Thus, three factors, namely light, carbon dioxide, and chlorophyll, are consider

Question

Thus, three factors, namely light, carbon dioxide, and chlorophyll, are considered important in determining the rate of photosynthesis. We will study in this lab how each of these factors influences the photosynthetic process.


A. Carbon Dioxide

Objective: To demonstrate that C02 is utilized in the photosynthetic process.
Procedure:

1. Fill 2 test tubes 1/4 full with Bromthymol Blue.
a. TT#1 - add 1 drop of HCl; record the color change
b. TT#2 - add 1 drop of NaOH; record the color change

2. Place 100 ml Bromthymol Blue in a small beaker and blow into it until a color change appears. Divide this solution equally into 4 test tubes and number the test tubes.
a. TT#1 - Blank.
b. TT#2 & #3 - Place 1 healthy green Elodea twig (of the same size) in each.
c. TT#4 - Control.
d. Wrap TT#3 & #4 completely with aluminum foil (to cut off light).
e. Place all 4 test tubes near a light source, equal distances away (but away from the light source to be used in Part B).
f. Remove the foil at the end of the lab period. Record the color changes and infer their significance.

Data:

Test Solution Color of Bromthymol Blue

HCl yellow

NaOH dark blue

CO2 (bubbled through)

Test Tube Color Before Color After
#1 yellow yellow

#2 yellow green blue

#3 yellow light green

#4 yellow yellow

Question 1. Which of the test tubes changed color? Why? (explain the controls)

Explanation / Answer

The natural color of bromothymol blue in neutral solution is bluish green. Hence in the (a) tube the ions are protonated giving a yellow color. In the (b) tube the ions are deprotonated giving a dark blue color. ---------------------------------------------------------------------------------- In the second expt, when we breathe carbon dioxide into the tube, it dissolves in the solution forming carbonic acid. this turns the green color to yellow. This is the color seen in tube 1 and tube 4 as they are control and blank. in tubes 2 and 3 , a twig of Elodea is placed. as they are plants, they use carbon dioxide dissolved in the solution. the tube of light green color is slowly changing back to normal as the plant absorbs carbon dioxide. the tube of green blue is seen as the solution comes to neutral pH.

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