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Growth of Onions in Bleach Lab Report

Marwa Abdulmalik IB No: 000707-‐0001

Design

Aspect 1: Defining and Selecting Variables

Aim: The aim of this experiment is to investigate the growth of onion roots in water with different amounts of bleach over time.

Hypothesis: As the amount of bleach in the water increases, the growth of the roots decreases. This hypothesis is based on the fact that bleach is a pollutant, and is mostly used for sterilization purposes, which ultimately means it kills organic matter.

Background Information:

Onions, like all organisms, require basic needs to grow, and like plants, need sunlight and water. Onions, specifically though, have shallow roots, and therefore require a large amount of water to grow. Not only do they need this water, but this water must be untainted, so that the onions can get as much as they can from it. Bleach, which usually contains chlorine, is a common chemical used to whiten certain fabrics, through oxidization. Bleach is also used for sterilization, which controls bacteria and viruses, which are sometimes necessary for plants to obtain their nutrients. The choice of onions is due to the fact that it is an easy plant to grow, and bleach to test its power in stopping plant growth, and because it is easy to obtain.

Variables:

Independent: Amount of bleach

Dependent: Length of onion root

Controlled: Amount of water in each beaker, temperature of room, Time

Aspect 2: Controlling Variables

Equipment:

-‐ 15 beakers -‐ 15 onions -‐ water -‐ bleach -‐ ruler -‐ measuring tube -‐ labels

Describe how you are going to measure the independent variable.

The independent variable, bleach, will be measured using the measuring tube, in order to put the same amount of bleach required in each tube, under the unit of cm3.

Describe how you are going to measure the dependent variable.

The dependent variable, which is the length of the onion root, will be measured using a ruler and the unit of cm, to ensure the most accurate length.

Describe what you did to make sure the controlled variables remained constant.

The controlled variables remained constant through the cautious measurement of the amount of water in each beaker, to ensure that the onion’s roots could reach the water and to make sure all the onions were growing with the same amount of water. Also, all the beakers were placed in the same room, therefore were all undergoing the same temperature and growing under it. The temperature was kept at constant room temperature with the automatic air conditioning system. Both these controlled variables made it possible for all the onions to be growing under the same conditions. Time will be controlled by a clock, and by recording the time intervals between the measurements of the roots.

Aspect 3: Developing a Method of Collection

Procedure:

1. Take 15 beakers, and label each three with the numbers 0,5,10,15, and 20. 2. Fill all beakers with water. 3. Add no bleach to the 3 beakers labeled 0. 4. For the rest of the beakers, add an amount of bleach corresponding to the

label on the beaker (in cm3) using the measuring tube. 5. Measure the length of the onion roots at 0 hours and record the results. 6. Repeat the measuring of the onion roots between different time intervals

to record the growth of the roots.

State the range of values that you are going to use for the independent variable.

The bleach will be within a range of 0 cm3 and 20 cm3.

State how many times you are going to repeat the measure of the independent variable.

3 times.

Data Collection and Processing

Raw Data

Table 1: Length of Roots at 72 hours

Amount of Bleach

(cm3)

±0.5

Length of Roots

(cm)

±0.05

Trial 1 Trial 2 Trial 3

0 Beaker 1 7.00 7.00 7.00

Beaker 2 6.00 6.00 6.50

Beaker 3 3.50 3.70 4.00

5 Beaker 1 0.20 0.30 0.30

Beaker 2 1.00 1.30 0.90

Beaker 3 0.50 0.50 0.50

10 Beaker 1 0.10 0.10 0.20

Beaker 2 0.50 0.30 0.40

Beaker 3 0.70 0.60 0.70

15 Beaker 1 0.50 0.20 0.30

Beaker 2 0.20 0.20 0.30

Beaker 3 1.00 1.50 0.70

20 Beaker 1 1.00 0.50 0.60

Beaker 2 0.50 0.70 0.50

Beaker 3 0.60 0.80 0.30


Amount of Bleach

(cm3)

±0.5

Length of Roots

(cm)

±0.05


0 Beaker 1 7.50 7.50 5.00

Beaker 2 8.40 8.20 7.50

Beaker 3 5.00 5.50 4.60

5 Beaker 1 0.20 0.20 0.10

Beaker 2 1.20 1.50 1.00

Beaker 3 0.20 0.20 0.30

10 Beaker 1 0.20 0.30 0.20

Beaker 2 0.40 0.50 0.30

Beaker 3 0.20 0.50 1.00

15 Beaker 1 0.50 0.30 0.20

Beaker 2 0.80 0.30 0.50

Beaker 3 0.50 0.60 0.80

20 Beaker 1 0.30 0.40 0.50

Beaker 2 0.20 0.30 0.50

Beaker 3 0.60 0.50 0.60


Amount of Bleach

(cm3)

±0.5

Length of Roots

(cm)

±0.05


0 Beaker 1 8.00 7.50 7.70

Beaker 2 9.50 9.0 9.50

Beaker 3 6.00 5.80 5.60

5 Beaker 1 0.20 0.20 0.30

Beaker 2 2.00 1.10 1.90

Beaker 3 0.30 0.30 0.70

10 Beaker 1 0.20 0.20 0.30

Beaker 2 0.50 0.40 0.60

Beaker 3 0.90 0.80 1.00

15 Beaker 1 0.50 0.40 0.40

Beaker 2 0.50 0.30 0.40

Beaker 3 0.80 0.70 1.00

20 Beaker 1 1.10 1.20 1.30

Beaker 2 0.60 0.50 0.50

Beaker 3 0.60 0.50 0.60


Amount of Bleach

(cm3)

±0.5

Length of Roots

(cm)

±0.05


0 Beaker 1 7.90 8.10 8.00

Beaker 2 9.60 10.10 10.20

Beaker 3 7.50 6.90 7.60

5 Beaker 1 0.20 0.40 0.40

Beaker 2 2.60 2.70 2.80

Beaker 3 0.90 1.00 0.90

10 Beaker 1 0.40 0.20 0.40

Beaker 2 0.50 0.60 0.50

Beaker 3 1.70 1.80 1.90

15 Beaker 1 0.50 0.60 0.50

Beaker 2 0.40 0.90 0.10

Beaker 3 1.20 1.30 1.20

20 Beaker 1 1.30 1.40 1.30

Beaker 2 0.70 0.80 0.70

Beaker 3 0.80 0.90 0.90


Amount of Bleach

(cm3)

±0.5

Length of Roots

(cm)

±0.05


0 Beaker 1 8.00 8.00 8.20

Beaker 2 9.50 10.30 10.20

Beaker 3 7.60 7.00 7.70

5 Beaker 1 0.30 0.40 0.40

Beaker 2 2.60 2.80 2.70

Beaker 3 1.00 1.00 0.90

10 Beaker 1 0.40 0.20 0.50

Beaker 2 0.40 0.60 0.60

Beaker 3 1.80 1.80 1.70

15 Beaker 1 0.60 0.60 0.50

Beaker 2 0.50 0.90 0.20

Beaker 3 1.30 1.30 1.30

20 Beaker 1 1.40 1.40 1.30

Beaker 2 0.60 0.80 0.70

Beaker 3 0.90 0.90 0.80

Mean (average)

Example Calculation:

Average in each beaker:

(7.00 + 7.00 + 7.00) / 3 = 7 (Ans 1)

(6.00 + 6.00 + 6.50) / 3 = 6.2 (Ans 2)

(3.50 + 3.70 + 3.40) / 3 = 3.5 (Ans 3)

Total Average of root length with 0 cm3 of bleach at 0 Hours

(Ans 1 + Ans 2 + Ans 3) / 3 = 5.6 cm

Mean Tables:

Table 6: Average Root Length at 72 hours

Amount of Bleach

(cm3)

±0.5

Mean Root Length

(cm)

±0.05

0 5.6

5 0.6

10 0.4

15 0.5

20 0.6


Amount of Bleach

(cm3)

±0.05

Mean Root Length

(cm)

±0.05

0 6.5

5 0.5

10 0.4

15 0.5

20 0.4


Amount of Bleach

(cm3)

±0.05

Mean Root Length

(cm)

±0.05

0 7.6

5 0.7

10 0.5

15 0.5

20 0.7


Amount of Bleach

(cm3)

±0.05

Mean Root Length

(cm)

±0.05

0 8.4

5 1.3

10 0.9

15 0.7

20 0.9


Amount of Bleach

(cm3)

±0.05

Mean Root Length

(cm)

±0.05

0 8.5

5 1.3

10 0.9

15 0.8

20 1

Percentage Change


At 0 hours

[(Length with most bleach – Length with no bleach) / (Length with no bleach)]

[(0.6 – 5.6) / (5.6)]*100

=[-‐0.89]*100

= -‐89.2%

Percentage Change Tables:

Table 11: Percentage Change at Different Time Intervals

Time

(hours)

Percentage Change

%

72 -‐89.2

120 -‐93.8

214 -‐90.7

238 -‐89.2

210 -‐88.2

Rate of Change:


At 0 bleach

[(Length at 310 hours – Length at 72 hours) / (310 – 72)]

[(8.5 – 5.6) / (238)]

[(2.9) / (238)]

[0.012]

Table 12: Rate of Change at Different Bleach Levels

Amount of Bleach

(cm3)

Rate of Change

(cm-‐1 h-‐1)

0 0.012

5 0.002

10 0.002

15 0.001

20 0.002

Standard Deviation:


At 0 hours with 0 bleach

STDV = √(|7 – 5.6| + |6.2 – 5.6| + |3.7 – 5.6|)^2 / (3 – 1)

= 1.72

5.6 + 1 STDV

= 7.32

5.6 – 1 STDV

=3.88

5.6 + 2 STDV

= 9.04

5.6 – 2 STDV

= 2.16

Table 13: Standard Deviation at 0 hours

Amount of Bleach

(cm3)

Standard Deviation

Average + 1 STDV

Average – 1 STDV

Average + 2 STDV

Average – 2 STDV

0 1.72 7.32 3.88 9.04 2.16

5 0.42 1.02 0.18 1.44 -‐0.84

10 0.25 0.65 0.15 0.90 -‐0.10

15 0.49 0.99 0.01 1.48 -‐0.48

20 0.06 0.66 0.54 0.72 0.48


Amount of Bleach

(cm3)

Standard Deviation

Average + 1 STDV

Average – 1 STDV

Average + 2 STDV

Average – 2 STDV

0 1.50 8.00 5.00 -‐ -‐

5 0.57 1.07 -‐0.07 1.64 -‐0.64

10 0.20 0.60 0.20 -‐ -‐

15 0.15 0.65 0.35 0.80 0.20

20 0.15 0.55 0.25 0.70 0.10


Amount of Bleach

(cm3)

Standard Deviation

Average + 1 STDV

Average – 1 STDV

Average + 2 STDV

Average – 2 STDV

0 1.75 9.35 5.85 11.1 4.10

5 0.75 1.45 -‐0.05 2.20 -‐0.80

10 0.35 0.85 0.15 1.20 -‐0.20

15 0.23 0.73 0.27 0.96 0.04

20 0.37 1.07 0.33 1.44 -‐0.04


Amount of Bleach

Standard Deviation

Average + 1 STDV

Average – 1 STDV

Average + 2 STDV

Average – 2 STDV

(cm3)

0 1.34 9.74 7.06 11.08 5.72

5 1.24 2.54 0.06 3.78 -‐1.18

10 0.81 1.71 0.09 2.52 -‐0.72

15 0.40 1.10 0.30 1.50 -‐0.10

20 0.30 1.20 0.60 1.50 0.30


Amount of Bleach

(cm3)

Standard Deviation

Average + 1 STDV

Average – 1 STDV

Average + 2 STDV

Average – 2 STDV

0 1.34 9.84 7.16 11.18 5.82

5 1.20 2.50 0.10 3.70 -‐1.10

10 0.78 1.68 0.12 2.46 -‐0.66

15 0.43 1.23 0.37 1.66 -‐0.06

20 0.36 1.36 0.64 1.72 0.28

Discussion

During the execution of this lab, the presence of more than one variable made it difficult to identify which would be the independent and which would be the dependent. After identifying the independent as the amount of bleach and dependent as the length of the onion root, I based the length of the roots on the amount of bleach, and carried on the make the percentage change and the rate of change to be in relation to the amount of bleach rather than the time taken, seeing as the main idea is to see the affect that bleach has on the growth of onion roots, and time inevitably will pass. Therefore the x axis on all the graphs was shown to be the amount of bleach rather than the time, and this is to show the negative correlation that is present between the amount of bleach and the growth of the root. As shown in graphs 1-‐5, the average of the length of the root slowly declines as the amount of bleach increases. What is noticed in these 5 graphs is that the slope from no bleach to 5 centimeters cubed of bleach is very steep and steeper than the others, as all other slopes after this one are less steep. This is to show the danger that the bleach poses on the roots of the onion, and most other plants, as even a small amount was able to hinder the growth of this onion, and adding more bleach helped this process happen gradually.

The graphs from 6-‐10 show the percentage change occurring. The percentage change is the change in the growth of the root in relation to the amount of bleach added. Once again there is negative correlation, and the percentage itself is negative. This is because the change was not a positive one, where the length of the root increased, rather it decreased as the bleach increased. All the graphs showed a great percentage change, ranging from 88-‐93. This large percentage shows the extent to which the change is occurring. The presence of the bleach is not causing a minor change to the growth of the plant but rather a great one that is very close to 100%.

The rate of change of the growth in accordance to the time is to investigate the role of bleach in plant growth. The rate of change is there to show to what extent each hour that the bleach is in the water does to a centimeter of onion root. Although it is a slow rate and the numbers are decimals, there is still an effect to some extent. When this rate is taken too far, it might damage the onion roots greatly. Although in this experiment the roots only stopped growing and were not damaged, if they were kept for a longer period of time the onion could have been at risk. This is why bleach is sometimes used in small amounts, but even these small amounts should not be kept for a long time because they ultimately damage the root.

Conclusion

In conclusion, this experiment showed that there is a negative correlation between the amount of bleach and the growth of the roots of an onion. This is because of the sterilizing power of the bleach that does not allow the onion roots to take in as many nutrients as they need to. It kills the bacteria that absorbs nutrients for the plants, and plants aren’t able to be nourished. This sterilizing power of bleach, although harmful to plants, is the exact reason why humans in the real world use it. Bleach is used to get rid of the bacteria that are unwanted to humans, but are helpful to plants. It also has multiple uses such as whitening

and disinfecting, all through the process of oxidation. This process of oxidation is what damages these roots of onions and plants and keeps them from growing at a normal rate.

Evaluation:

Throughout this experiment there were many difficulties while executing it and writing up the lab report. There were many sources of error involved, which included adding the wrong amounts of bleach, or having different amounts of water in each beaker to start with. Also, the biggest source of error that has affected my lab report was the measuring of the onion roots. The onion roots were mostly very small, and hard to measure with the naked eye and a regular ruler. A lot of errors could have been as to the accurate length of the root. Also, in many onions there were a lot of small roots, and one long one, which made some of the calculations inaccurate, and caused outliers to appear. In addition to that, every time we measure the onion roots, we would forget which root we measured, which led us to choosing a random one and measuring it 3 times. This is what led to having the data increase and decrease with time instead of just increasing or just decreasing. This is the main issue which has led to the range being between 2 standard deviations instead of just 1. Although the sources of error were many, there are ways of improvement for all. First of all is to have the same person measure the water and bleach to ensure that they are keen on keeping the amounts equal. Also to have equipment that make measuring the water and the bleach easier and erase room for mistakes. As for the onion roots, a simple mark on one of the roots that were to be measured would have kept the measurements accurate and the person who was measuring on track. This lab report was difficult but it also presented itself as a new challenge to face and conquer.

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