Roots Flashcards
Three (3) functions of roots
- Anchoring the plants firmly to substrate
- Absorbing water and minerals
- Producing hormone
Types of Root Systems
- Fibrous Root System
- Tap Root System
main root of a primary root system, growing vertically downward.
taproot
increase the surface area of a plant’s root system and can be found in great abundance in several plant species
lateral roots
cylindrical extensions of root epidermal cells that are important for acquisition of nutrients, microbe interactions, and plant anchorage
root hairs
External Structure of Roots
- root hairs
- area of cell differentiation
- area of cell elongation
- area of cell division
- root cap
Internal Structure of Roots
- root hair
- epidermis
- cortex
- stele
central core of the stem and root of a vascular plant, consisting of the vascular tissue (xylem and phloem) and associated supporting tissue
stele
outer layer of a stem or root in a vascular plant, lying below the epidermis but outside of the vascular bundles
cortex
Primary meristems
- Protoderm
- Ground meristem
- Procambium
- Apical meristem
Parts of stele
- endodermis
- pericycle
- phloem
- xylem
thin layer of tightly packed cells that act as an impermeable barrier or water repellant layer (the Casparian strip) through which water can move only one way, toward the center of the root system
endodermis
important tissue in roots, as this is the site where branch or secondary roots arise
pericycle
the continuous arrangement of protoplasts of a plant, which are interconnected by plasmodesmata.
Symplast
consists of non protoplasmic parts such as cell wall and intracellular space.
Apoplast
between protophloem and metaphloem
tangential
between companion cells and procambium cells
periclinal
different arrangements of the number of protoxylem groups in roots in cross-sectional view
- Diarch
- Triarch
- Tetrarch
- Polyarch
having two xylem strands or groups
diarch
having three xylem strands or groups
triarch
having four xylem strands or groups
tetrarch
having many protoxylem groups
polyarch
Features of Protoxylem and Metaxylem:
Time of formation
Protoxylem
- first formed xylem
Metaxylem
- late formed xylem
Features of Protoxylem and Metaxylem:
Life time
Protoxylem
- short period
Metaxylem
- long period
Features of Protoxylem and Metaxylem:
Fibers
Protoxylem
- lack fibers
Metaxylem
- has fibers
Features of Protoxylem and Metaxylem:
Vessels
Protoxylem
- narrow in diameter
Metaxylem
- broader vessels
Key to label:
Dermal
epidermis
Key to label:
Ground
- cortex
- endodermis
Key to label:
Vascular
- vascular cylinder
- pericycle
- core of parenchyma cells (monocots)
- xylem
- phloem
guides root growth and development by modulating cell division, cell expansion and stem cell differentiation
auxin maximum
found on the roots of plants, primarily legumes, that form a symbiosis with nitrogen-fixing bacteria
Root nodules
nitrogen-fixing soil bacteria
rhizobia
detached living portion of a plant (such as a bud or shoot) joined to a stock in grafting
scion
- increase the absorptive and transport capacities of the root system
- roots do not arise on pre-existing roots and are not radicles
adventitious roots
- lubricates passage of the
root through the soil - causes soil to release its nutrient ions and permits the ions to diffuse more rapidly toward the root
mucigel
- thick layer of cells at forefront of growing tip
- Cells secrete mucigel to help them glide through the soil but the soil is just plain scratchy and these cells are constantly being destroyed.
Root cap
- Includes the apical meristem, which is a group of cells specialized for the production of new cells
- located at the farthest point of the tissue or the organ produced (found in both shoots and roots)
- just behind the root cap
Zone of Cell Division
- Just behind the root apical meristem
- region where cells expand greatly
- some meristematic activity continues, but mostly cells are enlarging
- Cells begin to differentiate into a visible pattern, although none of the cells is mature
Zone of Cell Elongation
- The vascular tissues of the root become differentiated
- Instead of forming bundles containing xylem and phloem, as in leaves and young shoots, the xylem forms a solid mass in the center, surrounded by strands of phloem
Zone of Maturation/
Zone of Cell Differentiation
- taproot develops from the primary root (radicle)
- there is one single large root with smaller branch roots
Taproot system
- fibrous roots come out directly from the hypocotyl or may branch off from the primary root
- the primary root degenerates so that there are many smaller roots of the same diameter and size
Fibrous root system
Modifications in Roots
For
1. food storage
2. mechanical support
3. vital functions
4. other functions
For storage of food
- fusiform roots
- napiform
- conical
- tuberous
- fasciculated
- nodulose
- moniliform
- annulated
- spindle-shaped taproots
- swollen in the middle and tapering on both ends
fusiform roots
- spherical-shaped taproots
- much swollen at the top and abruptly tapers towards the lower end
napiform roots
- cone-shaped taproots
- broad at the top and gradually tapers towards the lower end
conical roots
- irregularly swollen taproots
- does not form a definite shape
tuberous roots
in adventitious roots, cluster of rootlets swollen at the base
fasciculated roots
in adventitious roots, the slender root becomes swollen at the apex
nodulose roots
in adventitious roots, the rootlets are repeatedly swollen giving a beaded appearance
moniliform roots
in adventitious roots, the root has ring-like swellings
annulated roots
For mechanical support
- prop roots
- stilt or brace roots
- climbing roots
- root buttress
arise from stem branches and grow vertically downwards to the ground
prop roots
arise from the nodes of the main stem
stilt or brace roots
arise from the nodes and clasp a support like fence, stake or another plant
climbing roots
in tall trees, the normal spreading taproots show ridge or plank like growth
root buttress
For vital functions
- assimilatory roots
- respiratory roots or pneumatophores
- floating roots
other term for respiratory roots
pneumatophores
roots become green and perform photosynthesis
assimilatory roots
roots become aerotropic and come out of the soil to facilitate oxygen supply to the roots beneath
respiratory roots or pneumatophores
- sponge roots with large aerenchyma providing buoyancy to the plant
- also respiratory in function
floating roots
For other functions
- clinging roots
- epiphytic roots
- parasitic or haustorial or sucking roots
- contractile or pull roots
- epiphyllous roots
in epiphytes, roots which arise to fix the plant to the substratum
clinging roots
aerial roots covered by a hygroscopic velamen tissue which absorbs water from the air
epiphytic roots
roots that penetrate the host plant and absorb nutrient from it
parasitic or haustorial or sucking roots
roots that undergo contraction at the uppermost part due to the changes in the shape of the cortical cells
contractile or pull roots
- roots arising from epiphyllous buds in some plant
- become functional when the buds detach from the plant
epiphyllous roots