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A-maze-ing Plants

Objective:  Students will demonstrate and observe the effect of light on plant growth.

Grade Level:  2-6

Groupings:  Small groups or entire class

Materials:  (per group) Several house plants grown on a windowsill in such a way that they are leaning in one direction; small potted plant (runner beans or sprouted potato plants work well); cardboard box with inner divider; utility knife (to be used by the teacher only); scissors; duct tape; flashlight.

Time Allotment:  45 minutes for set-up, two weeks for results


Directions:

1.  Show the students the house plants you have been growing on the windowsill. What do they observe about the way they are growing? (The plants lean in one direction, towards the window.) How can they explain this growth? (The plants grow toward the sunlight.) Go on a scavenger hunt in and around the school to look for other plants' growth responses to light. Discuss and compare students observations and examples.

2.  Explain that they will set up an experiment to see just how far some plants will grow to get light. Divide the students into small gorups and give each group a small potted bean or potato plant (or have them sprout their own) and a cardboard box with an inner divider. Explain to the students that they will shut the plant inside the box with only one opening for sunlight. Have them place the box on its side and cut a hole in the upper side to let in light. (They will need adult assistance to cut through the cardboard.)

students examining maze box 3.  With the box in this position, ask them to place their plant in one of the sections in the bottom of the box. Explain that they will create a maze of light from the top of the box to the plant at the bottom by cutting holes in the various levels of the divider. Ask the group to decide upon a sunlight path and mark the openings. Have them remove the inner divider to cut the holes.

4.  Have them water their plant thoroughly and place it inside the box. Provide duct tape to secure the plant to the base of the box and seal the box closed. Ask them to check for other openings by shining a flashlight into the hole and looking for places where light excapes. Ask them to seal with tape any openings as another light source could interfere with the experiment.

5.  Ask the students what will happen to the plant inside their boxes? Have each group record their predictions. Suggest they make a drawing of their maze and predict where the plant will grow. Will the plant be able to work its way through the maze to the light? If so, how long will it take? How long will it take to reach certain points along the way?

6.  Have the groups place their boxes in sunny locations, either in windows or under grow lights. Explain that they will open their box once or twice a week to water the plant. Have them observe and record the plant's growth by marking it inside the maze box. Have them measure the length of their plant and note its appearance and health. After two weeks, have the groups compare their a-maze-ing results.

Extensions:

aHave the class set up two separate control experiments. Using the same type of plant, place one inside a cardboard box without any openings. Ask the students to record their predictions on how this plant will grow, noting differences in size, color, appearance. Grow a second plant completely unenclosed. Again have them record growth predictions, noting size, length, color and appearance.

bHang a maze box from the ceiling with the opening on the bottom of the box. Will the plant defy gravity and grow upside down to get to the light?


ON the BRIGHT SIDE

Plants can't move, or can they? Even though plants are firmly rooted in the ground, they can still respond to changes in their environment by changing patterns in their growth. Sunlight is one essential ingredient for plant growth, and plants have been known to 'bend over backwards' to get their share. Auxin, a growth hormone in plant stems, helps regulate shoot growth. When the auxin concentration is uniform around the stem, the shoot grows upright. But when sunlight varies, auxin is broken down on the sunnier side of the stem. The highter concentration of auxin on the shady side causes it to grow more and bend toward the light, until the sunlight and hence the auxin concentration around the stem, is once again in balance. This bending toward light is called phototropism, and it is a commonly observed response of plants in and around your home. It is why house plants lean towards the window, why trees branch over the road creating a shady tunnel, and why fallen trees turn at their tips and grow upright again.


* This material has been used with permission from Shelburne Farms, Copyright © 1995.

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