In what three terrestrial classes, which some cells of the embryo give rise to four extra embryonic membranes?
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The three terrestrial classes that give rise to the four extra embryonic membranes are mammals, birds, and reptiles.\n\nThe four membranes are:\n\nChorion. The outermost of the two fetal membranes - the amnion is the innermost --. which together surround the embryo. The chorion develops villi (vascular fingers) and gives rise to the placenta. In Greek, the word "chorion" means "skin or leather."\n\nAmnion. The amnion is a membranous sac which surrounds and protects the embryo. It is developed in reptiles, birds, and mammals, which are hence called 'Amniota'; but not in amphibia and fishes, which are consequently termed 'Anamnia'.\n\nAllantois. An extra-embryonic membrane of reptiles, birds, and mammals arising as a pouch, or sac, from the hindgut. In reptiles and birds it expands greatly between two other membranes, the amnion and chorion, to serve as a temporary respiratory organ while its cavity stores fetal excretions. In mammals other than marsupials the allantois is intimately associated with the chorion, contributing blood vessels to that structure as it forms—in conjunction with the endometrium, or mucosal lining, of the uterus—the placenta. \n\nYolk Sac. A membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals and functioning as the circulatory system of the human embryo before internal circulation begins.
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Well, the very basic need of developing embryos are food, water and protection.\nFood is usually provided as vitellum (egg yolk) in most vertebrates (including most fishes), although humans as placental mammals have done without the yolk and have a placenta through which the embryo gets nutrients from the mother.\nIn plants, the seed is an embryo with (usually) large amounts of food. Plant nutrients may be present as carbohydrates (starch, sugars, as in corn seeds), lipids (oils, as in peanut seeds) or even proteins (some beans such as soy).\n\nThe embryo of vertebrates needs to be protected within an aquatic medium, thus eggs either develop in water (as in fishes) or develop inside a capsule/eggshell/body cavity that has water (such as the amniotic sac within the womb in mammals). They also get water from their environment, their mother (in the case of viviparous animals) or metabolism of their food reserves.\n\nPlant embryos are able to extract water from their environment and also partly by metabolization of nutrients.  \n\nProtection is given by rigid shells or other covers that are usually provided by the parent organism, and sometimes (as in the case of the extraembryonic membranes of mammals and others) formed by the developing new being itself.\n\nThese are just some basic points, I hope it helps you to find more information in your textbooks.
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Ditto on druid's answer.  All three germ layers develop from the same "layer" (in a simple explanation, after gastrulation, the ecotoderm gives rise to the rest of the germ layers) ... therefore, they can't REALLY be separated out, even after full development.  Hence, the notochord is actually a derivative of all 3.  This is quite interesting and has many implications for much deeper research into embryology and the "sense" system after birth and onward ... things like synesthesia, perception, "consciousness," etc., and on.\nThe following link is a simple (doesn't get in depth into the explanation), yet GREAT diagram.  Enjoy!\n\nhttp://www.luc.edu/depts/biology/dev/layer.htm
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1. amnionic membrane, contains, pressure, shock, movement, temperature\n2. planceta\n\nFunction of the Planceta\n1. oxygen, nutrients\n2. wastes (like carbon dioxide)\n3. can't rmeber this one sorry\n4. plancenta does that
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Basically diplobiont. \nIn other organisms (plants, fungi), there are longer haploid or haploid + diploid phases. \nMetazoans are diploid; the only haploid stage in their life cycle are the gametes, which fuse to form the diploid zygote.
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Structure of the Amniotic Egg\nEvolution of eggs with a water-impermeable amniotic membrane surrounding a fluid-filled amniotic cavity permits embryonic development on land without danger of dessication. The main diagram shows the arrangement of membranes in a typical egg-laying oviparous vertebrates. In live-bearing viviparous vertebrates, the shell and chorionic membrane are absent and the allantoic and yolk sac membranes are incorporated into the connection with the maternal circulation\n( http://www.mun.ca/biology/scarr/Amniotic_egg.htm )\n\nThe amniotes are a microphylum of tetrapod vertebrates that include the Synapsida (mammals) and Reptilia (reptiles and dinosaurs, including birds). They are defined by embryonic development that includes the formation of several extensive membranes, the amnion, chorion, and allantois. Amniotes develop directly into a (typically) terrestrial form with limbs and a thick stratified epithelium, rather than first entering a feeding larval tadpole stage followed by metamorphosis as in amphibians. In amniotes the transition from a two-layered periderm to cornified epithelium is triggered by thyroid hormone during embryonic development, rather than metamorphosis [1]. The unique embryonic features of amniotes may reflect specializations of eggs to survive drier environments, or the massive size and yolk content of eggs designed for direct development to a larger size.\n\nFeatures of amniotes designed for survival on land include a sturdy but porous leathery or hard eggshell, and an allantois designed to facilitate respiration while providing a reservoir for disposal of wastes. Their kidneys and large intestines are also designed to retain water. Most mammals do not lay eggs, but corresponding structures may be found inside the placenta.\n\nThe first amniotes looked like small lizards, for instance Casineria kiddi who lived for about 340 million years ago, and their eggs were small and covered with a membrane, not a hard shell like often seen today. Some modern amphibians lay eggs on land but without any protection to speak of, while others like some lungless salamanders and Amphiuma also lay small eggs on land, but these are covered by a rubber-like membrane even if they lack advanced traits like an amnion. This kind of eggs became possible with internal fertilisation. The outer membrane, a soft shell, evolved as a protection against the harsher environments on land. It was probably because the embryos were safer on land than in water that some species got the habit of laying them out of the water. One can assume the ancestors of the amniotes laid their eggs in moist places, as such animals wouldn't have too many difficulties in finding depressions under fallen logs or other suitable places in the ancient forests, and dry conditions were probably not the main reason why the soft shell emerged.\n\nIn fish and amphibians there is only one inner membrane, also called an embryonic membrane. In amniotes the inner anatomy of the egg has evolved further, new structures have developed to take care of the gas exchanges between the embryo and the atmosphere, as well as dealing with the waste problems. To grow a thicker and thougher shell there were no other alternatives than finding new ways to supply the embryo with oxygen, as diffusion alone wouldn't be enough any more. After the egg had gotten these structures, further sophistication of them allowed the amniotes to lay much bigger eggs in much drier habitats. Bigger eggs meant bigger offspring, and bigger adults meant bigger eggs, which meant the amniotes had gotten the opportunity to grow bigger than their ancestors. But real growth was not possible until they stopped relying on small invertebrates as their main food source, and started to eat plants or other vertebrates, or returned to the water. New habits and heavier bodies meant further evolution for the amniotes, both in behavior and anatomy.\n\nThere are three main lines of amniotes, wh
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Multicellular organisms
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Both are eukaryotic (containing a "true nucleus").  \n\nAnimal Cells lack a cell wall and adjacent cells are connected by junctions (adhesive, gap or tight).  Animal cells contain centrioles (help create microtubules used in mitosis and meiosis) and lysosomes (organelles used to digest wastes and old organelles). During telophase and cytokinesis the cells separate via a cleavage furrow.\n\nPlant Cells contain a cell wall (think of the cell wall as the "skeleton" composed mainly of cellulose) and rely on turgor pressure to keep them upright.  Adjacent cells are connected by channels called plasmodesmata.  You will not find centrioles or lysosomes in a plant cell, but you will find a really cool organelle called a large centrol vacuole.  This organelle is where the water is stored in a cell and it helps maintain the turgor pressure described above.  It also acts as a lysosome, storing chemicals and waste products.  The Central vacuole can also store the pigments you see in flowers as well as poisons used to deter predators.  And of course, in a plant cell you will find the plasts as mentioned by someone earlier.. including the famous chloroplasts (the site for photosynthesis) as well as the chromoplasts (contain pigments) and amyloplasts (specialized for starch storage). During telophase and cytokinesis, the cells are separated by a structure called a cell plate.   \n\nUmmm, that's all I can come up with right now!
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Nature has determined this design to be the most efficient and useful for higher order organisms.  There are two types of cell "designs", prokaryotic (bacteria) and eukaryotic (plant and animal cells).  It is thought that at one point all living things were prokaryotic, then at some point in our evolution a nuclear envelope was developed and proved to be beneficial to the organism, thereby natural selection allowed for the continuation of a nuclear envelope.  As time went by plants and animals both evolved from some ancestor of this first eukaryotic cell and henceforth have similar cell designs.  As for the actual benefits of this design, the nuclear envelope of plant and animal cells serve to protect the DNA, and therefore genes, of the animal from damage, and also serves as a type of filter seperating cellular processess in the cytosol from gene regulation in the nucleus.
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Living cells such as eukaryotes have many organelles such as: a nucleus, Mitochondria, Rough and smooth endoplasmic reticulum (rough has ribosomes on the surface of it), Golgi body, Lysosomes, cytoplasm, ribosomes and so on\nOther types of cells include prokaryotes, these don't have a nucleus or any other membrane bound organelles... they also have other organelles of which I can't really be bothered listing at the moment. hehe
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echinoderms, chordates, hemichordates, protostomes, Ecdysozoa \nLophotrochozoa \nPlatyzoa
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Plant cells are surrounded by a cell wall and have chloroplasts and large central vacuoles.  Animal cells have lysosomes and centrioles.
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Skin, neural crest cells, and the neural tube are all derived from ectoderm in the embryo.\n\nMuscle cells are derived from mesoderm.
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That all living organisms (known to date) come from one ancestor (somewhat of a pre-cell)
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Erm... you're alive?\n\nThe mesoderm is a layer of cells that forms during embryogenesis in animals that have bilateral symetry (i.e. as opposed to radial symmetry). From this layer, all your organs form.\n\nFormed at the same time as the mesoderm is the ectoderm (from which your skin and neural tissue forms) and the endoderm (from which your gut and digestive tract form)
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Extra-Terrestrials\nALIENS
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The plant kingdom, one of four eukaryotic kingdoms, is composed of multicellular, autotrophic organisms that photosynthesize to fix inorganic carbon (from atmospheric CO2) into organic molecules. Plants are the foundation of all terrestrial habitats, and serve as terrestrial Earth’s primary autotrophs, making organic molecules that will cycle through the food webs of most ecosystems. The photosynthetic capabilities of plants ultimately allow all terrestrial members of the animal kingdom to survive.\n\nOne hallmark of plant cells is the cell wall, which, in contrast to cell walls of single-celled organisms, is made of cellulose. The cell walls provide support for plant cells, as well as support and cohesiveness for plant tissue. Unlike the plasma membrane, the cell wall is not a semipermeable membrane, and so the shared cell walls between adjoining plant cells must have openings, plasmodesmata, to allow material transport and communication. Another distinguishing feature of plant cells is the large central vacuole, which stores a water reserve as well as essential chemicals, waste products of cellular metabolism, and sometimes other species-specific functions, such as storage of poisons or flower pigments. The central vacuole can also aid in cell growth by absorbing water.\n\nExcluding a few photosynthetic protists and cyanobacteria, plant cells are the only cells that contain chloroplasts. These organelles carry out the processes of photosynthesis, converting light energy into chemical energy and storing it as sugar. As well as producing food for ecosystems, photosynthesis releases oxygen molecules as byproducts, which replenish atmospheric oxygen used in cellular respiration and form a layer of ozone, O3, which shields the earth from solar ultraviolet rays.\n\nPlants probably evolved from multicellular green algae called charophytes and were the first multicellular organisms to colonize land. In order to do this, plants had to evolve several new characteristics in the form of distinct, specialized organs, which protists and algae lack. First of all, plants need to have a form of anchorage in the ground and rigid stem tissue for support. Thus, plants have developed root structures, which, in addition to anchoring a plant in the ground, allow the plant to take up chemical nutrients from the soil. Cellulose-containing cell walls developed in plant cells to maintain a form of rigidity in the part of the plant above ground. These account for the stiffness of plant stems and from the hardness of wood. Marine algae, which are suspended in water and can absorb nutrients from all around, have neither of these structures. Also, to prevent water loss in a terrestrial environment, plants evolved a waxy cuticle, which covers stem and leaf surfaces. Gases for photosynthesis can not diffuse across this cuticle, so tiny pores called stomata are present in the cuticle.\n\nBecause plants have organs that serve different functions, they must have systems to distribute necessary substances throughout the plant. Sugars, produced in photosynthesis, must be distributed to the body and roots of the plant that do not photosynthesize. Water and nutrients from the soil, taken up by the roots, must also make their way into the plant body and leaves. To perform these essential functions, plants contain a vascular tissue network, which consists small tubes running throughout the plant. There are two types of vascular tissue: xylem, which are small tubes dead cells that transport water and minerals up from the roots, and phloem, which are living cells that distribute sugars produced in photosynthesis.\n\nAlso characteristic of plants, as well as some algae, are gametangia that protect gametes. These are pockets of cells that protect the egg cell, and where the egg is fertilized.\n\nPlants have a life cycle unlike that of any animal, fungus, or bacteria. Probably a trait inherited from protistan (algal) ancestors, diploid and haploid generations alternate