are from physical science. Other concepts are from life sciences, such as plant physiology, plant growth, photosynthesis, respiration, plant diseases, and plant and insect interaction. Still other concepts are from the earth sciences, such as soil types, composition of the atmosphere, water cycle, solar energy, and mineral cycle. Finally, unifying concepts might be used to predict and justify a prediction about the plant in the jar. Those might include closed, open, and isolated systems; physical models; patterns of change; conservation; and equilibrium.

[See Unifying Concepts and Processes in Chapter 6]

The knowledge required to predict the life of a plant in a jar is not be limited to single concepts. A deeper understanding of

A well-crafted justification . . . demonstrates reasoning characterized by a succession of statements that follow one another logically without gaps from statement to statement.

the phenomena could be implied by a justification that includes knowledge of chemical species and energy. Keeping track of energy, of C6H12O 6 (sugar), CO2 (carbon dioxide), H2O (water), and O2 (oxygen), and of minerals requires knowing about the changes they undergo in the jar and about equilibria among zones in the jar (soil and atmosphere). The jar and its contents form a closed system with respect to matter but an open system with respect to energy. The analysis of the life expectancy of the plant in the jar also requires knowing that the matter in the jar changes form, but the mass remains constant. In addition, knowing that gases from the atmosphere and minerals in the soil become a part of the plant is important to the explanation.

A deeper understanding of science might be inferred from a prediction and justification that included knowledge of the physical chemistry of photosynthesis and respiration. Photosynthesis is a process in which radiant energy of visible light is converted into chemical bond energy in the form of special carrier molecules, such as ATP, which in turn are used to store chemical bond energy in carbohydrates. The process begins with light absorption by chlorophyll, a pigment that gives plants their green color. In photosynthesis, light energy is used to drive the reaction:

Respiration is a process in which energy is released when chemical compounds react with oxygen. In respiration, sugars are broken down to produce useful chemical energy for the plant in the reaction:

Photosynthesis and respiration are complementary processes, because photosynthesis results in the storage of energy, and respiration releases it. Photosynthesis removes CO2 from the atmosphere; respiration adds CO2 to the atmosphere.

A justification for a prediction about the life of the plant in the jar might include knowledge of dynamic equilibrium. Equilibrium exists between the liquid and vapor states of water. The liquid water evaporates continuously. In the closed container, at constant temperature, the rate of condensation equals the rate of evaporation. The water is in a state of dynamic equilibrium.



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