meristems - determines how the plant body develops after germination

• acts like stem cells in animals
• divides >> 1 meristematic cell, 1 cell able to differentiate
• apical meristems - elongates roots/shoots
  • located at tips of stems/roots, behind root cap
  • produces primary growth, primary tissues (xylem/phloem)
  • constantly divides >> adds cells to tips of plant body >> size lengthens
  • root cap cells, epicotyl/hypocotyls protect root/shoot meristems
  • primary meristems - protoderm (epidermis), procambium (vascular tissues), ground meristem (ground tissue)
• lateral meristems - peripheral cylinders of meristematic tissue, increases girth
  • produces secondary growth (sometimes not found in herbaceous, fleshy plants)
  • secondary growth >> treelike plants
  • 2 lateral meristems in woody plants - cork cambium (produces cork in outer bark), vascular cambium (produces secondary vascular tissue, between xylem/phloem)
  • secondary tissues - secondary xylem (main wood component), secondary phloem (near outer surface)

plant body organization - 4 types

• root system - anchors the plant, penetrates soil to absorb water/nutrients
• shoot system - stems for positioning leaves (site for photosynthesis)
  • produces flowers, fruits, seeds
  • axillary buds - apical meristems that replaces the main shoot when it gets eaten
• dermal tissue - epidermis covered by fatty cutin layer in young plants, bark in plants w/ secondary growth
• ground tissue - consists of mainly parenchyma cells (storage, photosynthesis, secretion)
• vascular tissue - xylem (transfers water/minerals), phloem (transfers carbohydrates, nutrients)

dermal tissue - epidermal cells, from the protoderm

• guard cells - cell pairs around a stoma (epidermal opening)
  • contain chloroplasts
  • stomata mostly on lower epidermis >> minimizes water loss
  • forms due to asymmetrical cell division
• trichomes - hairlike growths from epidermis
  • keeps leaf surfaces cool, reduces evaporation
  • can secrete toxic substances to deter herbivores
• root hairs - tubular extensions of epidermal cells
  • increases root surface area >> higher absorption efficiency

ground tissue - from ground meristem

• parenchyma cells - large vacuoles, thin walls
  • most common type of plant cell
  • have only primary walls
  • used to store food/water
  • can remain alive for over 100 years even after fully maturing
  • chlorenchyma - parenchyma cells w/ chloroplasts
  • aerenchyma - loose parenchyma cells, stores O2
• collenchyma cells - provides mechanical support for plant organs
  • lets plant bend w/o breaking
  • forms continuous cylinders beneath leaf petioles (stalks)
• sclerenchyma cells - have lignin in secondary cell walls
  • in leaf veins/stems, seed coverings
  • strengthens tissues
  • fibers - long/slender cells grouped in strands
  • sclereids - branched shape

vascular tissue - xylem (inside) / phloem (outside)

• water mov’t - gravity/atmospheric pressure moves water down
  • capillary action can’t move water more than 1 meter
  • tensile strength - tendency for water molecules to stick together
  • water evaporates at the top >> pulls adjacent molecules up
  • osmotic potential in roots + atmospheric pressure + negative pressure in stomata >> transpiration
• xylem - main water-conducting plant tissue
  • combination of vessels elements (formed from dead/hollow cylindrical cells) and tracheids (overlapping dead cells)
  • vessels conduct water better than tracheids (favored by natural selection)
  • transpiration - diffusion of water vapor from plant
  • primary xylem - from procambium
  • secondary xylem - from vascular cambium
• phloem - found near outer part of roots/stems
  • main food-conducting plant tissue (moves food slower than xylem moves water)
  • girdled (removing strips of bark) >> takes away phloem >> plant dies from starvation
  • sieve cells - found in seedless vascular plants, gymnosperms
  • sieve-tube members - found in angiosperms
  • sieve areas - clusters of pores, connects protoplasts in adjoining cells
  • sieve plates - larger sieve areas in sieve-tube members
  • sieve tubes - series of sieve-tube members connected end to end; no nucleus, mitochondria, chloroplasts
  • companion cell - adjacent specialized parenchyma cell associated w/ each sieve-tube member; supplies the sieve tubes w/ nutrients
  • plasmodesmata - cytoplasmic connections between adjacent cells