What will happen if a bacterial cell is placed in a hypotonic solution with penicillin?
Well, I would say that the bacterial cell would expand and eventually burst.
In a hypotonic solution, the cell's solute concentration is higher than that of the solution, and therefore its water concentration would be lower than that of the solution.
Osmosis states that water molecules tend to diffuse down a concentration gradient through a partially permeable membrane. So in this case, water molecules will enter the cell instead, and thus causing it to expand. If too much water enters the cell, then the cell will burst.
As an extra, the bacterial's cell wall helps it prevent from too much water entering in, which helps in preventing it from rupturing, but since there is penicillin inside the solution, it weakens the cell wall, and the bacteria therefore can still burst.
Here is a picture to help you visualize:
Well normally,when you place a bacterium in a hypotonic solution,it ruptures by swelling due to the osmotic gradient created by means of relatively hypertonic solution present inside the bacterial cell,but the process is relatively slower and some are totally resistant to such action by means of their cell wall properties.
Now, the drug PENICILLIN tends to destabilize the bacterial cell wall,so rupture will be easier due to vast amount of fluid accumulation.This is one of the mechanisms of action how Penicillin kills the bacteria sensitive to it.
BUT there are some bacteria like Mycoplasma, L forms ,which lack cell wall,so they have protective mechanism which prevents them to swell up by means of fluid entry from a hypotonic solution,as their cell membrane contains enormous amount of sterol which pushes water away from it.
Penicillin causes derepression of autolysis in such microorganisms,which ultimately causes their destruction due to activation of autolysis.