Final answer:
Humans cope with the toxic effects of free radicals through defense mechanisms like radical scavengers and antioxidants, but sometimes these mechanisms may be overwhelmed.
Step-by-step explanation:
Humans cope with the toxic effects of free radicals through various defense mechanisms. One of these mechanisms is the use of radical scavengers like vitamins C and E, which neutralize free radicals by donating hydrogen atoms and breaking the propagation chain reaction. Another defense mechanism is the use of antioxidants, found in fruits and vegetables, which work by being oxidized themselves and halting the destructive reaction cascades initiated by free radicals. However, sometimes these defense mechanisms may be overwhelmed by the accumulation of reactive oxygen species (ROS).