A Critical Look at Photosynthesis and Respiration 10/15

Integrated Science 3Name: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) / Mean / Standard Deviation
1
/
2
/
3
/
4
/
5
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) / Mode / Frequency Distribution
1 / 2 / 3 / 4 / 5 / Yellow / Green / Blue
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)

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):
Constants:

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

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