Biology 2014-2015

Roots
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Section 23-2 

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.