a 12V zener diode is connected in series with a resistance of 150 ohms and a load resistance of 1kiloohms is connected across the zener diode. The maximum zener current should not exceed 20mA and the minimum current is nearly zero . Calculate the operating range of the input voltage

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =