Reproduction

Reproduction is the process by which new organisms are generated. It is the mechanism of species ‎continuation. There are two means of reproducing: asexual and sexual reproduction.‎
Asexual Reproduction
Asexual reproduction produces offspring that are genetically identical to the parent because the ‎offspring are all clones of the original parent. This type of reproduction occurs ‎in prokaryotic microorganisms (bacteria) and in some eukaryotic single-celled and multi-celled ‎organisms.
Types of asexual reproduction
Binary Fission
Occurs in prokaryotic microorganisms and in some ‎invertebrate, multi-celled organisms. After a period of growth, an organism splits into two ‎separate organisms. Some unicellular eukaryotic organisms undergo binary fission by mitosis. ‎In other organisms, part of the individual separates, forming a second individual. This ‎process occurs, for example, in many asteroid echinoderms through splitting of the central ‎disk. Some sea anemones and some coral polyps also reproduce through fission .‎
‎Budding
Budding is a form of asexual reproduction that results from the outgrowth of a part of a cell or body ‎region leading to a separation from the original organism into two individuals. Budding occurs ‎commonly in some invertebrate animals such as corals and hydras . In hydras, a bud forms that ‎develops into an adult, which breaks away from the main body; whereas in coral budding, the bud ‎does not detach and multiplies as part of a new colony.‎
‎Fragmentation (regeneration)
Fragmentation is the breaking of the body into two parts with subsequent regeneration. If the animal ‎is capable of fragmentation, and the part is big enough, a separate individual will regrow.‎Many sea stars reproduce asexually by fragmentation. For example, if the arm of an individual sea ‎star is broken off it will regenerate a new sea star . Fishery workers have been known to try to kill ‎the sea stars that eat their clam or oyster beds by cutting them in half and throwing them back into ‎the ocean. Unfortunately for the workers, the two parts can each regenerate a new half, resulting in ‎twice as many sea stars to prey upon the oysters and clams. Fragmentation also occurs in annelid ‎worms, turbellarians, and poriferans.‎
‎Parthenogenesis
Parthenogenesis is a form of asexual reproduction where an egg develops into a complete individual ‎without being fertilized. The resulting offspring can be either haploid or diploid, depending on the ‎process and the species. Parthenogenesis occurs in invertebrates such as water fleas, rotifers, aphids, ‎stick insects, some ants, wasps, and bees. Bees use parthenogenesis to produce haploid males ‎‎(drones) and diploid females (workers). If an egg is fertilized, a queen is produced. The queen bee ‎controls the reproduction of the hive bees to regulate the type of bee produced.‎Some vertebrate animals, such as certain reptiles, amphibians, and fish, also reproduce through ‎parthenogenesis. Although more common in plants, parthenogenesis has been observed in animal ‎species that were segregated by sex in terrestrial or marine zoos. Two Komodo dragons, a ‎bonnethead shark, and a blacktip shark have produced parthenogenic young when the females have ‎been isolated from males.
Vegetative reproduction.
It usually ‎involves only the ‎plant's vegetative structures like roots, stems and leaves. For ‎example, raspberries can produce a new ‎generation using their stems; potatoes, ‎using their roots; and geraniums can be grown from any piece ‎of a parent ‎plant.
Sporulation
Some types of mold reproduce through sporulation. They produce reproductive ‎cells - spores - that ‎are stored in special spore cases until they are ready to be ‎released. After they are released they will ‎develop into new, individual ‎organisms. Bread mold reproduces by sporulation.‎
Gemmules
Gemmules are special structures that are found in sea sponges. A parent ‎sponge ‎releases gemmules that later develop into mature sponges.‎
Sexual Reproduction
Sexual reproduction is the combination of (usually haploid, or having a single set of unpaired ‎chromosomes) reproductive cells from two individuals to form a third (usually diploid, or having a ‎pair of each type of chromosome) unique offspring. Sexual reproduction produces offspring with ‎novel combinations of genes. This can be an adaptive advantage in unstable or unpredictable ‎environments. As humans, we are used to thinking of animals as having two separate sexes, male ‎and female, determined at conception. However, in the animal kingdom, there are many variations ‎on this theme.‎
Sexual reproduction in algae
The simplest form of sexual reproduction in algae is conjugation, in which two similar ‎organisms fuse, exchange genetic material and then break apart. Some multicellular ‎green algae undergo a process called alternation of generations. During this process, ‎generations of different types of organisms are produced: haploid and diploid. Haploid ‎generation reproduces sexually. It is followed by diploid generation that reproduces ‎asexually.‎
Sexual reproduction in flowering plants
Flowers contain both male and female parts. The female part is called the pistil, which ‎consists of the ovary, ovule, style and stigma at the tip. Inside the ovary are the ovules. ‎Each ovule contains an egg cell. The male structure is called the stamen. It consists of ‎the filament and the pollen-producing anther. A new seed is formed when an egg cell ‎joins with a pollen cell in the process of pollination. Pollination occurs when pollen grains ‎are carried from the anther of the stamen to the stigma of the pistil.
Sexual reproduction in animals
Animal male gamete is called spermatozoon or sperm. Sperm is a mobile cell that moves ‎using its 'tail', called flagellum. Female gamete is called an ovum. It does not move and it ‎is much larger than sperm.
Hermaphroditism
Hermaphroditism occurs in animals where one individual has both ‎male ‎and female reproductive ‎parts. Invertebrates, such as earthworms, ‎slugs, ‎tapeworms and snails, are often hermaphroditic.
‎ Types of fertilization
There are three main types of fertilization.‎
Internal fertilization
During internal fertilization, eggs are fertilized inside the female's body. Animals, like ‎reptiles and birds, lay eggs after fertilization. New offspring develop outside the female's ‎body. All eggs are covered by a protective shell. Mammal females, except monotremes, ‎develop a new embryo inside their body. This extra protection increases an organism's ‎chances of survival.‎
External fertilization
During external fertilization, the egg is fertilized outside the female's body. Male and ‎female gametes are released into these species' surroundings where they fuse, forming a ‎zygote. This type of fertilization usually occurs in water. Amphibians and fish are ‎examples of animals that reproduce in this way.‎