Roots
Type of Roots
§ Two main types of roots:
1. taproot - the primary root which grows long and thick (found mainly in
dicots)
ex) oaks, hickory, dandelions, carrots, beets, radishes
2. fibrous root - branch out to such an extent that no single roots grows
larger than the rest
ex) grasses
w helps to prevent topsoil from being washed away by heavy rain.
Root Structure and Growth
§ Roots contain cells from the three tissue systems:
1. dermal = epidermis (outer layer)
2. vascular = phloem and xylem
3. ground = cortex (between epidermis and vascular
cylinder)
§ The root system plays a key role in water and mineral transport.
§ Root hairs (tiny cellular projections) cover the surface and produce a large surface area through which water
can enter the plant.
§ Cortex is a spongy layer of ground tissue found just inside the epidermis and extends to the endodermis.
§ Endodermis completely encloses the root's vascular cylinder.
§ Root cap covers and protects the new celIs from the apical meristem.
§ Most of the increase in root length occurs immediately behind the meristem, where
cells are growing longer.
Root Functions
§ Roots anchor a plant in the ground and absorb water and nutrients from the soil.
§ How does water move through a root?
1. Water and minerals enter a plant through the
tiny root hairs.
w Water molecules move into the plant by osmosis
2. Water moves into the cortex, through the cells
of the endodermis, and
into the vascular cylinder.
w Cells in the endodermis are made waterproof by the Casparian strip
3. Water reaches the xylem, where it is transported
throughout the plant.