In species which produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual which produces the larger type of gamete—called an ovum (or egg)—and a male produces the smaller type—called a spermatozoon (or sperm cell).
The name gamete was introduced by the Austrian biologist Gregor Mendel.
Gametogenesis is the development of diploid germ cells into haploid eggs or sperm, (respectively oogenesis and spermatogenesis). It is different for each species but the general stages are similar. The development of eggs (oogenesis} and sperm (spermatogenesis) have many features in common. They both involve:
They also have major differences, especially
Morphology
Morphology may mean:
Morphology (biology)
Morphology is the study of animal or human form or body shape. It is the branch of biology dealing with the study of the form of organisms and their specific structural features.
The concept of morphology was developed by Johann Wolfgang von Goethe (1790) and independently by the German anatomist and physiologist Karl Friedrich Burdach (1800).
In general use, the word morphology refers to the form and structure of an organism as a whole, including all internal and external structures. This includes aspects of the outward appearance (shape, structure, colour, pattern) as well as the form and structure of the internal parts like bones and organs. Morphology is contrasted to physiology, which deals primarily with function.
In English-speaking countries, the term "molecular morphology" has been used for some time for describing the structure of compound molecules, such as polymers
Taxon
A taxon (plural taxa) is a taxonomic group or taxonomic unit. It is a group of organisms which a taxonomist decides belong together.
Taxa can be big or small, a fairly small taxon is the giraffes, a very big one is the beetles.
A taxonomist can assign a scientific name and rank to a taxon; this places it at a particular level in a hierarchy. It is not strictly necessary to assign either a name or a rank to a taxon, but doing so makes it much easier to refer to the taxon. However, many taxa have to wait for years before getting a name.
There is no limit to the number of ranks that may exist, but the most important ranks are, in hierarchical order:
Note: "Phylum" applies formally to any biologial domain but traditionally it was always used of animals whereas "Division" was traditionally often used of plants, fungi etc.
A simple phrase to remember the order is
"Dignified Kings Play Chess On Fine Green Silk" (there are many other such phrases).
A distinction is made between taxonomy and systematics. Systematics deals with how groups relate to each other. Taxonomy deals with making groups (taxa), deciding what belongs together. Taxonomy is also known as classification.
A special part of taxonomy is nomenclature. This consists of rules on what names to use. So a taxonomist first decides what does and does not belong in a group, and then uses nomenclature to decide what name this group should have. If a group is made larger or bigger it may get a different name. On the other hand, the same name may refer to a bigger taxon (according to one particular taxonomist) or a smaller taxon (according to some other taxonomist). This means that scientific names are not guaranteed to be stable. Most names are stable, but for some taxa there is no agreement on its name, because taxonomists do not agree what does belong together and what does not belong together.
A taxonomist can decide for himself what scientific reasons he adopts for making a group (a taxon). If he is not convincing in his choice, other taxonomists will not agree with him, and they will then make other arrangements. These days biological classification is mostly supposed be done according to evolutionary (phylogenetic) relationships, so far as these are known.
Domain (biology)
In biological taxonomy, a domain (also superregnum, superkingdom, or empire) is a taxon in the highest rank of organisms, higher than a kingdom.
Domain (or its synonyms) is the most inclusive of these biological groupings. The arrangement of taxa reflects the fundamental evolutionary differences in the genomes. There are several modern alternative domain classifications of life. Among them are:
After defining Archaea as a new domain, Woese redrew the taxonomic tree. His three-domain system is based upon genetic relationships. It divides life into 23 main divisions in three domains: Bacteria, Archaea, and Eukarya. Archaea are neither bacteria nor eukaryotes. Looked at another way, they are prokaryotes that are not bacteria.
Keratin
Keratin is one of a family of fibrous proteins. Keratin is what makes up hair in animals, as well as horns, nails, hooves, shells, beaks, and feathers. The name comes from Greek word "keras" meaning "horn".
Keratins are tough and insoluble. They form the hard but non-mineral structures in reptiles, birds, amphibians and mammals. A similar biological toughness is found in chitin.
Keratins are the main constituent of structures that grow from the skin:
Arthropods such as crustaceans often have parts of their exoskeleton made of keratin, sometimes in combination with chitin.
Keratins are also found in the gastrointestinal tracts of many animals, including roundworms (who also have an outer layer made of keratin).
Although it is now difficult to be certain, the scales, claws, some protective armour and the beaks of dinosaurs would, almost certainly, have been composed of a type of keratin.
The silk fibroins produced by insects and spiders are often classified as keratins, though it is unclear whether they are phylogenetically related to vertebrate keratins.
Silk found in insect pupae, and in spider webs and egg casings, also has twisted β-pleated sheets incorporated into fibers wound into larger supermolecular aggregates.
Fibrous protein
A fibrous protein or scleroprotein is one of the three main types of proteins. The others are globular and membrane proteins).
There are many types of scleroprotein, such as keratin, collagen, elastin, and fibroin. Such proteins protect and support. They form connective tissue, tendons, bone matrices, and muscle fibre.
Filament
Filament could mean:
In "physics and electrical engineering":
In "astronomy":
In "biology":
Other uses:
Protein filament
In biology, a filament is a long chain of proteins, such as those found in hair, muscle, or in flagella.
Hanami
Hanami () means "flower viewing" in Japanese. Enjoying beautiful flowers is an old Japanese custom. Cherry blossoms are the most popular. The custom of hanami is more than a thousand years old. It is still very popular in Japan. Hanami takes place in the spring. Cherry blossoms are there for only a week or two. The cherry trees flower in late March and early April. The blossoms do not stay fresh very long. After a little time, the blooming is over. Then the blossoms fall from the trees.
An older form of hanami also exists in Japan. It celebrates the plum blossoms, instead of the cherry blossoms.
The practice of hanami is many centuries old. It started during the Nara Period (710–784) when the Chinese Tang Dynasty influenced Japan in many ways; one of which was the custom of enjoying flowers. Though it was ume blossoms that people admired in the beginning, by the Heian Period (794–1185), sakura began to attract more attention. The sakura were considered sacred by the Japanese, and they were so important that they still are a cultural symbol of Japan. People believed in gods' existence inside the trees, and the hanami party was used in the beginning to divine that year's harvest and to announce the season of planting rice. Those who went to the hanami made offerings at the root of sakura trees, and after the ceremony, they took part in the offering drinking sake.