Key Terms for Biology

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Key Terms
Active transport: membrane proteins use cellular energy (usually ATP) to move molecules or ions across a plasma membrane against their concentration gradient. Allele: different forms of a gene
• genotype – the combination of alleles in an organism. Aquaporin: a specialised channel protein in the plasma membrane of a cell, which is selectively permeable to water. Attachment protein: a protein in the plasma membrane of a cell that attaches either to the cytoskeleton inside the cell, to other cells or to the extracellular matrix. Carrier protein: a membrane protein that facilitates the diffusion of specific substances across the membrane. The molecule to be transported binds to the outer surface of the carrier protein; the protein then changes shape, allowing the molecule to move across the membrane. Channel protein: a membrane protein that forms a channel or pore completely through the membrane and that is usually permeable to one or to a few water water-soluble molecules, especially ions. Chromosome: a DNA double helix together with proteins that help to organise and regulate the use of the DNA. Codominance: simultaneous phenotypic expression of two alternative alleles in a heterozygote. Concentration: the number of particles of a dissolved substance in a given unit of volume. Concentration gradient: the difference in concentration of a substance between two parts of a fluid or across a barrier such as a membrane. Diffusion: the net movement of particles from a region of high concentration of that particle to a region of low concentration, driven by the concentration gradient; may occur entirely within a fluid or across a barrier such as a membrane. Dominant: a variant of a trait the masks the presence of a recessive variant (e.g. T) Endocytosis: the process in which the plasma membrane engulfs extracellular material, forming membrane-bound sacs that enter the cytoplasm and thereby move material into the cell. Energy-requiring transport: the...
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