TOPIC 4 TRANSPORT OF MATERIALS IN FLOWERING PLANTS – Biology Notes Form Two New
Materials to be transported across the plant body are water, minerals and food. Apart from these nutrients, substances like the hormones also have to be transported. The transport of materials takes place through a specialized tissue called the vascular tissue.
The tissue is made up of xylem and phloem tissues. Xylem tissue transports water and mineral salts from the soil to all parts of the plant. Phloem tissue transports manufactured food from the sites of photosynthesis to all parts of the plant.
In between the xylem and phloem is the vascular cambium. The cells of cambium tissue divide to form a new xylem and phloem. As these cells divide and multiply, the plant increases its girth. The xylem grows inward from the vascular cambium while the phloem grows outward from the vascular cambium.
The arrangement of the vascular bundles in the stem, root and leaf of dicot and monocot plants differs in a number of ways.
The vascular tissue in the root is arranged in the inner portion of the root, which is called the vascular cylinder. A layer of cells known as the endodermis separates the vascular tissue from the ground tissue in the outer portion of the root.
The endodermis is exclusive to roots, and serves as a checkpoint for materials entering the root’s vascular system. A waxy substance called suberin is present on the walls of the endodermal cells.
This waxy region, known as the Casparian strip, forces water and solutes to cross the plasma membranes of endodermal cells instead of slipping between the cells. This ensures that only materials required by the root pass through the endodermis, while toxic substances and pathogens are generally excluded.
The outermost cell layer of the root’s vascular tissue is the pericycle, an area that can give rise to lateral roots. In dicot roots, the xylem and phloem are arranged alternately in an X shape, whereas in monocot roots, the vascular tissue is arranged in a ring around the pith
TOPIC 4 TRANSPORT OF MATERIALS IN FLOWERING PLANTS – Biology Notes Form Two New
CLICK HERE TO DOWNLOAD