Three Organs of a Plant

roots, shoots, and leaves

Roots

• anchors the vascular plant
• absorbs minerals and water, usually in root tips
• often stores organic nutrients
• gymnosperms and eudicots:taproots with lateral roots
• seedless vascular and monocots: fibrous root system
• many plants have modified roots: adventitious roots arise above ground from stems and even leaves. 

Stems (shoot system)

• Nodes-point of leaf attachment
• Internodes-segments between nodes
• Axillary buds- can form new shoots or branches
• Terminal buds can lead to apical dominance (grow up)
• Modified Shoots

Plant Organs Diagram

Leaves

• main photosynthetic organ-but stems can dominate too
• blade and petiole-base of leaf that forms sheath around leaf (monocots don't have petioles)
• simple vs. compound leaf

Plant Cell Types

• Dermal
  • Cuticle-waxy coating to preserve water
  • Guard Cells
  • Trichomes-appendages on roots facilitate absorption
• Ground
  • Parenchyma-photosynthesis and metabolism
  • Collenchyma-support
  • Sclerenchyma-storage, support, protection
• Vascular
  • Xylem-water and nutrients from roots
  • Phloem-sugars from leaves

• Alive at maturity 
• No secondary Walls
• Site of most plant metabolism
• Play a role in wound generation

Collenchyma Cells

• Alive at maturity
• No secondary second walls or lignin
• Flexible support

Xylem

• dead at maturity
  • tracheids
    • long & thin w/ tapered ends
    • lignin for structural support
    • less specialized than vessel elements
  • vessel elements
    • wider, shorter, less tapered 
    • have perforations for more efficient water flow

Phloem

• Sieve tube members
  • barely alive at maturity
  • lack nucleus, ribosomes, organelles
• served by nucleus of adjacent companion cells
  • connected by plasmodesmata

Meristem

a region of apical cell division that allows the plant to grow rapidly

Apical meristems-lengthen the plant (primary growth)

Lateral meristems-thicken the plant w/ bark and wood (secondary growth) Arise from the pericycle

Apical Meristem

produces three primary meristems: procambium, ground meristem, and protoderm

which develop into three tissue systems

Lateral Meristem

arise from pericycle

• interior vascular cambium
  • fusiform initials make cells elongated vertically form 2nd xylem &phloem
  • ray initials make cells elongated horizontally:transfer water, nutrients
• external cork cambium:meristem for tough covering, replaces epidermis
  • Rays maintain connectivity between 2nd xylem and phloem. Exchange water & nutrients, stores starch

Summary of primary/secondary growth in a stem