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A Study On Food Tests Biology Essay


The experiment is to utilize some chemical reagents to happen out what is contained in assorted nutrient substances, bimolecular.


To place what is contained in the trial solutions is the intent of these experiments.

Some definitions of the trial substances should be given. First, amylum. Starch, ( C6H10O5 ) N, a tasteless, white solid saccharide, happening in the signifier of minute granules in the seeds, tubers, and other parts of workss, and organizing an of import component of rice, maize, wheat, beans, murphies, and many other vegetable nutrients. Besides, it is made of polyglucose. ( answers.com 2009 )

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Second, it is stated that “Lipids are a slightly slackly defined group of molecules with one chief chemical feature: They are indissoluble in H2O ( Losos, Mason, Singer, 2008, P53 ) .” Lipid is a stuff which shops long-run energy, such as carnal fats, and besides oils, such as olive oil, and coconut oil. Besides, waxes, for illustration beeswax and cerumen are lipoids every bit good. ( Losos, Mason, Singer, 2008 )

Third, glucose ‘s definition is given. Glucose besides called maize sugar, is the most widely distributed in nature and the most of import, it is a simple sugar, with multi-hydroxy aldehydes ( baike baidu 2009 ) .

The 4th one is the definition of cut downing sugar. It is a monosaccharose or disaccharide sugar which can portion the negatrons to other molecules and hence, it can move as a reduction agent ( Encyclopedia.com 2009 ) . Besides, cut downing sugars can be tested by Benedict ‘s trial, and it can compare with the non-reducing sugar ( Encyclopedia.com 2009 ) .

The 5th one is biuret reagent. It is made of Cu sulphate and Na hydrated oxide. The bluish reagent turns violet in the presence of proteins, and alterations to tap when combined with short-chain polypeptides ( biosci.com 2009 ) .

Biuret ReagentAvailable at:

hypertext transfer protocol: //www.biosci.ohiou.edu/introbioslab/Bios170/170_2/biuret.htm

The last 1 is protein. The basal sequence of bases in the Deoxyribonucleic acid coding for the protein determines the specific order of the protein, a big molecule composed of one or more ironss of amino acids ( medterms.com 2009 ) .

These experiments are good for understanding substances and their alteration in belongingss under chemical status, such as its coloring material, provinces and chemical map. Besides, the stuff can be identified from seeing what happened after it reacts to another stuff.

Besides, there are some backgrounds of the trials should be given:

Starch composites with Iodine solution and the bluish coloring material occur.

I+ KI I + K

The ground is: amylum is a supermolecule which consists of glucoses. There are two types of glucose, unfastened concatenation and closed ring. Glucose which signifier is concatenation will non alter its colour when it reacts to iodine, merely the ring signifier will. The ground is I binds into the ring of glucose, the forces between molecules make these two stuffs combine. This construction makes all wavelengths of light except bluish get absorbed, hence, the blue colour occurs ( zhidao baidu 2009 ) .

The rule of cut downing sugar is, harmonizing to the chemical equation:

Cu + aldehyde Cu+ acid

The aldehyde is contained in glucose, hence, the reaction occurs. The coloring material occurs from light blue to ruddy precipitate.

Here is the theory of protein trial. It is claimed ( baike.baidu 2009 ) in the alkalic solution of NaOH, the biuret reacts with Cu ions ( Cu ) , a purple complex consequence. Therefore, the reaction between protein and biuret reagent occurs because of the combination of protein peptides ( baike baidu 2009 ) .

Besides, ethyl alcohol and lipid can fade out, and Van Der Waals force exists in them, on the other manus, there are hydrogen bonds in H2O and ethyl alcohol, it is stronger than Van Der Waals force, hence, the lipoid was threw out.


There were two simple points used in these experiments.

  1. Pipet
  2. Test tubing

In this practical, starch solution, Glucose solution and protein solution ( egg albumins ) , and lipid ( insignificant oil ) were used as samples.

To guarantee the experimental ‘ consequences were accurate, the process was read carefully before the practical have been done, such as utilizing a pipette to mensurate the 1cm of the trial solution, besides, careful experimental pattern was performed throughout.

The first trial is for amylum. 3 beads of iodine solution was added to 1cm of starch solution in a trial tubing. The alteration was observed.

The Second trial is for cut downing sugar. 2cmof the glucose solution was warmed to 60? in a H2O bath, and 5cmof Fehlings reagent was added.

The 3rd trial is for protein. Biuret reagent A was added to 2cm of the trial solution ( egg albumins ) until it was in surplus. Then the tubing was held at a 45? angle and a pipette was used to dribble in approximately 1 centimeter of Biuret reagent B.

The 4th trial is for lipoids, or oils. 2 cmof trial solution ( vegetable oil ) was added to 2 centimeter of ethyl alcohol in a trial tubing. It was shaken really smartly. Then 2 centimeter of cold H2O was added.


The tabular array shows the observation of the experiments.

Trial Samples


Iodine solution, Starch solution

From clear to blue-black coloring material

Fehlings Reagent, warmed Glucose solution

After a few proceedingss, from clear light blue to red, with some precipitate

Biuret Reagent A, egg albumins until it is in surplus

Biuret Reagent B

No alteration, clear solution

From clear to violet coloring material

Ethanol, lipoid

Three beds

Top is white liquid, non clear

Middle is xanthous, cloudy

Bottom is non clear, white

After agitating smartly, the beds assorted, go cloudy

Table 1


The observations of the experiments confirm the presence of the bimolecular.

The consequences from the trial tubing show clearly that there are color alterations due to the reaction between supermolecule and the assorted solutions.

The equipments are good for qualitative trials and convenient ; besides, the trials could be made quantitative. More pipettes would be better for making the experiment because there were a batch of solutions have to be tested. The ground would be to avoid possible taint. Besides, the chemicals are pure and easy to see the consequences.


Test solution A contains starch solution, ( a polymer of glucose ) , test solution B contains glucose solution ( a reduction sugar ) and the trial solution C is protein solution ( egg albumins ) . Although most of the experiments are successful, there is one experiment that could be improved. When the trial for cut downing sugar was being done, the trial tubing was non put into the 60? H2O to warm as the measure suggested. As a consequence, the coloring material alteration can non be seen clearly. To avoid this in future, the stairss of experiment have to be followed really carefully.


Answers.com ( 2009 ) Starch hypertext transfer protocol: //www.answers.com/topic/starch [ Access day of the month: 18/11/09 ]

Baidu Baike ( 2009a ) Glucose Physical belongingss Available at:

hypertext transfer protocol: //baike.baidu.com/view/16023.htm? fromenter=glucose [ Access day of the month: 18/11/09 ]

Baidu Baike ( 2009b ) Biuret Reaction The definition of biuret reaction Available at: hypertext transfer protocol: //baike.baidu.com/view/205762.htm [ Access day of the month: 19/11/09 ]

Baidu Zhidao ( 2009a ) Fehling reagents Available at:

hypertext transfer protocol: //zhidao.baidu.com/question/116314514.html [ Access day of the month: 20/11/09 ]

Baidu Zhidao ( 2009b ) which procedure does starch and Iodine react to each other? Available at: hypertext transfer protocol: //zhidao.baidu.com/question/49322696.html? si=6 [ Access day of the month: 19/11/09 ]

Biosci.com ( 2009 ) Biuret Reagent Available at:

hypertext transfer protocol: //www.biosci.ohiou.edu/introbioslab/Bios170/170_2/biuret.htm [ Access day of the month: 02/12/09 ]

Encyclopedia.com ( 2009 ) Reducing sugar Available at:

hypertext transfer protocol: //www.encyclopedia.com/doc/1O6-reducingsugar.html [ Access day of the month: 02/12/09 ]

Losos, J. K, Mason. Sing, S ( 2008 ) Lipids: Hydrophobic Molecules Biology ( 8th Edition ) New York: MrGraw – Hill

MedicineNet.com ( 2009 ) Definition of Protein Available at:


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