Sunlight and Plants

Sample Lesson for Grades 3-8

Dennis W. Sunal

The University of Alabama

Tuscaloosa, Alabama

Alternative Conception Addressed by the Lesson Plan: Direct sunlight is necessary for green plants to live and grow. Direct sunlight makes green plants healthy. Green plants always need direct sunlight .

Lesson Goal: To allow students to investigate and develop inferences about the role of sunlight in the nutritional needs of a green plant.

Prerequisites: Can measure height to the nearest millimeter or one/eighth inch.

Exploration:

Objective: The students will investigate the effects of sunlight on germinating seeds and young green plants.

Materials: For each group:

Four lima bean or corn seeds,

Potting soil, and

Four styrofoam cups

Procedure:

A. Organize small groups of four students; a materials manager, a reporter, one observer, and one illustrator. These roles could rotate over time.

B. Describe the materials and instructions needed for students to carry out the activity related to the effects of sunlight on growing plants. State the key questions: Is light necessary for plants to live and grow? Does sunlight make green plants healthy? and Do green plants always need light?

C. Provide each group with four lima bean or corn seeds, potting soil, and four styrofoam cups. Ask the students to design an experiment to test the effects of light on the growth of plants using the lima bean or corn seeds. An example of an experiment that might be designed by a group would involve students putting three inches of potting soil into each cup. Then the students could plant the lima bean seeds about one inch below the surface of the soil. They would add three tablespoons of water to each cup. One cup would be set on the windowsill or some bright spot in the room. One cup would be put in a closet or in a box that is sealed off from light. The other two cups should be put in parts of the room that are partially lit. One across the room from the windows and one behind or under a large object in the room. The students would keep a daily diary indicating at least the following observations: the date, a description of the seed or plant, a measure of the height of the plant and the number of leaves. The illustrator would make a sketch of the plant each day in the diary.

An experiment such as the one above will probably involve a week to ten days of plant growth time. Seeds generally require two to three days to germinate (when they break through the soil) and another week to grow tall enough to have leaves so that the effects of light become evident. The illustrator should draw the plants at regular intervals. The observers should record a description of the plant at the same intervals and use it to construct a table or bar graph of plant growth.

D. At appropriate points, the group should be allowed to discuss the results of the experiment they designed.

Evaluation: Each group should have a complete description of their hypothesis, procedure, data, and results. Group skills should be assessed by observing that students should join their groups quickly when asked and the group should review what needs to be done before starting.

Invention:

Objective: The students will describe the effects of sunlight on green plant growth during germination and on green plants after they have broken through the top of the soil (after germination).

Materials: For each student:

A lima bean seed soaked in water for 24 hours

Procedure:

A. Have each group present to the whole class their hypothesis, procedure, and results. Help students communicate the results of their activities using tables and/or bar graphs to justify their conclusions. Continuously help the students compare the results of each groupís experiment.

B. Write the key questions from the exploration on the board. Ask the student groups to discuss these questions based on the class discussion of their experiments. Ask them to report their answers to the whole class.

C. Explain that the discrepancy here involves the observation that seeds will germinate whether or not they are in the presence of light. Once germinated, the plants in the dark will grow faster than the plants in the light. However, they will be spindly and will have fewer leaves. If the experiment were stopped before the plants in the dark condition die, the students will be left with the alternative conception that light is not necessary for plants to live and grow.

D. Provide soaked lima bean seeds and a sheet of paper to all students. In groups, have them take apart the lima bean seed and tape the parts to the paper. At the bottom of the paper, ask the groups to discuss the function of each part. As an extension, another lesson could be performed where the students plant these parts to determine which one grows. The students should find the following parts: cotyledon(s), seed coat, cover, and an embryo. Tell the students that the embryo is the plant and that the cotyledons are food sacs (starch) that the embryo uses to develop roots and a stem with which to reach the soil surface. Corn seeds have only one food sac or cotyledon. The students should have observed this growth during the germination phase of the plant. State that the germination process does not require sunlight, as they have found in their experiments.

E. Ask the students to display the illustratorís pictures of plant growth following germination in dark and light conditions. Explain to the students that even though the plants in the dark grew faster before they started dying they did not look healthy. They did not have a very green color and they had very few leaves. Sunlight is necessary for the health of green plants. It is needed by green plants in order to make green chlorophyll and to make additional food. Without this additional food production, the green plantís food sac soon becomes used up and the green plant dies because it lacks the materials and the energy that the food provides for growth and maintenance.

F. Closure: Light is not necessary for seeds during the germination phase of growth. It is necessary following germination for health and continued growth.

Evaluation: Ask the students to create a poem about two plant seeds, one that landed on soil in a field and one that landed on soil in a cavity under a rock or in the woods. Assess students group skills by observing that they stay with their group while it is working and that pay attention to how much time they have to carry out each activity.

Expansion:

Objective: The students will solve everyday problems involving the role of sunlight on green plant growth.

Materials: for each student:

A map or drawing of an area with three vegetation zones:

deep forest, low shrubs, and meadow (figure 1)

A sheet of paper with a 3 x 4 matrix

Procedure:

A. Provide the following problems and ask the groups to discuss their answers and report them to the class. The students should provide supportive evidence for each of their responses to the problems. Write the following problems on the board. For problems one and two give the students a map (it may be teacher-drawn) of an area of mixed height and foliage. It may have an area of deep forest, an area of small bushes, and a meadow.

1) In which area will a squash seed planted three centimeters below the soil surface reach the soil surface the fastest. The temperature of the soil is the same in all areas.

2) Small squash plants are planted in each area. Draw the plants after 1, 2, 3, and 4 weeks. Provide each group with a 3 X 4 matrix on a whole sheet of paper.

3) A farmer purchased an abandoned coal mine to produce mushrooms for sale in grocery stores. The farmer spread lots of horse manure from his stables on the floor of the coal mine. The farmer successfully produced lots of large mushrooms for sale.

Teacherís note: Mushrooms are part of a class of plants called fungi. This class includes molds, mildew, rusts, and smut. They lack chlorophyll so they do not produce their own food. Fungi get their food from organic soil materials dissolved in water.

B. Ask the students to present their answers to each problem in a report to the class. Discuss the results in an interactive discussion.

C. Summarize the lesson by describing each of the activities in the order in which they were experienced in the lesson. Briefly indicate the main point developed in each activity.

Evaluation: Each student will respond to the following problem. The moon has a day that takes twenty-eight of our earth days. For fourteen earth days it is dark at a certain location on the moon and for fourteen earth days it is light. Describe by illustration and narrative the growth of a lima bean planted on the moon in a greenhouse in the middle of the lunar night. Remember that there will be two weeks of sunlight followed by two weeks of darkness every lunar month. Describe its growth for two lunar months. identify, investigate, and develop inferences about the role of sunlight in the nutritional needs of a green plant.

 

Figure 1: Vegetation zones.