parent_taxon adrorhizon
In biology , a species ( abbreviated sp ., with the plural form species abbreviated spp .) is the basic unit of biological classification and a taxonomic rank . A species is often defined as the largest group of organisms in which two individuals can produce fertile offspring , typically by sexual reproduction . While this definition is often adequate , looked at more closely it is often problematic . For example , in a species complex , the boundaries between closely related species become unclear or disappear altogether . Other ways of defining species include similarity of DNA , morphology , or ecological niche . The presence of locally adaptive traits may further subdivide species into infraspecific taxa such as subspecies . In biology , an organism is any contiguous living system , such as an ___MASK39___ , plant , fungus , archaeon , or bacterium . All known types of organisms are capable of some degree of response to stimuli , reproduction , growth and development and homeostasis . An organism consists of one or more cells ; when it has one cell it is known as a unicellular organism ; and when it has more than one it is known as a multicellular organism . Most unicellular organisms are of microscopic scale and are thus loosely described as microorganisms . Humans are multicellular organisms composed of many trillions of cells grouped into specialized tissues and organs . Adrorhizon purpurascens is a species of orchid ( family Orchidaceae ) . It is the only species in the genus Adrorhizon and one of three genera in the subtribe ___MASK67___ . The genus is native to southern India and Sri Lanka . Sexual reproduction is a form of reproduction where two morphologically distinct types of specialized reproductive cells called gametes fuse together , involving a female ' s large ovum ( or egg ) and a male ' s smaller sperm . Each gamete contains half the number of chromosomes of normal cells . They are created by a specialized type of cell division , which only occurs in eukaryotic cells , known as meiosis . The two gametes fuse during fertilization to produce DNA replication and the creation of a single - celled zygote which includes genetic material from both gametes . In a process called genetic recombination , genetic material ( DNA ) joins up so that homologous chromosome sequences are aligned with each other , and this is followed by exchange of genetic information . Two rounds of cell division then produce four daughter cells with half the number of chromosomes from each original parent cell , and the same number of chromosomes as both parents , though self - fertilization can occur . For instance , in ___MASK20___ reproduction each ___MASK20___ cell contains 46 chromosomes , 23 pairs , except gamete cells , which only contain 23 chromosomes , so the child will have 23 chromosomes from each parent genetically recombined into 23 pairs . Cell division initiates the development of a new individual organism in multicellular organisms , including animals and plants , for the vast majority of whom this is the primary method of reproduction . Deoxyribonucleic acid ( DNA ) is a molecule that carries the genetic instructions used in the growth , development , functioning and reproduction of all known living organisms and many viruses . DNA and RNA are nucleic acids ; alongside proteins , lipids and complex carbohydrates ( polysaccharides ), they are one of the four major types of macromolecules that are essential for all known forms of life . Most DNA molecules consist of two biopolymer strands coiled around each other to form a double ___MASK47___ . The ___MASK38___ is a large monophyletic tribe within the family of orchids . ___MASK67___ is an orchid subtribe in the tribe ___MASK38___ .