It is generally agreed by astronomers, geologists and biologists that the earth is some 4.5 - 5.0 thousand million years old.
Many biologists believe that the original state of the Earth bore little resemblance to its present-day form and had the following probable appearance.
It was hot (about 4000-8000 degree centigrade) and it is cooled carbon and the less volatile metals condensed and formed the earthâ€™s core, the surface was probably barren and rugged as volcanic activity, continuous earth movements and contraction on cooling, folded and fractured the surface.
The environment is supposed to be entirely different in those days. The lighter gases hydrogen, helium, nitrogen, oxygen and argon would have escaped because the gravitational field of the partially condensed planet would not contain them. In 1923 Alexander Oparin suggested on theoretical grounds he argued that organic compounds, probably hydrocarbons, could have formed in the oceans from more simple compounds, the energy for these synthesis reactions probably being supplied from the strong solar radiation which surrounded the earth before the formation of ozone layer, which now blocks much of it out.
The very useful chemical indicator of eutrophication is the biochemical oxygen demand (BOD) which measures the rate of oxygen depletion by organisms. It is assumed this primarily reflects microorganism activity in decomposing organic matter present in waters. Organic matters typically increases as waters become nutrient-enriched. However oxygen consumption by algae will inevitably also be included in the test. In practice this is normally not important, but in some cases it may account for up to 50% of the total BOD.
Some simple tests are carried out to identify some of the common biochemicals. More elaborate techniques exist for identifying and separating biochemicals. Of particular importance are chromatography and electrophoresis. It is recommended that we should be familiar with the following tests by using pure samples of the chemicals being tested. Once the techniques have been mastered and familiarity with the color changes obtained, extracts from various tissues can be studied.
A biochemist is often faced with the problem of wanting to identify chemicals (qualitative analysis) or to measure their amounts (quantitative analysis) in living tissue. Sometimes the chemicals can be tested for directly, but often some kind of extraction and purification process must first be embarked upon.
A convenient exercise is to take a range of common foods and plant material and to test for the range of biochemical listed in experiments. An extraction procedure is designed where possible to give a clear, colorless solution for testing, and you should note the rationale behind the procedures so that you could design your own if necessary.
Observations on tissues
It is often desirable to conduct biochemical studies on an individual organ or individual cells rather than on the body as a whole. But since the growing of single cells in multi celled organisms is not easy and also that after many generations cells from specialized tissues tend to revert to a more primitive type, the biochemist is forced to study either intact organs or preparations from these organs.
This is the simplest way to study intact cells organized in tissues.
This technique has been much used in the past for organs such as liver, kidney and brain and also for certain plant tissues like roots and tubers.
In this, the cells are broken up completely so that a homogeneous mixture is obtained which can be adequately oxygenated.
The centrifugal force exerted on a particle in the solution is expressed in multiples of the force exerted by gravity. The centrifugal force is proportional to the radius of the centrifugal head and to the square of the angular velocity.
Chromatography may be defined as the techniques of separation of substances according to their partition coefficients below two immiscible phases.
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