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
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