How To Grow The Tallest Plant
Summary
In this lab activity students design an experiment controlling one variable with the goal of growing a plant taller than a control plant.
CollapseLearning Goals
Students design a control experiment managing one variable.
Students work in groups and share data.
Students decide what data to collect.
Students make observations and collect data over three to four weeks.
Students analyze data, calculate growth rates, and graph control and experimental plant growth.
Reinforce the basics of the SI system of measurement.
Students work in groups and share data.
Students decide what data to collect.
Students make observations and collect data over three to four weeks.
Students analyze data, calculate growth rates, and graph control and experimental plant growth.
Reinforce the basics of the SI system of measurement.
Context for Use
This is an extended lab that allows students to design a control experiment with the ostensible goal of manipulating a variable resulting in the growth of the tallest plant. This lab is performed in a 7th grade classroom.
One of the variables that can easily be controlled is the amount of light. A three-tier plant rack with timers saves space. An alternative is to mount lights under classroom storage cabinets.
The time required is three to four weeks. The amount of time each day is limited to about five minutes for data collection. Occasionally extra time is needed for class discussion and unplanned problem solving.
Students work together in groups of four. Each student is responsible for growing one plant. The group first decides the growing conditions for the control plant: amount of light, fertilizer, soil, amount of water, etc. One of the students is assigned the task of growing and managing the control plant. The other three students each picks a single, different variable to change. Students record daily data for both the control plant and their experimental plant. The student that is managing the control plant selects an experimental plant in the group that has the best chance of becoming the tallest plant and uses that data. All four students are thus monitoring the control plant and one experimental plant.
One of the variables that can easily be controlled is the amount of light. A three-tier plant rack with timers saves space. An alternative is to mount lights under classroom storage cabinets.
The time required is three to four weeks. The amount of time each day is limited to about five minutes for data collection. Occasionally extra time is needed for class discussion and unplanned problem solving.
Students work together in groups of four. Each student is responsible for growing one plant. The group first decides the growing conditions for the control plant: amount of light, fertilizer, soil, amount of water, etc. One of the students is assigned the task of growing and managing the control plant. The other three students each picks a single, different variable to change. Students record daily data for both the control plant and their experimental plant. The student that is managing the control plant selects an experimental plant in the group that has the best chance of becoming the tallest plant and uses that data. All four students are thus monitoring the control plant and one experimental plant.
Description and Teaching Materials
Before beginning the experiment, students should bring in a container for growing plants. Milk cartons from lunch are a good size. Containers should be rinsed and marked for identification. Make suggestions on growing the plants but during the student planning and experiment do not provide too much assistance. Let the students make decisions. Use a phrase such as "What do you think? It is your experiment." Guide the students in changing only one variable. If the students' plants don't grow, it is usually the result of too much water and poor drainage, or too much fertilizer, try to get them to determine why. Allow these students to replant. Students will generally have the idea that plants receiving more light will grow taller than plants with less light, but the opposite is true. Bean seedlings grown in dark will become very tall with small leaves but they won't appear healthy.
Day 1.
Use the accompanying pre-writing sheet to guide their planning. Present the general problem of what conditions are needed to grow tall plants. Discuss variables that affect plant growth. Discourage the students from using a sugar based variable (sodas). The sugar will encourage bacterial growth and result in unwanted odors. Have the three grow lights set up and set to 8 hours, 16 hours, and 24 hours. Suggest that commercial containers have holes for drainage but let the students decide if they want to poke holes in their milk cartons.
Guide them on data collecting. Instruct them that they will have two data tables, one for the control and one for the experimental plant. Brainstorm what data should be collected. Guide them to date, plant height, their specific variable, and general observations. It is strongly recommended that they also have a column for number of growing days. This category is usefully for making graphs. Give them the option to include other categories such water, number of leaves, stem diameter, amount of light, etc. You may want them to mass their seeds and measure the depth at which the seeds are planted. Encourage them to measure everything. Some years students have tried measuring plant color by comparing to paint chip samples collected from paint stores and developing their own scale. If students are using alternate soil sources, fertilizer, etc., they are responsible for bringing them.
Day 2.
Provide bean seeds and potting soil. Students should have data tables prepared before planting the seeds. I usually instruct the students that they will be given about five minutes on each succeeding day for managing their plants and recording data. I tell them that they aren't to handle their plants anytime during the day except during the allotted time. This reduces accidental damage to plants when the plants get taller. Better results occur when the plants are handled as little as possible.
Day 3—Until End (about 3 weeks)
Give students about five minutes of class time each day for data collection. Once a week take pictures of the control plant next to the experimental plant. Students can make labels that are included in the photographs indicating age and height (see included sample pictures). The photographs can be shared with students in a number of ways: print them out and have the students glue them in their report, post them on the teacher's web site so the students can copy and paste in their report, or save in a shared network folder. If the students' plants don't grow, allow them to replant, but ask them what might the reason, and what they intend to do differently.
End.
Students write a formal report. The report should include a detailed procedure, line graph comparing control to experimental plant (y axis = plant height, x axis = number of growing days), plant pictures, data tables, calculations of the average growth rate (height of plant divided by number of growing days), weekly growth rates, hypothesis, acceptance or rejection of hypothesis. The student's grade is not based on how tall their plant is, but how well they do science.
Lab Planning: students work in groups and consider variables, plan experiment, and write a hypothesis. (Acrobat (PDF) 47kB Sep25 07) Sample of Digital Pictures (Acrobat (PDF) 366kB Sep25 07)
Day 1.
Use the accompanying pre-writing sheet to guide their planning. Present the general problem of what conditions are needed to grow tall plants. Discuss variables that affect plant growth. Discourage the students from using a sugar based variable (sodas). The sugar will encourage bacterial growth and result in unwanted odors. Have the three grow lights set up and set to 8 hours, 16 hours, and 24 hours. Suggest that commercial containers have holes for drainage but let the students decide if they want to poke holes in their milk cartons.
Guide them on data collecting. Instruct them that they will have two data tables, one for the control and one for the experimental plant. Brainstorm what data should be collected. Guide them to date, plant height, their specific variable, and general observations. It is strongly recommended that they also have a column for number of growing days. This category is usefully for making graphs. Give them the option to include other categories such water, number of leaves, stem diameter, amount of light, etc. You may want them to mass their seeds and measure the depth at which the seeds are planted. Encourage them to measure everything. Some years students have tried measuring plant color by comparing to paint chip samples collected from paint stores and developing their own scale. If students are using alternate soil sources, fertilizer, etc., they are responsible for bringing them.
Day 2.
Provide bean seeds and potting soil. Students should have data tables prepared before planting the seeds. I usually instruct the students that they will be given about five minutes on each succeeding day for managing their plants and recording data. I tell them that they aren't to handle their plants anytime during the day except during the allotted time. This reduces accidental damage to plants when the plants get taller. Better results occur when the plants are handled as little as possible.
Day 3—Until End (about 3 weeks)
Give students about five minutes of class time each day for data collection. Once a week take pictures of the control plant next to the experimental plant. Students can make labels that are included in the photographs indicating age and height (see included sample pictures). The photographs can be shared with students in a number of ways: print them out and have the students glue them in their report, post them on the teacher's web site so the students can copy and paste in their report, or save in a shared network folder. If the students' plants don't grow, allow them to replant, but ask them what might the reason, and what they intend to do differently.
End.
Students write a formal report. The report should include a detailed procedure, line graph comparing control to experimental plant (y axis = plant height, x axis = number of growing days), plant pictures, data tables, calculations of the average growth rate (height of plant divided by number of growing days), weekly growth rates, hypothesis, acceptance or rejection of hypothesis. The student's grade is not based on how tall their plant is, but how well they do science.
Lab Planning: students work in groups and consider variables, plan experiment, and write a hypothesis. (Acrobat (PDF) 47kB Sep25 07) Sample of Digital Pictures (Acrobat (PDF) 366kB Sep25 07)
Teaching Notes and Tips
Give the students wide latitude in selecting a variable to test, but don't allow students to test sugar based products or milk on plant growth because of bacterial growth.
Be strict on when the students can handle their plants during the day. You will have fewer problems if they handle their plants only during allotted class time.
Allow extra credit for extra graphs that students design.
Be strict on when the students can handle their plants during the day. You will have fewer problems if they handle their plants only during allotted class time.
Allow extra credit for extra graphs that students design.
Assessment
The assessment can be done in a number of ways: individual formal typed reports with title, problem, hypothesis etc., group posters emphasizing data collection and graphs, slide shows which include digital photographs and a discussion of validity of their hypothesis. Teachers should develop a rubric consistent with previous lab activities.
Standards
6.I.B.3-use the SI system of measurement
7.I.B.1-formulate a testable hypothesis
7.I.B.2-manipulate one variable
7.I.B.3-write a step-by-step procedure
7.I.B.4-related classroom investigations to scientific principles
8.I.B.1-parts of a scientific investigation
7.I.B.1-formulate a testable hypothesis
7.I.B.2-manipulate one variable
7.I.B.3-write a step-by-step procedure
7.I.B.4-related classroom investigations to scientific principles
8.I.B.1-parts of a scientific investigation