"Heat engines and heat pumps are similar in that they both operate on the principle that heat flows naturally from a hot substance to a colder one and, in the process, can be made to do work. However, there is an importance difference between them."

The answer is below

Explanation:

The difference between a heat engine and a heat pump is that a heat engine is a device that converts Thermal energy into Mechanical Energy while a heat pump is a system that extracts heat from a cold body and delivers it to a hot body.

A Heat Engine generates mechanical energy (work) from the temperature difference between two thermal reservoirs while a  Heat pump extract heat from a low temperature reservoir and delivers the heat energy to a high temperature reservoir.

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 =