Childhood Fish tank trick does the job

Had to teach the cohesion-tension theory of how water travels up the xylem.  So I used the old fish tank trick of using a tube to suck in water from a higher container and letting it flow into a lower one.  The continuous flow of water caused by the cohesion of water molecules and the tension of the water pulling on to the lower container amused the students as the container was subsequently emptied (some had predicted that it wouldn’t be emptied).  I was quite surprised that a majority of them had not seen this done.  Where is the childhood pastime of keeping fish gone… Either that or they now use pumps or have neopets.  Of course there is a humbling experience in all this as usual, praise the Lord.  One student ask why if he sucked on a straw from a cup, the water wouldn’t flow out like a fountain….  Gravity pulls one down to earth.