<span>Wings have evolved several times independently. In flying fish, the wings are formed by the enlargement of the pectoral fins. Some fish leap out of the water and glide through the air, both to save energy and to escape predators. If they were already gliding, then any mutation that would result in an increase of the gliding surface would be advantageous to the fish that has it. These advantageous may allow these fish to out-compete the others.
Wings have also evolved in bats, pterosaurs, and birds. In these animals, the wings are formed by the forelimbs. In some lizards that have evolved gliding flight, however, the "wings" or gliding surfaces may be quite different. The lizard Draco, for example, has gliding surfaces formed by an extension of the ribs. A number of extinct reptiles have similar gliding surfaces. Frogs that glide have expanded webbing on their hands and feet. Gliding ("flying") squirrels and marsupial sugar gliders have flaps of skin that lie between the front and rear limbs. These gliding animals all have one thing in common: a gliding surface that is formed by enlarging some parts of the body.
In pterosaurs, the wing is formed by an elongated finger and a large skin membrane attached to this finger. In bats, the wing is formed by the entire hand, with skin membranes connecting the elongated fingers. In birds, flight feathers are attached to the entire forelimb, while the fingers have fused together. In all of these animals except birds, the wing is a solid structure. In birds, however, the wing is formed by a large number of individual feathers lying close to each other and each feather is in turn formed by filaments that interlock.
Biophysicists have determined that flight most likely evolved from the tree down. That means most active flyers evolved flight from an animal that was already gliding. Gliding was therefore probably an indispensable intermediate stage in the evolution of flight. Since gliding has evolved in so many different groups of animals, it follows that the ancestors of birds, bats, and pterosaurs were almost certainly gliders.
Unfortunately, the fossil records of the immediate gliding ancestors of birds, bats, and pterosaurs are all missing. The first known bat and bird fossils are recognizable as flyers. The same is true of pterosaurs. Therefore the origin of these flyers remain a mystery and a subject of often acrimonious debate. There are people who claim that dinosaurs evolved insulation, which then evolved into feathers, but the evidence for that is lacking. The so-called proto-feathers found on some dinosaurs are indistinguishable from the collagen fibers found in the skin of most vertebrates. Some of the supposedly feathered dinosaurs, such as Caudipteryx and Protarchaeopteryx, are actually flightless birds. The same is probably true of Microraptor fossils, which are (as Alan Feduccia says) probably "avian non-dinosaurs."
Even though the immediate ancestor of birds remains a mystery, there is a fossil known as Longisquama insignis, which lived during the late Triassic. It has featherlike structures on its back. It was probably a glider of some sort. So, this animal may well be the distant ancestor of Archaeopteryx, the oldest known bird.
In sum, flying almost certainly evolved from animals that were already gliding, or from the tree down, not from the ground up. The dinosaurian origin of birds requires that dinosaurs evolved feathers from insulation and flight to have evolved from the ground up. Both of these requirements are extremely unlikely to have occurred in evolutionary history, because dinosaurs are almost certainly ectothermic (or "cold-blooded") and therefore they never evolved insulation, and because feathers are too unnecessarily complex to have evolved as insulation. Flight from the ground up is also dangerous because large animals that attempt to fly from the ground may crash and seriously injure or even kill themselves. We all know how dangerous an airplane can be if it loses power and crashes. Small and light weight animals, OTOH, that were already gliding can survive if their attempt to fly fails. Finally, if flight evolved from gliding, then why do animals glide? The answer is that gliding is energetically much cheaper than to descend a tree, walk along the ground, and then climb up another tree. Besides, it is almost certainly much safer to glide from one tree to another than to be walking on the ground for many arboreal animals.
See link below for details of why dinosaurs are considered ectothermic according to the available scientific evidence.</span>Source(s):<span>http://discovermagazine.com/1996/dec/aco...</span>
In asexual reproduction, reproductive organs aren't used but they're used.
advantage of sexual- A lot of genetic variation. since they have DNA of two parents. they can survive more and adapt more.
disadvantage of asexual- diversity is limited. Since the organism only gets the DNA of one parent, they wouldn't be able to really survive if something happened.They would easily be extinct.
Sorry I can't really cone up with better words but I hope you get the idea. it all comes down to natural selection really if you've learned about it. Hope it helped!!!
While a light microscope uses light to illuminate specimens and glass lenses to magnify images, an electron microscope uses a beam of electrons to illuminate specimens and magnetic lenses to magnify images. The resolution (the level of image detailing) is the main difference between these two microscopes.
A compound light microscope is a microscope with more than one lens and its own light source. In this type of microscope, there are ocular lenses in the binocular eyepieces and objective lenses in a rotating nose piece closer to the specimen.
1. Cycle - A cycle is the series of events regularly repeated in a particular order or sequence. The cycle can be repeated at a particular time or whenever they are started.
2. Material - It is the mixture or combination of various substances in a particular ratio. It can be living or nonliving and makes an object or organs.
3. Ecosystem - It is a geographical area where different forms of life or living or biotic factors and abiotic factors interact with one another and live in a stable form.
4. water cycle - hydrologic cycle or water cycle the cycle that deals with the movement of the water above or below of the earth through various forms. Sun plays important role in evaporating the water.
5. Nitrogen cycle - It is the cycle that deals with the movement of nitrogen or nitrogen compounds through various spheres of earth. It is a biogeochemical cycle which means it converts to various chemical compounds and interacts with the biosphere and atmosphere.
6. Oxygen Carbon - Dioxide Cycle - oxygen and carbon dioxide are the main part of the living organism to produce energy. Plants use atmospheric carbon dioxide to produce energy and release oxygen for cellular respiration.
7. Bacteria - it is a microscopic unicellular prokaryotic organism that different from eukaryotic and archaea organisms. These organisms lack a nucleus and double-membrane-bound organelles.
8. Evaporation - it is the process of the water cycle in which heat comes from the sun converts water into water vapor that moves to the atmosphere and forms clouds.
9. Nitrification - It is one of the processes of the nitrogen cycle in which oxidation of NH3 to nitrite followed by the oxidation of the nitrite to nitrate with the help of organisms present in the roots of plants and soil.
10. Photosynthesis is the process that converts light energy to chemical energy with the help of atmospheric water and carbon dioxide and makes glucose and oxygen.
