Roots

Question 1

Roots Functions

Answer 1

• Support (anchoring)
• Absorb water and minerals
• Conduct water and minerals to and from the shoots
• Store water or food

Question 2

How roots develop ?

Answer 2

Embryo contains a radicle
- Radicle –> is the embryonic root of the plant. May develop into:
* A long taproot
* Many adventitious roots (do not develop from another root, but develop from a stem or leaf)
* Fibrous roots system

Question 3

Root Structures

Answer 3

1. The root cap
2. The region of cell division
3. The region of elongation
4. The region of maturation

Question 4

Root Cap

Answer 4

• Composed of a thimble-shaped mass of parenchyma cells covering the tip of each root.
• Functions :Protect the delicate tissues behind it from damage as it pushes through soil particles, perception of gravity.

Question 5

(Root cap) Movement through soil

Answer 5

• Dictyosomes in the root cap’s outer cells
  secrete a slimy substance that moves
  into the cell walls and eventually exits
  Root Cap.
• Outer cells of the root cap constantly slough off and are replaced from
  the inside, forming a slimy lubricant, aids root tip movement through the soil.

Question 6

(Root Cap) Perception of Gravity

Answer 6

• Amyloplasts (a plastid) act as gravity sensors, collecting on the
  bottom of the root-cap cells.
• When a root that has been growing vertically is tipped horizontally, the amyloplasts tumble or float down to
  the new bottom of the cells in which they occur.

Question 7

Region of Cell Division

Answer 7

• Composed of an apical meristem in the center of the root tip
• Produce the surrounding root cap
• Most cell divisions take place next
  to the root cap

Question 8

(Region of Cell Division)
In both roots and stems, the apical meristem soon subdivides into three meristematic areas:

What are they ?

Answer 8

1. Protoderm (Gives rise to an outer layer of cells, the epidermis)
2. Ground meristem (Produces parenchyma cells of the cortex)
3. Procambium (Produces primary xylem and primary phloem)

Question 9

Pith

Answer 9

• Parenchyma tissue originates from the
  ground meristem
• Generally present in stems but is absent in most dicot roots
• Present in grass roots and those of most other monocots

Question 10

Region of Elongation

Answer 10

• Merges with the apical meristem
• The cells become several times their
  original length and wider
• Couse the root to lengthen
• Tiny vacuoles merge and grow until
  one or two large vacuoles have been
  formed
• Occupy up to 90% or more of the
  volume of each cell.
• Only root cap and apical meristem push through the soil
• Remainder of each root remains stationary for the life of the plant.
• If cambium is present, there is a gradual increase in girth through the addition of secondary tissues.

Question 11

Region of Maturation

Answer 11

• Most cells mature (or differentiate) into various distinctive types of the
  primary tissues in this regions.
• Region of differentiation
• Root-hair zone

Question 12

Cortex

Answer 12

• Tissue composed by parenchyma. May
  be many cells thick.
• Loosely packed to allow for water and
  minerals to move through the cortex
  without entering the cells.
• Mostly store food
• Similar to cortex of stems, except for
  the presence of an endodermis at its
  inner boundary.

Question 13

Endodermis

Answer 13

• Consists of a single-layered cylinder of compactly arranged cells whose primary walls are impregnated with suberin.
• The suberin bands, called Casparian strips, are on the radial and transverse walls
• The plasma membranes of the endodermal cells are fused to the
  Casparian strips.

Question 14

Vascular Cylinder

Answer 14

• Lies to the inside of the endodermis
• Most of the cells of the vascular
  cylinder conduct water or food in
  solution.

Question 15

• Lying directly against the inner boundary of the endodermis is an important layer
  of parenchyma tissue known as…
• Usually one cell wide, may in some plants
  be a little wider.
• The cells of the…..may continue to
  divide even after they have matured.
• Lateral (branch) roots and part of the
  vascular cambium of dicots arise within
  the….

Answer 15

Pericycle

Question 16

Xylem in Roots

Answer 16

• In most dicot and conifer roots, the primary xylem consists of a solid central core of water-conducting cells (Tracheids; Vessels)
• Arms tend to taper toward their tips and
  terminate just inside of the thin cylindrical
  pericycle layer
• There are usually four of these arms, with
  some plants having two, three, or several
• primary xylem surrounds pith parenchyma cells in monocot roots and those of a few dicots; in such plants, the arms may not be well defined

Question 17

Phloem in Roots

Answer 17

• Primary phloem forms in discrete patches between the xylem arms of both dicot and monocot roots.

Question 18

Movement of Water and Minerals
- There are two paths through which water and minerals can travel in a root.

What are they?

Answer 18

1. Apoplastic – movement through cell walls and intercellular spaces. Resistance to flow is approx. 50 times less than resistance of
   symplastic movement.
2. Symplastic – movement through living cells. Secondary route for water movement due to greater resistance to water flow.

Question 19

Some plants have roots with modifications that adapt them for performing
specific functions as well as the absorption of water and minerals in
solution.

Those are ??

Answer 19

Specialized Roots:

• Food-Storage Roots
• Water-Storage Roots
• Propagative Roots
• Pneumatophores
• Aerial Roots
• Contractile Roots
• Buttress Roots
• Parasitic Roots

Question 20

Food-Storage Roots

Answer 20

• Roots are enlarged and store large quantities of starch and other carbohydrates.
• CHOs may later be used for extensive
  growth.
• In carrots, beets, turnips, and radishes,
  food storage tissues are a combination of
  root and stem.

Question 21

Water-Storage Roots

Answer 21

• Characteristic of plants that grow in arid
  regions or in areas where there may be no
  precipitation for several months of the year.
• The water in the roots is apparently used by the plants when the supply in the soil is
  inadequate.

Question 22

Propagative Roots

Answer 22

• Many plants produce adventitious buds (buds appearing in places other.
  than stems) along the roots that grow near the surface of the ground.
• The buds develop into aerial stems called suckers, which have additional
  rootlets at their bases.
• The rooted suckers can be separated from the original root and grown individually.
• Cherries, apples, pears, and other fruit trees often produce suckers.

Question 23

Pneumatophores

Answer 23

• Water contains less than one-thirtieth the amount of free oxygen found in the air
• Plants growing with their roots in water may not have enough O2 available for normal respiration in their root cells
• Spongy roots, which extend above the
  water’s surface and enhance gas exchange between atmosphere and the subsurface roots to which they are connected

Question 24

Aerial Roots

Answer 24

• Velamen roots of orchids (May function in preventing loss of moisture from the root)
• Prop roots of corn and banyan trees
  (Support the plant in high wind)
• Adventitious roots of ivies
  (Helps in climbing)
• Photosynthetic roots of certain orchids

Question 25

Contractile Roots

Answer 25

Some herbaceous dicots and monocots
have contractile roots that pull the plant
deeper into the soil.

Question 26

Buttress Roots

Answer 26

• Some tropical trees growing in shallow
  soils produce huge, buttresslike roots
  toward the base of the trunk, giving
  them great stability
• Except for their angular appearance,
  these roots look like a part of the trunk

Question 27

Parasitic Roots

Answer 27

• Some plants, including dodders, broomrapes, and pinedrops, have no chlorophyll and have become dependent on chlorophyll-bearing plants for their
  nutrition (enable to do PS)
• Parasitize their host plants via peglike projections called haustoria, which develop along the stem in contact with the host.
• The haustoria penetrate the outer tissues and establish connections with the xylem and phloem.

Question 28

Mycorrhizae

Answer 28

• More than 95% of the plants have fungi associated with their roots.
• Mycorrhizae are fungi that have a symbiotic (mutualistic) relationship with the roots of many plants
• “mycorrhiza” means
  fungal root

Question 29

Mycorrhizae – Benefits to the plant

Answer 29

• The fungus can absorb and concentrate P much better than root hairs.
• The fungus also often forms a mantle of millions of threadlike strands that facilitate the absorption of water and nutrients

Question 30

Mycorrhizae – Benefits to the fungus

Answer 30

• The plant furnishes sugars and amino acids without which the fungus cannot survive.

Question 31

Ectomycorrhizae

Answer 31

• For some mycorrhizae, the fungal
  hyphae penetrate the root cortex, but
  the hyphae do not enter the cells
• On the root surface, the hyphae form
  a thin, encrusting layer called mantle
• This type of mycorrhiza is termed
  ectotrophic
• Common in trees like pines and
  oaks

Question 32

Endomycorrhizae

Answer 32

• In another type of mycorrhiza, the hyphae invade the cells of the cortex, and a mantle is not present.
• This type of mycorrhiza is termed endotrophic.
• Found in the majority of woody and
  herbaceous land plants.

Question 33

Nature of the Association
Between Rhizobia and Legumes

Answer 33

• Symbiotic relationship, mutually
  beneficial.
• Plants provide energy for rhizobia
  (sugars, carbohydrates, ATP) to fix N2.
• Rhizobia in turn provide N for
  production of proteins by the host.

Question 34

Is Nitrogen (N) is an important nutrients?

Answer 34

Yes, it is in fact the most common nutrient in plant.