Haploid cell: characteristic, division, reproduction

A haploid cell is one in which the nucleus contains a single set of chromosomes. This is basically gametes - that is, cells designed for reproduction. The majority of prokaryotic organisms also possess a haploid set of chromosomes. Somatic cells of eukaryotes (all but genital) are diploid, in plants they can be polyploid.

The structure of the prokaryotic cell

Prokaryotes are organisms consisting of a single cell, in which there is no nucleus. These include only bacteria. Most of them have a single set of chromosomes.

The structure of their cells differs from eukaryotic in that it lacks some organelles. For example, they do not have mitochondria, lysosomes, the Golgi complex, vacuoles, endoplasmic reticulum. However, like the eukaryotic, haploid cell of prokaryotes possesses a plasma membrane consisting of proteins and phospholipids; Ribosomes, which participate in the production of proteins; The cell wall, which in most cases is constructed from murein. Also in the structure of such a cell there can be a capsule, which includes substances such as proteins and glucose. Their chromosomes freely float in the cytoplasm, they are not protected by the nucleus or some other structure. Most often, the hereditary material of bacteria is represented by only one chromosome, on which information about the proteins that must be produced by the cell is recorded. The method of reproduction of such organisms is a simple division of haploid cells. This allows them to increase their numbers in the shortest possible time.

Cells of eukaryotes possessing a single set of chromosomes

In such organisms, haploid nuclei contain cells called gametes. They can be quite different from somatic. Reproduction by haploid cells is sexual, and a new organism can begin to develop only when two gametes are fused, synthesized by different individuals of the same species.

Formed by the fusion of two haploid cells is called a zygote, it already has a double set of chromosomes. Despite the fact that sex cells differ from somatic diploid ones, they can still have some organoids inherent in eukaryotes.

Gametes of animals

The sex cells of organisms belonging to this kingdom are called spermatozoa and ovules. The first are produced in the male body, the second - females. Egg cells are produced in the ovaries, and spermatozoa are produced in the testicles. Both are specialized haploid cells that have different functions.

Structure of eggs

Female sex cells are much larger than male sex cells. They are motionless. Their main task is to provide a zygote for the first time with nutrients necessary for division. The egg consists of a cytoplasm, a membrane, a gelatinous shell, a polar body and a nucleus in which the chromosomes carrying hereditary information are located. Also in its structure there are cortical granules, which contain enzymes that prevent other spermatozoa from entering the cell after fertilization, otherwise a polyploid zygote (with a triple or more chromosome set) could have formed, which would entail various mutations.

The egg of birds can also be considered an egg, but it contains a lot more nutrients, so that they are enough for the full development of the embryo. The female germ cell of mammals does not contain as many organic chemical compounds, because at later stages of embryo development through the placenta, it receives everything it needs from the mother's body.

In the case of birds, this does not happen, so the entire supply of nutrients must initially be present in the egg. The egg also has a more complex structure. On top of the yolk sac and the protein coat, it is covered with a shell that plays a protective function, and an air chamber is also present in the structure, which is necessary to provide oxygen to the embryo.

Structure of spermatozoa

It is also a haploid cell, intended for reproduction. Its main function is the preservation and transfer of paternal hereditary material. This haploid cell is mobile, has much smaller dimensions than the ovum, due to the fact that it does not contain nutrients.

The spermatozoon consists of several main parts: the tail, the head and the intermediate section between them. The tail (flagella) consists of microtubules - structures built from proteins. Thanks to him, the sperm can move to its goal - the egg, which it must impregnate.

The intermediate section between the head and tail contains mitochondria, which are spiraling around the middle part of the flagellum, and a pair of centrioles lying perpendicular to each other.

The first are the organelles, which produce the energy that is needed to move the gametes. In the head of the spermatozoon is the nucleus, which has a haploid set of chromosomes (23 in humans). On the outside of this part of the male germ cell is an autosome. In fact, it is slightly modified, increased lysosome. It contains enzymes that are necessary for the sperm to dissolve some of the outer shells of the egg and fertilize it. After the male sex cell merges with the female, a zygote is formed, which has a diploid set of chromosomes (46 in a human). It is already able to divide, from it a germ is formed.

Haploid cells of plants

The organisms of this "kingdom" produce similar sex cells. Women are also called ovules, and men's sperm cells. The first are in the pestle, and the second - in the stamens, in the pollen. When it hits the pestle, fertilization takes place, and then a fruit with seeds is formed inside.

In lower plants (spore) - mosses, ferns - alternation of generations is observed. One of them reproduces asexually (spores) and the other sexually. The former is called a sporophyte, and the second is called a gametophyte. In ferns, the sporophyte is a plant with large leaves, and the gametophyte is a small green structure in the form of a heart, and sexual cells are formed on it.