5 THE LIVING ENVIRONMENT
5E) FLOW OF MATTER AND ENERGY
Food. Students of all ages tend to use the term "food" in ways that are consistent with the everyday meaning of the term, not the biological meaning. They see food as substances (water, air, minerals, etc.) that organisms take directly in from their environment (Anderson, Sheldon, & Dubay, 1990; Simpson & Arnold, 1985). In addition, some students of all ages think food is a requirement for growth, rather than a source of matter for growth. They have little knowledge about food being transformed and made part of a growing organism's body (Smith & Anderson, 1986; Leach et al., 1992).
Organisms as chemical systems. Middle-school and high-school students have difficulty thinking of the human body as a chemical system and have little knowledge about the elements composing the living body (Stavy, Eisen, & Yaakobi, 1987). In particular, middle-school students think organisms and materials in the environment are very different types of matter. For example, animals are made of bone, muscle, skin, etc.; plants are made of leaves, stems, and roots; and the nonliving environment is made of water, soil, and air. Students see these substances as fundamentally different and not transformable into each other (Smith & Anderson, 1986).
Plant and animal nutrition. Some students of all ages hold misconceptions about plant nutrition (Bell & Brook, 1984; Roth & Anderson, 1987; Anderson et al., 1990). They think plants get their food from the environment rather than manufacturing it internally, and that food for plants is taken in from the outside. These misconceptions are particularly resistant to change (Anderson et al., 1990). Even after traditional instruction, students have difficulty accepting that plants make food from water and air, and that this is their only source of food. Understanding that the food made by plants is very different from other nutrients such as water or minerals is a prerequisite for understanding the distinction between plants as producers and animals as consumers (Roth & Anderson, 1987; Anderson et al., 1990).
Some students of all ages have difficulty in identifying the sources of energy for plants and also for animals (Anderson et al., 1990). Students tend to confuse energy and other concepts such as food, force, and temperature. As a result, students may not appreciate the uniqueness and importance of energy conversion processes like respiration and photosynthesis (Anderson et al., 1990). Although specially designed instruction does help students correct their understanding about energy exchanges, some difficulties remain (Anderson et al., 1990). Careful coordination between The Physical Setting and The Living Environment benchmarks about conservation of matter and energy and the nature of energy may help alleviate these difficulties (Anderson et al., 1990).
Decay. Some middle-school students think dead organisms simply rot away. They do not realize that the matter from the dead organism is converted into other materials in the environment. Some middle-school students see decay as a gradual, inevitable consequence of time without need of decomposing agents (Smith & Anderson, 1986). Some high-school students believe that matter is conserved during decay, but do not know where it goes (Leach et al., 1992).
Matter cycling. Middle-school students seem to know that some kind of cyclical process takes place in ecosystems (Smith & Anderson, 1986). Some students see only chains of events and pay little attention to the matter involved in processes such as plant growth or animals eating plants. They think the processes involve creating and destroying matter rather than transforming it from one substance to another. Other students recognize one form of recycling through soil minerals but fail to incorporate water, oxygen, and carbon dioxide into matter cycles. Even after specially designed instruction, students cling to their misinterpretations. Instruction that traces matter through the ecosystem as a basic pattern of thinking may help correct these difficulties (Smith & Anderson, 1986).