Compare and contrast alternating current and direct current. give two ways that they are alike and one way that they are different.

 One way they are different is a direct current is a set amount of current, meaning it has a constant rate whereas in contrast with alternating current, it alternates in a periodic pattern. 

  Electrons flow from a higher potential difference to a lower potential difference and this flow is known as current

                     I hope this helps some:)

Direct current is unidirectional. It always flows in the same direction from positive to negative.

Alternate current reverses direction in periods of time. Imagine a sine wave form, it has a maximum positive value then goes to 0 and reaches a minimum negative value then goes to 0 again and keeps going...

In other words:

They are alike because both can power an electrical device and rely on electrons flow to do so.

They are different because DC is unidrectional and AC reverses direction. Also, AC has associated frequency and DC has not or its "0". If someone ever tells you that the voltage for any system is 460V @60hz, you will definitely know they´re talking about Alternate Current.

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 =