Rhizome Stored rhizomes are subject to bacterial and fungal infections making them unsuitable for replanting and greatly diminishing stocks. However rhizomes can also be produced artificially from tissue cultures. The ability to easily grow rhizomes from tissue cultures leads to better stocks for replanting and greater yields. The plant hormones ethylene and jasmonic acid have been found to help induce and regulate the growth of rhizomes, specifically in Rheum rabarbarum (rhubarb). Ethylene that was applied externally was found to affect internal ethylene levels, allowing for easy manipulations of ethylene concentrations. Knowledge of how to use these hormones to induce rhizome growth could help farmers and biologists producing plants grown from rhizomes more easily cultivate and grow better plants. See also References Jump up ^ ῥίζωμα.
Archaea The Archaea ( Archaea were initially classified as bacteria, receiving the name archaebacteria (or Kingdom Monera), but this classification is outdated. Archaeal cells have unique properties separating them from the other two domains of life: Bacteria and Eukaryota. The Archaea are further divided into four recognized phyla. Classification is difficult, because the majority have not been studied in the laboratory and have only been detected by analysis of their nucleic acids in samples from their environment. Classification New domain Current classification The classification of archaea, and of prokaryotes in general, is a rapidly moving and contentious field. A superphylum - TACK - has been proposed that includes the Aigarchaeota, Crenarchaeota, Korarchaeota and Thaumarchaeota. This superphylum may be related to the origin of eukaryotes. Species The classification of archaea into species is also controversial. Origin and evolution R.S. Morphology
Cell nucleus HeLa cells stained for the cell nucleus DNA with the BlueHoechst dye. The central and rightmost cell are in interphase, thus their entire nuclei are labeled. On the left, a cell is going through mitosis and its DNA has condensed. Because the nuclear membrane is impermeable to large molecules, nuclear pores are required that regulate nuclear transport of molecules across the envelope. History Between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus. Structures Nuclear envelope and pores Nuclear pores, which provide aqueous channels through the envelope, are composed of multiple proteins, collectively referred to as nucleoporins. Nuclear lamina The nuclear lamina is composed mostly of lamin proteins. Mutations in lamin genes leading to defects in filament assembly are known as laminopathies. Chromosomes Nucleolus
Shedding light on the Black Death Seven hundred years ago, millions of Europeans were wiped out by a disease we still don’t entirely understand. The Black Death might seem like a pretty open-and-shut case at this point: It was caused by plague-bearing fleas that hitched rides on the rats that infested a grim and grimy medieval world. The End. But that simplified version only makes sense if you overlook some important facts about how the plague (which still exists) operates today. What’s more, DeWitte says, recorded symptoms from the Black Death don’t entirely match up with those of modern plague. Given the vast numbers of people who died in the Black Death, there are relatively few burials that can be absolutely confirmed as containing Black Death victims, and only Black Death victims. That's made it difficult to know whether Yersinia pestis — the bacteria that causes the plague — really is present in Black Death victims. The draft tells us a couple of things. Genetically, Y. pestis has barely changed.
Acetic acid bacteria Not to be confused with Acetobacterium, a distinct group of organisms. Occurrence Suppression The growth of Acetobacter in wine can be suppressed through effective sanitation, by complete exclusion of air from wine in storage, and by the use of moderate amounts of sulfur dioxide in the wine as a preservative.  Vinegar is produced when acetic acid bacteria act on alcoholic beverages such as wine. Some genera, such as Acetobacter, can oxidize acetic acid to carbon dioxide and water using Krebs cycle enzymes. As these bacteria produce acid, they are usually acid-tolerant, growing well below pH 5.0, although the pH optimum for growth is 5.4-6.3. One species of Acetobacter, Acetobacter xylinum, is able to synthesize cellulose, something normally done only by plants. Genus Acetobacter Acetobacter is a genus of acetic acid bacteria characterized by the ability to convert ethanol to acetic acid in the presence of oxygen. References Further reading
Root Primary and secondary roots in a cotton plant Large, mature tree roots above the soil Anatomy Root growth Roots of trees Early root growth is one of the functions of the apical meristem located near the tip of the root. Over time, given the right conditions, roots can crack foundations, snap water lines, and lift sidewalks. Growth from apical meristems is known as primary growth, which encompasses all elongation. The vascular cambium produces new layers of secondary xylem annually. Types of roots A true root system consists of a primary root and secondary roots (or lateral roots). the diffuse root system: the primary root is not dominant; the whole root system is fibrous and branches in all directions. Specialized roots Prop roots of Maize plant Roots forming above ground on a cutting of an Odontonema ("Firespike") The growing tip of a fine root Rooting depths Cross section of a mango tree Rooting depth records Root architecture Evolutionary history
Prokaryote Cell structure of a bacterium , one of the two domains of prokaryotic life. The division to prokaryotes and eukaryotes reflects two distinct levels of cellular organization rather than biological classification of species. Prokaryotes include two major classification domains: the bacteria and the archaea . Archaea were recognized as a domain of life in 1990. These organisms were originally thought to live only in inhospitable conditions such as extremes of temperature , pH , and radiation but have since been found in all types of habitats . [ edit ] Relationship to eukaryotes The division to prokaryotes and eukaryotes is usually considered the most important distinction among organisms. Prokaryotes lack distinct mitochondria and chloroplasts . In 1977, Carl Woese proposed dividing prokaryotes into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) because of the major differences in the structure and genetics between the two groups of organisms. [ edit ] Sociality Nanobe
Eukaryote Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells each with half the number of chromosomes as the original parent cell (haploid cells). Cell features Eukaryotic cells are typically much larger than those of prokaryotes. Internal membrane Detail of the endomembrane system and its components A 3D rendering of an animal cell cut in half. The nucleus is surrounded by a double membrane (commonly referred to as a nuclear membrane or nuclear envelope), with pores that allow material to move in and out. Vesicles may be specialized for various purposes. Mitochondria and plastids Simplified structure of a mitochondrion Plants and various groups of algae also have plastids. Cytoskeletal structures Cell wall Differences among eukaryotic cells
Bubonic Plague (the Black Death) Bubonic plague was one of the most feared diseases of the ancient and medieval worlds. Nobody could tell what caused it, and most people who got it died within a few days, screaming in pain. And when one or two people in a village got it, usually it spread to everyone else, and many of them died. Plague caused a fever, and black spots on your chest sometimes, and sometimes great big black swellings on your armpits and at the top of your legs. Today we do know what causes bubonic plague: it's a bacterium. DNA evidence shows that the plague came first from China, but the first recorded instance of people getting bubonic plague was in Constantinople about 570 AD. Plague epidemics were much worse in places where people were crowded together and didn't get enough to eat. More about bubonic plague (with pictures) Main medicine page Main science page Welcome to Kidipede! or *We don't use tracking and all ads are G-rated.