lecture 9: dermal and vascular tissue, plant growth: roots

Question 1

primary tissue types

Answer 1

◆ dermal tissues = covers and protects the plant
- epidermis
◆ vascular tissue = transports water, minerals, and sugars throughout the plant
- xylem, phloem
◆ ground tissue = anything not dermal or vascular
- parenchyma, collenchyma, slerenchyma
- can serve as the site of photosynthesis, provide the supporting matrix for the vasular tissue, and help store water + sugars

Question 2

dermal tissue (epidermis, trichomes, root hairs)

Answer 2

epidermis:
◆ the layer of tightly packed cells that forms the outermost tissue of all plant organs
◆ protects the plant from all enivonrment insults
◆ leaf and stem epidermal cells coated in a waxy cuticle that helps prevent desiccation
◆ pavement cells, guard cells
◆ trichomes
- hairlike growths
- function in defense, thermoregulation, reflection, evaporation
◆ root hairs
- increase SA for absorption of water and minerals

Question 3

vascular tissue (xylem [tracheids, vessel elements], phloem [sieve tube)

Answer 3

xylem:
◆ conducts water and minerals upward from the roots to the rest of the plant
◆ tracheids
- relatively narrow
- dead when functional
- open interiors and lignified cell walls
- no openings at end –> water moves laterally by pits where tracheid cells are in contact
◆ vessel elements
- also open, dead cells with lignified cell walls, wide
- open end to end, allowing free water movement

phloem:
◆ consisting of living cells that transports sugars and other organic nutrients to the rest of plant
◆ sieve tube elements
- connect end to end
- ends are not totally open (sieve plates / pores)
◆ companion cells
- paired non-conducting cells connected to sieve-tube elements
- channels called plasmodesmata pass sugars, nutrients, and large molecules to keep sieve-tube elements alive
- allows phloem to be living without having cellular organelles

Question 4

ground tissue (parenchyma, collenchyma, scelerenchyma [scelereids, fibers])

Answer 4

parenchyma:
◆ alive at maturity, simple cell walls
◆ performs diverse functions like photosynthesis, starch storage, water movement, differentiation

collenchyma:
◆ alive at maturity, colla = “glue”
◆ similar to above but thicker cell walls, particularly at the corners
◆ often parallel to the stem surface
◆ function to provide structural support

sclerenchyma:
◆ scleros = “hard”
◆ have lignin embedded in very thick cell walls
◆ function in support, especially in protection
◆ may be alive or dead
◆ scelereids
- small w/ thick walls
- often found in fruit walls like nut shells or in seed coats
- e.g., grit of a pear
◆ fibers
- eloongated and found in bunches
- function in structural support

Question 5

root development in eudicots: taproot, lateral roots

Answer 5

taproot:
◆ main vertical root, and the first root to grow
◆ in eudicots
◆ important component of root development/growth

lateral root:
◆ secondary branches
◆ arise from meristem

Question 6

root development in monocots: fibrous roots

Answer 6

◆ primary root dies, shallow network of fibrous roots establishes with new roots
◆ these roots come off the stem and where no one branch predominates

Question 7

root anatomy (root cap)

Answer 7

terminal structure that first encounters obstacles
- protects the RAM
- secretes a slime called mucilage that allows growth through soil
- site of gravity perception

Question 8

root anatomy (zones)

Answer 8

zone of cell division:
- includes RAM and its immediate products

zone of cell elongation:
- cells can grow up to 10x initial length, pushing tip down further into soil

zone of differentiation:
- area where cells take on their distinct types, e.g., root hairs emerge

Question 9

cortex and endodermis

Answer 9

cortex: starch-storing parenchyma with intercellular spaces
- part of ground tissue

endodermis: one cell thick layer that creates a selective boundary with vasculature

Question 10

pericycle

Answer 10

Outer vascular layer surrounding the xylem and phloem

Question 11

Macronutrients

Answer 11

C, H, O → fixed as sugars by photosynthesis (H2O + CO2)
P, K, N, S, Ca, Mg → all come from the soil (1-4% dry weight)

Question 12

Micronutrients

Answer 12

• Required in small amounts, mostly as enzymatic co-factors
• Too much can be a bad thing
• Cl, Cu, Fe, Mn, Zn, Mo, B, Ni

Question 13

apoplast(ic route)

Answer 13

• associated w/ Routes of movement through roots
  def:
• Everything exterior to cell membranes
• Water, minerals, and other dissolved substances can move through cell walls and intercellular spaces of cortex
• Water and substances moving by the apoplast get blocked from entering the vasculature at the endodermis cell wall

Question 14

symplast(ic route)

Answer 14

• All the cytosol contained within cell membranes
• Cytosol of neighboring cells connected by channels called plasmodesmata, which pass through cell membranes and walls
• Water and substances moving by the symplast can pass by plasmodesmata through the endodermis to the living cells of the vasculature

Question 15

transmembrane route

Answer 15

• Substances can pass between routes while still in the cortex via the plasma membrane
• This is a filter, as the plasma membrane is selectively permeable