Question

1. compare the atp available to cells when oxygen is present versus when it is absent. how might this help explain why brain and heart functions are so quickly affected when a person cannot breathe?

Explanation:

1. ATP Comparison: When oxygen is present, cells perform aerobic respiration (glycolysis, Krebs cycle, electron transport chain), producing a large amount of ATP (up to 36 - 38 ATP per glucose molecule). When oxygen is absent, cells rely on anaerobic respiration (e.g., lactic acid fermentation in humans), which only produces 2 ATP per glucose molecule.
2. Effect on Brain and Heart: Brain and heart cells have high energy demands (they are constantly active and rely heavily on aerobic respiration for ATP). When a person cannot breathe, oxygen supply stops, so cells switch to anaerobic respiration, which provides far less ATP. Since the brain and heart need a continuous, large supply of ATP to function (e.g., for nerve impulses, muscle contractions), the rapid drop in ATP production (due to lack of oxygen) quickly impairs their ability to work, leading to rapid dysfunction.

Answer:

• ATP Comparison: Aerobic respiration (oxygen present) produces ~36 - 38 ATP per glucose; anaerobic respiration (oxygen absent) produces only 2 ATP per glucose.
• Brain/Heart Impact: Brain and heart cells have high ATP demands (rely on aerobic respiration). When breathing stops, oxygen - dependent ATP production (aerobic) ceases, and anaerobic respiration (low ATP yield) cannot meet their energy needs. Thus, their functions (e.g., nerve signaling, cardiac muscle contraction) are quickly impaired.