Science Assessment

Students are expected to know that:

1. The reactants of cellular respiration are glucose and oxygen and the products are carbon dioxide and water.
2. During cellular respiration, bonds are broken between atoms of glucose molecules and oxygen molecules and new bonds form to produce carbon dioxide molecules and water molecules.
3. The process of cellular respiration releases energy because the energy released when bonds form between atoms of carbon dioxide and water molecules is greater than the energy required to break bonds of glucose and oxygen molecules.
4. Energy released during cellular respiration can be transferred to energy-requiring chemical reactions, such as those involved in building carbohydrate polymers in plants and protein polymers in animals.
5. Multicellular organisms need energy to move and grow. At the macroscopic level, muscle contraction moves the bones that are attached to muscles. Cellular respiration provides energy for muscle contraction and building muscles in animals and for building body structures in plants.
6. Some of the energy released during cellular respiration is used to produce ATP from ADP and inorganic phosphate (Pi).
7. The chemical reaction that converts ATP to ADP and an inorganic phosphate (Pi) provides the energy input for most energy-requiring processes in living systems, such as muscle contraction (motion) and making polymers for growth and repair.
8. Some of the energy released during cellular respiration is transferred to the cells’ surroundings.
9. Energy released as heat is used to maintain body temperature.
10. In the absence of oxygen, organisms, including humans, can partially break down glucose molecules (to lactic acid), releasing some energy. When oxygen becomes available, the breakdown products can be oxidized to form carbon dioxide and water and release more energy.
    • During fermentation, molecules from food are partially broken down in cells in the absence of oxygen into smaller molecules (but not completely into carbon dioxide and water). Compared to the chemical reactions that take place during cellular respiration, these reactions result in less ADP being combined with an inorganic phosphate to produce ATP; therefore, less energy is made available during fermentation than during cellular respiration for the chemical reactions that maintain an organism’s body functions. (College Board, S.4.2: Energy Transfer, grades 9-12)

Boundaries:

1. Students are not expected to know details of the metabolic pathways for glycolysis or cellular respiration or where they occur in cells.
2. Students are not expected to know the mechanism by which a chemical reaction involving ATP transfers energy to various energy-requiring biological processes. For example, they are not expected to know that the coupling mechanism for muscle contraction involves a single-step hydrolysis reaction that causes muscle proteins to toggle between two conformations. Nor are they expected to know that in most cases where ATP provides energy for chemical reactions in living organisms, the mechanism involves two steps—one, where the phosphate is transferred from ATP to an enzyme, and a second where the enzyme transfers the phosphate to another molecule (e.g., glucose). Students are not expected to know that ATP does not react with water in these reactions. (See Lehninger: Principles of Biochemistry Third Edition for a more complete explanation.)

Note on inclusion of ATP:

The college board includes the following ideas about the role of ATP in energy transfer in cells:

• The transfer of energy within living systems involves chemical reactions among ATP, H2O, ADP and an inorganic phosphate. The conversion of ATP to ADP and an inorganic phosphate drives other essential reactions in living systems. (College Board, S.4.2: Energy Transfer, grades 9-12)
• During cellular respiration, molecules from food — mainly sugars and fats — are converted in the presence of oxygen into carbon dioxide and water, and the chemical energy of that reaction is used to combine ADP and an inorganic phosphate to make ATP. (College Board, S.4.2: Energy Transfer, grades 9-12)

Students should know that:

1. The amount of chemical energy in a chemical reaction system before and after the reaction occurs depends on the types and number of atoms in the system and how they are arranged in molecules. Different systems of reactants and products typically have different amounts of chemical energy because they have different configurations of atoms.  
2. All chemical reactions involve both bond breaking and bond forming. Energy is always required to separate the atoms that make up molecules (bond breaking), and energy is always released when atoms connect to form molecules (bond forming). 
3. The relative amounts of energy required to break bonds and released when bonds are formed determines whether energy is given off to or taken in from the surroundings during a chemical reaction.
   1. For exothermic chemical reactions (reactions that release more energy than they take in), the amount of energy released as the product molecules form is greater than the energy required to separate the atoms of the reactant molecules. The energy transferred to the surroundings can be manifest as an increase in thermal energy or motion energy or the production of light or sound.
   2. For endothermic chemical reactions (reactions that take in more energy than they release), the amount of energy released as the product molecules form is less than the energy required to separate the atoms of the reactant molecules. The energy transferred from the surroundings can be detected by a decrease in temperature of the surroundings or the absorption of light or sound.
4. If energy is released during a chemical reaction, then the reverse reaction takes in energy [but the reverse reaction is not always possible]. If energy is taken in during a chemical reaction, then the reverse reaction releases energy (e.g., photosynthesis and cellular respiration).

Boundaries:

1. For this idea, dissolving is considered a chemical change (because the configuration of and interactions between atoms change). Therefore, item contexts may include the dissolution of ionic solids (e.g. cold packs).
2. Students are not assessed on the definitions of the words “endothermic” and “exothermic.”
3. Students are not expected to know that the energy that can be released from or absorbed by  the reactants in a chemical reaction depends on other conditions such as temperature or type of solvent.
4. Students are not expected to quantify how much chemical energy is stored in any particular chemical reaction system. Students are not expected to know or use formulas associated with chemical potential energy such as DHº = S(nDH_fº)(products) - S(nDH_fº)(reactants).  The sub-ideas above describe semi-quantitative relationships.