Plant Structure and Growth Chapter 35

I) Plant Body A) controlled by 1) genes: they determine what structures will form 2) Environment: can alter gene expression depending on what is needed

B) Basic Organs 1) Roots: * anchor * absorb minerals and water

a) fibrous roots: a1) found on monocots a2) spread out right under soil * good coverage for absorption * helps hold soil in place

b) Tapoot: Found on most dicots b1) long with branches for absorption b2) good anchor b3) stores food

c) adventitious roots c1) roots that come from leaves or stem c) adventitious roots c1) roots that come from leaves or stem * help support plant

2) The shoot system: stems and leaves a) Stem: a1) supports leaves at nodes * axillary bud: site on node where a branch can form

a2) terminal bud: top of stem where growth for height occurs a2) terminal bud: top of stem where growth for height occurs * this inhibits growth at axillary buds(apical dominance). If removed more branches will form

b) leaves: main site of photosynthesis b1) blade = leaf b2) petiole: attaches blade to stem

b3) monocot leaves: veins run parallel b4) dicot leaves: veins are branched

C) Plant Tissues: dermal, vascular, and ground 1) dermal(epidermis): layer of cells that protects the plant a) cells will have different structure depending on what it is covering a1) ex: cuticle/waxy covering

2) Vascular tissue: transports material through plant a) xylem: carry water and minerals a1) tracheids * long, tapered, with pits for water transfer

a2) vessel elements: short, wide, perforated ends a2) vessel elements: short, wide, perforated ends * water flows directly from one to another * string together to form vessels

b) Phloem: carry sugar and minerals b1) cells called sieve-tube members(stm’s) * holes at end of tubes form sieve plate * alive, but don’t have nucleus, ribosomes, etc.

b2) companion cell: live attached to stm’s b2) companion cell: live attached to stm’s * connected to stm’s by plasmodesmata (specialized openings between cells) * provide proteins to stm’s

3) Ground tissue a)all other tissue not vascular or epidermal a1) dicot stem: pith is inside of the vascular tissue, cortex is outside of it.

D) Tissues made up of three cell types 1) Parenchyma: Have thin, flexible primary walls, no secondary walls. a) do most metabolism of the plant a1) photosynthesis, starch storage

2) Collenchyma: thicker primary walls, they help support young parts of the plant. a) continue to elongate as the plant grows.

3) Sclerenchyma: Thick primary and secondary walls 3) Sclerenchyma: Thick primary and secondary walls. Secondary wall has lignin for extra strength.

a) dead at maturity, but formed as a helix so they stretch as the plant grows

II) Plant Growth * annuals: complete life cycle in one year then die * biennial: two years * perennial: grows year after year, completing many flowering cycles

A) Meristems 1) embryonic tissue where growth can occur

a) apical meristem a1) tips of buds and roots for elongation a) apical meristem a1) tips of buds and roots for elongation * elongation is called primary growth

b) lateral meristem: tissue inside the stems and roots of a woody plant that makes the plant thicker. b1) vascular cambium adds xylem and phloem b2) cork cambium adds cork

B) Root Growth 1) root cap a) protects root as it pushes through soil a1) secretes a polysaccharide that helps it slide through the soil

2) Zone of Cell Division a1) high concentration of mitotically dividing cells a2) quiescent center – resistant to damage to replace apical meristem if damaged

a3) procambium forms vascular tissue a4) protoderm turns into dermis a5) ground meristem forms ground tissue

3) Zone of Elongation a) cells elongate to push the root down through the soil

4) Zone of maturation a) area of final differnetiation

5) Stele – tube of xylem and phloem running through center of root a) pericycle: outermost cells that can create a lateral root

6) cortex: starch storage

7) Endodermis: ring of cells between the stele and the cortex a) casparian strip: ring of fat around each cell that forces water through the cells to the stele so water cant leak back to the cortex

C) Stems 1) vascular bundles: groupings of xylem and phloem that run the length of the stem.

D) Leaves 1) Stomata: opening in the leaf for gas exchange 2) opening is controlled by guard cells

3) mesophyll a) all tissue in between upper and lower epidermis

b) palisade payer: main layer of photosynthesis c) spongy mesophyll: cells surrounding veins inleaf and stomata. Have air spaces between them.

III) Secondary growth A) Stems 1) Vascular cambium a) produce xylem and phloem in woody plants a1) phloem to the outside, xylem to the inside

a2) annual rings. xylem grows larger in spring/summer than fall/winter a2) annual rings * xylem grows larger in spring/summer than fall/winter *Vascular growth animation

2) Cork cambium a) replaces/thickens epidermis a1) outermost layer is cork, with suberin added a2) inner layer is phelloderm a3) together they are called periderm

3) Bark: layers of cork, cork cambium, and living phloem

4) sapwood a) active xylem

5) heartwood a) dead xylem used for support *plant growth review