ZERO-IN

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The non-italicized font represents additional information included to support the teacher’s understanding of the content being introduced within the CELL.

MINDSET

This Investigation is designed to:

• continue to aid students in discovering in which parts of plants photosynthesis occurs and which pigment is required for photosynthesis,
• reinforce students’ understanding that photosynthesis produces sugar, and
• build students knowledge that sugar production leads to starch storage.

BE PREPARED

Teacher Preparation for the Investigation includes the following. This preparation should be done prior to students arriving in the lab.

• Place the Coleus plant in a sunny or well-illuminated location until the investigation begins. This insures that photosynthesis occurs and that students will have success with their experiment.
• Directly prior to the beginning of the investigation, fill a liter pitcher with hot water. If the water from the tap becomes hot, this should suffice. Heat the water on hot plates until hot but not boiling. This greatly decreases the time students must wait for the water to boil during their experiment.
• Place all materials at a central location.

Note: Each student lab group will need the materials listed below.

• Divide students into cooperative groups of five students.

Student Preparation for the Investigation includes having students gather the following materials. This preparation takes place on lab day after student lab groups have settled at their assigned lab tables.

Note: The materials are listed in students’ SDRs. 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

• Ask 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.
• Direct 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.”
• Tell 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, students do not need to use graduated cylinders to measure volume. They may simply pour the liquids into their beakers and use the graduations on the beakers.

• Direct one student from each lab group to collect the materials listed in their SDRs.

INVESTIGATE

• Remind students that they will continue to investigate photosynthesis, this time looking at starch production and the relationship between pigments and starch production.
• Encourage students to reflect on the PreLab video as they move through the procedural steps.
• Explain to students that during the Experiment, every procedural step is important. If one step is skipped, data can become invalid. To help students keep on track, direct them to read each step thoroughly, complete the step, then check it off (Read it – Do it – Check it off).
• Direct students to complete the procedural steps in their SDRs.

Note: The procedural steps are listed below for your reference. Teacher “Notes” are inserted, as needed, to help facilitate the lab.

Experiment:

1. 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).
2. While you are waiting for the water to boil, observe your Coleus leaf. Draw a picture of the leaf, looking especially at the various colors in the leaf.

Note: Students’ drawings should illustrate the green and white parts of the leaf.

3. Where on the leaf do you think sugar is produced and converted to starch? How do you know? Student predictions will vary. Students may feel that photosynthesis occurs throughout the entire leaf and therefore starch is stored in the entire leaf. Others may feel that photosynthesis only takes place in the green chloroplast-rich areas of the leaf, and therefore starch is stored only in those areas.

4. When the water on the hot plate begins to boil, place the Coleus leaf in the boiling water.
5. Start the stopwatch. Boil for 3 minutes, using the stopwatch to keep track of the time.
6. After 3 minutes, remove the beaker from the hot plate with the hot hand protectors.
7. Place the beaker aside and leave the leaf in the beaker.
8. Turn the dial on the hotplate so that the heat knob is set to 2 (100°) or 3 (150°).
9. Place the beaker of 50 ml of ethanol on the hot plate. The ethanol should become hot but should not boil.
10. If the ethanol begins to boil, turn down the heat to the lowest setting.
11. The hot ethanol will remove the pigments from the leaf, which will later make the starch easier to observe.
12. When the ethanol is hot, remove the Coleus leaf from the water and place it in the ethanol.
13. 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.
14. After 3 minutes, use the hot hand protectors to remove the beaker from the hotplate.
15. Remove the leaf from the ethanol using the stir rod or forceps and place it in the weigh dish.

16. Record: Write your observations of the leaf.

Note: Most of the pigment from the leaf is gone. The leaf is colorless, a cream-white color.

17. Cover the leaf with several drops of iodine. Leave the leaf in the iodine for approximately 3 minutes.
18. Remove the leaf from the iodine using the forceps.

19. Record: Observe the areas of the leaf affected by the iodine. Draw a picture of your leaf.

Note: Students’ drawings should illustrate that the areas of the leaf which were green are now dark bluish-black.

CLEAN UP

Let students know your expectations for clean up. Ask them to clean up.