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Investigation 2 – PreLab









Horticulturists improve crop yield, quality, nutritional value, and resistance to insects, diseases, and environmental stresses. They make plants more adaptable to different climates and soils and better fit for food uses or processes. They also grow and improve plants used for medicines or spices.


This Investigation is designed to help you to answer the following Focus Questions:

  • How do light and photosynthesis affect carbon dioxide levels? 
  • How do light and photosynthesis affect oxygen levels? 

Note: These questions are located in your SDR at the beginning and end of the Investigation.


As a class, read the Background(s) in the Investigation. When have finished, discuss the following concepts as a class:

  • Photosynthesis is a process carried out by some bacteria, algae, and plants.
  • During this process, energy from light is converted into the energy of chemical bonds.
  • Photosynthesis reduces carbon dioxide to three carbon sugars and oxidizes water to oxygen.
  • The reactants in photosynthesis reaction are carbon dioxide gas, CO2, and water, H2O.
  • The products are oxygen gas, O2, and sugar molecules.
  • In the chemical equation, the reactants are found on the left side of the yield arrow. The products of the reaction are found on the right side.

  • To observe the levels of carbon dioxide during photosynthesis, a pH indicator called phenol red can be used.
  • Phenol red is red in a basic solution and yellow in an acidic solution.
  • Carbon dioxide makes a solution more acidic, or more towards the yellow and orange colors when using phenol red.
  • When the carbon dioxide in a solution is used, the carbon dioxide level decreases. The solution then becomes more basic, or more towards the red or purple colors when using phenol red.


The following list includes Key Terms that will be introduced in this CELL. 

  • pH 

Note: A definition of this term can be found on the Introduction page to the CELL.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.


  • You will continue to investigate photosynthesis by observing carbon dioxide and oxygen quantities in water containing Elodea plants.
  • Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful in the lab.
  • After the video, divide into your lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.


You should review the Investigation and video in preparation for the Lab.