Background

Objectives

Students will experiment using various plant parts to discover where chlorophyll is located.
Students will understand that chlorophyll is a green substance that helps plants make sugar during photosynthesis.

Materials

Mortar and Pestle
Plant parts
Acetone
Coffee filters cut into 1in. by 2.5 in. strips
Labels or post-its

Season

Spring, Fall

Group Size

5 small groups

California State
Content Standards

L.S. 2.f, 2.g

fall_colors_la

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 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.

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

Decorate part of the garden in fall attire. This is fun to do in the middle of winter or spring. Be sure to use “fall leaves” as part of the decorations. The teacher can even wear fall attire or colors.

Ask the students Why are leaves green? Why do the change color? Have you ever seen this happen? Etc. Do not give them the answers now, wait until they have done half of the garden activity. (Note: during the wait time, discuss the role of chlorophyll, and why leaves are green and then can change color)

Garden Activity

Split students into 5 groups
- These groups are:
  - roots and petals
  - stems and seeds
  - green leaves and stems
  - dead leaves and green leaves
  - 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)
Ask students can 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
- Example:

Plant parts WITH Chlorophyll	Plant parts WITHOUT Chlorophyll
Green oak leaf	Dead oak leaf
Green leaf from bush	Rose petal

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

Wrap Up

Students can write a summary statement, their conclusions, and the result chart in their science notebook or other collectible journal.

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.