The correct answer for the above statement:
They firm up because celery is made of 95% water. So putting it in water provides an extra increase or range of energy that causes it to firm up. This is what the cooler drawer in your fridge is apparently for: it probably keeps the moisture in and prevents your carrots from drying out and your celery from going all limp (which of the path is also caused by it drying out). ... Some of the most common points involve being celery upright in a container of water.