Hands-on Science: Water Movement Through a Stem

Transcription

1 Hands-on Science: Water Movement Through a Stem Teacher Page: The two experiments included here can be used at various age levels. Older students can set up the experiments themselves (with adult assistance in cutting stems). For younger students, it would be best for the teacher to set up the experiments and have students observe and record results. Question and answer data sheets are provided for elementary levels. Picture data sheets are provided for primary levels. The scientific principle at work in both experiments is capillary action. Liquids are bound together by two forces: cohesion and surface tension. When a liquid comes in contact with an absorbent surface, adhesion draws the liquid into that surface. Cohesion, surface tension and adhesion all work together to defy gravity and pull water upward through the plant stem. Inside the stem are tiny tubes, called xylem. The water moves upward through the xylem and is distributed to leaves and other parts of the plant. In the experiments, students will be able to trace the route of the water up through the stem and into the flower petals. They will see how water and dissolved nutrients are moved up the stem and into all parts of the plant. An excellent way to illustrate capillary action is to dip the corner of a paper towel into a cup of water. The water will travel upward into the paper towel, defying gravity.

2 Experiment 1 Results You should see blue and red all the way up the stem, calyx, and into the petals. Each color will be on the same side of the flower as that colored water cup. This illustrates that the water moves straight up the stem and into the petals directly above. After the flower is cut in half, you should be able to see the colors inside the flower stem and calyx as well. Experiment 2 Results The red water should travel all the way up both stems and color the top end of both stems red. The capillary action draws the liquid into the xylem regardless of the orientation of the stem. When the stems are cut in half, you can see the xylem tissue stained red throughout the length of the stems.

3 Experiment 1: How does water flow up a stem? You will need: 1 white carnation 2 clear plastic cups red food coloring blue food coloring water sharp knife (for teacher s use) This experiment will take 3 days. Place 2 clear plastic cups in a sunny location. Fill ¾ to the top of each cup with water. Add several drops of blue food coloring to one cup of water and stir. There should be enough coloring to turn the water dark blue. Repeat this step with red food coloring in the other cup. Have an adult cut the carnation to the right length to fit in the cup. Then have the adult split the stem of the carnation from the bottom to just below the flower. Place the carnation so that half the stem is in the blue water and the other half is in the red water. On the data sheet, record the date and time your experiment began. Observe the carnation at each of the intervals listed on the data sheet and record your observations. After the 3 day observations, have an adult split the flower completely in half through the bloom.

4 Name: Data Sheet Experiment 1: How does water flow up a stem? Start date and time: 1 hour: 3 hours: 1 day: 2 days: 3 days: 1. Look closely at the flower. Can you see color along the stem and calyx? 2. Did each color move straight up the flower? 3. What did you observe on the inside of the stem, calyx and flower when it was cut in half? 4. What have the results demonstrated about how water flows up a stem?

5 Name: Date: Data Sheet Experiment 1: How does water flow up a stem? Color the pictures to show what the experiment looks like at different times. Start After 1 day After 2 days After 3 days

6 Experiment 2: Can water flow through a stem in either direction? You will need: 1 white carnation 1 clear plastic cup red food coloring water sharp knife (for teacher s use) This experiment will take 2 days. Fill the cup ¾ to the top with water. Add several drops of red food coloring to the water and stir. The water should be bright red. Cut two lengths of carnation stem, about four to six inches each. Each section should have leaves still attached. This will show which direction the stem is placed. Place one stem in the red water upright, with leaves pointing upward. Place the other stem in the red water upside down, with leaves pointing downward. On the data sheet, record the date and time your experiment began. Observe the stems at each of the intervals listed on the data sheet and record your observations. After the 2 day observations, have an adult split both stems completely in half.

7 Name: Data Sheet Experiment 2: Can water flow through a stem in either direction? Start date and time: 1 hour: 3 hours: 1 day: 2 days: 1. Is there red at the top of each stem? 2. Based on the results of this experiment, do you think that stem tissue will always pull water upward? Why or why not? 3. What do you think would happen if the stem were laying sideways with one end in water? Explain your answer. 4. When the stems were cut in half, what did you observe on the inside of each stem? Were they the same or different?

8 Name: Date: Data Sheet Experiment 2: Can water flow through a stem in either direction? Color the circles to show what the ends of the stems looks like at different times. Draw and color the inside of a stem after it was cut open. Start leaves up After 1 day leaves down leaves up After 2 days leaves down leaves up leaves down