shoots stems

plant bio

shoot function

• stem, leaves

• support- enable plants to increase height, length, SA

• conduction- conduct water, minerals, organic compounds

shoot apical meristem

• new cells produced by cell division adds cells to primary plant body

• results in a succession of repeated units called phytomeres

• surrounded by young leaves that fold over it & provide w/ protection

type 1

narrow interfascicular region- tissue region betw vascular bundles in stem

results in vascular cylinder- discrete pith/cortex

type 2

wide interfascicular regions surrounded vascular bundles - discrete pith/cortex

type 3

vascular bundle scatered throughout ground tissue in transverse section- no pith, only ground tissue

leaves

• simple: 1 blade per petiole

• compound: 2> leaflets attached to same petiole

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dicot leaf

blade- wide flat part

petiole- stalk part of leaves

monocot leaf

leaf blade

sheath: wraps around stem

epidermis

lack chloroplasts

secrete waxy layer, cuticle

have large # pores- stomates: water & gas exchange

tissues of leaves

• epidermis: provides structural support & retards water loss

• mesophyll: photosynthetic tissue of leaves

• xylem: conducts water & mineral

• phloem: conducts sugars

specialized cells

• trichomes: form hairs, functions- reflect sunlight, produce anti herbivory chems

• guard cells: each stomate surrounded by 2 guard cells- photosynthetic, control open/closing of stomate

• bulliform cells: in some grasses, control folding/opening of leaves

mesophyll

• betw upper & lower epidermis

• mesophyll cells are patenchyma cells: photosynthetic, chloroplasts

• monocots- mesophyll cells in similar shape

• dicots- mesophyll 2 layers, palisade, spongy

palisade layer

columnar shaped cells

photosynthetic activity takes place here

lots of gas exchange

upper layer

spongy layer

irregular shape

lower layers

sun & shade leaves

sun: thicker, double pallisade level, higher light intensities

shade: thinner, single level

adaptations for env extremes

xerophytes

hydrophytes

mesophytes

leaf abscission

-preceded by formation of abcission zone

-in woody flowering plants- abcission zone consists of 2 layers

-plant hormone ethylene promotes leaf abscission

-ab zone formed at base of leaf petiole