- the internal structure of a dicotyledon leaf and stem, and the structure of the cells that
make up the specialised tissues - the movement of water from the soil into the root
- transpiration and the loss of water vapour from the stomata
Investigation: Examining water uptake by the stem
Aim:
To examine water uptake by the stem
Apparatus:
- Water
- Food colouring dye (available at supermarket)
- White flower on a stem, e.g. Impatiens, carnation or chrysanthemum
- Scissors
- Two jars, cups or measuring cylinders
- Plastic tray
- Sticky tape
Method:
- Fill one jar with plain water, and one with water containing several drops of food
colouring dye. - Take the flower and carefully cut the stem lengthwise, either part way up the stem or
right up to the base of the flower (try both, the results will be different!) - Put one half of the stem into the jar containing plain water and one half of the stem
into the jar containing food colouring dye. To make it easier to insert the stalks without
breaking them, it helps to wedge paper underneath the jars so that you can tilt them
towards each other. Tape the jars or cylinders down onto a tray so that they do not fall
over. - Observe the flowers after a few hours and the next day, and note where the dye ends
up in the flower head. You can leave the flowers up to a week but be sure to make
sure that they have enough water.
Variation:Instead of using one cylinder with water and one with food dye, use two different
colour food dyes (e.g. blue and red). At first the flower will show two separate colours,
but as time goes by the whole flower will show both dyes. This is because water can move
sideways between xylem vessels through openings along their length. The ability of water to
move laterally between vessels is useful for when air becomes trapped in a vessel, causing
a blockage. If you cut the stem right up to the base of the flower, this will limit movement
between the xylem vessels.
Variation:Try using celery stalks with leaves. Cut open the celery stalk (cross-section) and
you will see that the little holes inside are coloured these are the vessels.
Results:
Chapter 6. Support and transport systems in plants 183