Background Information

Related Topics: classification, dichotomous keys, biodiversity, plants, germination, reproduction, change, ecosystem, matter, energy, measurement, fractions, percent

Ohio Academic Standards Alignment: Click here to view content standards alignment to Science for Ohio by grade level.

Classroom Time Required: 45 minutes (introduction and schoolyard seed hike), 45 minutes (seed identification), 45 minutes (dichotomous sorting introduction), 45 minutes (seed sorting), 45 minutes (closure/assessment)

How can students best collect and preserve their seeds and leaves?
- Number matching seeds and leaf samples with a fine tip marker and/or tape so they can be matched up during identification. Attach seeds to their labels.
- Press leaves in a large book or paper grocery bag within one hour of collection. This will allow them to dry flat and not curl up. Avoid keeping leaves in plastic bags as they will decay.
- Collect seeds in a paper bag so they may air dry and won't decay. Wait to collect fleshy seeds (i.e., apple, crabapple) until just prior to the due date to minimize rotting and/or dehydration.
Types of Tree Seeds

Nonflowering seeds (cone-bearing trees). Trees such as pines and spruces fall into this category. Female cones are often found on the upper limbs of adult trees. Male cones (usually much smaller) are often found on the lower limbs. Wind transfers pollen from the male cone upward to the female cone resulting in pollination, fertilization, and seed production.
Flowering seeds (fruit-bearing trees). Deciduous trees (those which lose their leaves annually) such as maple, ash, oak, redbud, etc., generally fall into this category. These trees typically flower and pollinate in the spring and produce seeds by summer or fall.

Seed Reproduction.

Pollination. Pollination is the process by which female (ovules) and male (pollen) reproductive cells (usually from different plants) are brought together to form seeds. Each seed contains an embryo plant. In local trees, this pollination usually occurs via wind or insects in the spring.
Fertilization. Once pollination occurs, male and female cells unite. When a pollen grain lands on a ripe stigma, the grain swells as it absorbs water, sugar, and other materials from the stigma. The pollen then germinates, growing a tube to the ovary. Male cells (gametes) are released through this tube. Usually one will fuse with the nucleus of the female cell (ovum) to create a seed embryo. Another will fuse with the central nuclei of the embryo sac to produce food for the embryo (endosperm) that will sustain it until germination occurs.
Fruit and Seed Production. After fertilization, each ovule becomes a seed with a protective seed coat. There are three main kinds of fruits: simple (single), aggregate (clusters), and multiple. The majority of tree fruits/seeds are simple.

Seed Dispersal.

Animal. Birds, mammals, and/or insects transport seeds away from the parent plant, thus avoiding competition for sunlight energy and water. Birds generally are attracted to colorful fruits (having a poor sense of smell). They eat the fruit and distribute the seeds with their own waste after traveling away from the parent plant. Not only does this give the seed fertilizer in which to grow, but the digestive system (often 103 degrees or so) provides a temperature boost needed by some seeds in order to begin germination. Author's aside...Perhaps one day my car will sprout?...I digress...On the other hand mammals such as bats are attracted to fruits with a strong odor (having poor vision). They also eat, travel, then disperse the seeds with their waste. Other mammals and birds, such as squirrels and blue jays, will inadvertently plant seeds while storing them for later consumption through burying or storing in tree hollows. Forgotten seeds that wouldn't survive digestion germinate into new plants. Another way animals disperse seeds is by carrying them in their fur until they are knocked loose far from the parent plant. Insects play an important role in seed dispersal as well by transporting smaller seeds away from the parent plant.
Wind. This form of seed dispersal is favorable to open areas and on the edges of plant communities where strong winds can move seeds a sufficient distance to avoid competition with the parent plant for sunlight energy and water. Maple seeds (with their helicopter wings) and cottonwood seeds (the loosely packed puffy white spheres that can be seen carrying a child's wishes through the air in late spring/early summer) are wind-dispersed.
Water. Although trees such as the coconut will use water to transport heavy seeds many miles, this form of seed dispersal is more often used by smaller plants in our area. In some cases, water carries the seed away. In other cases, water creates sufficient moisture in the plant to allow self-dispersal. In still other cases, drops of rain striking a plant may cause sufficient vibration to trigger a seed release.

Germination. Once a seed reaches the ground, it absorbs water and swells. The husk breaks open as the seed embryo inside sprouts. A root comes out and pushes down into the soil, while a shoot grows upward toward the sun. Note: There are many seeds in the soil waiting for the right conditions to germinate. Spring sunlight on a forest floor, a fallen tree that opens a window of light in the forest canopy, a warm spring rain, and a forest fire are just a few of the many triggers to germination for seeds awaiting the right conditions.
Seed Biodiversity. The greater the variety of seeds found within a particular area, the greater the biodiversity of plant life. This greater diversity of plant life can attract and support a wider variety of consumers such as birds, insects, amphibians, reptiles, and mammals. Biodiversity is the basis for the food web in any area. A high level of biodiversity also allows an area to be more resistant to stresses such as human activity, disease, fire, etc.
Seed Bank. A seed bank is a collection of seeds in the soil layer of an area that are ready to germinate when conditions are right. A diverse seed bank guarantees plant diversity for the future. Some seeds (maple, ash, oak, etc.) may reside in the seed bank until a fallen tree opens up a light source to begin germination. Other seeds (pine, spruce, etc.) may germinate well after a forest fire and be the first plants to start a new era of plant succession. Unlike other animals, humans have the ability to preserve or destroy the seed bank in an area.
- Human activities that preserve seed banks:
  - Supporting forested parks
  - Planting trees
  - Allowing yards to partially or totally return to forest
- Human activities that destroy seed banks:
  - Agriculture--farming prevents plants other than crops from growing
  - Mining--removes the seed bank from an area
  - Mowing--continued mowing of "grassy" areas prevents the growth of tree seedlings
Plant Products. Many human products are derived from plants. Greater plant diversity means a greater variety of plant products for use today and in future generations. Examples of plant products include foods, lumber, paper, rubber, cotton, medicines, oils, fuels, alcohol, dyes, resins, mulch, compost, etc.
Conservation to Preserve Biodiversity.
- Reduce. Use fewer paper products. Buy products low in paper packaging. When it comes to the environment, bigger is not always better. Make it a family challenge to reduce household waste to one trash and one recycling can each week.

Reuse. Use envelopes and other waste paper for scrap paper. Adopt an attitude that nothing should be used less than twice. The more we reuse, the less we have to cut down.
Precycle by buying products made from recyclable materials and/or products that can be recycled after use.
Recycle paper products at your curbside and at local paper collection centers. Keep a large box in your garage to collect paper that would otherwise go to a landfill. Encourage your school to start a classroom paper recycling program if it doesn't already have one. More recycling means fewer trees cut down.

Cautions. As with all outdoor activities, hand washing afterward is recommended. Also, remind students that poison ivy can spread its oil year-round, causing itching and discomfort. The oil is found on the leaves as well as the vine. Students who look for seeds in forested areas and around forest edges should be especially careful. Remember the phrase, "Leaves of three, let them be!" (See the Online Seed Tour for a photo.)
Misconception(s). Seeds can be sorted by attributes that are not lasting (i.e., seeds with scratches on the outside vs. seeds with no scratches on the outside or seeds that are wet vs. seeds that are dry). Fact: Seeds should be sorted by attributes that are true for all similar seeds and will continue to be attributes for the foreseeable future (i.e., color, size, and shape).
Expected Results. Students should bring a variety of seeds to school for the Dichotomous Seed Sorting Day. Some seeds will not be tree seeds, but this in unimportant for the sorting activity. After the identification day and dichotomous sorting introduction day, students should have the background knowledge necessary to accurately sort seeds by lasting attributes. The seed sorting day will provide multiple opportunities to practice dichotomous sorting of seeds (individually and in teams).