Why do hormones cause changes only in specific body organs?

The population of bacteria in a petri dish doubles every 40 seconds. the population of the bacteria is initially 400 organisms. what unit is most appropriate for the time at which the number of bacteria is 300? hour bacteria per hour second bacteria per second

Which of the following is an oxidation-reduction reaction? (pictured below)

What would happen if the tubing with the yellow band was placed in a beaker of distilled water?