Biology Lab Report ( Test For Organic Compunds ) 3f2d18

INTRODUCTION

The various molecules found in all life forms are called organic compounds because they are produced by organisms. Organic molecules are carbon based and range from small to enormous in size. These large molecules are composed of simpler, smaller molecules known as monomers that linked together into long chains or polymers. There are four major classes of important biological organic compounds with specific functions.

OBJECTIVE

Explain the specific laboratory tests used to identify reducing sugars, starch, lipids and proteins

DETERMINING THE PRESENCE OF REDUCING SUGARS

APPARATUS/MATERIAL

Test tubes, test tube rack, marker pen, distilled water, glucose solution, sucrose solution, starch solution, Benedict’s reagent, label stickers

PROCEDURE

1. From the bottom of 4 clean test tubes, 1cm and 3 cm was marked. The top end of the test tube was labelled 1, 2, 3, 4. 1. Each test tube was filled to the 1 cm mark with one of the following  Distilled water  Glucose solution  Sucrose solution  Starch solution 2. Each test tube was filled with 2cm Benedict’s reagent and was swirled to mixed. 3. All the test tube was placed in a test tube rack for 3 minutes. 4. The colour change was observed. Data was recorded in a table.

RESULT/DATA

Test tube 1

Observation (colour change) No changes

Conclusion Absent

2

Blue Brick red precipitate No changes

Present

Blue Greenish blue

Present

3

4

Absent

POST LAB QUESTIONS

1. Which test tube contains reducing sugars ?

Test tube 2 and test tube 4

2. Name the functional group present in carbohydrate molecule that can produce positive reaction with Benedict’s reaction. Carbonyl C = O

3. If onion juice mixed with Benedict’s reagent gives a mustard yellow colour, in what form is sugar stored in onions ?

In a form of reducing sugar , Fructose

DETERMINING THE PRESENCE OF STARCH

APPARATUS/MATERIAL

Test tube, test tube rack, marker pen, microscope, distilled water, glucose solution, sucrose solution, white tile, fresh potato, razor blade, clean microscope slides, coverslip, label stickers, starch solution

PROCEDURE

2. From the bottom of 4 clean test tubes, 1cm was marked. The top end of the test tube was labelled 1, 2, 3, 4. 3. Each test tube was filled to the 1 cm mark with one of the following :    

Distilled water Glucose solution Sucrose solution Starch solution

4. 3 drops of iodine solution was added to each test tube and swirled to mixed. The colour of each test tube was recorded. 5. The contents of the test tube was discarded and rinsed properly. Excess water was shake out from the test tubes. The next exercise used them. 6. A razor blade was used to cut a small, thin, slice of fresh potato. The potato slice should be transparent. 7. The potato slice was placed onto a clean microscope slide and wet mount was prepared. The potato slice was observed under low and high power. 8. The coverslip was removed and a few drops of iodine solution was added. The coverslip was replaced, iodine to penetrate was waited for a few minute and the potato was observed again under low and high power. The observation was draw.

RESULT AND DATA

Test tube 1

Observation (colour changes) No changes

Absent

2

No changes

Absent

3

No changes

Absent

4

Yellow Blue black

Present

POST LAB QUESTIONS

1. Draw the potato slide observed under a microscope.

Conclusion

2. Does a blue black colour present in any of the carbohydrates solutions beside starch ?

No

3. Is iodine test suitable to distinguish starch from sucrose ? Explain why

Yes because iodine dissolved in an aqueous solution of potassium iodide, reacts with the starch producing a purple black colour. The colour can be detected visually with concentrations of iodine as low as 0.00002M at 20°C. However the intensity of the colour decreases with increasing temperature and with the presence of water-miscible, organic solvents such as ethanol. Also the test cannot be done at very low pHs due to the hydrolysis of the starch under these conditions

DETERMINING THE PRESENCE OF PROTEINS

APPARATUS/MATERIAL

Test tube, test tube rack, small ruler, marker pen, distilled water, label stickers, honey solution, corn oil, egg white solution, 10 NaOH solution, 1 CuS

PROCEDURE

1. 4 test tubes was marked at 2cm and 4cm measured from the bottom of the test tube. The top end of test tube was labelled as 1, 2, 3, 4. 2. Each test tube was filled up to the 2cm mark with one of the following :    

Distilled water (tube 1) Honey solution (tube 2) Corn oil (tube 3) Egg white solution (tube 4)

3. 10 sodium hydroxide (NaoH) solution was added to each test tube up to the 4cm mark. 4. 5 drops of copper sulfate (CuS ) solution was added to each test tube and swirled to mix. The tubes was examined for the appearance of any violet colour and result was recorded. 5. The contens of the test tubes was discareded, washed and rinsed with detergent properly. Excess water was shake out from the test tube. Test tube was used for the next exercise.

RESULT/DATA

Test tube 1

Observation (colour change) No change

Conclusion Absent

2

Form 2 layer Upper layer : cloudly yellow Bottom layer : yellow Form 2 layer Upper layer : cloudly yellow Bottom layer : colourless with blue precipitate Violet

Absent

3

4

Absent

Present

POST LAB QUESTIONS

1. Which test tube contains protein ?

Test tube 4

2. Name the chemical bond in protein that can react with biuret reagent producing a violet colour.

Peptide bond

DETERMINING THE PRESENCE OF LIPIDS

APPARATUS/MATERIAL

Test tube, test tube rack, Sudan III dye, marker pen, small ruler, egg white solution, honey solution, corn oil, distilled water, label stickers

PROCEDURE

1. 4 test tubes was measured at 2 cm from the bottom of the tube. The top end of test tube was labelled as 1, 2, 3, 4. 2. Each test tube was filled up to the 2cm mark with one of the following :    

Distilled water (tube 1) Honey solution (tube 2) Corn oil (tube 3) Egg white solution (tube 4)

3. 10 drops of Sudan III dye was added to each test tube. 4. The tube was swirled to mix. The tube was examined for result. Result was recorded. 5. The contents of all tubes was discarded in the container designated for Sudan III disposal. Sudan III was ensure not to pour it down the sink drain. Test tube was cleaned thoroughly.

RESULT/DATA

Test tube 1

Observation (colour change) Light orange

Conclusion Absent

2

Light brown

Absent

3

Light orange with fat droplet

Present

4

Milky orange

Absent

POST LAB QUESTIONS

1. Which test tube contain lipids ?

Test tube 3

2. Which test tube as a control ?

Test tube 1

DISCUSSION

From the experiment, we can know identify suitable experiment for testing organic compounds such as carbohydrates, starch, lipids and proteins. Benedict’s reagent is used to determining the presence of reducing sugars that is carbohydrates. Benedict's reagent is used as a test for the presence of reducing sugars. This includes all monosaccharides and many disaccharides, including lactose and maltose. A positive test with Benedict's reagent is shown by a colour change from clear blue to a brick-red precipitate. Glucose solution shows the solution have reducing sugars by changing its colour blue to brick red precipitate. Iodine is used to determining the presence of starch in four test tube. Test tube 1 act as control. Test tube 4 show the presence of starch by changing its colour yellow to blue black. The Iodine test is used to test for the presence of starch. Iodine solution — iodine dissolved in an aqueous solution of potassium iodide— reacts with the starch producing a purple black colour. Next, Copper sulphate, Cus solution was used to determining the presence of proteins. Test tube 4 show changes its colour to violet that is egg white yolk. Copper(II) sulfate is also used in the Biuret reagent to test for proteins. Moreover, Sudan II was used to determining the presence of lipids. Sudan III changes colour of corn oil to light orange with fat droplet in it. Sudan dyes have high affinity to fats, therefore they are used to demonstrate triglycerides, lipids, and lipoproteins.

CONCLUSION

As a conclusion for this experiment, the specific laboratory test was used to identify reducing sugars, starch, lipids and protein. After using some chemical subtances such as Cus solution, Sudan III and Iodine , result show that different kind of subtances have different type of compounds. The test tube must be shaken to get better result and all of the test tube must be labelled to avoid error in data. For reducing sugars, carbohydrate may be classified as monosaccharides, disaccharides or polysaccharides. Some carbohydrates called reducing sugars have an aldehyde functional group as part of their molecular structure which make them react with Benedict’s reagent when heated. For starch, Iodine reacts with starch resulting in a dark, blue black colour that is a positive test for starch. The reaction occurs because starch is a coiled polysaccharide made of repeated glucose molecules. For protein, protein molecules contain multiple amino acid molecules linked together in long chain. The amino acid are linked by peptide bonds that react with copper sulfate that is used in the Biuret test producing violet colour. For lipids, lipis are nonpolar compounds composed of a glycerol molecule bonded to three fatty acid molecules. Solubility of Sudan III dye can be used as a positive test for lipids.