In this lesson students explore interactions between organisms such as predator/prey, parasites, competitors, pollinators and disease.
Write the words earth, ecosystem, community, population, species, organism, system, organ, tissue, cell, organelle, molecule and atom on sticky notes and place them on the board in random order. Ask students to arrange them from largest to smallest. Discuss how all these parts fit together. This is an opportunity for students to develop an understanding of the definitions used in this unit.
- Food web activity. Give each student a picture from the sheet Pictures of organisms and animals for food web activity (Word, 810 KB). Ask them to find a classmate carrying an organism that their own animal will eat and link to it by both students holding the picture or linking arms. All students should be joined to each other by the end of the activity.
- Discuss how all organisms are interdependent. Discuss what ‘interdependent’ means.
- Review the definition of food chains and food webs from year 7. Record the agreed definitions.
- Write the following organisms on sticky notes and place them randomly on the board – grass, cow, mosquito, fly, spider, frog, bird, human, snake. Ask the students to arrange the organisms into a food web.
- Ask what would happen if all mosquitoes were removed from the food web. (Answer: In the short term, spiders would starve and we would be overrun with flies and other insects. In the long term, spider numbers would increase as they would feed off the increased number other insects.)
- Describe how there are different types of relationships other than predator/prey. Introduce symbiotic relationships – mutualism, commensalism and parasitism. Watch the video clip Symbiosis: mutualism, commensalism, parasitism.
- Symbiosis activity. Divide students into six groups and show each group an image of a symbiotic relationship (see gallery of images below).
Ask students to identify the type of relationship in each picture and to justify their answer by describing how each organism benefits. Rotate the pictures around the groups. Ask what would happen to one of the organisms if the other were removed from the ecosystem.
- Students complete the worksheet Symbiosis Venn diagram (Word, 391 KB).
- Divide students into pairs and ask them to prepare a thirty-second mime of a type of symbiotic relationship. Each pair presents their mime to the class who guess the relationship being mimed.
Images of symbiotic relationships:
Barnacles on a whale
Nurse shark with remoras
© Jeffrey L. Rotman/Corbis
Human head louse
Source: © Sciepro/Science Photo Library/Corbis
Students doing homework together
Source: © LJM Photo/Design Pics/Design Pics/Corbis
Student copying classmate's work
Teenage student bullying a classmate and stealing his lunch money
Source: © Odilon Dimier/PhotoAlto/Corbis
Discuss the importance of determining relationships between organisms. Show students the news article Attack of the rats. Discuss the implications of the relationship between the bamboo fruit and a rat plague that occurs every 50 years.