Fourth-grade science students already know about the basic water, soil and sunlight needs of plants. Many students have also learned about other factors that affect plant growth, such as nutrients in fertilizer and what compost is. It can be difficult to hold students' attention with seed experiments, since they must wait for seeds to grow. Start some different projects a day or two apart, or have groups of students work on different projects to help ease the wait.
What are Effects of Light on Seed Germination and Growth?
Collect three clear plastic food containers with clear lids, the type used at deli counters. Find two identical shoeboxes or other boxes with lids that are big enough to hold the clear containers. Color the insides of both boxes black, or cover the insides with black paper. Students will also need about 60 seeds. Large seeds like corn or beans are easiest to monitor and measure results. Other supplies needed are white paper, scissors, tape, paper towels, water and a measuring cup.
Cut three or four small holes in the sides of one of the boxes. Cover the holes by taping pieces of the white paper over them. This allows only indirect light to enter the box. The second box has no holes and will be lightproof. Place one folded paper towel in the bottom of each of the three clear containers. Pour exactly the same amount of water into each container so the paper towel is completely saturated and about 1/2 inch of water is above the paper towel. Count the same number of seeds for each container, and place them in a single layer on the wet paper towels in the containers. Put the lids on the containers, and put one container in each of the boxes. One container will not be in a box, and will be the control.
Place the boxes and the container in a place where there is indirect light. Under a plant light is fine, as long as all three receive the same amount of light. Most students this age will come up with predictions as they watch the control seeds sprout and grow, so have them make a list of hypotheses from their ideas. Check the seeds in the boxes after five or six days. When the seeds in the boxes have germinated, students can measure the results by counting the seeds that sprouted, measuring the stem and root length, noting the color of leaves and writing any other differences they observe.
Will Seeds Grow with Liquids Other Than Water?
Let students choose seeds to grow, and have them select some liquids besides water to test on their seeds. Milk, juice and vinegar are good choices. Plain water is the control liquid. Provide four styrofoam cups and potting soil for each student or group. Have students label each cup with the liquid they will use with it. A ballpoint pen writes well on the cups. Students can then fill the cups with soil and plant identical seeds in each cup. Each cup should be "watered" with an equal amount of the appropriate liquid and placed where the cups receive equal light. Students can chart progress and draw conclusions from the results.
How Does Salt Affect Plants?
Materials needed are four identical plants, one cup each of table salt, road salt and water softener salt, four one-gallon jugs, plastic gloves, measuring cup and water. Students should measure one cup of each type of salt and place each salt in a jug, labeling the jugs. Fill all four jugs with water. Shake the salt jugs to dissolve the salt. One jug will be plain water, the control. Label each plant to match one of the jugs. Place the plants where they receive equal light. Use the matching jug to water each plant, measuring the same amount of water each time for each plant. Have students observe the plants daily and make notes for each plant on a chart.