Monday, September 19, 2011

Circle of (Plant) Life

The plants around us provide a perfect hands-on biology classroom for students of all ages.  From planting that first bean in a paper cup to conducting more involved and complicated high-school biology experiments, studying plants can be an effective, concrete, fun, and low-cost way for students to explore the living world. 

Kids start learning about photosynthesis from a very young age.  As toddlers begin exploring and playing outside, their observations help them form ideas about plants and how they grow.  By preschool age, many students have had the opportunity to plant seeds and water them to see them sprout.  They may find out that plants will die when we forget to water them or when they don’t get enough sun.  As students’ experiences with plants increase, their perceptions of the way plants grow may change.  Often, by the time photosynthesis is formally introduced in the older grades, students already have some misconceptions about the process.  If we can include photosynthesis in science lessons from kindergarten on, learning the details of the process and understanding the chemical reactions involved will be much easier and more rewarding in middle school and high school.

Since plants are living things, it’s natural for students to compare the functions of the plants to human functions.  Do plants eat, drink, and breathe like us?  How are they different?  How are they the same?

One common misconception going into the study of photosynthesis is that that plants get food from outside sources such as water and soil, much like humans get their food from outside.  All living things need to eat in order to have enough energy to stay alive.  Plants are the hard-working producers of the world, synthesizing their own food using energy from the sun.  They use carbon dioxide and water with the sunlight to make their own food internally.

FT Exploring has a very easy to understand introduction to photosynthesis.  This resource describes photosynthesis in a recipe format and includes diagrams that simplify the concepts.  It answers the questions of how plants eat, drink, and breathe, and shows how these functions are different for plants than for humans.  Teachers could use this introduction for a range of grades, going more in depth with the reactions for older students and sticking to the more basic facts with younger students.  The following diagram is from their site.  

In order for a plant to carry out photosynthesis, water must travel up into the plant from the roots.  This is a fun phenomenon to explore, and would work well for primary or secondary students.  You can introduce simple chromatography experiments with coffee filters and markers or allow students to place the stems of white carnations into water dyed with food coloring.   When bands of color travel out from a marker line or colored water travels to the tips of the carnation petals, students will gain a visual understanding of how water can make its way throughout a plant to take part in photosynthesis.  Take a look at one of our 2010 blog posts about fall lessons to see come neat chromatography ideas. 

Once students are on the right track with the basic concepts of photosynthesis, their learning in the later grades will be more successful.  If you have older students and are ready to go more in-depth with the topic, be sure to look at this comprehensive high school unit.  This unit includes inquiry-based problem solving, hands-on photosynthesis demonstrations using props like tennis balls and balloons, and easy-to-follow procedures.  Another experiment that could go along with that unit is Glucose Factory, where students experiment to see how much glucose is actually inside different plant parts.

~Peggy's Corner - September 16, 2011~

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