BSCS Science Tracks: Connecting Science & Literacy

Transcription

1 BSCS Science Tracks: Connecting Science & Literacy Second edition, 2006 by BSCS Investigating Life Cycles Unit Overview 5415 Mark Dabling Blvd. Colorado Springs, CO

2 Module Overview Introduction to Investigating Life Cycles Studying life cycles provides students with a sense of the continuity of life. Through an immersion in this concept, students come to understand that every type of living thing goes through a life cycle and that this life cycle is the basic mechanism through which species maintain populations. Students also come to understand that although the developmental pattern is predictable for most plants and animals, each kind of living thing has a unique sequence of life-cycle stages. Consequently, by understanding life cycles, students develop an appreciation for the diversity among living things. Module Overview What do children of this age believe about life cycles? The research is limited regarding children s knowledge and beliefs about the lifecycle concept per se, but some researchers have investigated students thinking regarding related concepts about plants, animals, growth, and the continuity of life. The results of this research are enlightening and should encourage you to ask questions of your students throughout this module as they investigate the life cycles of various organisms. Module Overview 21

3 Although students will not be classifying organisms in this module, they will compare animals and plants life-cycle stages and rates of development. Their ideas of what constitutes an animal and what constitutes a plant might influence some of these comparisons. The research, excerpts of which follow, indicates that some children hold the following misconceptions: Animals are vertebrates only. Stead (Bell) and her colleagues report that to many students animals are only the large land mammals, such as those found as pets, on farms or in zoos.... Only about half the pupils (age 15 years) categorized fish, boy, frog, snail, snake and whale as animal. Reasons for identifying something as an animal included: four legs, large size, land habitat, fur and noise production. (Driver, Squires, Rushworth, Wood-Robinson, 1994, p. 22) 22 Investigating Life Cycles

4 Animals cannot be both an animal and a bird, for example. Because upper elementary-school students tend not to use hierarchical classification, they may have difficulty understanding that an organism can be classified as both a bird and an animal. (AAAS,1993, p. 341) The category children call plants is narrow and restricted often to flowering plants. Elementary- and middle-school students hold a much more restricted meaning than biologists do for the word plant. Students often do not recognize that trees, vegetables, and grass are all plants. (AAAS, 1993, p. 341) Module Overview 23

5 Bell found children, from all age groups, who considered that a tree is not a plant, although they said it was a plant when it was little. Over half did not consider a seed to be a plant. It appears that many pupils view weeds, vegetables and seeds not as sub-sets of the set plants but as comparable sets.... Leach et. al. confirm that pupils chose plant, tree and flower as exclusive groups. (Driver, Squires, Rushworth, Wood-Robinson, 1994, p. 23) Regarding growth, development, and reproduction, the research findings are equally important in understanding students conceptual development of a concept such as a life cycle. Awareness of the following students misconceptions might be helpful in your work with students. 24 Investigating Life Cycles

6 Eggs and seeds are not alive. Seeds and eggs were included in examples chosen to elicit pupils criteria for designating something as living and 20 per cent of the sample gave the potential for growth as a criterion for deciding that these embryos are alive. However, some children believed that eggs and seeds are not alive even when they held that living things develop only from living things. (Driver, Squires, Rushworth, Wood-Robinson, 1994, p. 36) Development of organisms is inconsistent. Questions about the growth of chicks and caterpillars in their eggs revealed notions about embryonic development. Some children considered that the animal had always been there ready to hatch; others thought that distinct body parts came together in the egg. The majority of children suggested that a structurally complete, pre-formed miniature animal was feeding and growing in the egg. (Driver, Squires, Rushworth, Wood-Robinson, 1994, pp ) Module Overview 25

7 Animals and plants go through stages of life and death as they develop from one form to another. They believed in the possibility of living organisms developing from the non-living, stating seeds are dead, when we put them in the soil they get food and begin to live, or larvae change into pupae which are dead and then we get butterflies. However, most of the children did have a notion of the continuity of life, explicitly stating If the seed were not alive it would not be able to grow or expressing the idea that living organisms originate from other living organisms. (Driver, Squires, Rushworth, Wood-Robinson, 1994, pp ) Physical traits are inherited from only one parent or from a blending of the two parents. 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 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. (AAAS,1993, p. 341) 26 Investigating Life Cycles

8 The lessons in this module allow students to develop their understanding of the concept of a life cycle and related concepts by doing the following: Students confront their currently held beliefs as they explore the question What was it before? when given pictures of plants and animals. Students observe directly and document the growth and development of four organisms Triops, painted lady butterflies, darkling beetles, and sweet pea plants. Students compare their firsthand observations with what scientists know about the life cycles of organisms. Students extend their understanding by completing research projects about the life cycles of a variety of organisms, including humans. The module includes references to the reproduction of organisms and the involvement of male and female organisms in the reproductive process, but does not go into any detail about the processes of either sexual or asexual reproduction. The concept of reproduction is necessary for students to understand the continuous nature of life cycles, that life comes from existing life, and that mature organisms are capable of producing the next generation of like organisms. Module Overview 27

9 The lessons in this module provide students with hands-on, minds-on learning experiences; critical-thinking and inquiry skills; conceptually developmental and sequenced experiences; literacy strategies in reading, writing, listening, and speaking; opportunities to learn collaboratively with other students; and integrated activities that encourage curiosity and imagination. See the Module at a Glance on page 30 for a summary of the lessons and the development of the concept of life cycles. Conceptual Outcomes The following table illustrates the priority placed on conceptual development in the module and also displays the correlation of the module s conceptual outcomes with the content standards in the National Science Education Standards and the Benchmarks for Science Literacy. 28 Investigating Life Cycles