The Role of Interdependence for Pollination and Seed Dispersal

Background Information for Teachers

In order to survive in the wild, every animal or plant is dependent on many factors. These can include biological factors, such as other animals or plants, and abiotic factors, which include the sun, water, or air. For animals, the basic needs boil down to water, light, air, and some kind of shelter; whereas for plants, water, light, air, and nutrients are essential for survival.

Pollination and seed dispersal are great examples to illustrate the interdependence between living organisms, such as animals and plants, in nature. All plants need pollination to make seeds and fruits. Pollination occurs when pollen gets carried from the male part of one plant's flower to the female parts of a new flower (Figure 1). This female plant part, called the pistil, is usually a long stalk located in the center of the flower and is also made up of several parts, one of them being the stigma, which receives the pollen. The pistil contains the ovary at its bottom, which houses the female plant eggs, called ovules. When pollen is dropped onto the stigma of a new flower, the eggs, or ovules, inside the plant ovaries are fertilized. The fertilized ovules then grow into plant seeds and the ovary becomes the fruit. Most plants rely on pollinators to do the pollinating for them. These pollinators are usually animals like insects (bees, wasps, flies, moths, butterflies), birds, or bats. In turn, many of these pollinators are equally dependent on the plants or pollen as their food source. Without the pollen or nectar that they collect, they would not be able to survive.

Image Credit: Svenja Lohner, Science Buddies / Science Buddies
Figure 1. During pollination, a pollinator carries pollen from one flower to the stigma of another flower.

Seed dispersal is the next step in the life cycle of a flower. Once the fruits and seeds are ready, they have to get to a place where they can grow into a new plant. Nature has many different strategies for seed dispersal (Figure 2). A common one is dispersal by animals. This can happen in two different ways. The first one is seed dispersal via ingestion. Many trees or bushes—for example, many types of berries and some nut trees—surround their seeds with an edible and nutritious fruit. Birds and mammals are attracted by these fruits and will eat them. The seeds are usually not digested by the animal and will then be excreted. This gives the seeds a new place to grow. The second animal dispersal mechanism is used by plants that cover their seeds in hooks or spines. These so-called burrs are designed in a way that they attach to an animal's fur as it passes by. Eventually, the seed will fall off and grow a new plant. Burdock, sea holly, and cocklebur are some plant species that disperse their seeds in this way. Another seed dispersal mechanism that students might be more familiar with is the wind. Many plants grow their seeds in shapes that can be carried long distances by the wind. Propeller-shaped maple tree seeds and feathery dandelion seeds are some examples of wind-dispersed seeds.

Image Credit: Svenja Lohner, Science Buddies / Science Buddies
Figure 2. Some examples of seeds that are dispersed via animals, wind, and water.

In this lesson plan, students will create a pollination and seed dispersal web that demonstrates how all of these biological factors work together to allow plants and animals to reproduce in nature. Students will also realize that the removal of one part of the pollination or seed dispersal web has significant effects on the rest of the web members, as they are all connected. For example, the extinction of pollinators such as bees would have a huge impact on worldwide food production. According to BBC, they pollinate 70 of the approximate 100 crop species that feed 90% of the world!

Additional Background Links

• What is Pollination?, United States Department of Agriculture (USDA), U.S. Forest Service
• Seed Dispersal, The Seed Site
• Seeds-Hooks and Spikes, Global Zoo
• What would happen if bees went extinct?, BBC

Prep Work (15 minutes)

1. Print and cut out the Pollination Seed Dispersal Web Pictures.
2. Print and cut the Pollination Seed Dispersal Example Pictures.
3. Place the two flower images (slides 1 and 2 of the Example Pictures) next to each other on a table and put some whole black peppercorns on one flower.
4. Cut out the bee image (slide 3 of the Example Pictures) and put some double-sided tape on its back.

Engage (20 minutes)

1. Start the lesson by introducing your students to the concept of pollination and seed dispersal. Show students the two flower pictures on the table and ask:

   What do you see on the table?

   What do you think the pepper grains represent?

   Have students describe what they see. Elicit responses that mention that there are two flowers and that the pepper grains represent the pollen of the flower.

2. Explain to your students that to be able to make new flowers, the pollen (pepper) from one flower has to get to the other flower. Discuss with your students:

   How do you think the pollen can get from one flower to another?

   Listen to students' ideas. Prompt them to think about how, in nature, bees or other animals carry pollen from one flower to another.

3. Take the cut-out bee with the double-sided tape and demonstrate how the bee transports pollen from one flower to another. Fly the paper bee to the flower with the pollen (pepper) and land on it so that the double-sided tape picks up some of the pollen (pepper). Then fly to the other flower. Have one or two students repeat the pollination process using the paper bee with the double-sided tape. Then ask students to explain what happened.
4. Show the picture with the bee in the dandelion flower (slide 4 in the Example Pictures). Point out that the bee is covered in pollen.

   Do you know what animals that carry pollen from one flower to another are called?

   Explain to students that bees and other animals that transport pollen from one plant to another are called pollinators. This process is called pollination. Without pollination, flowers are not able to reproduce.

5. Show students the picture with the acorn tree branch. Tell them that all plants, including this acorn tree, grow from seeds. This means a plant has to spread its seeds to make new plants. Discuss:

   How do you think this acorn tree can spread its seeds (the acorn nuts)?

   Again, listen to children's answers. Focus on answers that mention that animals such as squirrels can take the nuts and bring them to another place, where they can grow into new trees.

6. Show the picture of the squirrel carrying the nut. Explain that many plants use animals for their seed dispersal. Briefly mention other means of seed dispersal via animals, such as animals carrying burs, animals eating and defecating seeds, etc. Examples are provided in the Background Information for Teachers.
7. Have children summarize their observations about pollination and seed dispersal.

   Can you explain what plants need animals for?

   Do the animals need the plants, too?

   Guide children to conclude that plants need the help of animals for pollination and seed dispersal in order to reproduce. On the other hand, the animals rely on the plants for food (nectar and nuts or berries). This means that plants and animals are working together in nature to make pollination and seed dispersal possible. Point out to children that when two things, such as animals and plants, are dependent on each other, this is called interdependence.

Explore (45 minutes)

1. Tell students that they will do an activity to model how animals and plants are dependent on each other during pollination and seed dispersal.
2. Split your class into two groups. One group will build a seed dispersal web, the other group will build a pollination web.
3. Show students the Pollination Seed Dispersal Web Pictures. Hand out one of the seed dispersal pictures to each student in the seed dispersal group and one of the pollination pictures to each student in the pollination group. Have students tape the picture to their chests. Each student represents the animal or plant shown on the picture.
4. Ask students to form two circles, one pollination circle and one seed dispersal circle. Have them introduce themselves as the animal or plant they represent.
5. Build the pollination and seed dispersal web, as follows.
   1. Hand out one ball of yarn to one student in each circle.
   2. Ask the student in each circle:

      Who (which animal or plant) in the circle do you need for pollination or seed dispersal?

      What other plant or animal could help you with pollination or seed dispersal?

   3. Let the students identify someone from their circle.
   4. Ask him/her to hold the end of the yarn tightly and toss or roll the ball to the other person.
   5. Let the student briefly explain why he/she thinks there is an interdependence between the two of them. For example, the bee might throw the yarn to the lily flower, or in the seed dispersal web, the squirrel could toss the yarn to the acorn tree.
   6. Repeat steps b-e with the students who are now holding the ball of yarn.
   7. Continue to build the pollination and seed dispersal web until every child holds the yarn at least once.
   
   Note: During the web-building process, the yarn can be tossed to one person more than once. If at any point you reach a dead end, cut the yarn with the scissors, and select another student to continue building the web. If students have difficulty tossing the ball of yarn, have them roll the yarn on the floor instead. It will become more complicated for them to catch or pick up the yarn if they already have a piece of yarn in their hands. In this case, help students pick up the yarn and place it in their hands. Also, keep reminding them to hold on to a piece of the yarn before tossing it to another student. Example pollination (left) and seed dispersal webs (right) that a class could create are shown in Figure 3, below.
   
   
   Image Credit: Svenja Lohner, Science Buddies / Science Buddies
   Figure 3. Example pollination (left) and seed dispersal (right) webs showing the interdependence between animals and plants for each process.

Reflect (30 minutes)

1. Once both of the webs have been built, cut the yarn and collect both of the balls of yarn. Instruct students to keep holding onto their yarn. While standing still in their pollination and seed dispersal web circles, start a group discussion.

   What does the structure that we built with the yarn look like?

   Help students realize that the structure looks like a spider web. Mention that the web they created is a web that demonstrates the interdependence between animals and plants for pollination and seed dispersal (an interdependence web).

2. Make students aware of the fragility of the created webs. Ask:

   What would happen if the bee (pollination web) or the squirrel (seed dispersal web) became extinct and left the web?

   Listen to students' speculations. Then have the child who represents the bee and squirrel drop his/her piece of yarn and sit down.

3. Continue to ask:

   What other plants or animals in our pollination or seed dispersal web might not get the help that they need without the bee or squirrel?

   Identify all the students (animals or plants) in the web that could benefit from the bee or squirrel and have them drop the yarn and sit down as well.

4. Discuss:

   What happened to our pollination and seed dispersal web?

   What do our observations tell us about interdependence in nature?

   Guide children to conclude that without the bee or squirrel, part of the pollination and seed dispersal web collapses. The web gets weaker. As a result, we should be concerned about the well-being of every kind of plant or animal, as many of them need each other for food, pollination, or seed dispersal. Each component of the web is important because it keeps the web strong.

5. Have students speculate what would happen if pollination or seed dispersal was not possible anymore due to the lack of pollinators, for example.

   What consequences would there be if plants were not be able to be pollinated or to spread their seeds anymore?

   Would the lack of pollination and seed dispersal only be problematic for plants, or also for animals and us humans?

   Listen to students' replies. Help them become aware of how important these processes are, not only for the plants and animals, but also for us humans. According to BBC, bees pollinate 70 of the approximate 100 crop species that feed 90% of the world. Without bees, all of these crops would not be able to grow anymore!

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Plant Scientist

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Career Profile

Plant scientists study how plants grow and reproduce. They could, for example, use their knowledge about seed dispersal and pollination to help farmers increase their crop yields. Read more

Environmental Scientist

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Career Profile

Environmental scientists study the environment to find out how they can best protect the environment from dangers such as human activities. For instance, they could study the effects of pollution or herbicides on pollinators like bees. Read more

Lesson Plan Variations

• Ask students to add more pollinators, seeds, animals, or plants to their interdependence webs. What other animals, plants, or other factor would fit into each of the webs?
• Have students find out more about the plant or animal they represented in their web. What is their role in pollination or seed dispersal? Let them share their findings with the class.
• Instead of the seed dispersal or pollination web, you can also create a food web. Demonstrate food chains by having students toss the yarn to animals or plants that are part of their food chain. A food chain could, for example, start with the grass, continue with a rabbit, and then end with a fox. Create multiple food chains within the circle to represent the whole food web. You can also include the sun in this activity, which provides all the plants with the energy they need to grow.