determination of the chemical composition of the cell

Cells contain different type of compounds including protein, lipids and carbohydrates.
This compounds have different functions within the cell and they are essential in effective
function of cells. Different material have varied composition of these compounds. There are
various approaches that are used identification of the compounds. For instance, lipids which
are composed of fats and oils are tested using the emulsion test which is wet chemistry
approach. When lipids, which are hydrophobic are dissolved in ethanol and then added to
water a cloudy while emulsion is formed as lipids do not dissolve in water (Ozturk,&
McClements, 2016). The presence of starch which is a complex carbohydrate is tested using
the iodine test. When there is starch, the iodine changes to intense blue-black colour which is
a result of formation of a complex compound (Miyazaki, Aso & Goda, 2018). Proteins are
identified by the use of the Biuret solution which is blue solution which turns pink-purple
after reaction with protein. Sugars which are simple carbohydrates are tested using the
Benedict solution which is blue compound composed of copper and sodium salts and it
changes to a range of colours depending on the concentration of sugar.
Purpose
The central objective of this test is to test for complex carbohydrates in particular starch and
emulsifiers in various products. Notably emulsifiers and carbohydrates are among the
chemicals that are founds in cells of both plants and animals.
Hypothesis
Test 1

The iodine will turn potato cubes and the spoon of starch dark purple but will not turn the
onion, lettuce leaf and water.
Test 2
For the butter the blue dye will float on top but for the egg yolk the blue dye will be spread
throughout the mixture.
Methods
Iodine Test
Procedure

1. A ¼ cup of water was added to a glass and a few iodine drops were added
2. In other drinking glass ½ teaspoon of starch was then put followed by a ¼ of water. A
   few iodine drops were then put and the colour change observed.
3. A small lettuce leaf was torn and iodine drops were added to the torn parts of the
   leave and the colour change observed.
4. The test was then repeated with vegetable oil, sugar and the starchy foods selected
   from the kitchen.
5. A small potato and onion cubes were cut and small drops of iodine were added and
   the colour change observed.
   Lipids
   Test for emulsifier
   Procedure
6. Water was heated to steaming and a cup of the heated water was added to a glass.
7. A teaspoon of butter was then added to the heated water and stirred. The cup was then
   let to sit for 5 min.
8. A drop of blue food colouring was then added and the mixed again.
9. An egg yolk was then separated with the white. The yolk was then broken in a
   drinking glass and mixed with water. A drop of the blue die was then added and
   observation made and recorded.
   Results
   Test 1: Iodine Test
   The table below show the results of test 1.

Iodine did not turn in water, onion and lettuce leaf but turned in potato cubes and starch.
The mixture of water and iodine was the negative control experiment and the mixture of
iodine and starch was the positive control experiment.
Test 2: Test for emulsifier
Ingredient Observation Conclusion
Butter Blue dye floated on water No emulsifiers
Egg yolk Blue dye distributed
throughout the water

Emulsifiers present

For butter, the blue dye floated on water which indicted that there was no emulsifiers in
butter. For the case of the egg yolk, the blue dye spread through the solution which
indicated the presence of emulsifier. The negative control experiment was the butter
experiment.
Discussion and conclusion
As stated, when starch comes in contact with iodine, they react to form a complex
with dark purple colour. With no starch, the amber colour of aqueous iodine is retained.
Lettuce leaf o not have starch but only have simple sugars that why the colour did not
change. However, this does not necessary mean that there is no starch found in the leave.
Starch is largely stored in the stroma of the chloroplast. The leave excess glucose is
converted into starch and stored in the stroma and therefore to be able to test for the
starch in the leaves one needs to denature the cells of the leaves through boiling. On the
other hand, the biggest % of a potato is starch that why it indicated the dark purple colour.
For the onion, about 70% is water and the rest is a combination of simple sugars and
fibres that why the colour did not change.
For the second test, the egg yolk contains emulsifiers that why a cloudy solution was
formed. Notably, lipids do not dissolve in water but they dissolve in the emulsifiers a
notion that explains the formation of the cloudy solution. Butter does not contain
emulsifiers and since lipids are hydrophobic and less dense than water, the butter floated
on water rather than rather than forming the cloudy suspension as observed in the case of
the egg yolk test. The emulsifier test is the reverse of the lipid test and it show the accrued
relevance of emulsifiers in chemistry and biology. They help stop lipids from separating
with water making resulting in formation of conjugates that enables physiological
processes involving lipids to occur smoothly. A viable example is the process of

emulsification that occurs in the small intestine where bile help in emulsification of lipids
to help in their further digestion.

References

Miyazaki, T., Aso, Y., & Goda, Y. (2018). Identifying the origin plant of starches by
numerical description of the coloration of iodine-starch reaction
solutions. Japanese Journal of Food Chemistry and Safety, 25(3), 145-151.
Ozturk, B., & McClements, D. J. (2016). Progress in natural emulsifiers for utilization in
food emulsions. Current Opinion in Food Science, 7, 1-6.