Why reproduction is important in animals

Without a mechanism for reproduction, life would come to an end. There are two types of reproduction to learn in elementary grades, asexual and sexual reproduction. Many teachers are afraid of discussing reproduction, but if presented as a factual lesson it is easy for the students to understand the principles without the standard giggles.

Asexual reproduction refers to simple cell division that produces an exact duplicate of an organism. There are many different types of asexual reproduction which can be discussed to show students the variability of modes of reproduction.

Some single-celled organisms reproduce by simple cell division, this is called binary fission. In this manner, the mother cell simply splits in half producing two daughter cells.

Some cells reproduce by unequal division of the cells, this is called budding. The XY system is also found in some insects and plants. Bird sex determination is dependent on the combination of Z and W chromosomes. Notice that this system is the opposite of the mammalian system because in birds the female is the sex with the different sex chromosomes.

The W appears to be essential in determining the sex of the individual, similar to the Y chromosome in mammals. Some fish, crustaceans, insects such as butterflies and moths , and reptiles use the ZW system. More complicated chromosomal sex determining systems also exist. For example, some swordtail fish have three sex chromosomes in a population. The sex of some other species is not determined by chromosomes, but by some aspect of the environment. Sex determination in alligators, some turtles, and tuataras, for example, is dependent on the temperature during the middle third of egg development.

This is referred to as environmental sex determination, or more specifically, as temperature-dependent sex determination. In many turtles, cooler temperatures during egg incubation produce males and warm temperatures produce females, while in many other species of turtles, the reverse is true.

In some crocodiles and some turtles, moderate temperatures produce males and both warm and cool temperatures produce females. Individuals of some species change their sex during their lives, switching from one to the other.

The wrasses, a family of reef fishes, are all sequential hermaphrodites. Some of these species live in closely coordinated schools with a dominant male and a large number of smaller females. If the male dies, a female increases in size, changes sex, and becomes the new dominant male. The fusion of a sperm and an egg is a process called fertilization.

This can occur either inside internal fertilization or outside external fertilization the body of the female. Humans provide an example of the former, whereas frog reproduction is an example of the latter.

External fertilization usually occurs in aquatic environments where both eggs and sperm are released into the water. After the sperm reaches the egg, fertilization takes place. Most external fertilization happens during the process of spawning where one or several females release their eggs and the male s release sperm in the same area, at the same time.

The spawning may be triggered by environmental signals, such as water temperature or the length of daylight. Nearly all fish spawn, as do crustaceans such as crabs and shrimp , mollusks such as oysters , squid, and echinoderms such as sea urchins and sea cucumbers. Frogs, corals, mayflies, and mosquitoes also spawn Figure Internal fertilization occurs most often in terrestrial animals, although some aquatic animals also use this method.

Internal fertilization may occur by the male directly depositing sperm in the female during mating. It may also occur by the male depositing sperm in the environment, usually in a protective structure, which a female picks up to deposit the sperm in her reproductive tract. There are three ways that offspring are produced following internal fertilization. This occurs in some bony fish, some reptiles, a few cartilaginous fish, some amphibians, a few mammals, and all birds. Most non-avian reptiles and insects produce leathery eggs, while birds and some turtles produce eggs with high concentrations of calcium carbonate in the shell, making them hard.

Chicken eggs are an example of a hard shell. The eggs of the egg-laying mammals such as the platypus and echidna are leathery. This process helps protect the eggs until hatching. This occurs in some bony fish like the platyfish Xiphophorus maculatus, Figure The eggs hatch and the offspring develop in the pouch for several weeks. Improve this page Learn More. Skip to main content. Module The Reproductive System. Search for:.