Introduction to General Biology:
They are composed from structures known as cells. Reproduce by genetic material known as DNA. They reply to stimuli from environment. Synthesize the energy substance known as adenosine triphosphate (ATP) from environment, and they live and grow utilizing that energy. Every living organism is composed of cells that are units of life. The cell includes the plasma membrane comprising of phospholipid bilayer. There are different types of cells, from liver cells, that are numerous dozen micrometers in diameter, to nerve cells, that are many meters long. Smallest size visible through naked eye is usually about 0.1 mm (100 µm) and through the light microscope is approx 0.2 µm (200 nm); anything less than 1 µm can't be seen plainly without the electron microscope. Though, living organisms can't be observed using the electron microscope.
Major characteristic of living organisms is that they make offspring which are same as themselves. Unicellular organisms in regular nutrition situation generate offspring by asexual reproduction, like by splitting (protozoa, etc.) or budding (baker's yeast). In the sexual reproduction, cells of offspring have same features as cells of their parents (features that surface) as long as their DNA doesn't mutate. Multicellular organisms, though, suffer sexual reproduction and create offspring which inherits half of every parent's genes. Genetic material (DNA) of humans and bacteria is alike in that it comprises of 4 bases- cytosine, guanine, thymine and adenine -that are characters in DNA code, but differences between DNA of the organisms are made by differences in ratios of the bases. Fact that the organisms share same genetic material is evidence for assertion that all organisms on earth evolved from the single organism.
Plasma membrane has proteins known as "receptors," that receive stimuli from outside environment. When outside stimuli like chemical substances or heat reach receptors, the series of different chemical reactions happens in cytoplasm. Living organisms perform metabolism (synthesis and degradation of substances) in the cells. Metabolism is the procedure in which organisms synthesize ATP to stock up energy, and release energy by hydrolysis, getting heat in process. There are several different kinds of animals in world. Several animals are quite similar to each other. Others are relatively different. Animals can be categorized based on the similarities. The main group of animals is categorized under Kingdom Animalia, also caleed as Metazoa. This kingdom doesn't have prokaryotes. All members of the kingdom are multicellular, eukaryotes. They are heterotrophs, they rely on other organisms indirectly or directly for food. Many animals swallow food and digest in internal cavity. Many organisms are motile that means they can move separately and impulsively.
General characteristics of the Kingdom Animalia are as follows:
Animals are multicellular, eukaryotic, and heterotrophic organisms. They contain numerous cells with mitochondria and they rely on other organisms for food. Most of the animals live in seas, fewer are observed in fresh water and even fewer on land. There are approx 9 to 10 million animal species which live in the earth. Only 800,000 species are recognized. Biologists identify 36 phyla in animal's kingdom. Sizes of animals ranges from few celled organism such as mesozoans to animals weighing several tons like blue whale. Bodies of animals are composed of cells organized into tissues that carry out specific functions. Kingdom Animalia has about 36 sub-divisions called as 'phyla'. Every phyla share specific properties structurally and functionally which together divide it from other phyla.
The phylum Annelida is composed of segmented worms, numbering approx 15,000 species. Body segmentation, the hallmark of annelids, was the main step in evolution of animals. Annelids are protosomes, it signifies that they have coelom created from cell masses. This coelom is separated into the series of frequent parts. This repetition is known as metamerism, and every segment is known as metamere. There are cluster of nerve cells and excretory organs in every metamere, but ventral nerve cords, dorsal and ventral blood vessel, and digestive tract pass through walls of segmentation and are thus unsegmented. The walls, or septum, are thin sheets of mesodermic tissue, isolating coelom. Apart from head and tail region, each with the opening of digestive tract, creating it complete tract, every segment in annelid is ring like and very alike.
Segmentation permits for flexibility and mobility due to annelids can twist at segmented parts. Thus, because segmented body is beneficial, it evolved twice, with protosomes, by phyla Annelida and Arthropoda, and again in deuterosomes, by phylum Chordata. Other characteristics of annelids are soft bodies which are sircular in cross section, repetition of organs in segmented parts, and body which is much longer than it is broad. There are 3 major classes in phylum Annelida.
The Vertebrata, or vertebrates, is the extremely varied group, ranging from lampreys to Man. It comprises every craniates, apart from hagfishes, and are classified mainly by the vertebral column, therefore their name. Majority of extant vertebrates are jawed vertebrates, or gnathostomes, however lampreys are jawless vertebrates. Though, in Late Silurian or Early Devonian times, approx 420 to 400 million years ago, circumstances was reverse, and majority of vertebrate species were jawless fishes ("ostracoderms", most probably more closely related to gnathostomes than to lampreys). Decline of jawless vertebrates and subsequent rise of gnathostomes occur about 380 million years ago.
The Vertebrata include all characteristics of the Craniata but share, additionally, the number of unique features that don't happen in hagfishes (Hyperotreti). These features are:
Metamerically arranged endoskeletal elements flanking spinal cord. There are basically 2 pairs of such elements in every metamere and on every side: interdorsals and basidorsals. In gnathostomes, there are two extra pairs ventrally to notochord: interventrals and basiventrals. These elements are known as arcualia and can fuse to notochordal calcification, centrum. Ensemble of arcualia , centrum is vertebra, and ensemble of vertebrae is vertebral column. Extrinsic eye muscles. These muscles are joined to eyeball and orbital wall, and make sure eye movements. Radial muscles in fins. These are tiny muscles related with each of cartilaginous radials of unpaired and paired fins. They make sure the undulatory movements of the fin web.
The Mammalia like zebras, cows, cats, elephants and whales and Human being(man). Adaptation of mammals to terrestrial life Lungs allow mammals to utilize atmospheric air. Homoiothermy make sure high sustained metabolic activity at all times. Internal fertilization and viviparous reproduction (that is bringing out young alive) make sure proper sustenance and growth of young protected from desiccation and predators.
The Adaptation of Reptilia to terrestrial environment. Use of lungs allows use of atmospheric air for respiration. Dry scaly skin decreases evaporation. Fertilisation is internal thus eradicating the requirement for the aqueous medium for meeting of gametes.
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