The following lesson can be used either as a way of approaching the scientific method, or ,alternately, during a biology unit on plant growth and reproduction.  In this lesson, students will be investigating how certain environmental factors can affect the germination and growth of various species of plant seeds.  Factors that may be investigated include gravity, light intensity, angle of  light incidence, humidity and pH.  Over the course of a one week period, the teacher and students will together:

•    determine their background knowledge on the topic of germination
•    discuss a set of pre-lab questions on the topic of germination
•    form their own investigative questions
•    create hypotheses from their questions
•    design and carry out their own experiments with plant seeds based on their questions
•    form conclusions and new hypotheses from their data and results
•    present their results to the class

• Students will use the various steps of the scientific method to construct and carry out a detailed laboratory investigation (including a control).
• Students will understand the basic processes of seed germination.
• Students will understand how various environmental factors may affect the process of seed germination in a variety of plant species.
• Students will organize and  present their findings to the class in a formal manner and answer any questions that their audience may have about their investigation.

All science students, grades 5-12
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Notes to the Teacher: to top

This activity will take approximately 5 class periods to complete.  It may take longer if students are expected to present detailed results from their investigation to their peers.  Remember that in this activity, students are forming their own questions and hypotheses on the subject.  Many students who have little or no previous experience with forming their own questions may need more than a little guidance and direction in this process. A certain amount of preparation is necessary for this lab.
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•  2 or more types of plant seed (radish, tomato, corn, sunflower or Wisconsin Fast Plants)
•  petri dishes
•  grid sheets photocopied onto transparencies (cut in the shape of a petri dish) to measure growth of seedling roots.
•  filter paper or thick paper towels cut to fit inside petri dish (circular shape)
•  scissors
•  germination chambers (build at least 5 from empty, plastic, 2-liter bottles) -click here for instructions:
•  fluorescent grow lamps or a sunny window
• a dark space
• acids of varying concentrations (pH 3, 4, 5, 6). Vinegar works well.

Tropism is the growth or bending of a plant in response to an outside source of stimulation.  There are many different kind of tropisms (click here for: ScienceNet - What are the different types of tropisms? ) .  Two of the most important types are gravitropism (also called geotropism), or how a plant grows in respond to gravity; and phototropism, how a plant grows in response to light. The teacher should acquire some background knowledge on both germination and on tropisms before attempting this lab with students.

Here are some links with important information on:

• Seed Germination
• Effects of gravity on seed germination

A. Pre-Lab
On the first day of this lab the goal for the teacher should be to determine what students may already think or know about the subject of seed germination and how seedlings respond to certain stimuli.  The following are possible pre-lab questions to ask your students to answer in pairs before discussing the lab:

• What is a seed?
• Why do plants have seeds?
• What is inside a seed?
• How does a seed know when to grow? (or) What causes a seed to begin growing?
• What comes out of a seed when it begins to grow?
• Does a seed know which way is up and down?
• Is it important for a seed to know up and down?
• Which parts of a plant need to grow up, which parts need to grow down?
• Would it be possible to 'fool' a seed into thinking up is down and down is up?  How could you do that?
• What sorts of environmental factors might affect seed germination

B.  Forming a Question

Begin the second day by showing students how a healthy seed germinates in a damp petri dish under normal conditions (You will need to set this up 2 or 3 days in advance to have a big enough seedling to show them).  Explain to them carefully how you set up the seeds in the petri dish (between the plastic and the damp filter paper) and left the petri dish in the water reservoir to germinate.  Students should know that they will all be germinating their seeds in the same manner during the investigation.

(An alternative to this is for students to perform a "cookbook" germination lab before designing their own experiments)

The groups of students should focus on forming questions that they would like to answer in a lab investigation.  Questions may be from the list generated the day before or may be new questions related to seed germination.  Students should be encouraged to pursue questions about how environmental factors such as light and gravity (or pH, humidity) will affect the germination of seedlings.

Common student questions may include:

• Changing the orientation of the petri dishes during germination,
• Altering angle or intensity of the light source,
• Altering the amount of water or
• Changing the pH of the solution used in the reservoir.

C.  Creating a Hypothesis and Designing an Investigation

After forming a question to investigate, students should create a hypothesis (an educated guess) based on their question.  Students may have more than one hypothesis for their problem.

Next, students should then be made aware of the materials and spaces available for the lab.  Once they have this information, the groups may begin to design their experimental procedure.  Students should make their materials, experimental procedure and control procedure very clear in writing.  Require each group to have their procedures checked by both a peer group and by the teacher before they are allowed to proceed.

D.  Doing the Experiment

Students should be given their materials for their experiments (including the control) and be allowed to set up their germinations.   Germinations will be allowed to run for several days and data will be collected everyday.  Each day students should:

• measure length of all seedling roots and stems
• make observations on orientation of root and stem growth
• describe overall health and appearance of seedlings
• sketch each of their seedlings

• What they learned from the lab
• What possible sources of error may be
• What further investigations could be done to understand their problem more deeply.
• Students should prepare their reports with visual data that may be shared with the entire class (overhead transparencies, posters, etc.)

F.  Presentations and Debriefing
 
Teacher should allow at least one class period for student groups to present their experimental results and conclusions to the class. Allow a few minutes at the end of each presentation for students in the audience to ask questions.  You may want to require each person in the audience to write down at least one question for each presenting group to answer.

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• Problem and hypothesis creation
• Written experimental procedure
• Accurately following written procedure
• Written conclusion
• Oral presentation to class

• Investigate seed germination in a variety of liquids and light intensities.
• Try different species of seeds
• This investigation may also be extended by looking at the affects of various environmental factors on plant growth in a soil medium.

http://nasc.nott.ac.uk:8100/EXPERIMENTS/seed_germination.html  --  a good "cookbook" germination lab
http://www.anet-chi.com/~manytimes/page38.htm --  for extensive information on germination
http://www.sciencenet.org.uk/database/Biology/Senses/b00568c.html    -- for tropisms information
http://biocomp.arc.nasa.gov/plants/.index.html    -- a web page dedicated to gravitropism.
http://www.aspp.org/education/gravitro.htm  -- a good "cookbook" investigation on gravotropism with some background
http://trc.ucdavis.edu/Coursepages/EXCITES/activities/grav.html  -- another excellent "cookbook" lab on gravitropism.
http://www.gene.com/ae/AE/SH/NSTA_NOR/morris_seeds.html  -- an open-ended lab investigation involving seeds and pH
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