Earlier I showed you how you could use food dye to investigate how water moves through celery.
Did you do it?! If you did, good on you! What did you find?
This is what I saw.
The first photo (on the left) shows the celery leaves after an hour in the food colouring and water. The other two photos were taken after a whole day. If you look closely you can also see a line of blue going up the stem.
The leaf got bluer the longer it sat in the blue water.
Why? Remember how water travels up tubes through the plant to the leaves? The blue dye is carried in the water, but it can’t get out of the leaf so it stops there. The longer you wait the more dye has stopped in the leaves, and that makes them go bluer.
When did you notice the leaves start to go blue? It happened quite quickly. The water travels quickly up the plant.
If more and more water goes into the leaves why aren’t they getting wetter? Or perhaps bigger?
The leaf only keeps as much water as it needs. The water that’s drawn up into the leaves escapes through tiny holes in the leaves. More water moves up through the stem to take its place.
Why can’t you see this water escaping? The water that escapes out of the leaves has evaporated – that means it has turned into a gas. Water gas is called water vapour and it’s invisible.
This is what I saw when I cut across the stalk. I cut the stems every 3 cm.
[NOTE: cm is short for centimeters. Scientists use the metric system to measure things. 3 cm is a bit bigger than an inch. There are 100 cm in one meter, 1,000 meters in a kilometre. So it’s easy to change from one unit to another!]
You can see the tubes that the water travels through the plant in. They’re called “xylem”. They look like blue dots because I’ve cut across them. In celery stems they’re big so they’re really clear when they’re stained with food dye. One of them is the blue line going up the stem in the top picture.
Do these tubes get bluer the longer they sit in the blue water (like the leaves)? That’s a good question. We’ll look that another time! But you can try and work it out for yourself whenever you like! How could you do it?! First try and work out the answer based on what you know. Then do an experiment to see if you’re right!