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Investigation 4 – PreLab









Plant physiologists carry out experiments to reveal how plants respond to pathogens and insect pests or to environmental stresses like drought, salinity, pollutants, and high and low temperatures.


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

  • In which parts of a Coleus leaf does photosynthesis occur? 
  • Which pigment is required for photosynthesis? 

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 finished, discuss the following concepts as a class:

  • The sugars made in the photosynthesis reaction cannot always be used right away by plants.
  • Plants store the sugars as starch.
  • When the plant needs energy, the sugar molecules are released from the starch.
  • Starch is stored in the part of plant leaves where photosynthesis takes place.
  • When placed in iodine, the starch in the leaf reacts with the iodine. The areas of the leaf which contain starch turn a dark bluish-black.


  • There are no Key Terms introduced in Investigation 4.

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.


  • Complete the Recall section in your SDR.
  • What is the equation for photosynthesis?
  • Which part of the equation tells us about sugar?
  • Where does the starch come from?
  • In Investigations 1 and 3, you began to determine which pigments are found in photosynthesizing plants and in which parts of plants photosynthesis occurs by using microscopy to investigate chloroplasts in cells.
  • In Investigation 4, you will continue to investigate photosynthesis, this time looking at starch production and the relationship between pigments and starch production.
  • Play the video below. Remember to follow along with your SDRs 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.