Identify how the physical barriers of the immune system protect the body against pathogens. check all that apply. 1. your nose produces oil to keep pathogens from entering the body through your nose 2. skin contains tightly packed cells 3. skin is tough, flexible, and waterproof 4. you cough when a pathogen enters your mouth 5. you sneeze when a pathogen enters your nose

the answer is; comparing the frequency of collisions with and without the device

this makes the anti-collision system an independent variable and the collisions a dependent variable. if there are fewer collisions with an anti-collision system that without, then it can be stated that the system is a success. essentially, collisions under an anti-collision system are compared with the frequency of collisions by cars with the human drivers.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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