Essential Science for Teachers: Life Science
Variation, Adaptation, and Natural Selection Featured Classroom: Dr. Kathleen Vandiver, Lexington, MA
Dr. Kathleen Vandiver, Lexington, MA
“I think being a sixth-grade teacher is one of the most challenging things I’ve done even as a Ph.D. because usually what an advanced degree gets you just covers a very narrow field. And so, one of the pleasures and challenges, actually, of teaching sixth grade is that you have to learn a lot of background information about all sorts of subjects. I’ve enjoyed it a lot, learning about astronomy and geology. And learning to know the names of my plants. Because as a cellular immunologist, it’s really a different world.”
School at a Glance:
William Diamond Middle School
- Location: Lexington, MA
- Enrollment: 694
- Average class size: 24
6% African American
- Percentage of students receiving free or reduced-price lunch: 4% versus a state average of 29%
Kathleen Vandiver teaches sixth-grade science at the William Diamond Middle School in Lexington, MA, an affluent suburb of Boston. Diamond Middle School’s 700 students perform well above state averages on state tests, and only 4% of them receive a free lunch. Diamond consistently ranks among the top middle schools in Massachusetts.
Kathleen has a Ph.D. in cellular biology. Prior to becoming a teacher, she worked on developing new instruments in biology. All that changed when she accepted an invitation to teach a small unit on the immune system to her son’s fourth-grade class. “I enjoyed it so much that it made me think about teaching, which I hadn’t considered beforehand. It was a real turning point.”
Lesson and Curriculum
Variation, Heredity, and Evolution; Exploring with Wisconsin Fast Plants
Lesson at a Glance:
Curriculum: Exploring with Wisconsin Fast Plants, Kendall/Hunt Publishing Company
Topic: Variation, Heredity, and Evolution
Kathleen, like Sally Florkiewicz in Program Four, worked with Fast Plants; however, where Sally used them to illustrate the plant life cycle to her third graders, Kathleen used them to demonstrate variation among plant populations to her sixth graders.
Kathleen explained that most of the setup for the lesson took place early in the year when she was showing her students how to do a controlled experiment. In that activity, she had each of her students care for six Fast Plants: two served as the controls, two had low doses of salt in their water, and the final two had high doses of salt in their water. Her students watered the plants using graduated cylinders and measured and recorded the height, number of leaves, and number of flowers on each of the plants for a period of several weeks. “What was really interesting was they weren’t sure whether salt was doing anything because some kids’ high-salt plants were the tallest of their six,” Kathleen commented.
For the activity taped for Session 5, Kathleen’s students measured the heights of a group of plants they had been growing. They recorded the height of each plant on a magnet, and posted the magnets on a graph at the front of the board. In total, the class measured the heights of 166 plants, and, after graphing them, they calculated the average and range heights of the population. The graph illustrated the wide variability in the population, and Kathleen asked her students to speculate on the cause of it: Was the range due to environmental or genetic causes? The class then considered the potential advantages and disadvantages of being a short or tall plant in the population, before discussing ways that the height of the population could change in future generations.
Kathleen’s students then calculated the average for just three plants, and then ten and twenty plants, to illustrate how misleading the data could be if the sample was too small. “We’d like to see at what point does the average reflect what we think is the true average,” explained Kathleen.
The goal was for her students to realize that they need to consider sample size as part of the scientific method. “In elementary school, when you’re trying to teach the general idea of an experiment, you must start off very simply,” said Kathleen, “but at some point, kids need to understand the importance of sample size.”
Kathleen added that an understanding of the scientific method in general, and of sample size in particular, encourages a healthy degree of skepticism in students about things they read in newspapers, claims for ads, etcetera – “If they don’t see that there’s a lot of good scientific method there, they will know not to take it for fact.”
Reflect on Your Teaching
- Students observe and quantify variation within a population.
- Students identify causes of variation in a population.
- Students hypothesize the advantages and disadvantages of specific variations.
- Students generate ideas for increasing the presence of a specific variation in subsequent generations.
Consider the goals for this lesson as listed above. How can you create a lesson appropriate for your classroom that will fulfill similar goals?
Session 1 What Is Life?
What distinguishes living things from dead and nonliving things? No single characteristic is enough to define what is meant by "life." In this session, five characteristics are introduced as unifying themes in the living world.
Session 2 Classifying Living Things
How can we make sense of the living world? During this session, a systematic approach to biological classification is introduced as a starting point for understanding the nature of the remarkable diversity of life on Earth.
Session 3 Animal Life Cycles
One characteristic of all life forms is a life cycle — from reproduction in one generation to reproduction in the next. This session introduces life cycles by focusing on continuity of life in the Animal Kingdom. In addition to considering what aspects of life cycles can be observed directly, the underlying role of DNA as the hereditary material is explored.
Session 4 Plant Life Cycles
What is a plant? One distinguishing feature of members of the Plant Kingdom is their life cycle. In this session, flowering plants serve as examples for studying the plant life cycle by considering the roles of seeds, flowers, and fruits. A comparison to animal life cycles reveals some surprising similarities and intriguing differences.
Session 5 Variation, Adaptation, and Natural Selection
What causes variation among a population of living things? How can variation in one generation influence the next generation? In this session, variation in a population will be examined as the "raw material" upon which natural selection acts.
Sessions 6 Evolution and the Tree of Life
Why are there so many different kinds of living things? Comparing species that exist today reveals a lot about their relationships to one another and provides evidence of common origins. This session explores the theory of evolution: change in species over time.
Session 7 Energy Flow in Communities
Communities are populations of organisms that live and interact together. The structure of a community is defined by food web interactions. The process of energy flow is the focus of this session as the interactions between producers, consumers, and decomposers are examined.
Session 8 Material Cycles in Ecosystems
Studying an ecosystem involves looking at interactions between living things as well as the nonliving environment that surrounds them. Life depends upon the nonliving world for habitat, as well as energy and materials. In this session, material cycles will be explored as critical processes that sustain life in an ecosystem.