To study how offspring are very much, but not exactly, like their parents in the context of the periodical cicadas.
The arrival of the periodical cicadas in the spring of 2004 provides a good opportunity for you to review with your students the concept of heredity and how offspring are very much, but not exactly, like their parents. Making use of an interactive slide show, this lesson provides students with an opportunity to consider the concept of heredity in the context of the periodical cicadas. It should probably be taught after you have already introduced this concept to students by having them consider organisms with which they are more familiar–like themselves, their classmates, and their pets.
At this grade level, you should lead students to make observations about how the offspring of animals compare to one another and to their parents. Children know that animals reproduce their own kind–rabbits have rabbits, cats have kittens that have different markings (but cats never have puppies), and so forth. This idea should be strengthened by a large number of examples, both plant and animal, that the children can draw on. (Benchmarks for Science Literacy, p.107.)
Research suggests that elementary-school, middle-school, and some high-school students express these misconceptions: some students believe that traits are inherited from only one of the parents (for example, the traits are inherited from the mother, because she gives birth or has the most contact as children grow up; or the same-sex parent will be the determiner); other students believe that certain characteristics are always inherited from the mother and others come from the father; and some students believe in a "blending of characteristics." (Benchmarks for Science Literacy, p. 341.)
Begin this lesson by reviewing what students know about heredity. Ask students to bring in pictures of themselves and their parents. Once students have their photos in hand, lead a general discussion about the similarities and differences between themselves and their parents. You might ask questions like:
- In what ways do you look like your parents?
- In what ways do you look different from your parents?
- Do you think that your parents passed on some of their physical traits to you? If so, what ones?
- What other traits do you think you got from your parents?
As you are conducting this discussion, remember that it is important to be cautious about having children compare their own physical appearance to that of their siblings, parents, or grandparents. At the very least, the matter has to be handled with delicacy so no one is embarrassed.
When you have finished this discussion, tell students that they will now compare the similarities and differences between the adults and children of an insect called a cicada.
Begin this part of the lesson by having students use their Changing Cicada student esheet to view a slide show about a cicada nymph turning into an adult cicada. Instruct students to pause at each slide so that you can discuss the images and the questions that go along with them as a class.
In addition to the questions and commentary included with the slide show, ask students questions like these as you go through the slides:
- Describe what the cicada nymph looks like in the first slide. Can you tell how many legs it has? What color is it? (The cicada nymph has six legs and is white. It is smaller than a penny.)
- Does the image of the cicada in slide #7 look any different than the first one you saw? What is different about it? (This nymph looks bigger and is more brown in color.)
- What does the adult cicada look like when it first gets out of its shell? What is different about it? (The adult cicada is white and it is larger than the nymph. It has a black spot near its head and it has wings!)
- Describe what the adult cicada looks like in the slide 17. (The adult cicada is black, it has orange yellow wings, and red eyes.)
- In what ways do the nymph and the adult look the same? (Answers could include that they both have six legs and they both have the same type of head with eyes on the side.)
As a way to enhance what students have learned from the slide show, provide them with the optional activity of being cicada hunters! This activity is best done when the cicadas are due to emerge from the ground – so the spring would be the best time. Hand out the Cicada Hunter student sheet and tell your class that they will do this part of the lesson at home with their parents. You may also want to send a letter home to parents so that they will understand what is expected of their children. The student sheet should provide all the information they need to be able to complete this activity at home with the help of their parents.
Students should be prepared to talk about their observations in class.
To assess student understanding of this lesson, ask students to create a poster that depicts the similarities and differences between a cicada nymph and an adult cicada. Students can use words and/or pictures to describe these similarities and differences. Feel free to either let students draw the cicadas themselves or use pictures from magazines or newspapers.
When students are done with their posters, display them around the room and hold a class discussion about what students have learned about these insects.
Cicadas belong to the order of insects called Hemiptera, or True Bugs. Students can visit Insects.org to learn more about other True Bugs, such as the Assassin Bug, the Giant Water Bug, and the Stink Bug.