Background

Chlorophyll is the molecule that absorbs sunlight and uses its energy to synthesize carbohydrates (complex sugars) from CO2 and water. This process is known as photosynthesis and is the basis for sustaining the life processes of all plants. Since animals (including humans!) obtain their food supply by eating plants, photosynthesis can be said to be the source of our life also.

Chlorophyll is found in the chloroplasts of green plants.  It is a photoreceptor cell, which means it traps the energy of the sun.  Chlorophyll is green in color, and is the reason that plants are green!  There are other colors found in a plant that are present but cannot be seen because chlorophyll is such a strong absorber of light.  When the chlorophyll molecule begins to weaken and decay in the autumn due to the plant’s survival techniques, these other colors can be seen. Molecules such as carotene and quercetin produce these fall colors of red, orange, yellow and brown. This is the changing of the leaves!

It is important for students to understand that in order for plants to photosynthesize, chlorophyll must be present, because the colored pigment is able to utilize the energy of the sun.  
 

Vocabulary

Chlorophyll:  the molecule in plants that absorbs light from the sun; it is reflects green light, therefore leaves appear green
Photosynthesis:  the process that plants use to make their own food (sugars and starches)
Starch:  the form of sugar that plants use to store their food

Attention Grabber

Set up the pictures included in the appendix in various places all around the classroom. It is useful to put the pictures in places where the students are able to gather comfortably and write. Divide the students evenly into groups. Designate a recorder for each group (the recorder can rotate to give more students a chance). Have the recorder write down an observation from each student. Have each group rotate through all of the     (Imagine from: www.ncjournalforwomen.com)
pictures.

After the students rotate, create a word chart using key words from student observations that compare the fall foliage to the normal green foliage.

                       

Vocabulary

(Introduce the vocabulary during the lesson and review after).

Chlorophyll: The green pigment found in most plants and algae. Chlorophyll captures the energy from the sun and is an essential component of photosynthesis.
Prediction:  A statement forecasting an outcome based upon related observations.
Hypothesis: A tentative assumption made in order to draw out and test its accuracy.

Garden Activity

•    Split students into 5 small groups of 2-4 students
•    These groups are:
      1.    roots and petals
      2.    stems and seeds
      3.    green leaves and stems
      4.    dead leaves and green leaves
    5.    roots and fruit
•    Students can obtain the majority of the plant parts they are testing from the         garden.  (Fruits, seeds, and petals may need to be found elsewhere depending on the season)
•    Show students how to use a mortar and pestle to smash the plant parts so that the materials inside the plants’ thick cells walls can come out. 
•    Explain that once they have ground up their plant parts, the teacher should add acetone to the plant.  The student will put a strip of filter paper (or coffee filter) in the bowl so that a little of the bottom of the strip is below the surface of the acetone.  In about 20 minutes, if there was chlorophyll present, they will see a green stripe on the piece of filter paper.
•    Pass out the mortar and pestle and allow students to do the above, letting the teacher know when they are ready for the acetone.
•    Wait 20 minutes. During this time, explain to students that plants make their own food by a process called photosynthesis.  Plants use carbon dioxide, water, and energy from the sun to make sugar, oxygen and water.  Chlorophyll is present in the part of the plant that makes the sugars!
•   Explain to students why leaves “change” color (see Background section) 
•   Have students make predictions as to which plant part will or will not contain chlorophyll.
•     Have the students look at their results
•    On the board, draw a chart where students can share their results while waiting for the experiment to take place.

Example:

•    Discuss with the class patterns of where chlorophyll is found and where it is not.

Wrap Up & Assessment

•    Have students can a summary statement, their conclusions, and create a result chart in groups. Work with students to create a graphic organizer that illustrates photosynthesis. This will use this as part of their presentation.
•    Have each group present their findings and conclusions to the class.

What’s Next?

•    The student can conduct a more advanced demonstration of plant respiration (or photosynthesis).  Attach a piece of construction paper or foil on a leaf so that part of the leaf is exposed to the sun and part is not.  Allow two days for the plant to photosynthesize.  Detach the leaf from the plant, take off the paper, and put a few drops of iodine on the leaf.   Iodine indicates the presence of starch (the form of sugar that a plant can store in its cells); therefore the section where the paper or foil was NOT attached should turn a black-purple color.   The purpose of this is to reiterate to students that plant need sunlight as energy to make its food (sugar).  Chlorophyll is present wherever photosynthesis is occurring.  
•    Use cut-outs of fall leaf colors to create a background on paper.  Have students write a poem about the changing of the leaves, seasons, smells, feelings, etc.
•    Take a field trip to the nearest park and go for a hike!  Allow students to explore different plants.  The students can even bring home “samples” to test for chlorophyll.
 

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