D开头的SAT2生物专业词汇

　　Darwin, Charles(达尔文)

　　English naturalist (1809–1882) who proposed the modern theory of evolution through natural selection. Darwin traveled aboard the HMS Beagle to the Galápagos Islands, where his revolutionary observations took shape.

　　Decomposer(分解者)

　　Organisms that consume waste products and dead organic material and constitute part of the food web, which also includes producers and consumers. Also called saprophytes. Decomposers liberate inorganic elements such as nitrogen and carbon and allow those elements to move back into their respective chemical cycles. Examples of decomposers are bacteria and fungi.

　　dehydration synthesis(脱水缩合)

　　A common biochemical reaction in which a new compound is formed by the joining of two compounds to release water. Occurs in the synthesis of polysaccharides and polypeptides. The reverse of hydrolysis.

　　deoxyribonucleic acid (DNA/脱氧核糖核酸)

　　A type of nucleic acid polymer built from sugar-phosphate backbones and nitrogenous bases. DNA’s sugar, deoxyribose, has one fewer oxygen atom than ribose, found in RNA. The nitrogenous bases adenine, cytosine, guanine, and thymine are used in DNA.

　　Dicot(双子叶)

　　A flowering plant (angiosperm) that possesses two cotyledons during embryonic development. Usually has taproots, flower parts in multiples of fours and fives, and branching veins in leaves.

　　Diffusion(扩散)

　　The transport or natural drift of molecules traveling from an area of higher concentration to an area of lower concentration. Diffusion does not require outside energy from the cell.

　　digestive system(消化系统)

　　The system of organs that converts food to usable nutrients through mechanical and chemical breakdown. Important components of the system are the alimentary canal, glands, esophagus, stomach, small intestine, large intestine, and rectum.

　　diploid number(双倍目)

　　The total number of chromosomes present in a somatic cell. The diploid number is twice the haploid number. In humans, the diploid number is 46.

　　Disaccharide(双糖)

　　A sugar compound consisting of two carbohydrate monomers.

　　Dominant(显性【尤指基因显性】)

　　Refers to an allele that controls the phenotype even when a different allele is also present, as in a heterozygote. Can also refer to the trait or phenotype produced by a dominant allele. Also known as Mendel’s law of dominance, based on Gregor Mendel’s observations that when two purebred individuals with different forms of the same trait are mated, only one of the two forms appears in the first generation of offspring. Mendel called the apparent form dominant and the suppressed form recessive.