Investigation 4 – Lab
This Investigation is designed to:
- continue to aid you in discovering in which parts of plants photosynthesis occurs and which pigment is required for photosynthesis,
- reinforce your understanding that photosynthesis produces sugar, and
- build your knowledge that sugar production leads to starch storage.
Student Preparation for the Investigation includes gathering the following materials.
Note: The materials are listed in your SDR. They are also listed below for your reference.
- (1) hot plate
- (1) hot hand protector
- (1) stir rod
- (1) forceps
- (1) Coleus leaf from the Coleus plant
- (1) stopwatch
- (1) weigh dish
- Have one student in each group to pour 200 ml of hot water into a 400 ml beaker and use a piece of tape to label the beaker “hot water.
- Have another student in each group to pour 50 ml of ethanol in a 400 ml beaker and use a second piece of tape to label the beaker “ethanol.”
- Finally, have a third student from each group to pour 20 ml of iodine into a 50 ml beaker.
Note: Because these amounts are approximations and do not need to be exact, you do not need to use graduated cylinders to measure volume. You may simply pour the liquids into your beakers and use the graduations on the beakers.
- You will continue to investigate photosynthesis, this time looking at starch production and the relationship between pigments and starch production.
- Reflect on the PreLab video as you move through the procedural steps.
- During the Experiment, every procedural step is important. If one step is skipped, data can become invalid. To help you keep on track, read each step thoroughly, complete the step, then check it off (Read it – Do it – Check it).
- Be sure to complete all of the procedural steps in your SDR.
Note: The procedural steps are listed below for your reference.
- Place the beaker of water on the hot plate and turn the temperature dial on the hot plate to a medium-high setting of 7 or 8 (or 350º C).
- While you are waiting for the water to boil, observe your Coleus leaf. Draw a picture of the leaf, looking especially at the various color patterns on the leaf.
Note: Your drawing should illustrate the green and white parts of the leaf.
- Where on the leaf do you think sugar is produced and converted to starch? How do you know?
- When the water on the hot plate begins to boil, place the Coleus leaf in the boiling water.
- Start the stopwatch. Boil for 3 minutes, using the stopwatch to keep track of the time.
- After 3 minutes, remove the beaker from the hot plate with the hot hand protectors.
- Place the beaker aside and leave the leaf in the beaker.
- Turn the dial on the hotplate so that the heat knob is set to 2 (100°) or 3 (150°).
- Place the beaker of 50 ml of ethanol on the hot plate. The ethanol should become hot but should not boil.
- If the ethanol begins to boil, turn down the heat to the lowest setting.
- The hot ethanol will remove the pigments from the leaf, which will later make the starch easier to observe.
- When the ethanol is hot, remove the Coleus leaf from the water and place it in the ethanol.
- Begin timing. Leave the leaf in the ethanol for approximately 3 minutes, or until the leaf is a cream color. If the ethanol starts to boil, remember to turn down the heat.
- After 3 minutes, use the hot hand protectors to remove the beaker from the hotplate.
- Remove the leaf from the ethanol using the stir rod or forceps and place it in the weigh dish.
- Record: Write your observations of the leaf.
Note: Most of the pigment from the leaf should be gone. The leaf will likely be colorless, or a cream-white color.
- Cover the leaf with several drops of iodine. Leave the leaf in the iodine for approximately 3 minutes.
- Remove the leaf from the iodine using the forceps.
- Record: Observe the areas of the leaf treated with the iodine. Draw a picture of your leaf.
Be sure to clean up your lab bench after the experiment. Be particularly careful in removing any spilled iodine with a wet paper towel.