Animals have a diploid life cycle, in which the organism is diploid, and the only haploid cells are the gametes. There are male and female organisms, and the male provides sperm which fertilizes the female`s egg cell. The fertilized egg is called a zygote, and develops into a multicellular embryo which eventually becomes a new diploid organism.
While this general scheme holds for many animals, there are numerous exceptions. Some insects, notably social insects such as bees, may produce haploid offspring, and animals such as Hydra may reproduce by asexual budding. There is also a great deal of variation among organisms that do follow the general scheme. For example, the two sexes may be found on the same organism, so that each organism may contribute sperm to the other`s eggs (a condition known as hermaphroditism). The sperm may be transferred to the eggs while still within the female, or be shed over the eggs after their release from the female`s body. The zygote may develop within the female (as in mammals), outside the female`s body (as in frogs), or even within the male`s body (as in certain fish).
We suggest that you go deeper into our exhibits on animals to learn more about the many ways that animals go and have gone about their lives, or you can look at the alternation of generations page to find out more on how animals differ from other organisms.
One feature common to all animals is their ecological role as consumers, that is, they cannot manufacture their own food, and so must eat other organisms, or from other organisms, to obtain nourishment. There are three basic categories of consumers:
parasite - A parasite lives on or within another organism (the host), and obtains nourishment from the host without killing or swallowing it. These organisms range from ticks to tapeworms, and may be relatively harmless or may cause disease.
detrivore - Detrivores feed on dead organisms, or on organic nutients in the soil or water. These organisms are vital to the food web because they recycle nutrients which would otherwise become unavailable. Earthworms and vultures are both examples of detrivores.
Many animals specialize in their roles as consumers, they may feed exclusively on one food or one kind of food. Certain bats, for instance, are frugivores, and eat only fruits. These specialists often play important roles in the lives of the species with which they interact. In the case of the fruit bats, the bats are crucial for dispersing the seeds contained within the fruits.
For more information on the many and diverse roles of animals, explore further into the animal exhibit.