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Notes for the Instructor

In this activity, students will continue to learn about trace evidence as they examine pollen left behind at the cookie jar crime scene. Pollen is a powdery substance released by plants in order to reproduce. It travels through the air and settles on almost any surface. Many of us know it as a yellow dust or film that descends on everything each spring and summer.

However, in addition to helping plants reproduce, pollen can help scientists. Palynology is the science of analyzing pollen and spores. Each plant has its own unique type of pollen. In forensics, we can apply Locard’s Exchange Principle to the study of pollen. Pollen found at a crime scene can be traced to a specific location where particular types of plants are present. Studying pollen can help narrow down the number of suspects, connect a suspect to a crime scene, or conclude that a suspect was not present at the scene.

Palynology comes into play in The Cookie Jar Mystery when small pieces of pollen are discovered on the broken cookie jar. After learning about palynology, Mrs. Randall checked a piece of the broken cookie jar with a magnifier and found small bits of pollen! Mrs. Randall thinks that the pollen may have been transferred from the cookie thief ’s clothes to the crime scene.

Mrs. Randall examined the clothing from each suspect. Each revealed tiny amounts of pollen that had been previously overlooked. Next she matched those pollens to ones found in different locations around the school to obtain larger samples.

There are four major features of pollen that make it a useful type of trace evidence:

  • Microscopic size: most pollen grains are 10- 70 μm (a micrometer: 1/1,000,000 meter) in diameter, which is the distance across the grain. There are 1,000 μm in a millimeter.
  • Complexity: because it is made up of several parts, the pollen or spores that one plant makes are different from the pollen or spores from other plants. Scientists can link pollen found in many different locations with the plant that it came from.
  • Resistance: pollen and spore walls are hardy. Under the right conditions, pollen can be preserved in rocks for millions of years.
  • Abundance (great quantities of): most flowers use the wind, insects and small animals to take their pollen from the male part of the flower to the female part of the flower. They make a lot of pollen to make sure this happens. Most pollen ends up as part of the soil, dust and rocks. Pollen is everywhere.

Remember, plants each produce large amounts of their own unique type of pollen. In this lesson, students will be challenged to compare and contrast different kinds of pollen. Using hand lenses, your students will describe and sketch the different samples of pollen involved in this case. Then they will attempt to match samples from the suspects to the pollen found at Mrs. Randall’s crime scene.

Note: Due to the difficulty of obtaining pollen samples, some of the “pollens” in this activity are simulated using non-toxic, household ingredients.

The activities in this lesson address Next Generation Science Standards practices of Planning and Carrying Out Investigations and Analyzing and Interpreting Data. In addition, they address Common Core Learning Standards. See the appendix on page 105 for more details.