Cellular Respiration In Pea Seeds Biology Essay

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Cellular respiration is a chemical reaction where the intake of oxygen and glucose produces carbon dioxide and water. This prevalent catabolic reaction occurs in the mitochondria of cells.1 The purpose of this experiment is to compare rates of cellular respiration in pea seeds that are in different stages of development.2 This experiment also tests the effect of temperature on the rate of cellular respiration in the pea seeds. It is probable that germinating pea seeds will have a higher rate of cellular respiration because they are harnessing more energy in their quick growth and development; it is likely that the dried seeds will have a very small rate of cellular respiration due to their dormant state. Furthermore, temperature will affect the movement of particles in the experiment. At higher temperatures it is probable that the particles will move faster, so the occurrence of more collisions and reactions between particles would result in an increased rate of cellular respiration.

The graduated cylinder was filled with 25 mL of water. 25 germinating pea seeds were placed in the cylinder and the volume of the seeds was recorded by measuring the displacement of the water. The germinating peas were then removed from the water and patted dry with a paper towel. The graduated cylinder was again refilled with 25 mL of water. This time, 25 dried peas were placed in the water. To ensure the volume was equal in the different experimental groups, glass beads were added into the cylinder until an equal amount of water had been displaced. The beads and dried peas were then removed and patted dry with a paper towel. The graduated cylinder was filled again with 25 mL of water and only glass beads were used to create a third experimental group, again of equal volume. These groups were named 1, 2, and 3. All these steps were repeated to produce groups 4, 5, and 6. These six experimental groups (2 with only germinating peas, 2 with dried peas and glass beads, and 2 with only glass beads) all contained equal volume. 2

Absorbent cotton was soaked with KOH and placed in the bottom of all six respirometers. A layer of dry nonabsorbent cotton was placed on top of the soaked cotton. Respirometers 1 and 4 were filled with the glass beads, respirometers 2 and 5 were filled with the dried peas and glass beads, and respirometers 3 and 6 were filled with the germinating peas. 2

Two water baths were settled at room temperature. Ice was added to one of the baths until the temperature reached 10°C (temperature was maintained at 10°C throughout the experiment by adding ice or water in response to changes in temperature). Tape was used to make a sling across the tops of the baths to keep the tips of the respirometers from submerging underwater. A small weight was attached to the bottom of each respirometer so that they would sink to the bottom of the bath. Respirometers 1, 2, and 3 were placed in the room temperature water bath, with care taken to ensure that the tips of the respirometers lay on the sling. The same thing was repeated for respirometers 4, 5, and 6 with the 10°C water bath. The groups were left alone for an equilibrium adjustment period of 7 minutes. After this time elapsed, the sling was removed and all the respirometers were submerged completely in the water. Another equilibrium adjustment period of 3 minutes ensued. Following this, the amount of water that had entered the respirometers was measured and recorded as the initial results. The respirometers were checked every 5 minutes (for 20 minutes) to observe and record the amount of water that had entered into each of the respirometers.2

Table 1: Respirometer Set Up

Respirometer

Temperature

Contents

1

Room

Beads Alone

2

Room

Dry Peas and Beads

3

Room

Germinating Peas

4

10°C

Beads Alone

5

10°C

Dry Peas and Beads

6

10°C

Germinating Peas

Results:

Volume of germinating peas: 10 mL

Volume of dried peas and glass beads: 10 mL

Volume of glass beads: 10 mL

Table 2: Experiment Results

Temperature

Time

Beads Alone

Dry Peas and Beads

Germinating Peas

(°C)

(min)

(measured in mL of water that entered the respirometer)

25

0

0.10

0.08

0.15

5

0.10

0.08

0.25

10

0.10

0.08

0.35

15

0.09

0.07

0.41

20

0.09

0.07

0.50

10

0

0.19

0.18

0.21

5

0.17

0.18

0.33

10

0.16

0.16

0.36

15

0.15

0.15

0.41

20

0.15

0.15

0.45

Discussion:

This experiment was set up so that the changes in O2 could be measured through the amount of water that entered the respirometer. When respiration occurred in the experiment, the oxygen and glucose were converted to carbon dioxide, water, and energy (C6H12O6+6O2→6CO2+6H20+Energy). The CO2 produced from cellular respiration was converted to potassium carbonate in a chemical reaction with the potassium hydroxide (CO2+2KOH→K2CO3+H2O).2This reaction removed gaseous carbon dioxide, so the only variable gas in the chamber was oxygen. As cellular respiration occurred, the peas would consume the oxygen in the chamber to fuel the respiration reaction, causing more water to enter the respirometer as the gas levels decreased. Therefore, the rate at which water entered the respirometer was directly related to the amount of oxygen consumed as respiration took place.

The experiment proved the hypothesis right because the data and graphs show an increase in water entering the respirometers, especially in those containing the germinating peas. The germinating peas probably experienced respiration at the fastest rate because they need more energy to facilitate their quick stage of growth. The germinating peas in the room temperature bath were experiencing a slightly higher rate of respiration than the germinating peas in the 10˚C bath. Figure 3 shows a slightly steeper average incline of the line that depicts the amount of water entering the respirometer of the room temperature germinating peas as compared to that of the 10°C germinating peas. However, the variation in rate of respiration due to the change in temperature is not very drastic; this is shown by the closeness of the results of the different groups, despite the change in temperature. An increase in temperature would excite molecules and make reactions happen more quickly, but not so much as to cause a drastic variation in the rate of respiration.

Table 4 shows the actual rate of consumption of O2 in the different experiments. The hypothesis is supported by the fact that the highest O2 consumption rate is the germinating peas at room temperature. Furthermore, the dry peas have a very small rate of consumption of O2. This is most likely due to the dormant state of the seed; a seed in a dormant state only requires a small amount of energy to maintain homeostasis, so the rate of cellular respiration should be much lower. As the glass beads do not experience cellular respiration, they are not included in the table. Instead, the difference in water changes in the respirometer with the glass beads was used to correct the data collected from the other experiments.

Due to the slight convection the water baths, the temperature of the baths was probably not thoroughly consistent. Even a slight change in temperature or pressure would change the volume of the gases in the respirometer due to the direct variation of temperature and volume in the standard gas law PV=nRT. The control group, the respirometers containing only glass beads, should not have experienced any change in the amount of water entering the respirometer because no respiration would have been taking place. Therefore, any changes in water levels can be attributed to variations in pressure and temperature. As it is reasonable to expect similar changes in data in the respirometers containing the germinating peas and dry peas, the data for those groups was corrected to minimize skewed data due to changes in temperature and pressure.

Table 3: Experiment Calculations

Temperature

Time

Beads Alone

Dry Peas and Beads

Germinating Peas

(°C)

(min)

Reading at time X

Diff.*

Reading at time X

Diff.*

Corrected Difference

Reading at time X

Diff.*

Corrected Difference

25

0

0.10

0.08

0.15

5

0.10

0.00

0.08

0.00

0.00

0.25

0.10

0.10

10

0.10

0.00

0.08

0.00

0.00

0.35

0.20

0.20

15

0.09

-0.01

0.07

0.01

0.02

0.41

0.26

0.27

20

0.09

-0.01

0.07

0.01

0.02

0.50

0.35

0.36

10

0

0.19

0.18

0.21

5

0.17

-0.02

0.18

0.00

0.02

0.33

0.12

0.14

10

0.16

-0.03

0.16

0.02

0.05

0.36

0.15

0.18

15

0.15

-0.04

0.15

0.03

0.07

0.41

0.20

0.24

20

0.15

-0.04

0.15

0.03

0.07

0.45

0.24

0.28

* Difference calculated by: (reading at time X)-(reading at time 0)

Corrected difference calculated by: (Diff. in peas at time X)-(Diff. in beads at time X)

Table 4: Rates of Respiration2

Condition

Calculation

Rate (mL O2/min)

Germinating Peas- 25ËšC

0.018

Germinating Peas- 10ËšC

0.014

Dry Peas- 25ËšC

0.001

Dry Peas- 10ËšC

0.004

Citations

(1) Campbell, Neil A., and Jane B. Reece. AP* Edition Biology. Seventh ed. San Francisco: Pearson Education, 2005. Print.

(2) "LAB ONE Diffusion and Osmosis." Biology Lab Manual For Students. College Entrance Examination Board, 2001. 1-5. Print.

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