Lab The Carbon Cycle and Photosynthesis/Respiration



Lab: The Carbon Cycle & Photosynthesis/Respiration

Overview:

Carbon is the fourth most abundant element in the universe, and is absolutely essential to life on earth. In fact, carbon constitutes the very definition of life, as its presence or absence helps define whether a molecule is considered to be organic (living) or inorganic (nonliving). Every organism on Earth needs carbon either for structure, energy, or, as in the case of humans, for both. Discounting water, you are about half carbon. Additionally, carbon is found in forms as diverse as the gas carbon dioxide (CO2), and in solids like limestone (CaCO3), wood, plastic, diamonds, and graphite.

The movement of carbon, in its many forms, between the atmosphere, oceans, biosphere, and geosphere is described by the carbon cycle. Biology plays an important role in the movement of carbon between land, ocean, and atmosphere through the processes of photosynthesis and respiration. Virtually all multicellular life on Earth depends on the production of sugars from sunlight and carbon dioxide (photosynthesis) and the metabolic breakdown (respiration) of those sugars to produce the energy needed for movement, growth, and reproduction. Photosynthesis is a complex series of reactions carried out by algae, phytoplankton, and the leaves in plants, which utilize the energy from the sun. Plants take in carbon dioxide (CO2) from the atmosphere during photosynthesis, and release CO2 back into the atmosphere during respiration through the following chemical reactions:

Respiration:

C6H12O6 (sugar) + 6O2 ( 6CO2 + 6 H2O + energy

Photosynthesis:

energy (sunlight) + 6CO2 + H2O ( C6H12O6 + 6O2

Through photosynthesis, green plants use solar energy to turn atmospheric carbon dioxide into carbohydrates (sugars - Glucose). Plants and animals use these carbohydrates (and other products derived from them) through a process called respiration, the reverse of photosynthesis. Respiration releases the energy contained in sugars for use in metabolism and changes carbohydrate “fuel” back into carbon dioxide, which is in turn released to back to the atmosphere.

On land, the major exchange of carbon with the atmosphere results from photosynthesis and respiration. During daytime in the growing season, leaves absorb sunlight and take up carbon dioxide from the atmosphere. At the same time plants, animals, and soil microbes consume the carbon in organic matter and return carbon dioxide to the atmosphere. Photosynthesis stops at night when the sun cannot provide the driving energy for the reaction, though respiration continues. This kind of imbalance between these two processes is reflected in seasonal changes in the atmospheric CO2 concentrations.

Pre-Lab Questions:

1. What element determines whether an object is considered living or nonliving?

2. What is photosynthesis?

3. What is respiration?

4. What organisms can carry out photosynthesis?

5. How do the process of photosynthesis and respiration fit into the Carbon Cycle?

6. Using the Fact Sheet provided fill in the blanks using the following terms: Base, Acid, Neutral

pH of 1 = ________________ pH of 7 = ________________ pH of 14 = ________________

Materials:

• 1 sprig of Elodea (water plant)

• 1 large test tube

• 1 piece pH paper (per day – 3 days)

• Test Tube Rack for class

• Distilled Water

• 1 small piece Masking Tape

Procedure:

Day 1

1. My group is assigned the following location: (please circle) Light Dark

2. Label the test tube with your names, period location, and assigned location (light or dark)

3. Fill the test tube with distilled water about ¾ to the top

4. Test the pH of your water by carefully dipping a small piece of pH paper into the water.

5. Hold the pH paper in the water for 5 seconds, take it out, and let the color develop for 30 seconds.

6. Compare the color of your wet pH strip with the pH chart provided.

7. Record the pH number on your data sheet for Day 1 in the correct table (Light or Dark)

8. Place your sprig of Elodea into your test tube. Careful – don’t overflow!

9. Take your test tube to the correct test tube rack in the front of the room, which your teacher will then place overnight in either a light or dark area.

10. Exchange your data with your neighboring lab group. (ex. If you did light, find a group who did dark)

Day 2

11. Test the pH of your water by carefully dipping a small piece of pH paper into the water.

12. Hold the pH paper in the water for 5 seconds, take it out, and let the color develop for 30 seconds.

13. Compare the color of your wet pH strip with the pH chart provided.

14. Record the pH number on your data sheet for Day 2 in the correct table (Light or Dark)

15. Exchange your data with the same group from Day 1. (ex. If you did light, find a group who did dark)

Day 3

16. Test the pH of your water by carefully dipping a small piece of pH paper into the water.

17. Hold the pH paper in the water for 5 seconds, take it out, and let the color develop for 30 seconds.

18. Compare the color of your wet pH strip with the pH chart provided.

19. Record the pH number on your data sheet for Day 3 in the correct table (Light or Dark)

20. Exchange your data with the same group from Day 1. (ex. If you did light, find a group who did dark)

Data Table:

Record your pH in the data table below.

| |Light |Dark |

| | | |

|Day 1 | | |

| | | |

|Day 2 | | |

| | | |

|Day 3 | | |

Analysis Questions:

Use the fact sheets provided to help answer the questions listed below.

Dissolved Oxygen

1. During the Daytime, when light is available, what gas do plants produce?

2. During the Nighttime, when no light is available, what gas do plants release?

3. When is the level of oxygen at its lowest? Why?

pH

1. What does pH define?

2. What is the pH of distilled water?

3. What is the pH of pure rain?

4. What is the pH of bleach?

5. What is the pH of lemon juice?

6. a. What do active plants and animals produce when they breathe?

b. This gas dissolves in water to form what?

c. What happens to the pH level of the water?

Lab Results

1. Why did we use distilled water in this lab?

2. a. What happened to the pH of the water in the Light test tube over the course of the three days?

b. Did the water become more acidic (1), more basic(14), or remain unchanged (7)?

3. a. What happened to the pH of the water in the Dark test tube over the course of the three days?

b. Did the water become more acidic (1), more basic(14), or remain unchanged (7)?

4. After three days of this lab, which test tube contained more carbonic acid? Explain.[pic]

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