Biology chapter 7

1. Cellular respiration is the process by which cells convert glucose and oxygen into energy (ATP), carbon dioxide, and water. The overall reaction for cellular respiration is:

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP)

- The reactant that we breathe in: O2 (oxygen)

- The product that we breathe out: CO2 (carbon dioxide)

- The reactant that accepts electrons from glucose: O2 (oxygen)

- The product that gains electrons from oxygen: H2O (water)

- The reactant that gives up electrons: C6H12O6 (glucose)

- The reactant that has large amounts of chemical potential energy: C6H12O6 (glucose)

2. To draw a mitochondrion:

- Draw an oval shape to represent the outer membrane.

- Inside the oval, draw a squiggly line to represent the inner membrane.

- The space between the outer and inner membranes is the intermembrane space.

- The innermost area enclosed by the inner membrane is the mitochondrial matrix.

3. The four stages of cellular respiration:

- Glycolysis:

- Reactants: Glucose, 2 NAD+, 2 ADP + 2 Pi

- Products: 2 Pyruvate, 2 NADH, 2 ATP

- Location: Cytoplasm

- Breakdown of Pyruvate:

- Reactants: 2 Pyruvate, 2 CoA, 2 NAD+

- Products: 2 Acetyl-CoA, 2 CO2, 2 NADH

- Location: Mitochondrial matrix

- Citric Acid Cycle (Krebs Cycle):

- Reactants: 2 Acetyl-CoA, 6 NAD+, 2 FAD, 2 ADP + 2 Pi

- Products: 4 CO2, 6 NADH, 2 FADH2, 2 ATP

- Location: Mitochondrial matrix

- Oxidative Phosphorylation:

- Reactants: 10 NADH, 2 FADH2, O2, ADP + Pi

- Products: H2O, 34 ATP

- Location: Inner mitochondrial membrane

4. Energy transformations during cellular respiration:

- Chemical potential energy in glucose is converted into ATP.

- During glycolysis, the chemical energy of glucose is partially converted into ATP and NADH.

- In the Citric Acid Cycle, the energy from Acetyl-CoA is transferred to NADH, FADH2, and ATP.

- In Oxidative Phosphorylation, the energy from NADH and FADH2 is used to create a proton gradient, which drives the synthesis of ATP.

5. Path of electrons during cellular respiration:

- Electrons start in glucose.

- They are transferred to NAD+ and FAD, forming NADH and FADH2.

- NADH and FADH2 carry electrons to the Electron Transport Chain (ETC).

- Electrons move through the ETC, ultimately reducing oxygen to form water.

6. The Electron Transport Chain (ETC) gets energy to pump hydrogen ions against the gradient by transferring electrons through a series of protein complexes. As electrons pass through these complexes, energy is released, which is used to pump hydrogen ions from the mitochondrial matrix into the intermembrane space, creating a gradient.

7. ATP Synthase uses the hydrogen gradient to make ATP by allowing hydrogen ions to flow back into the mitochondrial matrix through the enzyme. This flow of ions provides the energy needed to convert ADP and Pi into ATP.

8. NADH and FADH2 play crucial roles in Oxidative Phosphorylation by donating electrons to the Electron Transport Chain. They bring high-energy electrons from glycolysis, the breakdown of pyruvate, and the Citric Acid Cycle to the ETC, where their energy is used to produce ATP.

9. To draw a mitochondrion showing the hydrogen gradient:

- Draw the outer and inner membranes as described earlier.

- Indicate high hydrogen ion concentration in the intermembrane space.

- Indicate low hydrogen ion concentration in the mitochondrial matrix.

- Show arrows indicating the movement of hydrogen ions through the ETC and ATP Synthase.

10. If the final electron acceptor, oxygen, is not present, the Electron Transport Chain cannot function. This causes a backup of electrons in the chain, halting ATP production through oxidative phosphorylation. Cells must rely on anaerobic processes like fermentation to produce ATP, which is less efficient and leads to the accumulation of lactic acid or ethanol, depending on the organism. This is why oxygen is essential for efficient energy production in cells.

11. Fermentation involves glycolysis and an extra step called NAD regeneration (NADH → NAD+). During glycolysis, glucose is broken down into pyruvate, producing ATP and NADH in the process. In the absence of oxygen, oxidative phosphorylation (which normally regenerates NAD+ from NADH) cannot occur. Without NAD+ regeneration, glycolysis would halt because NAD+ is a necessary reactant for the glycolytic pathway. Fermentation steps, such as converting pyruvate to lactic acid or ethanol, regenerate NAD+ from NADH, allowing glycolysis to continue and produce ATP anaerobically.

12. Comparison of fermentation and cellular respiration:

- Stages used:

- Fermentation: Glycolysis followed by NAD+ regeneration steps (e.g., lactic acid fermentation or alcohol fermentation).

- Cellular respiration: Glycolysis, the Krebs cycle (citric acid cycle), and oxidative phosphorylation (electron transport chain).

- Oxygen requirements:

- Fermentation: Does not require oxygen (anaerobic).

- Cellular respiration: Requires oxygen (aerobic).

- ATP production:

- Fermentation: Produces a small amount of ATP (2 ATP per glucose molecule).

- Cellular respiration: Produces a large amount of ATP (approximately 30-32 ATP per glucose molecule).

Cells capable of fermentation will preferentially carry out cellular respiration because it generates significantly more ATP per glucose molecule than fermentation. This higher ATP yield is crucial for cellular activities and energy-intensive processes.

13. Cells that are capable of fermentation will preferentially carry out cellular respiration because cellular respiration is much more efficient in terms of ATP production. While fermentation produces only 2 ATP molecules per glucose molecule, cellular respiration can produce approximately 30-32 ATP molecules per glucose molecule. This higher efficiency allows cells to meet their energy needs more effectively and sustain more complex and energy-demanding functions.

14. Comparison of the products of lactic acid fermentation and alcohol fermentation:

- Lactic acid fermentation: The end product is lactic acid (or lactate). This process occurs in muscle cells and certain bacteria.

- Alcohol fermentation: The end products are ethanol (alcohol) and carbon dioxide (CO2). This process occurs in yeast and some types of bacteria.