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 How do Increased CO2 Levels Affect Plant Growth?

Author:  Jerry Hays, Hominy Middle School, Hominy, OK


Concepts:

All organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions while living in a constantly changing external environment. (NSES Content Standard C, Level 5-8) 

          The number of organisms an ecosystem can support depends on the resources available and abiotic factors, such 
          as quantity of light and water, range of temperatures, and soil composition. Given adequate biotic and abiotic 
          resources and no disease or predators, populations (including humans) increase at rapid rates. Lack of resources 
          and other factors, such as predation and climate, limit the growth of populations in specific niches in the 
          ecosystem.(NSES Content Standard C, Level 5-8) 
 

Teacher background:  This investigation is designed to show how an increase in carbon dioxide levels would affect plant crops.  It also shows relationships to temperature and water vapor if implemented.   Students should be familiar with the greenhouse effect, control experiments, and photosynthesis prior to this lab.

Background: Scientists have been testing complicated models to measure the amount of carbon dioxide in the atmosphere for the past thousands of years. Their conclusion is that CO2 levels are now at their highest level in centuries. (For CO2 emissions charts, click HERE).
The reasons for this increase in CO2 are several-fold.  Most scientists agree that the increase is mainly due to humans and their industrial revolution, which release stored CO2 from underground deposits. Processes like the burning of fossil fuels, deforestation, and the use of cement are the most direct causes.
The problem with increased CO2 is its affect on global warming.  CO2 is not a pollutant but it does trap infrared heat from radiating back into space. This phenomenon is known as the greenhouse effect. This global warming then affects global ecosystems by having effects on water vapor and other climate features.
If CO2 levels continue to rise, the results to the planet are difficult to gauge.  Some scientists believe that ocean levels may rise, ice caps could melt, droughts could occur, climates may change, and that life in general would be greatly affected.  

Subject:  Science

Level:  Grades 6-8

Time:  1 week

Objectives:  Students will understand how CO2 emissions affect plant growth and contribute to global warming.

 

Materials:

    • 2 large soda bottles with the top removed (or large beakers)
    • 2 peat cups (or some other means of germinating plants)
    • 1 small cup or dish
    • Several crop seeds (i.e. barley, wheat, corn, peas, etc.)
    • Potting soil
    • 10 grams of baking soda
    • 20 ml of vinegar
    • thermometer

 

Hypothesis:

State a hypothesis that explains what effect increased CO2 levels will have on plant growth.
 

Procedure:

    1. Germinate the seeds in moist potting soil in the peat cups.
    2. Next to the peat cups place the small dish with the baking soda in it. Add the vinegar to this dish. This produces a chemical reaction that will produce carbon dioxide.
    3. Place a thermometer next to the system
    4. Cover the system with a soda bottle and place it in a well-lighted area.
    5. Make a control experiment using the same seeds and procedures but with out the dish of baking soda and vinegar.
    6. Monitor the progress of the plant growth, water vapor and temperature for one week, checking daily.
    7. Compare the data to the control group and enter your data on the chart.
    8. Answer the review questions.

 
 

Chart of affects of CO2 on plant growth

day 1

day 2

day 3

day 4

day 5

Noticeable water vapor

 

 

 

 

 

Daily temperatures 
 

 

 

 

 

 

Plant growth 
 

 

 

 

 

 

Control

 

 

 

 

 

Noticeable water vapor

 

 

 

 

 

Daily temperatures 
 

 

 

 

 

 

Plant growth 
 

 

 

 

 

 

 
 
 

Review Questions:

    1. How did this lab reflect the green house effect?
    2. Was water vapor noticeable in the system? Explain.
    3. How was temperature changed in the overall system?
    4. Which conditions were variables in the control group?
    5. Did increased carbon dioxide cause plants to grow better?
    6. What may be some consequences of increased carbon dioxide in the atmosphere to climate and crops?
    7. What sources of error could have occurred in this experiment?

 
 

Modification:

Try the experiment again using Elodea in a closed system such as a soda bottle with water. Before sealing one of the systems take a straw and blow into the water. In the other system simply seal it up. Monitor the two systems for several days and record the results. Why would blowing into the container through the straw create different conditions?
 
 

 < Back to Activity List / Go to CO2  Emissions Charts  / Main Page

 

 
 

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