Background Information:
Green plants use sunlight to make glucose. To do so, the plant must use carbon
dioxide and water in a process called photosynthesis. The glucose made by
plants is used by plants and animals as a source of energy. To release the
energy contained in the bonds of glucose, the glucose must be converted to
ATP. The process by which ATP is made from glucose is called cellular
respiration. Respiration also produces waste products including carbon dioxide
and water, which are the same substances that served as raw materials for
photosynthesis. In water, carbon dioxide dissolves to form a weak acid. As
a result, an acid-base indicator such as bromothymol blue can be used to
indicate the presence of carbon dioxide. In this laboratory investigation,
you will use bromthymol blue to explore the relationship between photosynthesis
and respiration.
Problem
What is the relationship between the processes of photosynthesis and respiration?
Materials
2 123ml flasks rubber stoppers 100 ml graduated cylinder 2 Elodea light source
drinking straw
Procedure
1. Using a graduated cylinder, measure out 100ml of bromthymol blue solution
for each of the two flasks. Caution: Bromthymol blue is a dye and can stain
your hands and clothing. 2. Insert one end of a drinking straw into the
bromthymol blue in one of the flasks. Gently blow throught the straw. Keep
blowing until there is a change in the appearance of the bromthymol blue
solution. Repeat this procedure with the other flask. Record your observations
in the data table. 3. Place a sprig of Elodea into each flask. Stopper the
flasks. 4. Place one flask in the dark for 24 hours. Place the other flask
on a sunny windowsill for the same amount of time. 5. After 24 hours, examine
each flask. Note any change in the appearance of the bromthymol glue solution.
Record your observations in the data table.
Data:
{ Place Data Table Here }
Analysis:
1. What was the color of the bromthymol blue solution before you exhaled
into it? After you blew into it? Why did it change color?
2. Why did we use bromthymol blue in this experiment?
3. Why was Elodea place in both flasks?
4. What differences did you observe between the Elodea in the light and the Elodea in the dark? Why did this occur?
5. What is photosynthesis and how do our results demonstrate the requirements necessary for this process to occur?
Questions? Comments??
Shannon Tice