Plant Roots Flashcards
2.31 State the primary functions of the root
The primary functions of the root are:
1) Anchorage / Support of plant in the growing medium
2) Water uptake from growing medium
3) Mineral uptake from growing medium
* Roots carry their vascular bundles in the central region, the stele
2.32a Describe a ‘tap root’ to include its origin
A tap root is the main root of a primary root system which grows vertically downwards. It has many smaller lateral (secondary) roots growing out from it at intervals. The tap root is not dominant so the whole root system branches in all directions to produce an extensive rooting system.
Origin: A tap root develops from radicle (embryonic plant root) in the embryo
2.32b Describe ‘lateral roots’ to include their origin
Lateral roots (secondary) extend horizontally from the primary root, smaller than the primary root
Lateral roots originate from the pericycle of the primary root
2.32c Describe ‘fibrous’ roots to include their origin
A fibrous root system is formed when the secondary roots equal or exceed the primary root in size and there is no well defined single tap root. They are formed from thin, moderately branching roots which grow down and out to form a mass of small roots typically shallower in depth than a primary root system
Origin: Grow from the base of stem
2.32d Describe ‘adventitious’ roots to include their origin
Adventitious roots are lateral roots coming from organs other than the main root system, such as the stem, branches and leaves.
Origin: Adventitious roots are lateral roots that do not derive from the radicle of the plant embryo. They grow from unusual places, including stems and other organs
2.33 Describe the difference between monocotyledon and dicotyledon roots
Dicotyledon roots:
- typically have tap root system
- root stele (central vascular region) system with relatively few arms
- vascular cambium present - experience secondary growth
Monocotyledon roots
- NO vascular cambium, therefore no secondary growth
- tap root soon dies off and is replaced by adventitious roots forming a fibrous root system
- root stele (central vascular region) with mulltiple arms
2.34 Transverse Dicotyledonous Root
Produce a drawing of a transverse sections through a young dicotyledon root to show the following internal features:
- epidermis
- cortex
- endodermis
- pericycle
- phloem
- xylem
- cambium
Drawing of young dicotyledonous transverse (P.o.H.p81 Fig 6.6b)
- epidermis
- cortex
- endodermis
- pericycle
- phloem
- xylem
- cambium
2.34 Produce a drawing of a longitudinal sections through a young dicotyledon root to show the following external features:
- root cap
- apical meristem
- zone of elongation
- zone of differentiation
- root hairs
- root hairs
drawing showing
- root cap
- apical meristem
- zone of elongation
- zone of differentiation
- root hairs
- root hairs
2.34a Describe and state the function of the ‘root cap’
Description: The root cap: is a layer of mature cells protecting the apical meristem at the tip of the root. Root cap cells are geotropic, directing the root system downwards. In addition they secrete a lubricating fluid to help the root tip grow through the soil
Function: The root cap protects the apical meristem from damage
2.34b Describe and state the function of the ‘apical meristem’
Description: The apical meristem is a tissue of actively dividing cells
Function: The apical meristem triggers the growth of new cells at the tip of the root system
2.34c Describe and state the function of the ‘zone of elongation’
Description: Zone of elongation is located immediately behind the apical meristem. Cells enlarge and then elongate here due to water pressure pushing outward on the cell membrane
Function: Zone of elongation increases the size of newly formed undifferentiated cells, thereby increasing the lenght of the root
2.34d Describe and state the function of the ‘zone of differentiation’
Description: In the zone of differentiation the undifferentiated cells become mature and develop into specalised plant tissue. Cell structue and chemisty changes, cell walls become rigid and connections between the cell walls form (plasmodesmata)
Function: The zone of differentiation enables undifferentiated cells to mature into specalised functions, enabling the plant to create more complex structures.
2.34e Describe and state the functions of ‘root hairs’
Description: Root hairs are lateral extensions of the epidermal cells on the surface of the root, and are continually being sloughed off by the soil and regrown. They are located just behind the root tip in the zone of differentition.
Function: Root hairs enable the absoption of water and nutrient through their masssvely incresed surface area.
2.34f Describe and state the function of root ‘epidermis’
Description root Epidermis is made ouf thin walled cells, typically one cell layer thick. Root epidermis lacks cuticle as mitigating water loss is unnecessary in the root since it is typically surrounded by a moist growing medium
Function: Epidermis protects against mechanical injury and attact of the root. The epidermis also have an important absorptive function enabling water and mineral uptake through the process of osmosis
2.34g Describe and state the function of root ‘cortex’
Description: root cortex is paranchymatous tissue located between the epidermis on the outside and the endodermis on the interior.
Function: root cortex: site of respiration providing energy for root growth and absorption of mineral nutrients. The cortex may also store food (starch) where root is a perennating organ.
2.34h Describe and state the function of root ‘endodermis’
Description: Endodermis is the innermost cell layer of root cortex
Function: endodermis regulates the movement of water and nutrients from the cortex into the stele (central valscular region) of the root
2.34i Describe the structure and state the function of root ‘pericycle’
Description: root pericycle a thin layer of plant tissue between the endodermis and the phloem
Fruction: Pericycle regulates the formation of lateral roots
2.34j Describe the structure and state the function of root ‘phloem’
Description: root phloem are long tube like cells (sieve tubes) They have cellulose walls and are living unlignified cells with no nucleus. The end walls are only partially broken down to leave sieve-like structures (sieve plates) at intervals along the sieve tubes. Each has a companion cell which regulates the movement of water through the sieve tube.
Fuction: root pholem transport of food and plant hormones from the leaves to the rest of the plant
2.34k Describe the structure and function of root ‘xylem’
Description: root xylem is the woody element of the vascular bundle. The arrangement of xylem tissue varies between species but often appears in transvers section as a stat with several ‘arms’. This arrangement helps to maximise water up take
Function: root xylem transport water and disolved nutrients from the root up to the rest of the plant. It also provides physical support.
2.34l Describe and state the function of root ‘cambium’
Description: root cambium is a lateral meristem found only in dicotyledonous plants . It is a thin layer of growing tissue that produces new cells
Function: root cambium is responsible for the secondary growth of roots in dicotyledonous plants
2.35a Describe how the root is adapted to perform other functions including storeage / perennation
Roots adapted for storage / pernnation swell to store enough food or water to sustain the plant during the unfavourable season, and develop into one or more new plants the following year. They are distinct from tap roots, examples include:
swollen tap root e.g. Daucus carota (carrot)
root tuber e.g. Dahlia spp. develop near the base of the plant, often from adventitious roots. Root tubers can be distinguished from stem tubers in having lateral roots and no nodes
2.35b Describe how the root is adapted to perform other functions including: climbing
Roots which are adapted for climbing are adventitious roots which develop along the stem allowing it to attach to vertical surfaces. This adaptation enables the plant to access more light for photosynthesis and to optimally position flowers for pollination
e.g Hedera helix (Ivy)
2.35c Describe how the root is adapted to perform other functions including: support / prop
Adapted adventitious roots are found in many tropical plant species where they provide support
buttress roots are plank-like outgrowths of the stem supporting tall forrest trees growing on shallow soils e.g. Ficus spp.
stilt roots drop down from branches to the ground e.g. in margroves
Plants may send out ‘prop roots’ from stems to help provide support e.g. on mature plants of Zea mays (sweetcorn)
