Experiment Amount Of Soybeans Effecting Amino Acids Biology Essay


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Soybeans contain a high level of soy protein which is made of components called amino acids. Amino acids are organic compounds containing an amine group (NH2), a carboxylic acid group (COOH) and either of the 20 side groups. When a sequence of amino acids is linked together they have various functions which are significant for the survival of organisms. Amino acids are amphoteric (can act as a base or acid). Even though most amino acids are neutral, some amino acids have acid-base properties due to the acid-base property of the side group. In soy protein, there are more amino acids with acidic side groups (e.g. glutamic acid) than basic side groups (e.g. arginine) as it is a type of protein which is high in glutamic acid, so more acidic properties can be seen at a very small level.

Research Question

How does the change in the amount of soybeans affect the amount of amino acids produced when added to 6of protease solution?

Independent Variable

The amount of soybeans - Measured in numbers without a unit, calculated by counting the number of soy beans. The values that will be used are: 0, 2, 4, 6, 8.

Dependent Variable

The pH of the solution after added to 6 of protease solution - Measured in pH by using a pH probe.

Controlled Variables

Volume of protease solutions - The solutions will be measured to 6 every try with a 10 measuring cylinder.

Type of enzyme - The same type of protease will be used.

Surface area of soybeans - Soy beans of about the same size will be chosen for the experiment.

Volume of soy beans - Soy beans of about the same size will be chosen for the experiment.

Mass of soybean - Soy beans of about the same mass will be chosen for the experiment.

Temperature of the reaction - The experiment will be carried out in a water bath of 40°C.

Type of soybeans - The same type of soy beans that comes from the same source will be used.


Soybean x20

Water bath x1

pH probe x1

A bottle of distilled water x1

50 beaker x5

10 measuring cylinder x1

Boiling tube x5

Stopwatch x1

Procedures for the experiment

Measure 6 of protease solution for each of the 5 boiling tubes.

Place the soybeans in the boiling tubes according to the amounts 0, 2, 4, 6, 8 respectively and place the boiling tubes on a boiling tube rack.

Place the boiling tube rack in a water bath of 40°C.

Wait for 30 minutes to ensure all the protein is reacted.

Pour each of the solutions into a separate beaker.

Gently swirl the solutions around to ensure the amino acids produced are equilibrium in the solutions.

Rinse the pH probe with distilled water.

Measure the pH of each of the solutions appropriately (Rinse the pH probe with distilled water every time before measuring).

Risk Assessment

In this experiment there are a few safety precautions that are needed to be taken. Gloves and safety glasses should be worn when handling with protease as they can cause irritation, itching and discomfort, in case of any broken glass they can also be worn to protect your eyes and hands from cuts. For that reason it is important to be very careful when handling with boiling tubes to avoid unnecessary injuries and risk infection, especially with an amount of such number. Chairs should be tucked away to avoid tripping.

Set -up

Test tube (x5)

Protease solution


40°C Water

Water bath


The pH of the solution will be recorded by the pH probe in pH units.

The results should be recorded on a table like the one below.

Number of soybeans

pH of the solution (pH) +/-0.01

Standard Deviation

Try 1

Try 2

Try 3


Then a line graph showing how the change in the number of soybeans affect the pH value of the solution when added to of protease solution should be drawn, which will show the relationship between the two variables. The line graph can then be reflected back to the research question. Then a conclusion can be drawn according to the results and an evaluation can then be written to reflect to the limitations and weaknesses of the experiment.


The higher the amount of soybeans, the higher the amount of amino acids produced.

Raw data table to show the effect of the change in the amount of soybeans on the amount of amino acids produced when added to of protease solution

Number of soybeans

pH of the solution (pH)


Standard Deviation (2d.p.)

Try 1

Try 2

Try 3


































The Mean Average

The mean average is calculated by adding the 1st, 2nd and 3rd try and is then divided by 3.


=7.21 (3s.f.)

How to Work out Standard Deviation

- Work out the mean of your data (add the data together and divide by the number of readings).

- Calculate the difference between each reading and the mean value.

- Calculate the square of each of these differences.

- Add each of these squared differences together.

- Divide the total by the number of readings.

- Find out the square root of this number. This is called standard deviation.

The equation below is used to calculate the standard deviation.

Error Bars

Error bars are used to indicate the error or uncertainty of a measurement. They give an idea of how accurate a measurement is.

Measurement + Standard Deviation

Measurement - Standard Deviatione.g.


Soybeans are round and smooth textured seeds, with a beige coloured hull. The hull of a mature soybean is hard and water resistant and it protects the cotyledon and hypocotyl from harm. The hilum, also called the scar, is the small opening in the hull which allows the absorption of water for sprouting. The soybeans I used were about 9mm in length and 6mm diameter,


The results I have obtained show me the trend of the effect of a change in the amount of soybeans on the amount of amino acids produced when added to 6 of protease through the graph I had drawn. The amount of amino acids produced is measured by the pH of solution and the measurements are shown on the raw data table and graph along with the standard deviation of the data which are then used for drawing error bars on the graph.

As expected, the results show me that as the amount of soybeans increases the pH value of the solution decreases, which also means that the amount of amino acids produced increases as the amount of soybeans increases, and as the graph indicates, the trend is not proportionate. For example, for an amount of 2 soybeans, the pH was 6.96, for an amount of 4 soybeans, the pH was 6.87 and for an amount of 6 soybeans, the pH was 6.82. This means that the increase of the amount of amino acids decreases between every value. A higher number of soybeans increases the amount of amino acids produced because soybeans contain a type of protein called soy protein, which contains an abundant supply of amino acids. Even if amino acid itself is amphoteric, soy protein is high in a type of amino acid called glutamate (glutamic acid C5H9NO4) and there are more amino acids with acidic side groups than basic side groups, causing it to slightly show more acidic properties.

Furthermore, through observing the trend, the pH should continue to decrease with an increase in the number of soybeans, but there would be less decrease between each value and would potentially come close to leveling out but not totally leveled out.

There are no anomalous results present in this investigation as there are no points on the graph that is located far away from the general trend of the graph.


Weaknesses and limitations

There were some errors in this experiment due to the limitation of the precision of the equipment that I used which may have undermined my conclusion. One potential random error is due to the pH probe that was used, causing the pH value recorded to have an uncertainty of +/-0.01; this affects the accuracy of the results but not to an extent that the trend of the graph will change. The other possible random error is due to the measuring cylinder that was used to measure the 6 of protease, thus the volumes of protease have an uncertainty of +/-0.2; however, this does not affect the results in terms of having all the protein broken down since all the experiment was designed to have all the protein broken down, but this may affect the results in terms of the concentration of the amino acids produced as it might dilute the concentration of the amino acids produced , lowering the pH value of the solution.

There may also have been systematic errors since different soybeans may have slightly different sizes, surface area and content of soy protein. This causes the results to be less reliable as it affects the amount of soy protein available for the protease to react with and the amount of amino acids produced. This may significantly affect the pH of the solutions and thus affect the trend of the results.

Furthermore, even though soy protein is high in glutamic acid (17g per 100g) it is still mostly composed of neutral amino acids and a small percentage of basic amino acids. This means that not all the amino acids produced is accounted in the results, but only 17% of it. This also dilutes the concentration of glutamic acid, causing the results to be less distinctive

Additionally, soy protein contains trypsin inhibitors, a type of serine protease inhibitor which causes soy protein to be very resistant to the enzyme protease. This greatly reduces the effects of the protease solution on the soy protein, causing the experiment to take longer and the results to be less distinctive.

Another systematic error is that the amount of time used may not be enough for all the soy protein to be broken down since soy protein contains protease inhibitors which slow down the rate of the reactions.

Improving the investigation

There are a number of ways to improve this investigation. I have only taken 3 repeats of each measurement of absorbance for each number of soybeans; 5 repeats could have been used to improve the results because an increasing number of repeats would increase the accuracy of the mean averages as it would reduce the impact of random errors as they will cancel out. Using more sensitive measuring equipment or measuring equipment which show more significant figures can also reduce the uncertainties; a measuring cylinder that gives volume to +/-0.1or a pH probe that measures pH to more decimal places.

Blending a measured amount of soybeans mixed with a measured amount of water can solve the problem of having different bean sizes, soy protein content and surface area because blending the soybeans can maximize the surface area and soy protein exposure, causing the experiment to be more effective and less time consuming, thus increasing the reliability of the results.

To account for all the amino acids produced, a process called deamination could be done. Deamination is the removal of an amine group from a molecule. Enzymes which catalyse this reaction are called deaminases. Through removing the amine group NH2, the basic side of all the amino acids would be removed and only the acidic carboxylic side COOH would be left, making all the neutral amino acids to be acidic and basic amino acids to be neutral. This can cause the results to be more distinctive and more reliable.

To destroy the trypsin inhibitors, the soybeans must be heated in water for about 20-30 minutes. However, the temperature must not be too high as it may also damage the soy protein inside the bean. This can greatly increase the effectiveness of the protease enzyme and thus reducing the time needed to conduct the experiment.

To further ensure that all the soy protein has reacted, more time could be used to conduct the experiment so more reliable and accurate results could be measured.

Alternative Method

Other than measuring the pH of the solution, a substance called Folin's reagent could have been used to measure the amount of amino acids. Folin's reagent (C10H5NaO5S) is a chemical reagent which is used to measure levels of amines and amino acids. As the reagent produces a fluorescent red color in alkaline solutions, a process called decarboxylation could be done to remove the carboxyl group rather than deamination which removes the amine group in amino acids so the basic group is measured instead of the acid group, the enzyme involved in this is decarboxylase. However decarboxylation releases carbon dioxide, so your head should keep a safe distance from the reaction.

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