A definition of animals
Sinking or settling of the Earth's surface. Freshwater Sharks Bite Children at 35th Beach. In humans, the four dominant phyla are Firmicutes , Bacteroidetes , Actinobacteria , and Proteobacteria. In , Sir Edward Mellanby incorrectly identified rickets as a vitamin A deficiency because he could cure it in dogs with cod liver oil. Absorption of Micronutrients and Water into the Bloodstream. Human Physiology - Cell structure and function. Southern for transferring DNA fragments, separated in electrophoretic gels, onto membrane filters.
Meanings of biological terminology
The cells of the body taken as a whole, in opposition to germ cells. Any cell in the body except gametes and their precursors. The incorporation new genetic material into somatic cells for therapeutic purposes. The new genetic material cannot be passed to offspring.
A mutation in a non-reproductive cell. Blocks of mesoderm along the sides of a chordate embryo. Southern for transferring DNA fragments, separated in electrophoretic gels, onto membrane filters.
Used to detect specific fragments by complementary radioactive probes. In taxonomy , a division of a genus. A given type of organism is treated as a species if it is assigned a binomial name. However, there is no general consensus among scientists concerning how to decide whether any given group of organisms should be so treated, since there is no general agreement among biologists on the definition of the word species.
A graphic of all an organism's chromosomes , each labeled with a different color. An instrument that measures the intensity of a light beam of a particular wavelength, both before and after passing through a light-absorbing medium. During spermatogenesis , the immature products of the second meiotic division. During spermiogenesis , each haploid spermatid develops, without further division, into a functionally mature spermatozoon. Either of two types of cells that originate from the spermatogonium during spermatogenesis and that develop, via division into spermatids.
The first of these two types is the primary spermatocyte , which is a mature sex cell that develops from the spermatogonium without division.
The second is the secondary spermatocyte , which is produced from the primary spermatocyte by division. The process producing spermatozoa. A mature male haploid gamete capable of active movement by means of a undulipodium. During spermatogenesis , spermatozoa form in huge quantities within the seminiferous tubules of the testes. In shape, a spermatozoon resembles a tadpole.
It has an oval, flattened head containing a haploid nucleus. A human spermatozoon is about 0. When a spermatozoon pierces an ovum it loses its tail as the two cell fuse. The process during which spermatids mature into fully functional spermatozoa. S phase The portion of interphase during which chromosomes are replicated. The family of birds comprised of the penguins. The order of birds comprised of the penguins. The genus of birds comprised of the banded penguins.
A ring of muscle controlling passage of an orifice. A developmental defect characterized by failure of fusion of vertebral arches, with or without protrusion and dysplasia of the spinal cord or its membranes.
The column of nervous tissue that in vertebrates runs along the back, and that in bony animals is enclosed within the vertebral column. In humans, it gives rise to all the nerves of the trunk and limbs. The prominence at the posterior extremity of a vertebra.
A genus of helical microorganism belonging to the family Pseudomonadacea Spirillum minus is the causative agent of rat-bite fever. Any member of Spirochaetes, a phylum of helical bacteria. Three spirochete genera , Borrelia , Leptospira , and Treponema , contain organisms that are important causative agents of human disease. A device for measuring respiratory capacity. The study of the internal organs. An angular bend in the large intestine between the transverse and descending colons.
Inflammation of, and resulting damage to, the vertebrae. A supposed process — that has never actually been observed — in which living things arise from nonliving matter. A case containing developing spores. A new type of organism arising in a single generation. The term is usually applied to plants, but sometimes, especially in older literature, also to animals for example, Darwin called the Ancon sheep a sport.
The name is derived from the Latin term lusus naturae , "sport of nature," which expressed the idea that nature was in some way play a game and entertaining itself when it made new organisms in this way. The production of spores. The most diverse order of Class Reptilia; includes the lizards, snakes, and worm lizards. The positive square root of the variance ; a commonly used measure of variability.
Sore throat caused by staphylococcus. Presence of staphylococcus in the blood. A genus of gram-positive cocci usually present on human skin and mucous membranes.
Under the microscope it can be seen that staphylococci are round in shape i. Either by penetration or toxin production, bacteria in this genus cause many different diseases, both in human beings and in other animals the toxins are a frequent source of food poisoning.
A muscle of the soft palate. It narrows the fauces and blocks off the nasopharynx. Starch polymers are cleaved by the enzyme amylase. The persistence of a fossil form unchanged over geological time. Presence of excessive fat in the stools. Able to tolerate only a narrow range of temperatures. The flat bone at the front of the chest that connects the ribs on one side with those on the other.
An individual segment of the sternum. Cholesterol is the most widely known sterol. The sticky tip of a carpel ; the stigmata are the parts of a flower that receive pollen. Microscopic pores in the epidermis of plants; stomata allow gas exchange with the atmosphere. A baglike, elastic portion of the digestive tract following the esophagus. Lying beneath the diaphragm. It secretes acidic gastric juices that convert proteins into peptones. It lies between the stratum granulosum and stratum corneum.
Caused by or related to streptococci. A genus of gram-positive cocci , of which most strains are harmless. However, some are both common and among the most dangerous of human pathogens. Streptoccocal inflammation of the skin. Large mineral structures formed in shallow water by microorganisms , especially cyanobacteria. Some stromatolites are among the most ancient fossils known, dating to about 3. The determination, by means of both experimental techniques and computer simulation, of the three-dimensional structures of proteins.
A protein that contributes to cell or tissue structure. A slender, pointed process on a bone at the attachment point of certain muscles in particular, the styloid process of the temporal bone. Pertaining to or connecting the lower jaw mandible and the styloid process.
A waxy, waterproof, air-proof substance found in the layers of dead cork cells that sheathe woody stems and mature roots.
The infiltration of plant cells with suberin. In taxonomy , a division of a kingdom ; specifically, a category ranking beneath an kingdom, but above a phylum.
South of the Sahara Desert, in Africa. Sinking or settling of the Earth's surface. An enzyme that hydrolyzes sucrose into fructose and glucose. Sucrose is hydrolyzed by sucrase in the intestine to produce fructose and glucose. Synthetic substances containing the sulfonamide group, many of which are used as antimicrobial agents. The first antibiotics discovered were sulfonamides. An essential component of all living cells, sulfur is present in the amino acids cysteine and methionine.
Within the human body, sulfur occurs in many bacterial defense molecules. It is also present in many antibiotics, and, in its elemental form is an important fungicide, particularly within the context of organic agriculture.
Heteropaternal superfecundation occurs when separate fertilizations result from two or more inseminations administered by two or more different males. In addition to the usual number. A compound that contains the superoxide anion. An enzyme that catalyzes the conversion of superoxide into hydrogen peroxide and oxygen.
Above or on top of the kidney. An operation; 2 the branch of medicine dealing with such procedures; 3 the room in which such procedures are carried out 4 British the room where a doctor sees patients. Svedberg unit S A sedimentation coefficient of 1 x 10 sec.
A relationship, between two distinct types of organisms, in which they live together. Symbiosis is of three types: Occupying overlapping geographic regions. Webbing or fusion between two or more fingers. Under such circumstances, it is generally claimed that the trait arose after the divergence of the most recent common ancestor of the taxa in the related group, but before the divergence of those taxa.
Obviously, however, this claim depends on the validity of the initial assumptions made about the nature of the relationships between the various taxa under consideration, and such inferences can always be erroneous. The junction between neurons that permits a one neuron to pass a signal to another. To join or fuse; within the context of biology this term is used primarily with regard to meiotic synapsis. Mammal-like reptiles or reptile-like mammals that flourished in the late Paleozoic and early Mesozoic.
The intimate fusion of homologous chromosomes during prophase I of meiosis. Of or pertaining to a synapse. The bulbous structures on the end of an axon , each of which contains many synaptic vesicles. One of the many minute vesicles in a synaptic knob where neurotransmitters are stored.
Pertaining to or being a syncytium. A single cell containing multiple nuclei. Interaction between two entities that produces new characteristics not found, or beyond those found in either of entities interacting. Involving, or characterized by synergy. These plans are established during the embryonic stages of development and limit the size and complexity of the animals. Symmetry, number and relative development of tissue layers, presence and nature of body cavities, and several aspects of early development define these fundamental modes of organization.
Although the two phyla in this subkingdom, Porifera sponges and Placozoa, lack clearly defined tissues and organs, their cells specialize and integrate their activities. Their simplicity has been adaptive, and sponges have remained important in benthic marine habitats since their origin. The sessile, filter-feeding way of life shown by sponges has favoured a body plan of radial symmetry, although some members have become asymmetrical.
The shape of the creeping, flattened placozoans is irregular and changeable. The two coelenterate phyla Cnidaria and Ctenophora advanced in complexity beyond the parazoans by developing incipient tissues—groups of cells that are integrally coordinated in the performance of a certain function.
For example, coelenterates have well-defined nerve nets, and their contractile fibres, although only specialized parts of more generalized cells, are organized into discrete muscle units. Because discrete cells of different types do not carry out the internal functions of the animals, coelenterates are considered to be organized at only a tissue level. The integration of cells into tissues, particularly those of nerve and muscle, permits a significantly larger individual body size than is possible with other modes of body movement.
Flagella and cilia become ineffective at rather small size, and amoeboid movement is limited to the size a single cell can attain. Muscles contract by a cellular mechanism basically like that used in amoeboid locomotion—interaction of actin and myosin filaments. Through coordinated contraction of many cells, movement of large individuals becomes possible. Coelenterates, like parazoans, have only two body layers, an inner endoderm primarily for feeding and an outer ectoderm for protection.
Between the endoderm and the ectoderm of coelenterates is the mesoglea , a gelatinous mass that contains connective fibres of collagen and usually some cells.
Both layers contain muscle fibres and a two-dimensional web of nerve cells at the base; the endoderm surrounds a central cavity, which ranges from simple to complex in shape and serves as a gut, circulatory system , and sometimes even a skeleton. The cavity is also used for gamete dispersal and waste elimination. Cleavage of a fertilized egg produces a hollow sphere of flagellated cells the blastula.
Invagination of cells at one or both poles creates a mouthless, solid gastrula; the gastrula is called the planula larva in species in which this stage of development is free-living. The inner, endoderm cells subsequently differentiate to form the lining of the central cavity.
The mouth forms once the planula larva has settled. Although the details of early development are different for parazoans and coelenterates, most share a stage in which external flagellated cells invaginate to form the inner layer, which lines the cavity, of these diploblastic two-layered animals.
This is characteristic of invagination during the development of all animals. All coelenterates are more or less radially symmetrical. A radial form is equally advantageous for filtering, predatory, or photosynthetic modes of feeding. Tentacles around the circumference can intercept food in all directions.
All animals except those in the four phyla mentioned above have bilaterally symmetrical ancestors and contain three body layers triploblastic with coalition of tissues into organs. The body plans that are generally recognized are acoelomate, pseudocoelomate, and coelomate. Acoelomates have no internal fluid-filled body cavity coelom. Pseudocoelomates have a cavity between the inner endoderm and the middle mesoderm body layers.
Coelomates have a cavity within the mesoderm , which can show one of two types of development: Most protostomes show schizocoelous development, in which the mesoderm proliferates from a single cell and divides to form a mass on each side of the body; the coelom arises from a split within each mass.
Deuterostomes show enterocoelic pouching, in which the endoderm evaginates and pinches off discrete pouches, the cavities of which become the coelom and the wall the mesoderm. The animals in these major divisions of the Bilateria differ in other fundamental ways, which are detailed below. Unlike sessile sponges or floating jellyfish , the Bilateria typically move actively in pursuit of food, although many members have further evolved into sessile or radial forms.
Directed movement is most efficient if sensory organs are located at the head or forward-moving end of the animal.
Organs of locomotion are most efficiently arranged along both sides, a fact that defines the bilateral symmetry; many internal organs are not in fact paired, whereas muscle layers, limbs, and sensory organs almost invariably are. The diffuse nerve net of coelenterates coalesces into definite tracts or bundles, which run posteriorly from the anterior brain to innervate the structures of locomotion. Flatworms phyla Platyhelminthes , Nemertea , and Mesozoa lack a coelom, although nemerteans have a fluid-filled cavity at their anterior, or head, end, which is used to eject the proboscis rapidly.
The lack of a fluid-filled cavity adjacent to the muscles reduces the extent to which the muscles can contract and the force they exert see below Support and movement. Because most also lack a circulatory system, supplying muscle tissues with fuel and oxygen can be no faster than the rate at which these substances diffuse through solid tissue.
Flatworms are thus constrained to be relatively flat and comparatively small; parasitic worms, which do not locomote, can achieve immense lengths e. The larger of the free-living flatworms have extensively divided guts, which reach to within a few cells of the muscles, thus compensating for the lack of a circulatory system.
Most flatworms have but one opening to the gut. Nemerteans, in addition to a coelom-like housing for their proboscis, have attained a one-way gut and a closed circulatory system. Both increase their ability to move food and oxygen to all parts of the body.
Flatworms are considered to be the ancestors of all other Bilateria. The pseudocoelomates include the nematodes, rotifers, gastrotrichs, and introverts. Some members of some other phyla are also, strictly speaking, pseudocoelomate. These four phyla of tiny body size many species no larger than the bigger protozoans are placed together in part because they lack mesoderm on the inner side of the body cavity. Consequently, no tissue, muscular or connective, supports the gut within the coelomic fluid.
For tiny organisms, this is advantageous for conservation of tissue: The inconspicuousness of most of these phyla has led to a slow advancement in understanding their phylogenetic position in the animal kingdom. The advantage of a true coelom is the ability of the inner mesenteric mostly connective tissue layer to suspend the central gut in the middle of the animal. Otherwise, in those animals with a body cavity used in locomotion, gravity would pull the gut down and severely curtail body size.
Coelomates have attained vastly larger body sizes than has any other group of animals. Within the coelomates, the coelom has been of variable significance to the form and diversity of the various phyla.
For example, it is essential for the burrowing abilities of annelids and related phyla. It has largely lost this significance in the arthropods, however, which have transferred locomotion to limbs supported by an exoskeleton rather than a coelomic hydroskeleton. Suspension is the main function of the coelom in vertebrates, which achieve the largest body sizes among animals by virtue of an endoskeleton that does not need to be shed during growth.
The protostome coelomates acoelomates and pseudocoelomates are also protostomes include the mollusks, annelids, arthropods, pogonophorans, apometamerans, tardigrades, onychophorans, phoronids, brachiopods, and bryozoans. Deuterostomes include the chaetognaths, echinoderms, hemichordates, and chordates. In early development protostome coelomates mostly differ from deuterostome coelomates in the following ways: Deuterostomes , in contrast, show indeterminate, radial cleavage, with the dividing cells becoming layered and the fate of early cells a product of where they are positioned later in development.
The two phyla that have clearly dominated both land and sea since nearly the beginning of animal evolution are the arthropods and chordates, protostomous and deuterostomous coelomates, respectively.
A key to arthropod success has been the differentiation of many serially repeated parts, in particular jointed appendages with a rigid exoskeleton , to perform the varied functions necessary to maintain life. The exoskeleton, however, sets a moderate upper limit to body size. In contrast, vertebrates share all habitats with arthropods by virtue of the larger maximum size permitted by the development of an internal rigid skeleton.
More than does a coelom, the evolution of rigid, jointed skeletons has allowed these two phyla to dominate most animal communities. Large size is often competitively advantageous but unobtainable by many animals because of constraints of basic body plan.
Intrinsically small animals sometimes become large in the same way that protozoans evolved into metazoans: This type of asexual sociality forms the colonoids of sponges, coelenterates, bryozoans, hemichordates, and tunicate chordates, all of which were primitively small, sessile filter feeders. Staying together after asexual budding of new individuals gave a competitive edge to monopolizing available space.
With slight modifications so that all individuals in the colony could share equally in the gains, these larger entities had the energy reserves necessary to outcompete smaller organisms for space.
This type of sociality has evolved in ways that complicate the definition of individuality. For instance, Portuguese men-of-war and their kin some hydrozoan coelenterates look and act like single individuals, yet their components develop as genetically identical units, each homologous to a whole jellyfish or polyp.
It is a question whether such an animal should be considered one individual or many. A different type of sociality emerged among mobile complex animals that can individually attain large size. In fact, the largest known living animals, the whales and elephants, comprise two of a very few mammalian orders that contain only social species. The pattern of evolution on Earth has favoured sociality in the smallest and the largest mostly vertebrates of animals, albeit for different reasons.
The smallest seek the advantages of being large, as protozoans did to form the first animals. The large animals can communicate; they spread out to find food, which all can share, and they protect one another. Among the social groups of large animals, only humans have differentiated their functions to such an extent that their societies begin to behave as individuals. Insect societies show behaviours halfway between societies based on genetically identical members and those created by genetically different individuals; such properties largely reflect their intermediate degree of genetic relatedness.
Insects are more cooperative and show a greater degree of altruism than is true of vertebrate societies. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.
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