A haploid cell is one that contains a single set of chromosomes in its nucleus. These are mainly gametes - that is, cells intended for reproduction. Most prokaryotic organisms also have a haploid set of chromosomes. Somatic cells of eukaryotes (all but sex cells) are diploid, in plants they can be polyploid.
Structure of a prokaryotic cell
Prokaryotes are organisms consisting of a single cell that does not have a nucleus. These include only bacteria. Most of them have a single set of chromosomes.
The structure of their cell differs from the eukaryotic one in that it lacks some organelles. For example, they do not have mitochondria, lysosomes, the Golgi complex, vacuoles, or the endoplasmic reticulum. However, like the eukaryotic, the haploid prokaryotic cell has a plasma membrane composed of proteins and phospholipids; ribosomes that are involved in the production of proteins; cell wall, which in most cases is built from murein. Also, in the structure of such a cell, a capsule may be present, inwhich includes substances such as proteins and glucose. Their chromosomes float freely in the cytoplasm, not protected by the nucleus or any other structure. Most often, the hereditary material of bacteria is represented by only one chromosome, which contains information about the proteins that should be produced by the cell. The method of reproduction of such organisms is a simple division of haploid cells. This allows them to noticeably increase their numbers in the shortest possible time.
Eukaryotic cells with a single set of chromosomes
In these kinds of organisms, the haploid nuclei contain cells called gametes. They can be very different from somatic. Reproduction by haploid cells is sexual, and a new organism can only begin to develop when two gametes synthesized by different individuals of the same species merge.
Formed by the fusion of two haploid cells is called a zygote, it already has a double set of chromosomes. Although germ cells differ from somatic diploid cells, they may still have some eukaryotic organelles.
Animal gametes
The sex cells of organisms belonging to this kingdom are called sperm and eggs. The former are produced in the body of the male, the latter in the female. Eggs are produced in the ovaries and sperm are produced in the testicles. Both are specialized haploid cells that have different functions.
Structure of eggs
Female reproductive cells are much larger than male ones. They are motionless. Their main task is to provide the zygote for the first time with the nutrients necessary for division. The egg cell consists of cytoplasm, membrane, gelatinous membrane, polar body and nucleus, which contains chromosomes that carry hereditary information. 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 set of chromosomes) could form, which would entail various kinds of mutations.
A bird's egg can also be considered an egg, but it contains many more nutrients to be enough for the full development of the embryo. The female reproductive cell of mammals does not contain so many organic chemical compounds, since at later stages of embryo development through the placenta, he receives everything he 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 has a more complex structure. On top of the yolk sac and protein coat, it is covered with a shell that plays a protective function, and there is also an air chamber in the structure, which is necessary to provide the embryo with oxygen.
The structure of spermatozoa
This is also a haploid cell meant to reproduce. Its main function is the preservation and transmission of paternal hereditary material. This haploid cell is mobile, much smaller than the egg cell, due to the fact that it does not contain nutrients.
Spermatozoon consists of several main parts: a tail, a head and an intermediate section between them. The tail (flagellum) consists of microtubules - structures built from proteins. Thanks to him, the spermatozoon can move towards its target - the egg, which it must fertilize.
The intermediate section between the head and tail contains mitochondria that spiral around the middle part of the flagellum and a pair of centrioles that lie perpendicular to each other.
The first are organelles that produce the energy needed to move the gamete. In the head of the spermatozoon is the nucleus, which has a haploid set of chromosomes (23 in humans). On the outer side of this part of the male germ cell is an autosome. In fact, it is a slightly modified, enlarged lysosome. It contains enzymes that are necessary for the sperm to dissolve part of the outer shells of the egg and fertilize it. After the male germ cell merges with the female, a zygote is formed, which has a diploid set of chromosomes (46 in humans). She is already able to divide, and the embryo is formed from it.
Haploid plant cells
The organisms of this "kingdom" produce similar sex cells. Women's are also calledeggs, and men - sperm. The first are in the pistil, and the second are on the stamens, in the pollen. When it hits the pistil, fertilization occurs, and then a fruit is formed with seeds inside.
In lower plants (spores) - mosses, ferns - there is an alternation of generations. One of them reproduces asexually (spores), and the other - sexually. The former is called the sporophyte and the latter the gametophyte. In ferns, the sporophyte is represented by a plant with large leaves, and the gametophyte is a small green heart-shaped structure, on which germ cells are formed.
