Biology Lab Report 5

Title : Identification of Some Biological Important Chemical CompoundsApparatus : Please refer to Biology Handbook page 112Material : Please refer to Biology Handbook page 112Method : Please refer to Biology Handbook page 112

Starch

Hypothesis : The colour of iodine will change from yellow to blue.Result :

Figure 2: Image of potato after dropping dilute iodine; 100x

Discussion : The blue-black colour of iodine shows that starch is present in the food.

Glucose

Hypothesis : The glucose solution will change colour from blue to brick-red colour after testing with Benedict's reagent.Result :

Figure 3: Image of apple after heating.

Discussion : All monosaccharide sugars and certain disaccharides will reduce copper sulphate, producing a precipitate of cuprous oxide on heating. The colour and and density of the precipitate gives rough indication of the amount of sugar; a brown or red precipitate means progressively that more sugar is present while green precipitate indicates lower sugar content.

Sucrose

Hypothesis : The sucrose solution will change colour from blue to brick-red colour after being hydrolyse into its constituent monosaccharides and then testing with Benedict's reagent.Result :

Figure 5: Image of sucrose solution after heating.

Discussion : Sucrose which is disaccharide does not reduce copper sulphate. By hydrolysing it into monosaccharides, sugar can be detected using Benedict reagent.

Cellulose

Hypothesis : The wool will change colour into purple when Schultz's solution is added.

Result :

Figure 7: Image of the wool after dropping Schultz's solution.Discussion : Cellulose will stain purple with Shultz’ solution.

Lignin

Hypothesis : The colour of the match will turn into red after phloroglucinol is added .Result :

Discussion : Lignin or wood will stains red with acidified phloroglucinol

Lipid

Hypothesis : Olive oil will produce red stain with Sudan III Result : Discussion : Lipid or wood stains red after dipping it into a mixture of phloroglucinol and hydrochloric acid..

Protein

Hypothesis : A brick-red colour precipitate will show up in food that contains protein. Result :

Discussion : About six drops of Millon’s reagent is added to 2cm³ of an egg albumen and boiled. A brick-red colour indicated presence of protein.

Investigating Unknowns

Lipid

Eight more solutions are used to test presence of lipid.

Solution Red stain appearsOil palmseedStarch solutionPotato tuberGlucoseSucrosePlantEgg albumenSoaked peas

Protein

LIMITATIONS AND RECOMENDATIONS

1. The test on starch and protein must be carried out at room temperature and for the solution used (biuret and iodide) must not be heated.

2. The test for lipids required dry and grease free test tube.3. Because Millon Reagent contains mercury salt that is dangerous, we must handle

it carefully.4. The Benedict and Millon test should not be heated directly under the flame be-

cause it may spills the solution.5. For the sucrose, we need to neutralize the acid carefully because we don’t want to

turn it into an alkali solution.6. If the apple is sliced too thick, we might not see the tissue under the microscope,

so the apple need to be sliced as thin as possible.7. For the wood, use the older part of the tree to get a better result.

IB DIPLOMA BIOLOGY LAB REPORT PRACTICAL 5

Title : Identification of some biological important chemical compoundObjective : a) To identify some biological important chemical compound

b) To know the specific reagent for certain chemical constituentApparatus : Refer to Biology handbook page 112Materials : Refer to Biology handbook page 112Procedure : Refer to Biology handbook from page 113 to page 115

Data Collection:

A. STARCH

Reagent Observation DetailsDilute Iodine The solution’s colour changes from

yellow to blue-blackWhen starch is mixed with iodine in water, an intensely colored starch/iodine complex is formed. But it seems that the iodine gets stuck in the soluble starch. The starch forces the iodine atoms into a linear arrangement in the central groove of the soluble starch coil, giving the complex its intense blue color.

B. GLUCOSE AND FRUCTOSE

Reagent Observation DetailsBenedict’s

reagentFor glucose

The solution’s colour changes from blue to brick-red

For fructose The solution’s colour changes

from blue to brick-red

Aqueous glucose/fructose is mixed with Benedict's reagent, a solution of copper sulfate, sodium hydroxide, and tartaric acid. The mixture is heated. Carbohydrates which react with Benedict's reagent to reduce the blue copper (II) ion to form a brick red precipitate of copper (I) oxide are classified as reducing sugars.

C. SUKROSE

Reagent Observation DetailsBenedict’s reagent With no hydrolysing

No colour change

With hydrolysing The solution’s col-

our changes from blue to brick-red

Sucrose is disaccharide that does not reduce copper sulphate. Therefore, it should be hydrolysed into its constituent monosaccharides before testing it with benedict’s reagent. Sucrose then will react with Benedict's

reagent to reduce the blue copper (II) ion to form a brick red precipitate of copper (I) oxide.

D. CELLULOSE

Reagent Observation DetailsSchultz’ solution

The solution’s colour changes from colourless to purple

Schultz’ solution reacted with cellulose to produced purple stained. In the experiment, when the reagent is put on the cotton and also in the solution, both of the produce purple-coloured stains indicating that both of them possess cellulose.

E. LIGNIN

Reagent Observation DetailsAcidified

Phloroglucinol When tested on toothpick, colour of

toothpick becomes red When solution is tested on plants

item, colour of xilem seen to be red in colour

Acidified phloroglucinol can react with lignin to produce red stain. After testing with toothpick and xilem, both of them stained red indicating that both of them contain lignin.

F. LIPIDS

Reagent Substances Observation Details

Sudan Ш Oil palm and water

Initial Colour Final ColourBasically, when Sudan III reacted with lipid, a red-stained oil layer separate out and floats

Two separate layers are formed

The top one yel-low (oil) the bottom colour-less (water)

Two layers are formed

Top red and bot-tom dark red

on the water surface.

Sudan Ш Pure oil palm oil

The oil palm is pale yellow in colour

The entire solu-tion is red in colour

The red settles at the base of the test tube, whilst the top layer is a dark yel-low with red droplets suspended in it

Ethanol Palm oil and water

Initially clear, slightly cloudy when water is added

A thin top, layer of cloudy, light yel-low, followed by a long rung of cloudy white and a thin bottom layer of dear yellow

Ethanol reacted with lipids to form a cloudy white precipate. In the experiments, cloudy white precipate formed after some time representing that the palm oil contained lipid.

G. PROTEIN

Reagent Observation DetailsMillon’s Reagent

The solution’s colour changes from colourless to brick-red

Millon tests for phenolic -OH group present in sample such as protein. Millon’s reagent is prepared from mercuric and mercurous nitrate in nitric acid. When protein is heated with Millon's reagent, a white precipitate is formed and on heating changes to brick

red.Xanthoproteic

test The solution’s colour which is deep-

yellow disappearsXanthoproteic Acid Test tests R Group. This is a test for specific functional groups that a positive test is formation of a deep-yellow orange or orange-red color. A deep-yellow partial precipitate, which disappears, on shaking, indicates protein.

Biuret test A blue ring appears at the surface of the solution.

On shaking, the blue ring disappears. The solution’s colour turns purple

Biuret array is a test for peptide bonds present in the sample such as protein. Under alkaline conditions, peptide bonds are cleaved and react with a copper reagent to yield a purple colour.

H. INVESTIGATING UNKNOWNS

Reagent Observation DetailsDilute Iodine No colour changes spotted. The solu-

tion remains yellowBasically, if starch is mixed with iodine in water, an intensely colored starch/iodine complex is formed. However, when iodine is dropped into the unknown solution, no colour changes which is from yellow to blue-black is spotted. Therefore, there is no starch in the unknown.

Benedict The solution’s colour changes from blue to brick-red

When benedict reagent is dropped into the unknown solution, the colour changes. This mean the unknown do has glucose/carbohydrates in it. This is because carbohydrates react with Benedict's reagent to reduce the blue copper (II) ion to form a brick red precipitate of copper (I) oxide. Even so, the unknown solution does not have sucrose in it because red-brick precipitate can be obtained without hydrolysing it.

Schultz’ Solution

The solution’s colour changes from colourless to purple

Cellulose stained purple with Schultz’ solution. Then, when the reagent is being tested with the unknown solution, the solution’s colour changes from colourless to purple. For this reason, the unknown should comprise cellulose in it.

Acidified Phloroglucinol

No colour changes spotted. The solu-tion colour remains red.

Acidified phloroglucinol can react with lignin to produce red stain. However, not all structure in the unknown actually reacted with the reagent to produce red stained. Only certain part such as skin and pips stained red with the reagent

Sudan III The solution’s colour changes to blurred red.

Fundamentally, a red-stained oil layer that separate out and float on the water surface indicates the existence of protein in the solution. Still, when Sudan III is added up to the solution, a blurred red-stained oil layer appears. This mean, there is not much lipid exist in the unknown.

Millon’s Reagent

The solution’s colour changes from colourless to blurred brick-red

Hypothetically, when protein is heated with Millon's reagent, a white precipitate is formed and on heating changes to brick red. However, when the unknown is heated, a blurred brick-red precipitate produced, meaning that the amount of protein in the unknown is not much.

MICROSCOPE OBSERVATION

Chemical compound

Reagent Observation under magnification of x100

FructoseBenedict’s

reagent

The Light photomicrograph drawing of cell of apple

Lignin Sudan III

The Light photomicrograph drawing of xilem of plant stem

ProteinMillon’s reagent

Light photomicrograph drawing of cell of pea

Unknown

Benedict’s reagent

The Light photomicrograph drawing of unknown cell

Sudan III

The Light photomicrograph drawing of unknown cell

Millon’s reagent

The Light photomicrograph drawing of unknown cell

DISCUSSION

1) Benedict’s reagent was used to determine the presence of reducing sugar in the sub-stances that had been tested.

2) Millon’s reagent was used to determine the presence of protein in the substances that had been tested.

3) Iodine was used to determine the presence of starch in the substances that had been tested.

4) Schultz’ solution was used to determine the presence of cellulose in the substances that had been tested.

5) Hydrochloric acid was used to hydrolyse sucrose to glucose which is a reducing sugar.

6) Acidified phloroglucinol was used to determine the presence of lignin in the sub-stances that had been tested.

7) Sudan III reagent was used to determine the presence of lipid in the substances that had been tested.

LIMITATIONS AND RECOMENDATIONS

8. The test on starch and protein must be carried out at room temperature and for the solution used (biuret and iodide) must not be heated.

9. The test for lipids required dry and grease free test tube.10. Because Millon Reagent contains mercury salt that is dangerous, we must handle

it carefully.11. The Benedict and Millon test should not be heated directly under the flame be-

cause it may spills the solution.12. For the sucrose, we need to neutralize the acid carefully because we don’t want to

turn it into an alkali solution.13. If the apple is sliced too thick, we might not see the tissue under the microscope,

so the apple need to be sliced as thin as possible.14. For the wood, use the older part of the tree to get a better result.

CONCLUSION

Biological chemical compounds can be identified by using certain scientific methods.