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 are expected to know that:

1. The need for energy during exercise causes the rate of cellular respiration in muscle cells to increase, providing more energy for motion and releasing more energy to the cells’ surroundings.
   1. The human circulatory system responds by dilating surface capillaries, increasing blood flow to the skin where energy can be transferred to the body’s surroundings.
   2. The human integumentary system responds by sweating, which cools the body down as it evaporates from the surface of the skin.
2. As cellular respiration speeds up, cells use reactants glucose and oxygen faster and produce products carbon dioxide and water faster.
   1. The human digestive system responds by breaking down stored glycogen to glucose (in the liver) and releasing glucose into blood vessels for transport to muscles.
   2. The human respiratory system responds by increasing the breathing rate, allowing the organism to breath in oxygen faster and breath out carbon dioxide faster.
   3. The human circulatory system responds by increasing the heart rate, allowing it to pump blood carrying glucose and oxygen to body cells faster and carbon dioxide to lungs faster (and also to transfer energy faster from muscle cells to the skin).