TEACHER GUIDE
TOPICS: Plant reproduction, seed structure, dispersal, and
germination.
LEVEL: Middle and high school.
TIME: One class period for field work; 20 min to set up germination experiment; one class period for data collection and analysis. The field work (steps A-C) could be assigned as homework if students are capable of identifying plants independently. February or March is recommended for this activity. Many seeds are still present and easy to collect while the long cold exposure should result in good germination rates.
ADVANCE PREPARATION: Locate an area within walking distance of the school where winter remnants are plentiful; a vacant lot or abandoned field is suitable. Advise student to dress properly for field work with warm boots, hat, gloves, and so on.
PREDICTION: In class discussion, encourage creative, logical, and
critical thinking. We recommend that you introduce the following
ideas if they are not suggested by students: Students may think
that bigger is better; in fact, seed size has little to do with
germination rate under uniform conditions. (See Results note
below.) Seedling growth is another issue; in general, larger
seeds store more nutrients for the young plant, thus increasing
the chance for survival if germination occur under favorable
conditions for growth. However, weed seeds tend to be small
resulting in the wide seed dispersal characteristic of weed
species
.
FIELD PROCEDURE: You may wish to work with your class as a
team so that one seed sample from each species will be
brought back to the lab for testing
.
STEP D2. Use distilled water or a dilute solution of mold
inhibitor to keep seeds moist
.
STEP D3. If 25 seeds are not available for a particular
species, be sure to have students note the actual
number placed in the dish so that % germination can be
calculated in step H
.
RESULTS: The data table will probably reveal no relationship
between seed size and germination rate. Since conventional
lab activities are usually designed to demonstrate differences,
your students may need guidance in dealing with negative results.
"No difference" is a common conclusion in scientific research,
and it offers a chance to discuss other explanations for the
phenomenon under study (seed germination, in this case).
See discussion questions 9-11 for some suggestions.
QUESTIONS 8-11 require higher order thinking skills. We
recommend that you discuss these questions in class
before students write out their answers. Answers to
questions 2-5 will vary depending on the species
identified and tested for seed viability. The following
are typical answers
.
2. Goldenrod, aster, milkweed, ragweed are common in
open fields and abandoned lots
.
3. Fluffy parachutes called plumes are found on milkweed,
aster, thistle, cattail. The function is to disperse the
seeds by wind
.
4. Burdock and beggar-ticks have hooks for attachment to
animal fur
.
5. Milkweed and dock have relatively large seeds; aster,
goldenrod and mullein have very small seed
.
6. Answers will vary depending on species tested as
well as the date of collection. Many northern
seeds require an extended chilling period before they
will break dormancy and begin germination
.
7. There is usually little if any correlation between seed
size and germination rate. See Prediction and Results
notes above
.
8. Moisture, oxygen, and warmth are conditions necessary
for seed germination. Many northern plants require prior
exposure to a period of cold for maximum germination
.
9. Perhaps some of the seeds did not germinate because they
were not fully mature, or were damaged, or were not subjected
to the proper conditions to break dormancy, which may
include a long chilling period. See Teacher Background
"Dormancy and Seed Germination".