NATURAL WATER PUMPS

When you look at a tree, you only see a part of it. Unseen roots spread out underground as wide as the branches above. These roots anchor a tree in the ground and hold it up against the force of the wind. Roots also help the tree to grow, by taking up water and nutrients from the soil through the trunk to the leaves. Trees act like a natural pump – many trees over 165 feet tall pump hundreds of gallons of water a day in order to grow. You can suck a drink up through a straw, but trees cannot do this. They use a method called osmosis to draw the water upward. The first experiment shows how osmosis works. Water inside the roots (sap) has a higher concentration of sugar than the water outside. The process of osmosis draws water from the soil, where the concentration is low, to inside the root, where concentration is high.

The second experiment uses colored water to show how water actually travels up a plant’s root. All living things are made up of little units called cells. Water can travel through cell walls but sugars cannot. During osmosis, water always moves in a set direction – from the side where there is less sugar dissolved in it to the side where there is more.

HOW OSMOSIS WORKS

Large potato, ruler, chopping board, peeler, knife, teaspoon, two shallow dishes, water, sugar.

STEP 1
You will need a large, smooth potato about 4in long 2 ½in across. Carefully peel the potato on a chopping board to protect the work surface.

STEP 2
Cut the peeled potato in half, and then slice off the rounded ends. You will now have two round potato slices. Each slice should be about 1 ½in thick.

STEP 3
Use a teaspoon to scoop out a hollow in each potato slice. Place each slice in its own shallow dish and fill the dishes with water to about 1½in in depth.

STEP 4
Half fill both hollows with water. Add ½tsp of sugar to one hollow. Cover and leave the potatoes for one day.

STEP 5
The level of liquid in the sugary hollow has risen. Osmosis has made more water move into this potato from the dish. The level in the other potato has not risen.

OSMOSIS IN COLOR

Water, two tall drinking glasses, water-soluble ink or food dye, white carnation, scissors, tape.

STEP 1
Pour some water into tall drinking glasses. Add a few drops of ink or food dye to one of the glasses to give the water a strong, bright color.

STEP 2
Use scissors to split the stem of the carnation lengthwise to about half way up the stem. Bind the stem with tape, so that it does not split any further.

STEP 3
Place the glasses side by side on a window sill, and stand one half of the stem in each glass. Lean the flower against the window if it will not stand up on its own.

STEP 4
After a few hours, check to see what has happened. One half of the flower will be colored with the dye. The other half of the flower will have remained white.