Plant seed dispersal

Author(s): SEP staff

Lesson Overview

Grade level(s):

Grade 2

Subjects(s):

Biology/Life Science

Topic:

Plant seeds

Big ideas(s):

  • Wind, water and animals can transport seeds to new places where seeds can sprout far away from its parent plant to may have a better chance of growing into a healthy plant.
  • Certain structures/parts of seeds facilitate their dispersal

Vocabulary words:

Plants, seeds, dispersal, fruit, seed pod, wind/water/animal dispersal

What you need:

  • Variety of seeds with different dispersal methods:
    Wind dispersed (parachutes, gliders, helicopters) : Dandelion, milkweed, maple, box elder
    Animal dispersed (fruits, hitchhikers): Apple, berries, sunflower seed, cocklebur, speargrass, acorn
  • Trays for easy distrubution of seeds to pairs of students
  • Pictures of coconut, coconut palmtree, sprouting coconuts and island with lone palm tree (see examples attached to lesson)
  • Pictures of plant and seed pods of above seeds (examples attached)
  • Magnifying glasses
  • pieces of fur/fake fur
  • Cups of water
  • Books: "Planting the Wild Garden" by Kathryn Galbraith and "Miss Maple's Seeds" by Eliza Wheeler

Grouping:

Intro as whole group, activities in pairs

Setting:

Regular classroom

Time needed:

Part 1-3 should probably be done as 3 separate lessons (of about 45-60 minutes) that build on each other. The two books in part 3 can be read in two different lessons as well.

Author Name(s): 
SEP staff
Summary: 

The lesson starts with the puzzling question how a lone palm tree came to grow on a small island that has no other palm trees on it and introduces students to the idea of seeds being dispersed by water. Students then observe a number of different seeds, focusing on different seeds structures that could aid dispersal through wind, animals and water and then test their predictions.

Prerequisites for students: 

Students should be familiar with the different parts of a plant and their functions and should know that plants need water and sunlight (and air) to grow. It is helpful if students have used handlenses before this lesson.

Learning goals/objectives for students: 
  • Students will learn that a) wind, water and animals can transport seeds to new places where b) the seeds can sprout far away from its parent plant to may have a better chance of growing into a healthy plant.
  • Students will be able to explain how certain structures/parts of seeds facilitate their dispersal.
Content background for instructor: 

Seed dispersal is the movement or transport of seeds away from the parent plant. Plants have very limited mobility and consequently rely upon a variety of dispersal methods to transport their seeds, including both abiotic and biotic vectors.

Seed dispersal is likely to have several benefits for plant species. First, seed survival is often higher away from the parent plant. This higher survival may result from the actions of density-dependent seed and seedling predators and pathogens, which often target the high concentrations of seeds beneath adults. Competition with adult plants may also be lower when seeds are transported away from their parent.

Seed dispersal also allows plants to reach specific habitats that are favorable for survival, and seed dispersal may allow plants to colonize vacant habitats and even new geographic regions.

Animal dispersal
Animals disperse seeds in several ways.  First, some plants have barbs or other structures that get tangled in animal fur or feathers, and are then carried to new sites.  Other plants produce their seeds inside fleshy fruits that then get eaten be an animal. The fruit is digested by the animal, but the seeds pass through the digestive tract, and are dropped in other locations.  Some animals bury seeds, like squirrels with acorns, to save for later, but may not return to get the seed.  It can grow into a new plant.

Wind dispersal
The kind of seeds which are often wind dispersed are smaller seeds that have wings or other hair-like or feather-like structures.  Plants that produce wind blown seeds often produce lots of seeds to ensure that some of the seeds are blown to areas where the seeds can germinate.

Floating in water
Many aquatic plants and plants that live near water have seeds that can float, and are carried by water.  Plants living along streams and rivers have seeds that float downstream, and therefore become germinate at new sites.  The size of the seed is not a factor in determining whether or not a seed can float.  Some very large seeds, like coconuts, can float.

And some plants disperse their seeds in other ways...
Some plants have unique ways to disperse their seeds.  Several kinds of plants "shoot" seeds out of pods. The seeds can travel quite a few feet from the plant this way.

Getting ready: 

Assemble sets of seeds to be observed by pairs of students:

  • Seeds can be protected by placing them into containers and even gluing them to a background that contrasts in color. We used small petri dishes for a lot of the seeds and glued fragile seeds like the dandelion and milkweek seeds on dark constration paper.
  • Print out (and laminate) cards for each seed that shows the corresponding plant and the seed pods/seeds on the plant.

Day of the lesson:
Part 1:

  • Cut apple in half and crack open walnut so expose the seeds within.
  • Put sets of seeds, seed cards, magnifying glasses on trays for each pair of students

Part 2:

  • Assemble materials for experiment for each pair of students (cup/bowl with water, pieces of cloth/fur, seeds to test, magnifying glass)

Lesson Implementation / Outline

Introduction: 

Show students a coconut and ask them to describe it with words: brown, large, heavy, hard, rough….. Write words on board.
Ask them if they know what it is. Hear some suggestions. Then show them the picture of the single coconut tree on an island and tell them that this coconut will grow into this kind of coconut palm tree, that it is the seed of the coconut tree.
Ask students to discuss in pairs: "How did the coconut get onto the island to start growing there into this coconut tree?" Hear some students' thoughts. If no one thinks about the coconut getting washed onto the shore, show some pictures of beaches with coconut trees, the natural environment that they live in. Any new ideas?
Show picture of floating coconut and show inside of coconut. It is hollow inside/has air inside, which allows the heavy coconut to float.

"Why would it be good for the coconut tree to have seeds that can swim? What would be so bad about the coconut just dropping down from the tree and the seeds starting to grow there?" Show picture. There won't be enough space, soil, sun, nutrients for the new coconut trees to grow. The coconut seeds get washed out to sea and hopefully lands on some piece of beach that has more soil, space, sun and nutrients for the seed to grow.

Tell students that different plants have different kind of seeds that get moved to new places in a variety of different ways and that you have brought in a bunch of seeds for you to look at. Tell students that they will see that some seeds are small, some are large, some are heavy, some are light, some are hard, some are soft, some are fluffy, some are spiky, they have different colors (green, brown, black). Show students list of descriptive words.

"Do you think that all seeds are being moved to new places by the ocean? What other ways can you think of?"
Write the word "dispersed" on the board and explain what it means. Guide students to come up with water, wind, animals that disperse seeds.

Activity: 

Part 1: Observing seeds
Students will be given several different seeds and magnifying glasses and have to draw and describe each and then come up with claims of how these seeds might be moved to new places where there can grow into plants (Apple, walnut, cocklebur, spear grass, milkweed, maple see). See attached students hand-out.

Students work in pairs. Each student draws 3 different seed as seen with naked eye and then some magnified details that might explain the method of dispersal. Students make claims about seed dispersal method and use observations as evidence.

Claims: I think this seed gets dispersed by ________________, because ____________________.
Students share their observations and claims with their partner. Have students share out their ideas about how seeds are getting dispersed. Make sure that students use their observations as evidence for their claim.

Discuss the structures that allow seeds to be dispersed a certain way. Talk about how certain structures have different functions. [If time: Compare to man-made structures (wings, gliders, glue, Velcro).]

Part 2: Testing predictions
How could we test if our predictions are right? Ask students for ideas. Show available materials and decide as group on test methods:

  • Place each seed in water and see if it floats
  • Drop each seed standing up or in front of fan and see if it glides/flies
  • Touch seeds to fur and cloth and see if it sticks to it

Students record observations and draw conclusions (see attached student hand-out). Demonstrate with coconut to show that it floats in water.

Part 3 (based on lesson in "Perfect Pairs" by Melissa Stewart)
Read non-fiction book " Planting the wild garden"

Tell students that this book will tell them about a number of different ways that seeds can be dispersed and that you will create a table together as a class to record the different ways. Discuss which part of the book shows the dispersal way of the seeds that they have observed the day before.

Who/What disperses seeds? How?
Wind Blows seeds to new places
Bird Shakes seeds loose, eats seeds and releases them in droppings
Rain Washes seeds to new places
Stream Carries seeds to new places
Rabbit Shakes seeds loose
Fox Seeds catch on fur and fall off in new places
Raccoon Carries seeds to new places
Squirrel Buries seeds
Person Carries seeds to new places, blows seeds to new places

Looking for patterns/Structure & function
Have students discuss in pairs what seeds that are dispersed by wind/animals in have common? (use seeds from previous activities & pictures in book)
Have students share out with whole class. Possible answers include:
Wind dispersed seeds: small, light, have wings or "fluff"
Seeds eaten by animals: Edible fruit around seed, sweet, smell good, colorful
Seeds that "hitch-hike" on animals: have hooks or are sticky

Read Fiction book "Miss Maple's Seeds"
Tell students that even though this book is a fiction, the illustrations show real seeds and is based on fact about how seeds get dispersed.
Read the book with the students and discuss the different dispersal methods that are being mentioned. Encourage students to listen for reasons why a seed that has moved to a new place might grow better than right next to the plant that it came from.

The two books above also allow integration of ELA standards about non-fiction and fiction books.

Checking for student understanding: 

Options:

  • Students come up with their own plant and seed, draw it and describe in pictures and words how the seeds are being dispersed
  • Have students discuss in pairs and then share out with the whole group some of the following questions:
    "How are the seed dispersal methods that Miss Maple teaches her seeds similar to the ones described in Planting the Wild Garden? How are they different?"
    "What would happen if the animal that helps dispersing a plant's seeds would suddenly disappear/die out?"
(US) Next Generation Science Standards (NGSS)
NGSS Topics
Kindergarten through Grade 5: 
NGSS Performance Expectations
NGSS Performance Expectations: 
2-LS2-2
NGSS Science and Engineering Practices
NGSS Crosscutting Concepts