PLANT ORGANS: ROOTS

Roots

• A part of the body of a plant that develops, typically, from the radicle and grows downward into the soil, anchoring the plant and absorbing nutrient and moisture.

• Provide anchorage, absorption, conduction, and storage.

Taproot system

Fibrous root system

2 types of root systems:

Taproot system

A root system consisting of one prominent main root with smaller lateral roots branching from it.

Fibrous root system

A root system consisting of several adventitious roots of approximately equal size that arise from the base of the stem.

Adventitious organs occur in unusual locations such as roots that develop on a stem or

buds that develop on roots

Root caps

A covering of cells over the root tip that meristematic tissue protects the delicate directly behind it.

Root hairs

An extension of an epidermal cell of a root that increases the absorptive capacity of the root.

Epidermis

single layer of protective tissue that covers the roots.

Cortex

Composed parenchyma primarily of loosely arranged cells with large intercellular (between-cells) spaces, makes up the bulk of the root.

Endodermis

The innermost layer of the cortex of the root that from prevents water and dissolved materials entering the xylem by passing between cells.

Casparian strip

Pericycle

Layer of cells just inside the endodermis of the root; gives rise to lateral roots.

Stele

Cylinder of vascular tissues located at the center of a primary eudicot root.

Xylem

Centermost tissue of the stele. Tracheid and vessel elements of xylem conduct water and dissolved minerals.

Phloem

located in patches between the xylem arms.

Sieve-tube elements of phloem conduct

carbohydrates (sucrose).

Vascular cambium

Gives rise to secondary tissues in woody plants. sandwiched between the xylem and phloem.

Symplast

Apoplast

2 pathways in the vascular plant

Symplast

The region enclosed by the cell membranes, within which water and solutes can diffuse freely.

Apoplast

The space outside the plasma membrane

that allows free movement of material

Prop roots

Buttress roots

Pneumatophores

Contractile

4 Roots with Unusual Functions

Prop roots

Modified roots that arise from the stem of certain plants and provide extra support.

Buttress roots

Are large roots on all sides of a shallowly rooted tree. Typically, they are found in nutrient poor rainforest soils and do not penetrate to deeper layers.

Pneumatophores

Breathing roots to help plants that grow in very wet areas like swamps get enough oxygen. These roots basically act like snorkel tubes for plants, rising up above the surface of the water so that the plant can get oxygen.

Contractile

Continually pull the plants deeper into the ground as the stem elongates so it remains subterranean or at an appropriate level in the ground.

Fungi

Myco means?

Roots

Rhizae means?

Mycorrhizae

Is a term for symbiotic associations between plant roots and fungi. This mutalistic growth is in most cases beneficial to both the host plant and the fungi.

Fungus

Is able to absorb and concentrate phosphorus much better than it can be absorbed by the root hairs. Particularly susceptible to acid rain.

Ectomycorrhizae

The fungal mycelium encircles the root like a sheath.

Endomycorrhizae

The fungus penetrates root cells.

Ectomycorrhizae

Endomycorrhizae

2 types of mycorrhizal fungi

Rhizobia

Nitrogen-fixing bacteria which form associations with the roots of leguminous plants.

Nodule

Small swelling on the root of a leguminous plant in which beneficial nitrogen-fixing bacteria live.