Animal cells lack cell walls that characterize ready cells. The bodies of some animals are made up of cells organized into tissues, separately tissue narrow to some degree to perform detail functions. In most, tissues are organized into even to a greater extent specialized organs. Most animals are capable of complex and relatively speedy movement compared to plants and other organisms. Most reproduce sexually. Most animals are diploid, meaning that the cells of adults contain two copies of the genetic material. The development of most animals is characterized by distinctive stages, including a zygote, formed by the reaping of the first few division of cells following fertilization; a blastula, which is a hollow ball of cells formed by the create zygote; and a gastrula, which is formed when the blastula folds in on itself to form a double-walled structure with an opening to the outside, the blastopore.
Somewhere virtually 9 or 10 million species of animals inhabit the ground; the exact number is not known and even our estimates are very rough.
Animals range in size from no more than a few cells to organisms weighing many tons, such as blue whales and giant squid. By far most species of animals are insects, with groups such as mollusks and nematodes also being especially diverse. By this measure our own group, the vertebrates, is relatively inconsequential.
Mammals
The Class Mammalia includes more or less 5000 species placed in 26 orders. Systematists do not besides agree on the exact number or on how some orders and families are related to others. The Animal Diversity weathervane generally follows the arrangement used by Wilson and Reeder (2005). All mammals shell out at least three characteristics not found in other animals: 3 middle ear bones,...If you want to enamor a full essay, order it on our website: Orderessay
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