Transport in Plants In humans and many other animals, substances are transported around the body in the blood through blood vessels. Plants have two separate transport systems, they are: Xylem Vessels - transport water and inorganic ions from the roots to the stem and leaves. They are dead cells joined together to make up tubes. They have thick strong walls made of lignin, which gives the plant support. Phloem Vessels – transport substances made by photosynthesis from the leaves to the roots and other parts of the plant. Both of these tissues are arranged in vascular bundles found in the roots, stem and veins of a leaf.

Vascular Bundles Cross Section of a Root:

Cross Section of a Stem

The Pathway of Water Across a Root

In the Leaves

Water evaporates from the surface of the cells into the air spaces of the spongy mesophyll layer. The air spaces become full of water vapour. Water vapour diffuses through the stomata into the air. The water lost from the spongy cells is replaced by more water from the xylem. The evaporation of water from the leaves into the air through the stomata on the underside of the leaves is known as transpiration.

In the Leaves The continuous flow of water from the roots up to the leaves in the xylem is called transpiration stream. Transpiration provides the ‘pull’ that draws water through the xylem vessels.

Experiment: To demonstrate transpiration

Potometers: Experiment: Measuring the rate of water uptake