This is a simple activity involving the collection of pollen released by wind pollinated plants and requires a little more than one classroom period. It can be used to show how plants reproduce or to show that the quantity of pollen in the air is directly related to the amount of allergic response seen in the general population.
Students should have a knowledge of how to use a microscope and basic staining technique. The teacher needs to have microscope slides, coverslips, silicone grease, and stain available. It takes less than 15 minutes for the class to "grease" the slides and to set them outside for a 24 hour collection period. The slides are then stained using a stain specific to pollen and the samples are examined under the microscope. Both a qualitative and a quantitative analysis of the sample can be performed.
This activity can be carried to a much higher level if funding is available for an air sampling machine and research quality microscope.
Abstract Of Activity
Most students are aware of the fact that insects spread pollen from one colorful flower to the next as they collect nectar. They are often less aware of the role that pollen plays in plant reproduction or that many flowers are not bright and showy and pollinate by the wind. The level of pollen in the air can be measured in both a quantitative and qualitative manner. These measurements are directly related to the allergic response seen in the general population.
This activity is a simple method of sampling the air for pollen produced by inconspicuous (wind-pollinated) flowers. Pollen from trees, grasses, and weeds will be seen in your sample depending on the time of the year and the region of the country you take your sample in.
With some additional training and specialized equipment this activity can be expanded into a high level research project.
Pollen Collection And Identification
Coat a clean slide with a thin layer of silicone grease. An area of one square inch is appropriate. Put your initials on the edge of the slide.
Place the slide in an outside location overnight to pick up pollen from the air. A rooftop works well, but any flat area where the slides will be undisturbed will be fine.
After a twenty-four hour period bring the slides inside and stain the slides using Calberla's solution. Use a coverslip.
Scan the slide under low power. When you see pollen (which will appear as pink cells) switch to high power and draw several of them in detail. Be sure to include such details as relative size, number of pores, and furrows. A reference book will be useful in the identification process.
If this lab is performed during the height of the pollen season there may be enough pollen lying on flat surfaces to gather with your finger. Simply place it on the greased area of your slide and stain.
You can also gather some pollen from a colorful flower and compare that to the pollen you collected outside.
What is a pollen grain?
What part of the plant produces pollen?
Did the plants that produced these pollens have conspicuous or inconspicuous flowers? How do you know?
Describe what happens when a pollen grain lands on the stigma of the flower of the same species.
How could a daily pollen analysis (both qualitative and quantitative) of the air be useful to allergy sufferers?
For The Teacher
The following book will serve as an important reference guide when doing any research related to pollen:
Sampling and Identifying Pollens and Molds
An Illustrated Identification Manual for Air Samplers
E. Grant Smith, 1990
P.O. Box 8571
San Antonio, Texas 78208
The following company sells air sampling equipment and supplies:
Sampling Technologies, Inc.
10801 Wayzata Blvd. Suite 340
Minnetonka, MN 55305-1533
(800) 264-1338 FAX (800) 880-8040
Calberla's solution may be purchased from this company or can be made according to the following formula:
5 ml glycerol
10 ml 95% ethanol
15 ml distilled water
2 drops saturated, aqueous solution of basic fuchsin
To see the pollen properly they should be stained a light pink and not a dark red. It may be necessary to adjust the fuchsin concentration.
Answers To The Discussion Questions
A pollen grain is a structure that contains the male reproductive cell of a flowering plant.
The stamen (anther portion) of the flower produces pollen.
The pollen collected by the gravity method is due to wind pollination. Therefore, these flowers must be inconspicuous (not showy or sweet smelling).
After pollination the following series of events will occur. The tube nucleus of the pollen grain forms a tunnel to the ovule. The sperm nucleus divides as it travels down this tunnel. The first sperm nucleus fuses with the egg nucleus to eventually yield the embryo plant. The second sperm nucleus fuses with two polar nuclei in the ovule to form the triploid endosperm. This will provide the food for the developing embryo.
The daily pollen count, normally given in particles per cubic meter of air, is useful to allergists and allergy sufferers. Knowing the quantity of pollen in the air and the types of pollen present is helpful in prescribing the proper medication and treatment. For preventative measures, patients can stay inside more, use air conditioning, and start their medication sooner.