Work out the results expected of standard tests used by scientists to identify the presence of specific chemicals which may be found in cells.

3.        Steps 1, 2 and 3 were repeated using water in place of starch.

5.        Steps 1, 2 and 3 were repeated using  ground: potato, biscuit and meat. All ingredients were tested separately.

RESULTS:                         Table 2 – Results of Starch Testing

DISCUSSION / CONCLUSIONS:

Starch is needed by the plants as an energy supply.  It is used in place of other forms of carbohydrates as it is insoluble.  In this test water is used as a control and shows the results of the test when no starch is present.  When water and meat were used there was no change in the colour of the solution.  Since it is known that water is devoid of starch, the test indicates that there is also a minimal amount in meat.  The results of this investigation show that starch, potato and biscuit react similarly to this test.  Since it is known that the results for starch will be similar for other materials containing starch, it can be concluded that potato and biscuit contain starch.  In conclusion this test has identified starch within some common materials.

C. Benedict’s Test for Glucose

PROCEDURE:

1. 3mL of glucose solution was placed in a test tube.
2. 4mL of Benedict’s solution was added and the test tube swirled.
3. The solution was warmed in the water bath.
4. The resulting substance was observed and described in Table 3.
5. Steps 1, 2, 3 and 4 were repeated using water in place of glucose solution.
6. Steps 1, 2, 3 and 4 were repeated using ground: potato, biscuit and banana. All materials were tested separately.

RESULTS:                         Table 3 – Results of Glucose Testing

DISCUSSION / CONCLUSIONS:

Glucose is used as a direct source of energy for the body.  Starch is only used for storing energy and is later broken down into glucose, which is actually the compound used in respiration and is thus needed to release energy.

In this experiment water is used as a control and shows the results where no glucose is present.  When water, potato and dry biscuit were used there was no change in the colour of the solution.  Since it is known that water is devoid of glucose the test indicates that there is also a minimal amount in potato and dry biscuit.  The results of this investigation show that glucose, sweet biscuit and banana react similarly, if not as strong,  to this test.  Since it is known that the results for glucose will be similar for other materials containing glucose it can be concluded that sweet biscuit and banana contain glucose, although not at the same concentration.  In conclusion this test has identified glucose within some common materials.

D. Clinistix Test for Glucose

PROCEDURE:

1. The original colour of the clinistix was noted and recorded in Table 4.
2. 3mL of glucose solution was placed in a test tube. A clinistix was added and the colour change noted in table 4.
3. The above 2 steps were repeated with water in place of the glucose solution
4. The above 2 steps were repeated using ground: bread, sweet biscuit and lolly. All materials were tested separately.

RESULTS:                 Table 4 – Results of Glucose Testing using Clinistix

DISCUSSION / CONCLUSIONS:

Water is used as a control in this investigation and shows the results when no glucose is present.  The results of this investigation show that both glucose and lolly react similarly to this test. Bread and sweet biscuit also react, but produce a mere shadow of the glucose reaction.  This implies that there are high levels of glucose in the first two and lower levels in the second two.  In conclusion this test has identified glucose within some common materials.

E. Test for Cellulose

PROCEDURE:

1. Cotton wool was placed on a spotting tile.
2. Three drops of Lugol’s iodine solution was added to the cotton wool and the colour recorded in table 5.
3. Another piece of cotton wool was placed on the spotting tile and to this three drops of concentrated sulfuric acid was added, followed by three drops of Lugol’s iodine solution.
4. The colour change was again recorded in Table 5.
5. Steps 3 and 4 were repeated for bread, potato and biscuit. All materials were tested separately

RESULTS:                         Table 5 – Results of Cellulose Testing

DISCUSSION / CONCLUSIONS:

Cellulose is used in cell walls, adding strength and stability to the cell. In the test, cotton wool is used as a control.  It shows the results of the test where there is no broken down cellulose.  From the knowledge that cellulose is made of starch molecules joined together, it was determined that at first Lugol’s iodine solution had no affect on cotton wool, although cotton wool is made of cellulose. After adding the sulfuric acid, the cellulose was broken apart in the cotton wool and the Lugol’s iodine solution then detected the starch molecules and changed to a brown-red colour. Where cellulose and not other carbohydrates are present the H2SO4 is able to break down the molecule into starch.  Lugol’s Iodine solution is then able to identify the starch in these compounds, as it did in part B  The results of this investigation show that when sulfuric acid then Lugol’s Iodine solution is added to cotton wool, bread and biscuit a similar reaction takes place. This indicates that there was initially cellulose in all three.  Both potato (and sulfuric acid) and plain cotton wool tested negative.  This means that potato, despite being treated with sulfuric acid, has no starch.  This result can be interpreted as indicating that there was no initial cellulose to break down, and thus potato does not contain cellulose.  In conclusion this test has identified cellulose within some common materials.

F. Test for Lipids

PROCEDURE:

1.        Oil was rubbed on a piece of brown paper.

2.        The paper was held up to a light and determined to be transparent, translucent or opaque. The results were recorded in Table 6.

4.        The paper was left for ten minutes and the results were again recorded.

5.        The test was repeated with water, banana, potato and butter with all results recorded in Table 6. All materials were tested separately.

RESULTS:                         Table 6 – Results of Lipid Testing

DISCUSSION / CONCLUSION:

Lipids are an essential part of all diets as they help with four tasks:

• They serve as structural components of biological membranes.  
• They provide energy reserves.
• Both lipids and lipid derivatives serve as vitamins and hormones.
• Lipophilic bile acids aid in lipid solubilization.

As water contain no lipids it was used as a control. The results with oil are the desired results, for they are liquid lipids.  Both banana and butter were initially translucent, however after ten minutes butter became transparent.  This suggests that there is a moderate amount of lipid in banana and a high level of lipid in butter.  The results for potato are much like those for water, and suggest that they contain limited lipids. In conclusion this test has identified lipids within some common materials.

SUMMARY TABLE: