Root Structure and Function

Question 1

root function

Answer 1

• conduit of vascular cylinder (Stele): xylem/phloem
• absorption of water and nutrient minerals
• anchor plants
• water/food storage
• aide in asexual reproduction
• produce hormones and secondary metabolites, that regulate plant development and communication

Question 2

root systems

Answer 2

embryo radicle emerges immediately upon germination

radicle -> primary root -> secondary roots form

root systems can be fibrous or taproot

Question 3

root systems: fibrous

Answer 3

• found in monocots and some dicots
• made of large % fine roots of similar diameter
• adventitious roots form from stem or leaf
• lateral roots form from adventitious roots
• typically shallow, increased # root lead to improved water acquisition; not drought tolerant
• stabilize soil, decrease erosion

Question 4

monocot root

Answer 4

• a core of parenchyma cells (pith) is surrounded by rings of xylem and phloem
• pith cells arise from procambium and not ground meristem

Question 5

root systems: tap root

Answer 5

• found in dicots and gymnosperms
• thick tap root
• from tap root, thinner secondary roots (lateral roots) form
• dive deep into soil
• not as effective water absorption as fibrous root systems, but allow plants to survive under drought condiions
• in dicots, can be used for water/food storage

Question 6

dicot and conifer roots

Answer 6

• dicots and conifer gymnosperms have “arms” of xylem with phloem patches in between, no pith

Question 7

root specialization: water storage

Answer 7

• some members of pumpkin family Cucurbitaceae produce water storage roots
• help survive in arid environments
• roots function as water reserve

Question 8

root specialization: food storage

Answer 8

• many plants (root vegetables) store starch in roots: sweet potatoes, dandelions
• storage cells are increased number of parenchyma, formed by anomalous secondary growth

Question 9

external root structure

Answer 9

• lateral roots
• root hair
• root cap

Question 10

lateral roots

Answer 10

form from pericycle in region of root that has completed primary growth

Question 11

root hair

Answer 11

epidermal cell extensions; aide in water/nutrient absorption

Question 12

root cap

Answer 12

mass of parenchyma cells that cover each root tip
- protect tissues from damage as root grows, first cell layer has waxy cuticle
- secretes mucilage that aides in growth through soil and provides medium for beneficial bacteria
- amyloplasts in tip act as gravity sensors

Question 13

12 essential nutrient elements (minerals)

Answer 13

roots compete with negatively charged soil silicates (SiO4 -4) for minerals and water

macronutrients:
- primary: nitrogen, phosphorus, potassium
- intermediate: sulphur, calcium, magnesium

micronutrients:
- iron, zinc, manganese, molybdenum, copper, boron

Question 14

root hairs functions/characteristics

Answer 14

• adhere tightly to soil to compete for water/nutrients
• increase total surface area of absorption
• in growing roots, near root hairs are continuously formed with older root hairs dying off; root hairs always in zone of maturation near root cap

Question 15

root chemical protection

Answer 15

• woody gymnosperm roots have resin canals
• dicot taproots produce latex
• polyphenol flavonoids with anti-fungal, anti-viral, anti-microbial properties accumulate in root cell vacuoles

Question 16

root absorption

Answer 16

• to aide absorption, epidermal root hairs do not have a cuticle
• permeable to water, solutes, and potentially invasive microorganisms
• reduce %infection, roots impregnate key cell layers of cortex with suberin and lignin to restrict water/solute movement
• Casparian strips are deposits of lignin and suberin in radial primary cell wall and middle lamella of endodermis and exodermis

Question 17

casparian strips

Answer 17

deposits of lignin and suberin in the radial primary cell wall and middle lamella of endodermis and exodermis

Question 18

what plants have endodermis and exodermis?

Answer 18

all vascular plants have an endodermis, and almost all seed vascular plants have an exodermis

Question 19

endodermis and exodermis

Answer 19

• both part of root cortex and have casparian strips
• exodermis outermost cell layer of cortex
• endodermis innermost cell layer of cortex (layer above pericycle and vascular cylinder)
• passage cells of endodermis/exodermis lack casparian strips to allow passive transport of solutes into vascular cylinder; not always present

Question 20

Mycorrhizae mutualistic relationships

Answer 20

• > 75% vascular plant species have funal associations with roots, mycorrhizae essential for development
• mutualistic as both fungus and root benefit and are dependent
• fungi facilitate water/nutrient absorption, esp phosphorus
• root provides protection, sugars, and amino acids to fungus

Question 21

2 types of mutualistic fungi

Answer 21

ectomycorrhizae and endomycorrhizae

Question 22

ectomycorrhizae

Answer 22

• fungi remain on surface (epidermis), forming a mantle around the root
• plant: increase mineral absorption that accumulate in mantle coated root hairs
• fungi: solid substrate to grow on

Question 23

endomycorrhizae

Answer 23

• fungi penetrate root cortex (parenchyma cells)
• fungi form branching structures (arbuscules)
• plant: increased absorption of nutrients, esp phhosphorous
• fungi: food (carbohydrates) and protection

Question 24

bacterial root nodules

Answer 24

some species of bacteria (rhizobia) form association with legumes (Fabaceae)
- rhizobia have enzymes that convert (fix) N from atmosphere into plant usable formes (nitrates and ammonia)
- root nodules contain large numbers of nitrogen-fixing bacteria