Ch 8: Roots
Most roots have three functions:
- Anchoring the plant firmly in place.
- Absorbing water and Materials.
- Producing hormones.
In many cases, roots have functions in addition to or instead of anchoring, absorption, and hormone production. Taproots such as these in carrots and beets is the main storage site of carbohydrates during the winter months.
A Radicle is a direct continuation of the embryonic system.
A Fibrous Root System is a mass of many similarly sized roots.
Adventitious Roots These do not arise on preexisting roots. They increase the absorptive and transportive capabilities of the root system.
Any root that is born from another root is a Lateral Root
A Root Cap is a layer of Parenchyma cells that cover and protect the root apex.
Mucigel is the slimy material secreted by the root caps or root hairs.
The Zone of Elongation is the region of a root tip, just proximal to the root apical meristem. This is where the cells undergo pronounced elongation.
The Root Hair Zone is a region of the root tip, proximal to the Zone of Elongation, where epidermal cells grow out as root hairs.
Root Hairs are a short-lived trichome near a root apex. These increase the surface area and absorptive capacity of roots. Being single, slender cells, they enter soil pores that are too small for whole root tips to enter.
Root Apical Meristem the set of cells capable of dividing, located at the apex of the root. Produces the root itself and also the root cap.
A portion of the root apical meristem where cell division does not occur is the Quiescent Center
The Endodermis is a sheath of cells surrounding the vascular tissue of roots (And occasionally horizontal stems). Their Casparian strips prevent uncontrolled diffusion between root cortex and root vascular tissue by means of walls and intercellular spaces.
Casparian Strips are a layer of impermeable login and Suberin in the walls of endodermal cells, preventing diffusion of material through that portion of the wall.
Passage Cells are cells in the endodermis that has only Casparian strips whereas all surrounding endodermis cells have thickened waterproof walls.
Root Pressure ia the water in the root xylem is under pressure due to the active accumulation of salts by the endodermis and the accompanying influx of water.
A Prop Root is any root that grows through air or water before entering the soil. These help to stabilize the plants shoot.
Butteress Root is a root that grows asymmetrically to where it becomes very tall and thin. These can extend up the truck as much as a meter and gives the trunk lateral stability.
Mycorrhizae are fungi that form a symbiotic relationship with the roots of plants. These usually benefit the plant because they provide phosphorus.
An. Ectomycorrhizal Relationship exists to where the fungal hyphae penetrate between the outermost root cortex cells but never invade the cells themselves.
Endomycorrhizal Association is when the hyphae penetrate the root cortex as far as the endodermis. These can pass through the walls of the cortex but can't pass the Casparian Strips.
Nitrogen Fixation is the conversion of atmospheric nitrogen into any compound plants can use. These are typically either nitrate or ammonium.
During the invasion of roots by nitrogen fixing bacteria, the bacteria are encased in an invagination of the plants cell walls causing an Infection Thread
Root Nodule Several species of plants have a symbiotic relationship with nitrogen fixing bacteria. In some species, especially legumes, these become swollen and occupied by bacteria.
The Haustoria is a modified root and is a structure where a parasite draws nutrients from the plant. In fungi it is a Hypha.
