30.3 Roots

30.3 Roots

• Tendrils and thorns are aerial modifications of stems.

• The buckwheat vine is a weedy plant that climbs with the aid of tendrils.
• A person is climbing up a wooden stake.

• The roots of seed plants have three main functions: anchoring the plant to the soil, absorbing water and minerals and transporting them upwards.
• Some roots absorb and exchange gases.
• Most of the roots are underground.

• There are two types of root systems.
• Dicots have a tap root system, while monocots have a fibrous root system.
• Dandelions have tap roots that break off when trying to pull weeds, and they can regrowth another shoot from the remaining root.
• A tap root system is deep in the soil.
• Some plants have tap and fibrous roots.
• Plants with shallow root systems are more likely to grow in areas with abundant water.

• The root growth begins with seed.
• The radicle of the embryo forms the root system when it emerges from the seed.

• As the root pushes through the soil, the root cap gets damaged easily.
• The root tip has three zones: a zone of cell division, a zone of elongation and a zone of maturation and differentiation.
• The zone of extension is where the newly formed cells increase in length.
• The zone of cell maturation begins at the first root hair.
• The root tip is where the three zones are located.

• The zones of cell division are shown in a longitudinal view of the root.
• Cell division takes place in the apical meristem.

• The root has an outer layer of cells called the epidermis.

• The roots have a lot of cortex and little pith.
• Cells that store products are included in both regions.
• The cortex and the pith are located between the center of the root and the vascular tissue.

• Different cell types are revealed in the light micrograph of a wheat root cross section.
• The exodermis and xylem cells are red and the phloem cells are blue.
• Other cell types are black.
• The stele is the area inside thedermis.
• There are root hairs on the skin.

• The endodermis is the only part of the root that is exclusive to roots.
• There is a substance on the walls of the cells.
• Toxic substances and pathogens are usually excluded, but only materials required by the root pass through the endodermis.
• The xylem and phloem of the stele are arranged in a ring around the pith in dicot roots.

• The phloem cells and the larger xylem cells form a ring around the central pith.

• For specific purposes, root structures may be modified.
• Some roots have a store of starch.