Activity Type:
Organisms both cooperate and compete in ecosystems. When they have close and long-term interactions, their relationship is known as symbiosis. In symbiosis, at least one member of the pair benefits from the relationship. The other member may be injured (parasitism), relatively unaffected (commensalism), or may benefit as well (mutualism).
In this activity, students will sort and classify interactions between pairs of organisms under the appropriate symbiotic relationship of commensalism, parasitism, and mutualism. Then students will observe mutualism in action, as they perform a termite dissection.
Grade Level: 6th– 8th grade
Subject Matter: Life Science
National Standards: NS.5-8.1, NS.5-8.3
[attach lichen]
Lichens grow practically everywhere, but scientists have neglected them for years, says James Lendemer, a lichenologist with the New York Botanical Garden. Lendemer took Science Friday on a trip to the Tannersville Cranberry Bog in Pennsylvania to track down these misunderstood organisms.
Activity Materials
Images of organisms paired in symbiotic relationships (examples include anemone-clownfish for mutualism, flowers-bees or mistletoe-oak for commensalism, and tapeworm-human for parasitism)
Termite anatomy sheet (available here)
Compound microscopes
Pipettes – you can substitute eyedroppers. You will need one for each pair or group of students
Toothpicks – two for each pair or group of students
Tweezers – one pair for each pair or group of students
Glass slides with cover slips – one for each pair or group of students
Distilled water
Plastic cups – one for each pair or group of students
Termites – can be collected outdoors from rotting logs or purchased online. (See Termite Digestive Symbionts at www.carolina.com) Keep them in a covered container to prevent their escaping.
Vocabulary
Symbiosis: the close association between two or more organisms of different species.
Mutualism: a symbiotic relationship in which both organisms benefit.
Commensalism: a symbiotic relationship in which one organism derives benefit while the other organism is unaffected.
Parasitism: a symbiotic relationship in which one organism benefits and the other organism is harmed.
Endosymbiont: a symbiotic organism living within the body of its partner.
What To Do
1. Begin the lesson by having the students watch the Science Friday video, “Hunting The Wild Lichen.” Discuss with students the definition of symbiosis. Inform students that there are generally three types of symbiosis (mutualism, commensalism, and parasitism), and explain the differences between them.
Activity One: Symbiosis
Prep: Research and gather images of organisms paired to represent mutualism, commensalism or parasitism. Allow time during this activity for students to research the interactions between organisms, or to prepare to explain the relationship of the members of a pair of organisms to each other.
1. Display pictures of organisms paired in symbiotic relationships.
2. Have students create a three-column chart and label the top of each column “Mutualism,” “Commensalism,” and “Parasitism.”
3. Ask students to write the name of the paired organisms under the appropriate type of symbiotic relationship. How does each pair of organisms interact? How is each organism affected by the other – or not?
4. As a group, have students share their answers and explain why they chose each specific symbiotic relationship for each organism. Review the differences between mutualism, commensalism and parasitism.
5. Ask students if they think termites have a symbiotic relationship. Tell students that they will investigate this question by performing a termite dissection.
Activity Two: Termite Dissection
Note: Students can work in pairs or groups in order to conserve materials. To prevent termites from escaping, keep them in one single container, and then distribute them when students are ready to perform the dissection procedure.
1. Have students discuss what they know about termites. What is a termite? What do termites eat?
2. Hand out the termite anatomy sheet and review the location of the head, thorax and abdomen.
3. To each pair or group of students, hand out a glass slide, a pair of toothpicks, a pipette or eyedropper, and a small cup of distilled water. Have students follow the following set of instructions:
• Use tweezers to remove a termite from its container and place and hold the termite on the glass slide;
• Use the pipette/eyedropper to place a drop of water on the termite;
• Use one toothpick to remove the head and thorax while holding the abdomen with the tweezers;
• Place the slide cover slip on top of the termite to crush the abdomen.
4. Ask students to predict what they think they will see after placing the slide under the microscope.
5. Have students make observations of what they see under the microscope at various magnifications, starting at 4x, then 10x and 40x. Do they see organisms living in the termite’s hindguts? What do they think these organisms are?
What’s Happening?
Some symbiotic relationships can occur within the organism itself. Endosymbionts are organisms that live within the body or cell of another organism. Residing within the hindguts of a termite are millions of endosymbionts that are essential to the termite’s life.
Although termites are insects that eat wood, termites are not capable of digesting wood on their own. Endosymbionts that live within the intestines of the termite assist in converting the wood into nutrients that the termite is able to digest. One of the several types of endosymbionts that lives inside the termite are single-celled organisms called Trichonympha. Trichonympha have the enzymes needed to convert cellulose in wood into starches and sugars that the termite can use as nutrients. In exchange, these organisms benefit from a continuous supply of energy-rich cellulose and a suitable environment in which to live. The relationship between termites and their endosymbionts demonstrates a symbiotic relationship of mutualism.
Topics for Science Class Discussion
• What would happen if Trichonympha or any of the other endosymbionts did not live within the termite?
• How do newly hatched termites without endosymbionts survive?
• Compare and contrast termites and Trichonympha to humans and E. coli.
Extended Activities and Links
Have students go on a symbiosis scavenger hunt by looking around their environment or community for symbiotic relationships in plants or animals. Students should observe pets that could have symbiotic relationships, and conduct observations at a local park or in their backyards for symbiotic relationships in local plants or animals.
Have students research different types of endosymbionts that can live within humans. Students can choose one endosymbiont and create a poster presentation that includes an image and a description that they can present in class. Human parasites that live within the human body also are endosymbionts.
Examine the interrelationships between sharks and other marine species:
http://www.pbs.org/wnet/nature/lessons/symbiotic-strategies/video-segments/1496/
Explore the life cycle of various human parasites by playing the Parasite Pet Shop game online:
http://animal.discovery.com/tv/monsters-inside-me/pet-parasite/
Learn more about lichen symbiosis from the New York Botanical Garden:
http://www.nybg.org/bsci/lichens/lichen.html
This lesson plan was developed in partnership with the New York Hall of Science
