9-12

B2: Compare the process of photosynthesis and respiration, and describe the factors that effect them.

Curriculum Organizing Questions	Why is it sometimes said that the sun is the source of all life on earth? What gases are needed for plants to survive? How do living organisms influence the composition of the atmosphere? What factors affect the reaction rates for photosynthesis? For respiration? What are the optimal conditions for photosynthesis? For respiration? Are there differences in photosynthesis with different types of light? Why is photosynthesis so important? Does a seed need sunlight?
Elaboration	Students do not need to memorize the Krebs or Calvin cycles here. It is important that they understand the basic reactions and how they interrelate, as well as the fact that these reactions take place within cells.
Specific Ideas	Plants and many tiny plant-like organisms capture the sun's energy and use it to synthesize complex, energy-rich molecules (chiefly sugars) from molecules of carbon dioxide and water. Energy-rich molecules synthesized by plants serve, directly or indirectly, as the source of energy for the plants themselves and ultimately for all animals and decomposer organisms. Through the process of respiration, which requires oxygen, the molecules are broken down, releasing energy. Carbon dioxide is released to the atmosphere as a by-product of respiration.SFAA p. 46 Oxygen is released to the atmosphere as a by-product if photosynthesis. SFAA p. 46 Photosynthesis is also dependent on the amount and wavelengths (color) of light available. Photosynthesis and respiration are cellular reactions. Conditions within the cells (e.g., concentration, acidity, temperature, enzymes) can affect the reactions. When cells break down high energy molecules they usually temporarily store the energy released in phosphate bonds of a small high energy compound called ATP. NSES C5c
Developmental & Instructional Implications	Students seem to think of photosynthesis as a product, rather than a process and have little understanding of energy transfers in plant metabolism. Many students are confused by the energy transfer, and many may think that plants use heat from the sun as an energy source. The relationship between photosynthesis and respiration is difficult to understand and some students view photosynthesis as a plant version of respiriation. Many students do not understand that increased photosynthesis would lead to a lower concentration of carbon dioxide.Driver p. 32 Believing that there are producers in aquatic systems may be problematic for some students due to inexperience with these ecosystems. Some students may believe that carbon dioxide and sunlight can not get through water. Some students may think that water plants absorb carbon dioxide at night, or that bubbles from pond weeds contain carbon dioxide. Driver p. 34 A universal and persistant misconception is that plants get their food from the soil. Many people also believe that plants do not need oxygen. Driver pgs.31-32 Respiration is often taken to be synonymous with breathing. Driver p.33
Examples

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