Kids Research Express

Tick, common name for members of a group of large mitelike arachnids parasitic on mammals , birds , and reptiles . All ticks are bloodsucking parasites . Ticks are found in most parts of the world but are generally limited to those habitats frequented by their hosts—namely, woods, tall grass , and shrubby vegetation—where they climb onto plants and wait to jump on a passing host. Ticks are actually a specialized group of mites and share many features with other mites. In general, they are larger than most mites, ranging from about 0.2 to 0.6 cm (about 0.08 to 0.24 in) in length, although females may be 1 cm (0.4 in) or more in diameter when fully engorged with blood. The adult tick has a mitelike body with a tough skin and four pairs of clawed legs; tick larvae have only three pairs of legs. The mouthparts consist of a paired anchoring organ, or rostrum, covered with backward-curving hooks and equivalent to the pedipalps of other arachnids; and a pair of sharp mandibles that move back...

Cytology Cytology, branch of biology concerned with the study of the structure and function of cells as individual units, supplementing histology, which deals with cells as components of tissues. Cytology is concerned with the structure and activities of the various parts of the cell and cell membrane; the mechanism of cell division; the development of sex cells, fertilization, and the formation of the embryo; cell derangements such as those occurring in cancer; cellular immunity; and the problems of heredity. Cytology, branch of biology concerned with the study of the structure and function of cells as individual units, supplementing histology, which deals with cells as components of tissues. Cytology is concerned with the structure and activities of the various parts of the cell and cell membrane; the mechanism of cell division; the development of sex cells, fertilization, and the formation of the embryo; cell derangements such as those occurring in cancer; cellular immunity; and the...

Genetics, study of the function and behavior of genes . Genes are bits of biochemical instructions found inside the cells of every organism from bacteria to humans. Offspring receive a mixture of genetic information from both parents. This process contributes to the great variation of traits that we see in nature, such as the color of a flower’s petals, the markings on a butterfly’s wings, or such human behavioral traits as personality or musical talent. Geneticists seek to understand how the information encoded in genes is used and controlled by cells and how it is transmitted from one generation to the next. Geneticists also study how tiny variations in genes can disrupt an organism’s development or cause disease. Increasingly, modern genetics involves genetic engineering, a technique used by scientists to manipulate genes. Genetic engineering has produced many advances in medicine and industry, but the potential for abuse of this technique has also presented society with many ethica...

Parasite, organism that lives in or on a second organism, called a host, usually causing it some harm. A parasite is generally smaller than the host and of a different species. Parasites are dependent on the host for some or all of their nourishment. For example, a tapeworm, a flattened worm that lives in the gastrointestinal tract of mammals, lacks an intestine of its own and must absorb predigested food from the intestine of its host. This food is the tapeworm’s only energy source for growth and reproduction. Parasitism affects most life forms, from bacteria infected by the viruses known as bacteriophages, to humans, who are subject to more than 100 parasites known to cause disease. See also: Types and Forms of Parasites Parasites and Host Relationships Life Cyle of Parasites Parasites of Humans Parasites of Animals Parasites of Plants Parasitology

Biodiversity Biodiversity or Biological Diversity, sum of all the different species of animals, plants, fungi, and microbial organisms living on Earth and the variety of habitats in which they live. Scientists estimate that upwards of 10 million—and some suggest more than 100 million—different species inhabit the Earth. Each species is adapted to its unique niche in the environment, from the peaks of mountains to the depths of deep-sea hydrothermal vents , and from polar ice caps to tropical rain forests . Biodiversity underlies everything from food production to medical research. Humans the world over use at least 40,000 species of plants and animals on a daily basis. Many people around the world still depend on wild species for some or all of their food, shelter, and clothing. All of our domesticated plants and animals came from wild-living ancestral species. Close to 40 percent of the pharmaceuticals used in the United States are either based on or synthesized from natural compound...

. Extinction (biology), the end of existence of a group of organisms, caused by their inability to adapt to changing environmental conditions. Extinction affects individual species—that is, groups of interbreeding organisms—as well as collections of related species , such as members of the same family, order, or class (see Classification ). The dodo, for example, a species of flightless pigeon formerly living on the island of Mauritius, became extinct in 1665. About 10,000 to 12,000 years ago, the most of the woolly mammoths and the last of the mastodons , both members of the elephant family, died. And about 245 million years ago at the end of the Paleozoic Era, an entire class of primitive marine animals called trilobites disappeared forever. Fossils , the remains of prehistoric plants and animals buried and preserved in sedimentary rock or trapped in amber or other deposits of ancient organic matter, provide a record of the history of life on Earth. Scientists who study this foss...

Hydrozoa Hydrozoa, class of invertebrates belonging to the cnidarian phylum. The hydrozoans make up six orders. Most species of hydrozoans show alternation of generations . One generation consists of individuals called polyps and is almost always colonial; the colony is known as a hydroid because of the resemblance of its individual polyps to the noncolonial hydra, the simplest of all hydrozoans. The other generation, members of which are known as medusae, consists of free-swimming, sexual individuals that produce either eggs or sperm; the familiar jellyfish is a typical medusa. Each fertilized egg develops into a ciliated larva (planula), from which the hydroid develops and then gives rise to medusae by budding. Hydrozoans differ in their conformity to the typical alternation of generations. The order to which the hydra belongs has small medusae and sometimes no free-swimming forms at all. The siphonophoran order, containing the Portuguese man-of-war, has a short-lived medusa stage, t...

. Cnidarians, also known as coelenterates, diverse group of aquatic, invertebrate animals armed with microscopic stinging structures. Cnidarians make up the phylum Cnidaria, which encompasses more than 9,000 species, including corals , hydras , jellyfishes , Portuguese man-of-war , and sea anemones . Cnidarians live in all oceans, and a few species inhabit fresh water. Cnidarians have many shapes and they range in size from microscopic hydrozoans to jellyfishes that are 2 m (7 ft) in diameter with tentacles 30 m (100 ft) long. Although they have various physical characteristics, all cnidarians exhibit radial symmetry—that is, similar body parts radiate from a central mouth. Six to ten tentacles surround a cnidarian’s mouth to aid in the capture and ingestion of the animals they feed on. Cnidarians have a saclike body with a single mouth opening. The body wall is composed of two sheets of cells—an inner layer (the endoderm) and an outer layer (the ectoderm). A gelatinous mesoglea layer ...

. During the life cycle of cnidarians they may form two types of body structures, the polyp and the medusa. Some cnidarians alternate between polyp and medusa at different stages of their life cycles, some cnidarians live solely as polyps, and others only as medusae. A polyp has a cylindrical shape. The mouth, surrounded by tentacles, is located at one end of the polyp, and the opposite end of the polyp typically attaches to a rock or other object on the sea bottom. Polyps may be solitary, as in some types of hydras, or they may attach to other polyps to form a colony, as corals do. In some cnidarians, such as those from the genus Obelia, the polyps of a single colony may perform specialized functions. Some polyps in a colony capture food, others reproduce, and others protect the colony. The medusa body resembles a saucer or umbrella. The mouth is located in the center of the undersurface of the saucer-like body, surrounded by tentacles. Medusae are solitary and most swim freely in the...

Nematocysts The name cnidarian derives from the Greek word knidos, meaning “nettle,” referring to the microscopic stinging structures known as nematocysts found on cnidarian tentacles. A cnidarian will stun a prey animal with its nematocysts and then use its tentacles to bring the prey to its mouth to swallow. Each nematocyst contains a coiled tubule that shoots out like a harpoon with explosive force. There are about 30 kinds of nematocysts that work in different ways to stun prey. The tubules of some nematocysts wrap around prey. The tubules of other nematocysts stick to prey, while other tubules pierce the surface of small animals. The nematocysts of some cnidarians contain poison that can paralyze or kill prey. related topics: Cnidarians Polyp and Medusa Structures Reproduction in Cnidarians Types of Cnidarians

Reproduction in cnidarians Reproduction in cnidarians varies among the different species. They may reproduce by means of asexual reproduction, sexual reproduction, or both. Polyps generally perform asexual reproduction by budding, in which an outgrowth from the body wall separates to form a new polyp or medusa. Medusae primarily reproduce sexually—they produce gametes (sex cells), and a gamete (sperm) from a male medusa fuses with a gamete (egg) from a female medusa to form a zygote. The zygote develops into a larva, which in turn develops into a polyp or medusa. The medusae of some cnidarians may also form polyps by budding. The reproductive life cycle of a typical jellyfish illustrates both asexual and sexual reproduction. Males release sperm and females release eggs into the water. When an egg and sperm fuse during sexual reproduction, a larva develops that attaches to a rock or other object and develops into a polyp. In a type of asexual reproduction, the polyp divides to form a co...

Scientists divide cnidarians into four classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa. They base this division partly on whether the polyp or medusa is more conspicuous during an animal’s life cycle. Hydrozoa In Hydrozoa, the polyp phase dominates in the animal’s life cycle. Most hydrozoan polyps reproduce by budding to form a polyp colony that fastens to solid objects such as rocks and pilings. Some hydrozoan polyps also bud to form a medusa, which is generally small and lives only a short time. This class comprises about 3,100 species, including the freshwater hydra (which lacks a medusa stage), the Portuguese man-of-war, and fire coral. Scyphozoa The medusa phase dominates in most of the 200 species of scyphozoans, the cnidarians most frequently referred to as jellyfish. Scyphozoan medusae are larger and have a more complicated structure than the short-lived medusae of the hydrozoans. Scyphozoan medusae live several months or more, reproducing sexually to form small, inconspicu...

Invertebrate, any animal lacking a backbone. Invertebrates are by far the most numerous animals on Earth. Nearly 2 million species have been identified to date. These 2 million species make up about 98 percent of all the animals identified in the entire animal kingdom. Some scientists believe that the true number of invertebrate species may be as high as 100 million and that the work of identifying and classifying invertebrate life has only just begun. Invertebrates live in a vast range of habitats, from forests and deserts to caves and seabed mud. In oceans and lakes they form part of the plankton—an immense array of miniature living organisms that drift in the surface currents. Invertebrates are also found in the soil beneath our feet and in the air above our heads. Some are powerful fliers, using wings to propel themselves, but others, particularly the smallest invertebrates, float on the slightest breeze. These tiny invertebrates form clouds of aerial plankton that drift unseen thr...

Invertebrates: Reproduction and Life Cycle Invertebrates display a wide variety of methods of reproduction. Some invertebrates reproduce by asexual reproduction, in which all offspring are genetically identical to the parent. Asexual reproduction methods include fragmentation, in which animals divide into two or more offspring, and budding, in which animals sprout buds that break away to take up life on their own. The majority of invertebrates reproduce sexually. The genes from two parents recombine to produce genetically unique individuals. For most invertebrates, sexual reproduction involves laying eggs. With a few exceptions, such as scorpions and spiders, most invertebrates abandon their eggs as soon as they are laid, leaving them to develop on their own. When invertebrate eggs hatch, the animals that emerge often look nothing like their parents. Some are so different that, in the past, zoologists mistook them for entirely new species. Young like this are known as larvae. As they g...

. Zoologists (scientists who study animals) classify invertebrates into about 30 major groups, known as phyla. These phyla vary enormously in the number of species they contain. Arthropods (phylum Arthropoda) are the invertebrate phylum with the most species—more than one million known species and countless more awaiting discovery. The mollusks (phylum Mollusca) make up the second largest group of invertebrates, with at least 50,000 species. Among the simplest invertebrates are the sponges (phylum Porifera). Other major invertebrate phyla include the cnidarians (phylum Cnidaria), echinoderms (phylum Echinodermata), and several different groups of worms, including flatworms (phylum Platyhelminthes), roundworms (phylum Nematoda), and annelids (phylum Annelida). Invertebrates Phylum: Placozoa -> Microscopic marine animal. Flattened body composed of two outer layers of flagellated cells enclosing loose cells. Reproduces asexually and possibly sexually. – Examples: Single species identi...

Phylum Phylum, in biology , major category, or taxon, of organisms with a common design or organization. This design is shared by all members of the phylum, even though structural details may differ greatly because of evolution . The assumption is made by biologists that all members of a phylum have a common ancestry. A phylum is part of the hierarchy of classification of organisms. It is an arbitrary grouping; that is, it is developed from a combination of scientific observation, theorizing, and guesswork in an attempt to find order in the complexity of living and extinct life forms. The same is true of all classification levels above and below it except for species, which consist of organisms known to be capable, at least potentially, of interbreeding (see Species and Speciation ). related topics: animal phyla plant phyla

Evolution Evolution, in biology, complex process by which the characteristics of living organisms change over many generations as traits are passed from one generation to the next. The science of evolution seeks to understand the biological forces that caused ancient organisms to develop into the tremendous and ever-changing variety of life seen on Earth today. It addresses how, over the course of time, various plant and animal species branch off to become entirely new species, and how different species are related through complicated family trees that span millions of years. Evolution provides an essential framework for studying the ongoing history of life on Earth. A central, and historically controversial, component of evolutionary theory is that all living organisms, from microscopic bacteria to plants , insects , birds , and mammals , share a common ancestor. Species that are closely related share a recent common ancestor, while distantly related species have a common ancestor f...

. Arthropoda -> Largest and most diverse invertebrate phylum characterized by animals with jointed limbs, a segmented body, and an exoskeleton made of chitin. Arthropods are abundant and successful in almost all habitats. The exoskeleton is divided into plates that enhance flexibility and movement. Periodic molting of the exoskeleton permits growth. Arthropods have a complex brain and nervous system. Many arthropods have a compound eye made up of numerous light-sensitive parts. Reproduction is sexual. – Examples: Ants, beetles, butterflies, lobsters, shrimp, crabs, scorpions, spiders, ticks Ectoprocta or Bryozoa -> Small, mostly marine animals that resemble simplified horseshoe worms, with a lophophore surrounding the mouth. They live in colonies, attaching to the sea bottom or seaweed. Bryozoans are hermaphroditic and reproduce asexually (by budding) and sexually. – Examples: Moss animals Entoprocta or Kamptozoa -> Small, mostly marine animals with a globular body mounted ...

. Annelida -> Segmented worms with a muscular body wall used for burrowing. External hairs called setae aid in traction during burrowing. An internal coelom is divided into compartments by walls known as septum. The digestive system stretches from the mouth to the anus, differentiated into regions, each with a different function. Reproduction is sexual. – Examples: Lugworms, earthworms, leeches Pogonophora -> Deep-sea worms that live in chitinous tubes attached to the ocean floor. Their long, slender body has a beard of tentacles at the head end. There is no mouth or digestive system and these animals absorb all nourishment through the body surface. They reproduce sexually. – Examples: Bead worms Vestimentifera -> Giant deep-sea worms that live in chitinous tubes attached to the ocean floor. They derive nutrition using a specialized organ called a trophosome to digest sulfide-oxidizing bacteria. – Examples: Llamellibrachs Sipuncula -> Marine worms with a saclike body an...

. Kinorhyncha or Echinodera -> Tiny worms with spiny bodies. An outer protective cuticle is segmented and articulated. Found in the muddy bottoms of coastal waters, they feed on microorganisms and organic particles by means of a sucking pharynx. Reproduction is sexual. Examples: Echinoderes, Condyloderes Nematoda -> Commonly known as roundworms, these animals are one of the most diverse and geographically widespread invertebrate phyla. Free-living roundworms inhabit freshwater and marine habitats, as well as soil. Parasitic roundworms prey on both plants and animals, causing widespread agricultural damage and disease. Roundworms have long, cylindrical bodies with a mouth surrounded by lips and sensory papillae or bristles. Fluid in the body cavity distributes nutrients and oxygen—roundworms do not have special respiratory or circulatory systems. Roundworms prey on other invertebrates as well as diatoms, algae, and fungi. They reproduce sexually and larvae undergo at least four ...

. Ctenophora -> Jellyfish-like marine animals distinguished by eight rows of cilia that propel the body in swimming. They feed on other invertebrates using two retractable sticky tentacles to capture prey. All ctenophores are hermaphroditic and reproduce sexually. Many are luminescent. – Examples: Sea walnuts, comb jellies Platyhelminthes -> Structurally simple worms with no anus or circulatory system. Known as flatworms, their flattened bodies enable internal tissues to be near the skin surface, permitting gas and nutrient exchange with the environment. A muscular layer just beneath the skin layer aids in locomotion. Flatworms are hermaphrodites and reproduce sexually. They typically have a life cycle involving a parasitic larval stage. Many types of flatworms are parasites of vertebrates. – Examples: Flatworms, flukes, tapeworms Mesozoa -> Minute parasitic animals of invertebrates, particularly squids and octopuses. These worms have a simple, elongated, ciliated body. The...

Herding Dog A herding dog or pastoral breed is a dog that either has been trained in herding or that is a member of a breed developed for herding. Dogs can herd other animals in a variety of ways. Some breeds, such as the Australian Cattle Dog, typically nip at the animals' heels. Others, notably the Border Collie, get in front of the animals and use what is called eye to stare down the animals; they are known as headers. The Koolie has been observed to use both these methods and to jump on the backs of their charges. All herding behavior is modified predatory behavior. Commonly herded animals include cattle, sheep, and reindeer, although it is not unusual for poultry to be handled by dogs.. For more information about the topic Herding dog, read the full article at Wikipedia.org. Related articles: Companion dog — Companion dog usually describes a dog that does not work, providing only companionship as a pet, rather than usefulness by doing specific tasks. Many ... > read more D...

. Kingdom Animalia includes more than one million living species, grouped into more than 30 phyla. Vertebrates, members of the phylum Chordata, comprise only one percent of these organisms. Phylum Arthropoda is more successful in sheer numbers, total mass, and distribution than all other groups of animals combined. The remaining animal phyla are composed of mostly marine-dwelling organisms. THE MAJOR PHYLA : Acanthocephala (Spiny-Headed Worm) Annelida (Annelids) Arthropoda (Arthropods)-> subphyla: Chelicerata, Crustacea, and Unirama Brachiopoda (Lampshell) Chaetognatha (Arrowworm) Chordata (Chordates)-> subphyla: Cephalochordata, Tunicata , Vertebrata ( fishes , amphibians , reptiles , birds , and mammals ) Cnidaria (Cnidarians) Ctenophora (Comb Jellies) Cycliophora (Symbion) Echinodermata (Echinoderms)-> Subphyla: Pelmatozoa, Eleutherozoa Echiura (Spoonworm) Ectoprocta (Moss Animals) or Bryozoa Entoprocta (Entoprocts) Gastrotricha (Gastrotrich) Gnathostomulida ...

Animal Husbandry pertains to breeding, feeding, and management of animals, or livestock, for the production of food, fiber, work, and pleasure. Modern methods concentrate on one type of animal in large, efficient farming units that generate animal products at the highest rate of return for investment. Intensive husbandry conditions include large numbers of animals in small lots, enriched feed, growth stimulation by various means, and vaccination against disease. Most of the world’s domestic animals, however, are raised in small units under less efficient conditions and at lower rates of return. Animals furnish more than one-fourth of the world’s total value of agricultural products. They supply a much higher proportion of human food in the developed countries than elsewhere. In the United States, animal products account for more than one-half of the total agricultural income. Traditional husbandry practices are closely associated with the degree of control needed over the animals that ...

Tardigrade Tardigrade, any of a group of tiny arthropod -like animals characterized by four pairs of stubby legs ending in large claws, a stout body, rounded back, and lumbering gait. They are also known as “water bears.” Tardigrades live worldwide in moist land habitats, along rocky shorelines, and on the bottoms of streams, lakes, and oceans. Their most striking feature is their ability to temporarily enter a nearly lifeless state known as anabiosis, which helps them survive environmental extremes. About 400 species of tardigrades are known and they range in length from 0.1 to 0.5 mm (0.004 to 0.02 in). Tardigrades are most commonly found in association with the water film on mosses, liverworts, and lichens. Their densities may reach 2 million individuals per sq m (185,874 per sq ft) of moss. Some live in hot springs and a few live in a symbiotic relationship with or on the bodies of other animals. Tardigrades use a pair of oral stylets, or needle-like mouthparts, to pierce the walls...