Male

A male (♂) organism is the physiological sex that produces sperm. Each spermatozoon can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. Most male mammals, including male humans, have a Y chromosome, which codes for the production of larger amounts of testosterone to develop male reproductive organs.

Not all species share a common sex-determination system. In most animals, including humans, sex is determined genetically, but in some species it can be determined due to social, environmental or other factors. For example, Cymothoa exigua changes sex depending on the number of females present in the vicinity.

Overview

The existence of two sexes seems to have been selected independently across different evolutionary lineages (see convergent evolution). The repeated pattern is sexual reproduction in isogamous species with two or more mating types with gametes of identical form and behavior (but different at the molecular level) to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction.

Maleč

Maleč is a village and municipality (obec) in Havlíčkův Brod District in the Vysočina Region of the Czech Republic.

The municipality covers an area of 12.09 square kilometres (4.67 sq mi), and has a population of 721 (as at 28 August 2006).

Maleč lies approximately 20 kilometres (12 mi) north of Havlíčkův Brod, 42 km (26 mi) north of Jihlava, and 97 km (60 mi) east of Prague.

References

Plant reproductive morphology

Plant reproductive morphology is concerned with the physical form and structure (the morphology) of those parts of plants directly or indirectly concerned with sexual reproduction.

Among all living organisms, flowers, which are the reproductive structures of angiosperms, are the most varied physically and show a correspondingly great diversity in methods of reproduction. Plants that are not flowering plants (green algae, mosses, liverworts, hornworts, ferns and gymnosperms such as conifers) also have complex interplays between morphological adaptation and environmental factors in their sexual reproduction. The breeding system, or how the sperm from one plant fertilizes the ovum of another, depends on the reproductive morphology, and is the single most important determinant of the genetic structure of nonclonal plant populations. Christian Konrad Sprengel (1793) studied the reproduction of flowering plants and for the first time it was understood that the pollination process involved both biotic and abiotic interactions. Charles Darwin's theories of natural selection utilized this work to build his theory of evolution, which includes analysis of the coevolution of flowers and their insect pollinators.

Lap

A lap is a surface (usually horizontal) created between the knee and hips of a biped when it is in a seated or lying down position.

See also

Lap (disambiguation)

A lap is the area on top of the thighs of a sitting person.

Lap may also refer to:

LAP may refer to:

Lapping

Lapping is a machining process, in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine.

This can take two forms. The first type of lapping (traditionally called grinding), involves rubbing a brittle material such as glass against a surface such as iron or glass itself (also known as the "lap" or grinding tool) with an abrasive such as aluminum oxide, jeweller's rouge, optician's rouge, emery, silicon carbide, diamond, etc., between them. This produces microscopic conchoidal fractures as the abrasive rolls about between the two surfaces and removes material from both.

The other form of lapping involves a softer material such as pitch or a ceramic for the lap, which is "charged" with the abrasive. The lap is then used to cut a harder material — the workpiece. The abrasive embeds within the softer material, which holds it and permits it to score across and cut the harder material. Taken to a finer limit, this will produce a polished surface such as with a polishing cloth on an automobile, or a polishing cloth or polishing pitch upon glass or steel.