but there is no doubt that osmosis plays an important role.(IX class
plasmamembrane)
Every living cell acts as an osmotic system, the cytoplasm lining of
the cell wall acts as the semipermeable membrane. Observe the following
figure, notice how do roots penetrate into soil? You will find that the root
hairs grow out into the spaces between the soil particles and that the hairs
are surrounded by moisture.
Note:In fig-16 Arrow marks shows the direction of flow of water.
The soil water is an extremely dilute solution of salts. Soil water
concentration is more dilute than that of the cell sap in the root hair;
therefore water will pass into the vacuole of the root hair by osmosis.
Recall the process of osmosis that you have learnt in the chapter “moving
of substances through plasma membrane” in class IX. The entry of water
dilutes the contents of the root hair vacuole so that it becomes more dilute
than it’s neighbouring cell.
So, water passes into the neighbouring cell which in turn becomes
diluted, finally water enters the xylem vessels. As there are vast number of
root hairs and root cells involved, a pressure in the xylem vessels develops
which forces the water upwards. This total pressure is known as root
pressure. Root pressure is not the main cause of movement of water in
xylem but it is certainly one of the factor. The other factors are also there.
You will learn about those reasons in higher classes in detail.
Activity-6
What is root pressure
Take a regularly watered potted plant and cut the stem portion 1 cm
above the ground level. Then connect a glass tube by means of strong rubber
