Deserts cover about one fifth of our planet, and are caused by extremely low rainfall over an area. Theses biomes are nonetheless home to many plants and animals which have through the course of their evolution adapted to this dry environment.
Hot and Dry Desert is, as you can tell from the name, hot and dry. Most Hot and Dry Deserts don't have very many plants. They do have some low down plants though. The only animals they have that can survive have the ability to burrow under ground. This is because they would not be able to live in the hot sun and heat. They only come out in the night when it is a little cooler.
A cold desert is a desert that has snow in the winter instead of just dropping a few degrees in temperature like they would in a Hot and Dry Desert. It never gets warm enough for plants to grow. Just maybe a few grasses and mosses. The animals in Cold Deserts also have to burrow but in this case to keep warm, not cool. That is why you might find some of the same animals here as you would in the Hot and Dry Deserts.
Deserts cover about one fifth of the Earth's land surface. Most Hot and Dry Deserts are near the Tropic of Cancer or the Tropic of Capricorn. Cold Deserts are near the Arctic part of the world.
Hot and Dry Deserts temperature ranges from 20 to 25° C. The extreme maximum temperature for Hot Desert ranges from 43.5 to 49° C. Cold Deserts temperature in winter ranges from -2 to 4° C and in the summer 21 to 26° C a year.
The precipitation in Hot and Dry Deserts and the precipitation in Cold Deserts is different. Hot and Dry Deserts usually have very little rainfall and/or concentrated rainfall in short periods between long rainless periods. This averages out to under 15 cm a year. Cold Deserts usually have lots of snow. They also have rain around spring. This averages out to 15 - 26 cm a year.
Hot and Dry Deserts are warm throughout the fall and spring seasons and very hot during the summer. the winters usually have very little if any rainfall. Cold Deserts have quite a bit of snow during winter. The summer and the beginning of the spring are barely warm enough for a few lichens, grasses and mosses to grow.
Hot and Dry Deserts vegetation is very rare. Plants are almost all ground-hugging shrubs and short woody trees. All of the leaves are replete (packed with nutrients). Some examples of these kinds of plant are Turpentine Bush, Prickly Pears, and Brittle Bush. For all of these plants to survive they have to have adaptations. Some of the adaptations in this case are the ability to store water for long periods of time and the ability to stand the hot weather.
Hot and Dry Deserts animals include small nocturnal (only active at night) carnivores. There are also insects, arachnids, reptiles, and birds. Some examples of these animals are Borrowers, Mourning Wheatears, and Horned Vipers. Cold Deserts have animals like Antelope, Ground Squirrels, Jack Rabbits, and Kangaroo Rats.
Coastal and Cold desert
Coastal deserts are found in areas that are moderately warm to cool, such as the Neotropic and Nearctic realm. The winters are usually cool and short, while the summers are long and warm The soil is mostly sandy with a high alkaline content, it is also very porous, so rain seeps quite rapidly into the ground. Most of the flora in the coastal desert features thick foliage, with good water retention, and their roots are close to the surface of the ground in order to get enough water before it drains into the soil.
Cold Desert's plants are scattered. In areas with little shade,about 10 percent of the ground is covered with plants. In some areas of sagebrush it reaches 85 percent. The height of scrub varies from 15 cm to 122 cm. All plants are either deciduous and more or less contain spiny leaves.
Animals of the coastal desert include rough skinned amphibians, birds of prey, scavenger mammals reptiles and insects; most have adapted quite well to the climate, and again, they are largely nocturnal during the warmer months.
Perhaps the strangest of all desert biomes is the cold desert, as our perception of the desert is usually associated with the heat of the sun. But even if there is a moderately high amount of snow and rainfall during the wintertime, the soil is too heavy and alkaline. Alluvial fans pull some of the salt through the porous soil, so plant life can survive, but then again, as with its arid counterparts, the cold desert offers less than ideal conditions for sustaining delicate plants and animals.
Most of the animals in the cold desert are burrowers, even the carnivores and reptiles which even though cold-blooded, have made their homes in the cold desert.
Deer and other larger herbivores are only found during the winter, as the supply of grass is more abundant during that period.
Semi Arid Deserts
The major deserts of this type include the sagebrush of Utah, Montana and Great Basin. They also include the Nearctic realm (North America, Newfoundland, Greenland, Russia, Europe and northern Asia). The summers are moderately long and dry and like hot deserts, the winters normally bring low concentrations of rainfall. Summer temperatures usually average between 21 - 27° Centigrade. Temperature do not normally go above 38° Centigrade and evening temperatures are cool, at around 10° Centigrade. Cool nights help both plants and animals by reducing moisture loss from transpiration, sweating and breathing.
Animals that live in the Desert Biome
Different animals live in the different types of deserts. Animals that live in the desert have adaptations to cope with the lack of water, the extreme temperatures and the shortage of food. To avoid daytime heat, many desert animals are nocturnal. They burrow beneath the surface or hide in the shade during the day, emerging at night to eat. Many desert animals do not have to drink at all, they get all the water they need from their food. Most desert animals are small.
Rarer, but important, are physiological adaptations such as aestivation (dormancy during summer), the absence of sweat glands, the concentration of urine, localized deposits of fat in tails or humps and salt glands to secrete salt without loosing fluids.
Reptiles with their waterproof skin, production of uric acid instead of urine, hard-shelled eggs and ability to gain body heat directly from the sun and to retreat to shade or underground to avoid heat are exceptionally well adapted to dry lands and, not surprisingly, diverse there.
There are relatively few large mammals in deserts because most are not capable of storing sufficient water and withstanding the heat. Deserts often provide little shelter from the sun for large animals. The dominant animals of warm deserts are non mammalian vertebrates, such as reptiles.
Desert plants
Desert plants are uniquely adapted to life in a harsh and sometimes extreme environment. They often look unusual, and are sometimes quite beautiful. While desert plants are often greatly enjoyed in nature, they are also experiencing a growing popularity among landscapers. The same traits which allow desert plants to endure in the desert also make them suitable for low water gardening and xeriscaping. In hot, dry climates, desert plants can be used to assemble a striking and very water efficient garden. In cooler regions, desert plants sometimes do well in greenhouse conditions.
Several traits set desert plants aside from others. The first is that they tend to be designed to store water, and to use water efficiently. Cacti and succulents, for example, both have dense flesh which is designed to store large amounts of water. Many plants also have long roots to reach deep into the water table for water. Other plants deal with hostile conditions by dying off during extreme weather, and reviving during the rainy season to briefly bloom and scatter seeds. During this small window of time, many visitors come to see the profusion of desert wildflowers.
Many people associate cacti and succulents with the desert, but there are also a range of other plants. Desert wildflowers such as cliffrose, primrose, chuparose, brittlebush, sagebrush, sand verbena, yellow beeplant, and woolly daisies are common. There are also desert versions of familiar flowers like marigolds, lupines, poppies, sunflowers, chicory, mallow, dandelion,a and lily. During their blooming season, these wildflowers light up the desert with color.
Deserts also host an assortment of trees and shrubs such as creosote bush, crucifixion bush, desert willow, elephant trees, mesquite, ponderosa pines, Joshua trees, and acacias. Many of these trees have minimal foliage, since water loss through leaves is undesirable for them. They may also be bedecked in thorns to discourage hungry animals, and they often have thick, fleshy trunks and branches.
Major biomes
Dinoflagellates are unicellular protists which
exhibit a great diversity of form. The largest, Noctiluca, may be as large as 2 mm in diameter! Though not large
by human standards, these creatures often have a big impact on the environment
around them. Many are photosynthetic, manufacturing their own food using the
energy from sunlight, and providing a food source for other organisms. Some
species are capable of producing their own light through bioluminescence,
which also makes fireflies glow. There are some dinoflagellates which are parasites
on fish or on other protists. 
Both heterotrophic (eat other organisms) and autotrophic (photosynthetic)
dinoflagellates are known. Some are both. They form a significant part of
primary planktonic production in both oceans and lakes. Most dinoflagellates go
through moderately complex life cycles involving several steps, both sexual and
asexual, motile and non-motile. Some species form cysts composed of
sporopollenin (an organic polymer), and preserve as fossils. Often the
tabulation of the cell wall is somehow expressed in the shape and/or
ornamentation of the cyst.
