Answer:
1] he could have used bottles or beakers to hold the beakers 2] to avoid diseases and circumstances he could wash his face with water which are not rare in labs or report to a adult
Explanation:
Then the model will become useless. originally the bottle should be air tight only tubes connected to the balloons, so that pressure can be shown when you adjust the plastic sheet in the bottom of the model. but now if there's a hole, air can move freely in or out the bottle and the model will not be able to show anything that occurs during respiration
From a special disc shaped tissue called as placenta