Respiration Rate of Peas Under Different
Salinities
1 INTRODUCTION
1.1
SUMMARY AND BACKGROUND
In this experiment, we are trying to find the effect of salinity on the respiration rate of peas.
Cellular respiration is performed by living organisms in order to transfer energy from one molecule to
another; taking account of all of the energy-rich molecules involved in the respiration, there are ATP,
NADH, and FADH2, to which NADH and FADH2 are used in electron transport chain to attach phosphates
onto ADPs with ATP Synthase. In brief, there are four stages to cellular respiration: Glycolysis, Link
Reaction, Krebs Cycle, and Electron Transport Chain; to which at the end of the whole process, about 38
ATP are produced from 1 glucose molecule. These processes involves usage of water, little ATP, NADH
and FADH2, etc. along with many enzymes to continue the process.
Rate of respiration could be measured in different ways, but from the equation: C6H12O6 + 6O2 ->
6H2O + 6CO2 we know that O2 gases are used and CO2 are produced as the only byproducts that is not
used up in respiration (NADH, FADH2) in equal quantity, thus we can measure the rate of respiration
depending on the vacuum created by a solution called KOH solution that reacts with CO2, thus both
gases are being used up within an air-right space. By attaching a small tube with food coloring in it, the
vacuum will draw the color into the tube; by measuring the distance and time of the traveling food
coloring, rate of respiration can be determined by dividing distance by time.
1.2
HYPOTHESIS
My hypothesis is that, as the salinity increases the rate of respiration in cells declines due to
exposure to higher concentration of salt solution in comparison to the cells, thus causing it to shrink and
possibly deforms the mitochondria to which reduces their surface area with overlapping cristae, while
causing lack of water to perform certain reactions during the Citric Acid Cycle (or known as Krebs Cycle).
1.3
EQUIPMENT
The equipment used during the experiment are the following:
-
550 ml of water (500ml dived evenly into 5 beakers, 50ml used for KOH solution)
5* 200ml beakers, +5% uncertainty
5* Boiling tubes
Glass stirrer
Salt (Sodium Chloride)
5* Stoppers with 1 central hole
5* Tiny tubes
Cotton
-
Spoonful of KOH
Clay
50* similarly sized peas (grouped into 10 peas per group, total 5 groups)
Small Forceps
Digital Weighing Machine, +0.01g uncertainties
5* timers
Food color
Plastic droppers
Ruler
1.4
PROCEDURE
Note: # indicates that an error has occurred during our experiment that did not fit the procedure
1. Gather all the needed materials
2. Pick out similarly sized peas and group them into 5 groups of 10 peas
a. Note: Peas must not be frozen
3. Rinse all equipment
4. Prepare 0.0 mol, 0.2 mol, 0.4 mol, 0.6 mol, and 0.8 mol of salt solutions, given 100 ml water per
each solution; stir each solution with glass stirrers until they are properly dissolved
a. 0.0 mol salt solution: 100 ml water
b. 0.2 mol salt solution: 100 ml water + ( ~1.16 g + 0.01 g ) salt
c. 0.4 mol salt solution: 100 ml water + ( ~2.33 g + 0.01 g ) salt
d. 0.6 mol salt solution: 100 ml water + ( ~3.5 g + 0.01 g ) salt
e. 0.8 mol salt solution: 100 ml water + ( ~4.67 g + 0.01 g ) salt
5. #Soak each groups of peas in different solutions for 5 to 10 minutes, 5 timers are needed
6. Meanwhile the peas are soaking:
a. Set up 5* boiling tubes lying horizontally on stable surface
b. Split the cotton into 10 medium pieces; keep 5 pieces dry
c. Prepare KOH solution with 50 ml of water with spoonful of KOH
i. Stir with glass stirrer until KOH is properly dissolved
7. Take the peas out when timers hit 5 to 10 minutes
8. Carefully shake the excess water out and put the peas into 5* different boiling tubes
9. Use forceps or glass stirrers to put in the dry cotton close to the peas
10. Meanwhile above steps are performed (or perform the following steps within a short period of
time)
a. Use forceps to dip 5* cotton pieces into the KOH solution
b. Squeeze out the excess KOH solution
11. Place the cotton pieces with KOH solution near the opening of the boiling tubes while leaving
some space
12. Tightly place the stoppers onto the boiling tubes
13. Place the tiny tubes through the hole of the stoppers, #seal up the remaining opening with clay
14. Use the plastic droppers to obtain tiny drops of food color, then transfer them into the tiny
tubes
15. Quickly mark down the location of the starting position and start the timers
16. #Wait until there are significant movements made as the boiling tube creates vacuum, quickly
stop the timers and mark down the location that the coloring have traveled to; record the time
a. Marked locations must be the same side
17. Measure the distance between the two marks, record
18. Clean up the equipment, materials used and operating area
2 RESULTS
2.1
RESULTS AND OBSERVATION
Here is the raw data table obtained from experiment,
Distance Travelled and Time Elapsed by Food Coloring in different Salt Concentrations
Salt Concentration (mole)
Distance Travelled (cm)
Time Elapsed (sec)
0.0
~2
38
0.2
~1
~120
0.4
~1
~180
0.6
~2
~30
0.8
~2
~5
In this case the independent variable is salt concentration with the dependent variable of
reaction rate (or rate of respiration), which is calculated from distance travelled and time elapsed.
During the experiment, the vacuums are created at a much quicker rate than I have expected
(aside from our errors). Also, quite a few of the movements of the food colorings seemed to be sudden
bursts, where the food coloring will suddenly travel around a fourth of the length of tiny tubes1; thus
close and careful observations are required in order to measure the distance and time properly. With
our errors of not making the tubes air-tight, I am a little surprised that vacuums are created at such rate
even long after its been first created and put into the tube, as I have at first assumed that as KOH
solution continues to react, it depletes its source by forming a new compound like rusting.
Also during the wait from our error of not making it air tight, I have also assumed that the
quantity of the peas in the boiling tube is not enough to “convert” O2 into CO2 fast enough, although the
quantity was fine too, despite its volume in proportion to the volume of the boiling tube.
2.2
DATA PROCESSING
Here is the data after some calculations
Salt
Concentration
(mole)
0.0
1
Rate of Respiration in different Salt Concentrations
Distance
Time Elapsed
Time Elapsed
Travelled
Rate of Respiration (cm / min)3
(sec)
(Minute)2
(cm)
~2
38
0.633
3.16
Generally, sudden movement with higher rate in comparison to prior the movement
Values are rounded to nearest thousandths
3 Values are rounded to nearest hundredths
2
0.2
~1
~120
2.000
0.50
0.4
~1
~180
3.000
0.33
0.6
~2
~30
1.000
2.00
0.8
~2
~5
0.083
24.10
*Note: Due to spacing issues, graph is attached at the end of the report
Minutes are used for seconds for a larger value to plot on graph, and it makes it easier to differentiate
between each rate.
According to the graph, the reaction rate declines as the salinity increase until a certain point, 0.4 mole
salt solution, reaction rate rises significantly afterwards, especially the rate-difference between 0.6 mole
and 0.8 mole salt solution. To which 0.8 mole salt solution’s data point seemed like an outlier, as it
created a large spacing and thus the graph had to be shrunk down.
Beakers used for salt solutions all had uncertainty of +5%, thus we could assume that the
volume of the water measured would range from 190 ml to 210 ml of actual water volume. With the
digital weighing machine computing up to hundredth place, we could assume the uncertainty for the
quantity of the salt used fluctuation value is +0.01 g.
3 CONCLUSION
The experiment proved my hypothesis, ‘as the salinity increases the rate of respiration in cells
declines’ incorrect, as the data points and graph from the experiment showed two patterns instead of a
continuous declining respiration rate as salinity increases. The first being the declining rate as salinity
increases from 0.0 mole salt solution, or water, to 0.4 mole of salt solution; then from 0.4 mole salt
solution to 0.8 mole salt solution there are extreme gaps in between 0.6 mole and 0.8 mole salt
solution: 2.00 cm/min and 24.10 cm/min respectively, to which is susceptible to being a result of errors
that occurred during the experiment4 . In general, the graph almost portrayed a positive parabola line
that opens upward, or towards positive y-axis.
Originally I thought my hypothesis is as such due to cell shrinking due to osmosis and having lack of
water during Krebs Cycle to which some reactions requires input of water, what I have ignored as a
possible factor that contributes towards such result would be the optimal salinity of pea cells, to which
definitely differs from cells in other organisms, such as potatoes. Under the assumption that our
experiment results are correct, the optimal salinity according to what we have gathered is 0.8 mole salt
solution to which rate of respiration was at the highest in our data. We could also assume that there are
multiple semi-optimal salinities as 0.0 mole salt solution (or water) had the second quickest rate after
0.8 mole salt solution5, which could purely be a result of error from our experiment. Overall, my graph
showed a positive semi-linear relationship between rate of respiration over molar concentration of salt
solution, thus as molar concentration of salt solution increases, the rate of respiration generally
increases with it and vice versa; proving my hypothesis to be incorrect.
4
5
Though errors will not be discussed here; instead its discussed in Error under Analysis section after Conclusion
Unless it is an outlier as the value drastically differs from the rest of the values
4 ANALYSIS
4.1
ERRORS
There are multiple errors made throughout the entire experiment. First, two groups of peas (0.0
and 0.2 mole solutions) are soaked for approximately 15 minutes where the rest of the peas are soaked
for approximately 3 minutes, which might cause the first two peas to be completely balanced with the
solutions while the rest are still incomplete with osmosis. Second, volume of peas are approximated,
thus might cause small value differences due to small differences between each groups’ volume.
Third, failure to create an air-tight environment for the boiling tubes for an extended period of
time. This one error would, at high possibility, led to other unwanted error in control groups, such as the
KOH solution soaked in cotton pieces might exhausted certain degree of “resources” prior to our fixing.
Fourth, failure to control the distance between each cotton pieces (dry and KOH soaked), which might
causes slight delay in the creation of vacuum. Fifth, different sizes of KOH soaked cotton piece which
might led to differing quantity of KOH solution for each boiling tube that alters the creation of vacuum
and thus the time it takes for the food coloring to move.
Uncertainties made in equipment, as beakers all had uncertainties of +5% and digital weighing
machines with +0.01 g, thus causing slight value differences under the condition of smaller values (tens
and hundreds).
4.2
GRAPH
The graph itself have presented all the values we have got from the experiment. Though there are
more spaces for more precise representation of the reaction rate (respiration rate) of peas, as the graph
only shows an approximate in the hundredths place digits due to lack of length in the graphing paper.
And a single break is used in order to maintain the minimum precision in graph, due to the large value
difference between 0.6 mole salt solution and 0.8 salt solution.