Observing the Relationship Between Photosynthesis and Respiration

Name ______Date ______

Observing the Relationship between Photosynthesis and Respiration

Green plants are autotrophic. They use the solar energy to make food. The production of food also requires raw material from the environment. When plants synthesize food, in the form of plant carbohydrates (glucose), they use carbon dioxide and water. The process of making carbohydrates with the aid of solar energy is known as photosynthesis. The carbohydrates plants make are used by plants and animals alike as a source of energy. To release the energy contained in the bonds of carbohydrate molecules, the chemical reaction of photosynthesis must be reversed. The process in which energy is released from the chemical bonds of glucose is called respiration. Since all living things need a constant flow of energy, all living things undergo Respiration all of the time. Respiration also produces waste products, carbon dioxide and water, which are the same substances that served as the reactants for photosynthesis.

In this experiment, you will examine the reactions of photosynthesis and respiration and also see how photosynthesis and respiration are the reverse processes.

Materials: per group

2 - 125 mL flask2 Elodea springsGOGGLES

2 pieces of aluminum foilWaterLight source

Bromothymol bluedrinking straw

Procedure:

1. Measure 100mL of water into two flasks and put 10 drops of bromothymol blue into each of two flasks.
2. Insert one end of a drinking straw into the bromothymol blue water of one of the flasks. Covering up the top of the flask, GENTLY blow through the straw.

***What substance were you adding to the bromothymol blue solutions as you blew into it? ______.

Keep blowing until there is a change in appearance from blue to yellow. Record this information on your data sheet. Repeat this procedure for the other flask.

1. Place a sprig of Elodea into each flask. Secure a piece of aluminum foil over the opening
2. Place one flask in the dark for 24 hours and the other an area with light.
3. After 24 hours, remove the flasks from their locations and make observations on the data table

Observations: Change in color of flask in light and in dark.

Treatment / Bromothymol Blue (color)
Color of flask with only Bromothymol Blue
After you breathed into the flask
Elodea flask (In the light)
Elodea flask (In the dark)

Analysis:

1. What was the color of the bromothymol blue solution before you exhaled into it and then after you exhaled into it?

Before ______After ______

1. What substance was added to the bromothymol blue solution when you blew into it? ______

1. What process produced the above substance? ______

1. What was the color of the bromothymol blue solution in the flask that was placed in the dark and the one in the light after 24 hours?

Dark ______Light ______

1. What substance did the Elodea plant remove from the bromothymol blue solution in the light flask as it underwent photosynthesis? ______

1. What substance did the Elodea leaf in the flask in the light add to the bromothymol blue solution? ______

1. What substance did the Elodea plant remove from the flask in the dark from the bromothymol blue solution? ______

1. What did the Elodea plant add to the flask in the dark to the bromothymol blue solution? ______

1. For the plant in the light, what carbohydrate molecule did it produce as a result of photosynthesis? ______

1. For the plant in the dark, what food substance did it break down to release energy for it to stay alive? ______

1. In the space below, write the general formula for photosynthesis

______+ ______+ ______Energy ______+ ______

1. In the space below, write the general formula for respiration

______+ ______+ ______+ ______Energy

1. What do you notice about the two formulas above?

1. When does a plant undergo photosynthesis to make plant carbohydrates?

1. When does a plant undergo respiration to release the energy found in the bonds of plant carbohydrates?

1. Which process, photosynthesis or respiration, must occur at a faster rate and why?

1. Get flasks from the cabinet and light.

1. Make observations as to the color of each flask and record it on the front page of your lab

1. Throw the aluminum foil away and empty the liquid into the green strainer in the sink near the lights. If the elodea gets stuck in the flask, use the back of a test tube brush to pull it out.

1. Put the emptied flask in the dishwasher in the back room