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Centrales Térmicas Del Norte
The Coscinodiscophyceae are a proposed class(s) of diatoms. They are similar to the Centrales, a traditional, paraphyletic subdivision of the heterokont algae known as diatoms. The order is named for the shape of the cell walls (or valves or frustules) of centric diatoms, which are circular or ellipsoid in valve view. The valves often bear radially symmetrical ornamental patterns that can appear as dots when viewed with an optical microscope. Some also bear spines on their valves, which may either increase cell surface area and reduce sinking, or act as a deterrent to zooplankton grazers. Unlike pennate diatoms, centric diatoms never have a raphe. In terms of cell cycle, vegetative cells are diploid and undergo mitosis during normal cell division. In sexual species, oogamous meiosis produces haploid gametes, either ova or sperm cells. These fuse to produce a zygote which expands in size to develop into an auxospore from which full-sized vegetative cells are produced. In so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Class (biology)
In biological classification, class () is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are domain, kingdom, phylum, order, family, genus, and species, with class ranking between phylum and order. History The class as a distinct rank of biological classification having its own distinctive name – and not just called a ''top-level genus'' ''(genus summum)'' – was first introduced by French botanist Joseph Pitton de Tournefort in the classification of plants that appeared in his '' Eléments de botanique'' of 1694. Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine a distinct ''grade'' of organization—i.e. a 'level of complexity', measured in terms of how differentiated their organ systems are into distinct regions or sub-organs—with a distinct ''type'' of construction, whic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Cycle
The cell cycle, or cell-division cycle, is the sequential series of events that take place in a cell (biology), cell that causes it to divide into two daughter cells. These events include the growth of the cell, duplication of its DNA (DNA replication) and some of its organelles, and subsequently the partitioning of its cytoplasm, chromosomes and other components into two daughter cells in a process called cell division. In eukaryotic cells (having a cell nucleus) including animal, plant, fungal, and protist cells, the cell cycle is divided into two main stages: interphase, and the M phase that includes mitosis and cytokinesis. During interphase, the cell grows, accumulating nutrients needed for mitosis, and replicates its DNA and some of its organelles. During the M phase, the replicated Chromosome, chromosomes, organelles, and cytoplasm separate into two new daughter cells. To ensure the proper replication of cellular components and division, there are control mechanisms kno ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taxonomy (biology)
In biology, taxonomy () is the science, scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxon, taxa (singular: taxon), and these groups are given a taxonomic rank; groups of a given rank can be aggregated to form a more inclusive group of higher rank, thus creating a taxonomic hierarchy. The principal ranks in modern use are domain (biology), domain, kingdom (biology), kingdom, phylum (''division'' is sometimes used in botany in place of ''phylum''), class (biology), class, order (biology), order, family (biology), family, genus, and species. The Swedish botanist Carl Linnaeus is regarded as the founder of the current system of taxonomy, having developed a ranked system known as Linnaean taxonomy for categorizing organisms. With advances in the theory, data and analytical technology of biological systematics, the Linnaean system has transfo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Auxospore
Auxospores are specialised cells in diatoms that are produced at key stages in their cell cycle or life history. Auxospores typically play a role in growth processes, sexual reproduction or dormancy.Hoek, C. van den, Mann, D. G. and Jahns, H. M. (1995). Algae : An introduction to phycology', Cambridge University Press, UK. Mechanism Auxospores are involved in re-establishing the normal size in diatoms, as successive mitotic cell divisions leads to a decrease in cell size. This occurs because each daughter cell produced by cell division inherits one of the two valves that make up the frustule (a silica cell wall), and then grows a smaller valve within it. Consequently, each division cycle decreases the average size of diatom cells in a population. When its size becomes too small, a dividing diatom cell produces an auxospore to expand its cell size back to that which is normal for vegetative cells. Auxospores can also play a role in sexual reproduction in diatoms, and may be fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zygote
A zygote (; , ) is a eukaryote, eukaryotic cell (biology), cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. The sexual fusion of haploid cells is called karyogamy, the result of which is the formation of a Ploidy#Haploid and monoploid, diploid cell called the zygote or zygospore. History German zoologists Oscar Hertwig, Oscar and Richard Hertwig made some of the first discoveries on animal zygote formation in the late 19th century. In multicellular organisms The zygote is the earliest developmental stage. In humans and most other Anisogamy, anisogamous organisms, a zygote is formed when an egg cell and sperm, sperm cell come together to create a new unique organism. The formation of a cell potency, totipotent zygote with the potential to produce a whole organism depends on epigenetics, epigenetic reprogramming. DNA demethyla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sperm Cell
Sperm (: sperm or sperms) is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, which are known as spermatozoa, while some red algae and fungi produce non-motile sperm cells, known as spermatia. Flowering plants contain non-motile sperm inside pollen, while some more basal plants like ferns and some gymnosperms have motile sperm. Sperm cells form during the process known as spermatogenesis, which in amniotes (reptiles and mammals) takes place in the seminiferous tubules of the testicles. This process involves the production of several successive sperm cell precursors, starting with spermatogonia, which differentiate into spermatocytes. The spermatocytes then undergo meiosis, reducing their chromosome number by half, which produces spermatids. The spermatids then mature and, in animals, c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ovum
The egg cell or ovum (: ova) is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is not capable of movement (non- motile). If the male gamete (sperm) is capable of movement, the type of sexual reproduction is also classified as oogamous. A nonmotile female gamete formed in the oogonium of some algae, fungi, oomycetes, or bryophytes is an oosphere. When fertilized, the oosphere becomes the oospore. When egg and sperm fuse together during fertilisation, a diploid cell (the zygote) is formed, which rapidly grows into a new organism. History While the non-mammalian animal egg was obvious, the doctrine ''ex ovo omne vivum'' ("every living nimal comes froman egg"), associated with William Harvey (1578–1657), was a rejection of spontaneous generation and preformationism as well as a bold assumption that mammals also reproduced v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gamete
A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. The name gamete was introduced by the German cytologist Eduard Strasburger in 1878. Gametes of both mating individuals can be the same size and shape, a condition known as isogamy. By contrast, in the majority of species, the gametes are of different sizes, a condition known as anisogamy or heterogamy that applies to humans and other mammals. The human ovum has approximately 100,000 times the volume of a single human sperm cell. The type of gamete an organism produces determines its sex and sets the basis for the sexual roles and sexual selection. In humans and other species that produce two Morphology (biology), morphologically distinct types of gametes, and in which Gonochorism, each individual produces only one type, a femal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Haploid
Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, respectively, in each homologous chromosome pair—the form in which chromosomes naturally exist. Somatic cells, Tissue (biology), tissues, and Individual#Biology, individual organisms can be described according to the number of sets of chromosomes present (the "ploidy level"): monoploid (1 set), diploid (2 sets), triploid (3 sets), tetraploid (4 sets), pentaploid (5 sets), hexaploid (6 sets), heptaploid or septaploid (7 sets), etc. The generic term polyploidy, polyploid is often used to describe cells with three or more sets of chromosomes. Virtually all sexual reproduction, sexually reproducing organisms are made up of somatic cells that are diploid or greater, but ploidy level may vary wid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meiosis
Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one copy of each chromosome (haploid). Additionally, prior to the division, genetic material from the paternal and maternal copies of each chromosome is crossed over, creating new combinations of code on each chromosome. Later on, during fertilisation, the haploid cells produced by meiosis from a male and a female will fuse to create a zygote, a cell with two copies of each chromosome. Errors in meiosis resulting in aneuploidy (an abnormal number of chromosomes) are the leading known cause of miscarriage and the most frequent genetic cause of developmental disabilities. 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. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oogamy
Oogamy is a form of anisogamy where the gametes differ in both size and form. In oogamy the large female gamete (also known as ovum) is immotile, while the small male gamete (also known as spermatozoon) is mobile. Oogamy is a common form of anisogamy, with almost all animals and land plants being oogamous. Oogamy is found in most sexually reproducing species, including all vertebrates, land plants, and some algae. The ancestral state of sexual reproduction is believed to be isogamy, with oogamy evolving through anisogamy. Once oogamy evolves, males and females typically differ in various aspects. Internal fertilization may have originated from oogamy, although some studies suggest that oogamy in certain species may have evolved before the transition from external to internal fertilization. In streptophytes, oogamy occurred before the split from green algae. Occurrence Oogamy is found in almost all animal species that reproduce sexually. There are exceptions, such as the op ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Division
Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukaryotes, there are two distinct types of cell division: a vegetative division (mitosis), producing daughter cells genetically identical to the parent cell, and a cell division that produces Haploidisation, haploid gametes for sexual reproduction (meiosis), reducing the number of chromosomes from two of each type in the diploid parent cell to one of each type in the daughter cells. Mitosis is a part of the cell cycle, in which, replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. In general, mitosis (division of the nucleus) is preceded by the S stage of interphase (during which the DNA replication occurs) and is f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
