Pop & Ag #___
A Critical Look at Photosynthesis and Respiration
Integrated Science 3
Name:
10/15
Per:
 Background
When carbon dioxide dissolves in water a series of reactions occur that increase the acidity of
water. Acidity can be measured quantitatively or qualitatively. pH strips or meters are used to
quantitatively measure acidity and are based on the pH scale of 0-14. pH values of 0-6 are acidic, 7 is
neutral, and 8-14 are basic. pH can be measured qualitatively using bromthymol blue – a solution that
changes color with changes in acidity. Bromothymol blue is green when neutral and becomes yellow as
acidity increases and blue as a solution becomes more basic.
Based on information above and an understanding of photosynthesis and respiration a classroom
of students conducted the following experiment testing the effects of light, plants and animals on
environmental conditions. Students were organized into five groups. Each group had eight bottles into
which they placed 500 ml of water and 3 ml of bromothymol blue. Each group further set-up the bottles
based on the table below:
BOTTLES
CONTENT
CONDITIONS
BOTTLES
CONTENT
CONDITIONS
1
Water only
Light
5
Water only
Dark
2
Elodea plant
Light
6
Elodea plant
Dark
3
Snail
Light
7
Snail
Dark
4
Elodea plant and Snail
Light
8
Elodea plant and Snail
Dark
The materials used to set-up the bottles was the same for each group, same species of snail, type of
bottle and species of plant.
Once the bottles were appropriately set-up (using the same species of snail, type of bottle and
species of plant) lids were securely placed on the bottles and they were put in the designated
environments – light or dark. Bottles 1-4 were placed on a light rack and exposed to light for 24-hours.
Bottles 5-8 were places inside a cabinet in complete darkness for 24-hours.
Students measured the acidity of each bottle using pH strips and by making observations of color.
They results of the experiment were compiled and are represented in the data tables provided.
 Procedures
1. Each table group will analyze the experiment described in this handout, and then present to the
entire class one treatment of the experiment from the completed organizer. Ours is: _______________
2. Complete the Experimental Organizer provided based on the information provided in the above
description of the entire experiment.
3. Draw a picture of the experimental design. Include all eight bottles.
4. Write a hypothesis that predicts the expected results for your assigned treatment (bottle). Include
predictions for both photosynthesis and cellular respiration.
5. Create the expected data values for both the quantitative (pH) and qualitative (color) data collected.
6. As each group presents, record the hypothesis and expected data and explanation for their
treatment (bottle) on the chart in this lab. Once each group has presented, work with your
classmates to write revise any issues on your diagram.
7. Answer the discussion questions which follow on a separate piece of paper and staple to this lab
before handing in.
 Discussion – Answer the following on a separate sheet of paper using complete sentences.
1. Using your understanding of photosynthesis and respiration, explain why certain bottles turned
yellow in color and had a lower pH.
2. Using your understanding of photosynthesis and respiration, explain why certain bottles remained
green in color and had a neutral pH.
3. Using your understanding of photosynthesis and respiration, explain why certain bottles turned blue
in color and had a higher pH.
 Data
The Effects of Light, Plants and Animals on Environmental Conditions
BOTTLE
CONTENTS
(LIGHT/DARK)
PH (0-14)
1
2
3
4
5
MEAN
STANDARD
DEVIATION
Water Only
(light)
Water Only
(dark)
Elodea plant
(light)
Elodea plant
(dark)
Snail (light)
Snail (dark)
Elodea plant and
Snail (light)
Elodea plant and
Snail (dark)
The Effects of Light, Plants and Animals on Environmental Conditions
BOTTLE
CONTENTS
(LIGHT/DARK)
COLOR (Y = YELLOW, G = GREEN, B = BLUE)
1
2
3
4
Water Only
(light)
Water Only
(dark)
Elodea plant
(light)
Elodea plant
(dark)
Snail (light)
2
MODE
5
FREQUENCY DISTRIBUTION
YELLOW
GREEN
BLUE
Snail (dark)
Elodea plant and
Snail (light)
Elodea plant and
Snail (dark)
 Experimental Organizer
Title:
Hypothesis:
Independent Variable:
 continuous
X discontinuous
Levels of I.V.
(indicate
control
treatment):
# of trials you
will conduct
for each
treatment:
Dependent Variable(s) – describe quantitative and qualitative data
Quantitative Measurements (include units):
Qualitative Measurements (include units):
3
Constants:
4
More CO2 =  acidity = pH 0 – 6 = yellow color
Less CO2 =  acidity = pH 8 – 14 = blue color
Neutral = pH 7 = green color
BOTTLE
CONTENTS
(LIGHT/DARK)
MEAN
MODE
EXPLANATION
Water Only
(light)
Bottle 1
Elodea plant
(light)
Bottle 2
Snail (light)
Bottle 3
Elodea plant
and Snail
(light)
Bottle 4
Water Only
(dark)
Bottle 5
Elodea plant
(dark)
Bottle 6
Snail (dark)
Bottle 7
Elodea plant
and Snail
(dark)
Bottle 8
5