How would your result have been affectted if you had stored your beakers uncovered for one week in the student cabinet?

While performing any kind of experiment in lab one must be very careful about contamination from other resources.

If you had stored the beaker uncovered for a week, there are 100% chances that your sample will get contaminated either from airborne bacteria in the atmosphere of the lab, other bacteria's from surroundings, or viruses or fungi or any other kind of microbes. If beaker is open there also dust particles that penetrate in it.

So, It is necessary that you should cover your beaker properly with plastic or glass lid or aluminum foil etc while incubation for the smooth results of your experiment.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.