Cell Respiration


Cell Respiration

In this experiment, you will work with seeds that are living but dormant. A seed contains an embryo plant and a food supply surrounded by a seed coat. When the necessary conditions are met, germination occurs, and the rate of cellular respiration greatly increases. In this experiment you will measure oxygen consumption during germination. You will measure the change in gas volume in respirometers containing either germinating or non-germinating pea seeds. In addition, you will measure the rate of respiration of these peas at two different temperatures.

Before doing this laboratory you should understand:

  • how a respirometer works in terms of the gas laws; and
  • the general processes of metabolism in living organisms.

After doing this laboratory you should be able to:

  • calculate the rate of cell respiration from experimental data.
  • relate gas production to respiration rate; and
  • test the effect of temperature on the rate of cell respiration in ungerminated versus germinated seeds in a controlled experiment.

Cellular respiration is the release of energy from organic compounds by metabolic chemical oxidation in the mitochondria within each cell. Cellular respiration involves a series of enzyme-mediated reactions. The equation below shows the complete oxidation of glucose. Oxygen is required for this energy-releasing process to occur.

C6H12O6 + 6O2 —–> 6 CO2 + 6 H2O + 686 kilocalories of energy / mole of glucose oxidized

By studying the equation above, you will notice there are three ways cellular respiration could be measured. One could measure the:

1. Consumption of O2 ( How many moles of oxygen are consumed in cellular respiration?)

2. Production of CO2 ( How many moles of carbon dioxide are produced by cellular respiration?)

3. Release of energy during cellular respiration.

In this experiment, the relative volume of O2 consumed by germinating and non-germinating (dry) peas at two different temperatures will be measured.

Background Information:
A number of physical laws relating to gases are important to the understanding of how the apparatus that you will use in this exercise works. The laws are summarized in the general gas law that states:

PV = nRT


P is the pressure of the gas,

V is the volume of the gas,

n is the number of molecules of gas,

R is the gas constant ( its value is fixed), and

T is the temperature of the gas (in K0).

This law implies the following important concepts about gases:

1. If temperature and pressure are kept constant, then the volume of the gas is directly proportional to the number of molecules of gas.

2. If the temperature and volume remain constant, then the pressure of the gas changes in direct proportion to the number of molecules of gas present.

3. If the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume.

4. If the temperature changes and the number of gas molecules is kept constant, then either pressure or volume ( or both ) will change in direct proportion to the temperature.

It is also important to remember that gases and fluids flow from regions of high pressure to regions of low pressure.

In this experiment, the CO2 produced during cellular respiration will be removed by potassium hydroxide (KOH) and will form solid potassium carbonate (K2CO3) according to the following reaction.

CO2 + 2 KOH —-> K2CO3 + H2O

Since the carbon dioxide is being removed, the change in the volume of gas in the respirometer will be directly related to the amount of oxygen consumed. In the experimental apparatus if water temperature and volume remain constant, the water will move toward the region of lower pressure. During respiration, oxygen will be consumed. Its volume will be reduced, because the carbon dioxide produced is being converted to a solid. The net result is a decrease in gas volume within the tube, and a related decrease in pressure in the tube. The vial with glass beads alone will permit detection of any changes in volume due to atmospheric pressure changes or temperature changes. The amount of oxygen consumed will be measured over a period of time. Six respirometers should be set up as follows:

1RoomGerminating seeds
2RoomDry Seeds and Beads
4100CGerminating Seeds
5100CDry Seeds and Beans

 1.Prepare a room-temperature bath (approx. 25 degrees Celsius) and a cold-water bath (approx. 10 degrees Celsius).

2.Find the volume of 25 germinating peas by filling a 100mL graduated cylinder 50mL and measuring the displaced water.

3.Fill the graduated cylinder with 50mL water again and drop 25 non-germinating peas and add enough glass beads to attain an equal volume to the germinating peas.

4.Using the same procedure as in the previous two steps, find out how many glass beads are required to attain the same volume as the 25 germinating peas.

5.Repeat steps 2-4. These will go into the 10-degree bath.

6.To assemble 6 respirometers, obtain 6 vials, each with an attached stopper and pipette. Number the vials. Place a small wad of absorbent cotton in the bottom of each vial and, using a dropper, saturate the cotton with 15% KOH (potassium hydroxide). It is important that the same amount of KOH be used for each respirometer.

7.Place a small wad of dry, nonabsorbent cotton on top of the saturated cotton.

8.Place the first set of germinating peas, dry peas & beads, and glass beads in the first three vials, respectively. Place the next set of germinating peas, dry peas & beads, and glass beads in vials 4, 4, and 6, respectively. Insert the stopper with the calibrated pipette. Seal the set-up with silicone or petroleum jelly. Place a weighted collar on each end of the vial. Several washers around the pipette make good weights.

9.Make a sling of masking tape attached to each side of the water baths. This will hold the ends of the pipettes out of the water during an equilibration period of 7 minutes. Vials 1, 2, and 3 should be in the room temperature bath, and the other three should be in the 10 degree bath.

10.After 7 min., put all six set-ups entirely into the water. A little water should enter the pipettes and then stop. If the water continues to enter the pipette, check for leaks in the respirometer.

11.Allow the respirometers to equilibrate for 3 more minutes and then record the initial position of the water in each pipette to the nearest 0.01mL (time 0). Check the temperature in both baths and record. Record the water level in the six pipettes every 5 minutes for 20 minutes.

Table 5.1: Measurement of O2 Consumption by Soaked and Dry Pea Seeds at Room Temperature (250C) and 100C Using Volumetric Methods.

Beads AloneGerminating Peas

Dry Peas and Beans

Reading at time XDiff*Reading at time XDiff*Corrected Diff. ^Reading at time XDiff*Corrected diff ^
Initial – 0
5- 10
10 -15
Initial – 0
5- 10
10 -15

* difference = ( initial reading at time 0) – ( reading at time X )

^ corrected difference = ( initial pea seed reading at time 0 – pea seed reading at time X) – ( initial bead reading at time X).

Analysis of Results:
1. In this investigation, you are investigating both the effect of germination versus non-germination and warm temperature versus cold temperature on respiration rate. Identify the hypothesis being tested in this activity.



2. This activity uses a number of controls. Identify at least three of the control, and describe the purpose of each control.







3. Graph the results from the corrected difference column for the germinating peas and dry peas at both room temperature and 100C.

a. What is the independent variable? ____________________________________________________

b. What is the dependent variable? ______________________________________________________

Graph Title: _____________________________________________________________________

Graph 5.1


4. Describe and explain the relationship between the amount of oxygen consumed and time.





5. From the slope of the four lines on the graph, determine the rate of oxygen consumption of germinating and dry peas during the experiments at room temperature and 100C. Recall that rate = delta Y/delta X.

Table 5.2

ConditionShow Calculations HereRate in ml.O2 / min
Germinating Peas/100C 




Germinating peas /Room Temperature 





Dry peas/100C 




Dry Peas /Room Temperature 





6. Why is it necessary to correct the readings from the peas with the readings from the beads?





7. Explain the effect of germination ( versus non-germination) on peas seed respiration.





8. What is the purpose of KOH in this experiment?





9. Why did the vial have to be completely sealed around the stopper?





10. If you used the same experimental design to compare the rates of respiration of a 25 g. reptile and a 25 g. mammal, at 100C, what results would you expect/ Explain your reasoning.







11. If respiration in a small mammal were studied at both room temperature (210C) and 100C, what results would you predict? Explain your reasoning.





12. Explain why water moved into the respirometer pipettes.







DNA & Protein Synthesis Chapter 10 Worksheet


    DNA & Protein Synthesis


Section 10-1 DNA

1. What does DNA stand for?

2. What is DNA’s primary function?

3. What is the function of proteins?

4. What are the repeating subunits called that make up DNA?

5. Name the 3 parts of a DNA nucleotide.

6. Sketch and label a DNA nucleotide.

7. Name the 4 nitrogen bases on DNA.

8. What is the difference between a purine & a pyrimidine?

9. Name 2 purines.

10. Name 2 pyrimidines.

11.Who is responsible for determining the structure of the DNA molecule & in what year was this done?

12. The model of DNA is known as a ____________________________ because it is composed of two ___________________ chains wrapped around each other.

13. What makes up the sides of a DNA molecule?

14. What makes up the “steps” of a DNA molecule?

15. How did Rosalind Franklin contribute to determining the structure of DNA?

16. What type of bonds holds the DNA bases together? Are they strong or weak bonds?

17. What makes up the “backbone” of the DNA molecule?

18. On DNA, a ____________________ base will always pair with a __________________ base.

19. What is the most common form of DNA found in organisms?

20. How many base pairs are in a full turn or twist of a DNA molecule?

21. Name the complementary base pairs on DNA.

22. How many hydrogen bonds link cytosine & guanine? adenine & thymine?

23. How does the nucleotide sequence in one chain of DNA compare with the other chain of DNA?

24. Why must DNA be able to make copies of itself?

25. Define DNA replication.

26. What is the first step that must occur in DNA replication?

27. What acts as the template in DNA replication?

28. What is a replication fork?

29. What enzymes help separate the 2 strands of nucleotides on DNA? What bonds do they break?

30. What is the function of DNA polymerases?

31. ____________________ are joined to replicating strands of DNA by ________________ bonds.

32. If the sequence of nucleotides on the original DNA strand was A – G – G – C – T – A, what would be the nucleotide sequence on the complementary strand of DNA?

33. Does replication of DNA begin at one end and proceed to the other? Explain.

34. Why does DNA replication take place at many places on the molecule simultaneously?

35. When replication is complete, how do the 2 new DNA molecules compare to each other & the original DNA molecule?

36. Is DNA replicated (copied) before or after cell division?

37. Sketch & label DNA replication. (Figure 10-5, page 188)

38. What is the error rate in DNA replication? What helps lower this error rate to 1 in 1 billion nucleotides?

39. What is a mutation?

40. Name several things that can cause DNA mutations.


Section 10-2 RNA


41. What sugar is found on DNA?

42. What base is missing on RNA, & what other base replaces it?

43. Uracil will pair with what other on DNA?

44. Is RNA double or single stranded?

45. Name the 3 types of RNA and tell the shape of each.

46. Which type of RNA copies DNA’s instructions in the nucleus?

47. Which type of RNA is most abundant?

48. What does tRNA transport?

49. What 2 things make up ribosomes?

50. Define transcription.

51. In what part of a cell are proteins made?

52. What is RNA polymerase & tell its function.

53. What are promoters?

54. Where does RNA polymerase bind to the DNA it is transcribing?

55.What makes the beginning of a new gene on DNA in eukaryotes?

56. What do promoters mark the beginning of on prokaryotic DNA?

57. When a promoter binds to DNA, What happens to the double helix?

58. Are both strands of DNA copied during transcription?

59. As RNA polymerase moves along the DNA template strand, what is being added?

60. What bases pair with each other during transcription?

61. What is the termination signal?

62. What happens when RNA polymerase reaches the termination signal?

63. What are the products of transcription called?

64. Transcripts are actually ____________________________ molecules.

65. In transcription, ________________________’s instructions for making a protein

are copied by _______________________.

66. Which RNA molecules are involved in the synthesis (making) of a protein?

67. What happens to the newly made mRNA molecule following transcription in the nucleus?


Section 10-3 Protein Synthesis


68. What makes up proteins, what are the subunits called, & what bonds them together?

69. How many different kinds of amino acids make up proteins?

70. What determines how protein polypeptides fold into 3-dimensional structures?

71. Why does a protein need a 3-dimensional structure?

72. What is the genetic code & why is it important?

73. What is a codon & what does each codon code for?

74. How many codons exist?

75. Name the amino acid coded for by each of these codons:

a. UUA

b. AUU

c. UGU

d. AAA

e. GAG

f. UAA

76. What codon starts protein synthesis?

77. What codons stop protein synthesis?

78. Proteins are synthesized (made) at what organelle in the cytosol?

79. Sketch and label a tRNA molecule & tell its function.

80. Define translation & tell how it starts.

81. Where are amino acids found in a cell & how are they transported?

82. What is an anticodon & where is it found on tRNA?

83. What codon on mRNA would bind with these anticodons: (use table 10-1, page 194)

a. AAA

b. GGA

c. UAC

d. CGU

84. What are ribosomes made of and in what 2 places can they be found in a cell?

85. What is the difference between proteins made by free ribosomes & those made by attached, membrane proteins on the ER?

86. How many binding sites are found on the ribosomes and what does each site hold?

87. To start making a protein or _________________________________, a ribosome attaches to the ______________________________ codon on the __________________ transcript.

88. The start codon, AUG, pairs with what anticodon on a tRNA molecule?

89. What amino acid does the start codon always carry?

90. What type of bonds are the ones that attach amino acids to each other in a growing polypeptide?

91. __________________________ are linked to make proteins as a ______________________ moves along the mRNA transcript.

92. What ends translation?

93. Can more than one ribosome at a time translate an mRNA transcript? Explain.

94. What determines the primary structure of a protein?

95. What would the translation of these mRNA transcripts produce?