calvin cycle. It is abundant in leaves and can also bind oxygen, causing photorespiration under certain conditions.

Nuclear division that produces two daughter nuclei genetically identical to the parent cell, usually followed by cytokinesis. It underlies growth, repair, and asexual reproduction in multicellular organisms.

Two successive nuclear divisions that halve the chromosome number and generate genetic variation through crossing over and independent assortment. It produces haploid gametes or spores from diploid cells.

Exchange of corresponding segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis. It recombines alleles and is a major source of genetic variation in offspring.

The ordered sequence of events through which a cell grows and divides, comprising interphase and the mitotic phase. Interphase includes G1, S, and G2, with DNA replication occurring during S phase.

The principle that the two alleles of a gene separate during gamete formation, so each gamete carries only one allele. Fusion of gametes at fertilisation restores the pair in the offspring.

The principle that alleles of different genes assort independently of one another during gamete formation when the genes are on different chromosomes. It predicts the ratios observed in dihybrid crosses.

One of two or more alternative forms of a gene occupying the same locus on homologous chromosomes. Alleles may be dominant or recessive and determine the variation seen in a trait.

The genetic constitution of an organism at one or more loci, described by the alleles it carries. It interacts with the environment to produce the observable phenotype.

The observable characteristics of an organism, including appearance, physiology, and behaviour. It results from the interaction between genotype and environmental factors.

The tendency of genes located close together on the same chromosome to be inherited together more often than expected by independent assortment. Recombination frequency reflects the distance between them.

The synthesis of an RNA molecule from a DNA template, catalysed by RNA polymerase. In eukaryotes it occurs in the nucleus and is followed by processing before translation.

The process in which ribosomes read messenger RNA codons and assemble the corresponding sequence of amino acids into a polypeptide. It requires transfer RNA, ribosomes, and energy.

A triplet of nucleotides in messenger RNA that specifies one amino acid or a stop signal during translation. The genetic code is degenerate, meaning several codons can encode the same amino acid.

A bacterial enzyme that recognises a specific short DNA sequence and cuts the double strand at or near that site. It is widely used to create recombinant DNA molecules in genetic engineering.

A small, circular DNA molecule that replicates independently of the bacterial chromosome. It is commonly used as a vector to carry foreign genes into host cells.

A DNA molecule formed by joining genetic material from different sources, often a gene inserted into a vector. Such molecules are central to cloning, gene therapy research, and biotechnology.

An in vitro technique that amplifies a specific DNA segment through repeated cycles of denaturation, primer annealing, and extension by a heat-stable DNA polymerase. It produces millions of copies from a tiny sample.

A protein produced by plasma cells that binds specifically to an antigen, marking it for neutralisation or destruction. Its Y-shaped structure contains variable regions that determine binding specificity.

The ability of an organism to resist infection or disease by recognising and eliminating pathogens or foreign substances. It involves innate defences and adaptive responses mediated by lymphocytes and antibodies.

Any substance, often a protein or polysaccharide, that the immune system recognises as foreign and can trigger a specific immune response. It typically contains epitopes to which antibodies or T cells bind.

The differential survival and reproduction of individuals whose inherited traits make them better suited to their environment. Over generations it changes allele frequencies in populations and drives adaptation.

Random change in allele frequencies in a population from one generation to the next, especially strong in small populations. Unlike natural selection, it is not driven by fitness differences.

An inherited feature that improves an organism's ability to survive and reproduce in its environment. It arises through natural selection acting on variation within a population over many generations.