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Muscle Origin and Insertion: Definition and Actions
The major is well suited for those who plan to teach biology, who wish to enter government or industrial employment in health or environmental professions, or who prefer educational breadth as an end in itself. Department of Agriculture introduced the Food Guide Pyramid. Your next lesson will play in 10 seconds. Job Options and Requirements Lawyer for Contracts: Pre-medical and Human Health Professions--This area emphasizes preparation for further study in medical school or allied human health professions such as dentistry, optometry, genetic counseling, physical therapy, occupational therapy, physician assistant, nursing, chiropractic, and others. They help maintain cellular membranes.

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Molds are multicellular fungi that reproduce by the formation of spores single cells that can grow into a mature fungus. Spores are formed in large numbers and are easily…. Division of organisms into kingdoms In plant: Definition of the kingdom In microbiology: Fungi bioluminescence In bioluminescence: The range and variety of bioluminescent organisms cereal crop damage In cereal farming: Fungus diseases conservation and biodiversity In conservation: How many species are there?

Articles from Britannica Encyclopedias for elementary and high school students. Help us improve this article! Contact our editors with your feedback. Introduction Importance of fungi Form and function of fungi Size range Distribution and abundance Basic morphology Structure of the thallus Sporophores and spores Growth Nutrition Saprotrophism Parasitism in plants and insects Parasitism in humans Mycorrhiza Predation Reproductive processes of fungi Asexual reproduction Sexual reproduction Sexual incompatibility Sexual pheromones Life cycle of fungi Ecology of fungi Lichens Basic features of lichens Form and function of lichens Evolution and phylogeny of fungi Outline of classification of fungi Classification of the fungi Distinguishing taxonomic features Annotated classification Critical appraisal.

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Course materials are presented via audiovisual materials. Course materials are presented viaaudiovisual materials. Methods of instruction include audio visual materials and computer-based training. April - November December - Present. Version 1 and 2: Introduction to criminology; crime categories, characteristics and elements; measuring crime through criminal justice research; crime patterns and trends; victimization in criminal justice; rational choice and trait theories in criminology; social structure and social process theories in criminology; social conflict theories and restorative justice; developmental theories of crime; overview of violent crime; types of murder; types of sex crimes; basics of property crime; economic and public order crimes; crimes of moral turpitude; political crime and terrorism; understanding cyber crime; American criminal justice systems; law enforcement in America; and punishment and corrections.

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Major topics include an overview of anatomy and cell biology; human respiratory system; cardiovascular system; blood vessels; digestive system; urinary system; endocrine system; the brain; the nervous system at the cellular level; the five senses; muscle physiology; gross anatomy of muscular system; connective tissue; skeletal system; and male and female reproductive systems.

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Course materials are prestend via audio visual materials. Credit may only be awarded for this course or Biology National College Credit Recommendation Service. Search Google Appliance Enter the terms you wish to search for. Search for an Organization: Search by Course Title: Source of Official Student Records Mr. 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.

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