Primary vs Secondary growth Plant Form Function 2 Secondary Growth Primary growth increases length of stem axis new cells originate from meristems at tips of roots shoots Secondary growth increases width of stem or trunk new cells originate from vascular cambium Bio 1B Instructor Thomas Carlson 1 Monocot Stems Trunks 2 Eudicot Secondary Growth Majority of monocots do not have secondary growth Large palm trees e g coconut trees do not have true secondary growth but rather produce woody tissue from primary growth that make up the trunk Certain monocots e g Agavaceae family have a specialized type of secondary growth that is different than eudicot secondary growth Monocot secondary growth information will NOT be required for the exam The following slides on secondary growth refer to eudicots and not monocots 3 4 5 6 Meristems and Cell Production Annual vs Perennial Plants Apical Meristem Figs 35 11 35 12 35 13 35 16 Lab manual 4 1 4 2 Annual plant that goes through entire life cycle with flowering fruit production and death within one year Secondary growth does not occur in annual plants Perennial plant that lives multiple years and may have a below ground stem called a rhizome e g goldenseal or an above ground trunk and branches e g shrubs and trees 4 3 primary tissues increase length of shoot and root axis Vascular Cambium Lateral Meristem Figs 35 11 35 12 35 19 35 20 35 21 Lab manual 4 6 4 11 secondary tissues for wood production increase in girth width Cork Cambium Lateral Meristem Figs 35 19 35 22 Lab manual 4 5 4 6 4 9 4 10 4 11 secondary tissues for cork bark production increase in girth width 7 8 Secondary growth in young stems tissues from outer to center Fig 35 11 9 11 Periderm Cork cambium Ground tissue cortex Primary phloem Secondary phloem Vascular cambium Secondary xylem Primary xylem Ground tissue pith 10 12 Secondary Growth in Eudicots Figs 35 11 35 12 35 19 35 20 35 22 Lab manual 4 6 4 11 increases width girth of stem trunk feature of eudicots and gymnosperms occurs in both roots and stems new cells develop from vascular cambium 13 14 Vascular Cambium Development Figs 35 11 35 13 35 17 35 19 20 35 22 Lab manual 4 6 4 11 cambium develops from cells between primary xylem and primary phloem within bundles cambium also develops within parenchyma cells in regions between bundles these regions merge to form a continuous ring of cells that is one layer thick 15 16 17 18 Secondary Growth in Eudicots Figs 35 11 35 12 35 19 35 20 35 22 Lab manual 4 6 4 11 Bark Fig 35 18 35 21 35 23 tissue outside of vascular cambium made up of secondary phloem cork Vascular Cambium single layer of cells in ring in stem trunk secondary xylem formed to inside of cambium to produce wood secondary phloem forms to the outside of cambium Wood tissue inside of vascular cambium all cells internal to the vascular cambium are secondary xylem except for a small amount of primary xylem 20 19 Secondary growth in tree trunks tissues from outer to center Fig 35 11 35 19 35 22 Periderm Cork cambium Secondary phloem Vascular cambium Secondary xylem sapwood Secondary xylem heartwood 21 22 23 24 Phloem Cell Types Fig 35 10 35 11 35 14 35 17 20 35 22 Lab Man Fig 4 3 4 11 Contains sieve cells sieve tubes and companion cells Sieve tube member elongated food conducting plant cell with clusters of pores at both ends allowing sap to flow to adjacent cells Sieve tube members are stacked end to end to form sieve tubes Companion cell specialized cell found adjacent to sieve tube member 25 26 Phloem Transports Sugars Fig 35 10 35 11 35 14 35 17 20 35 22 Lab Man Fig 4 3 4 11 Plant vascular tissue that transports sugars from the photosynthetic leaves DOWN to other parts of the plant including the roots where sugars are converted into starch for storage In the early Spring in many tree species in northern latitudes the starch in the roots is broken down into sugars which are transported UP the tree in the phloem to the small branches to provide nutrients for developing leaves shoots 27 Most Typical Function of Phloem Phloem cells transports photosynthate in the form of sugar both up and down the tree 29 28 Functions of Xylem The main function of xylem is to transport water and minerals absorbed by the roots up the tree Some tall tree species e g redwoods Douglas firs are known to absorb water from fog through open stomata in leaves In these circumstances the movement of water in the xylem is downward in tree There are also examples where the xylem fluid transports sugars upward in the tree e g in the Spring in sugar maples when the starches stored in the roots are converted to sugars which are transported up the tree by xylem to provide food and energy for the developing buds and leaves 30 Xylem Transports Water Minerals Xylem Fig 35 10 35 11 35 14 35 17 20 35 22 Lab Man Fig 4 3 4 11 Fig 35 10 35 11 35 14 35 17 20 35 22 Lab Man Fig 4 3 4 11 Plant vascular tissue typically provides longitudinal transport of water minerals UP from roots plant vascular tissue provides longitudinal transport of water minerals up vertically from roots and in some species the water is transported from leaves down the tree tracheid vessel cell types dead at functional maturity provide structural support 31 Xylem Transport of Fluids Fig 35 10 35 11 35 14 35 17 20 35 22 Lab Man Fig 4 3 4 11 The main activity of the xylem is to transport water and minerals up the tree from the roots However in some species of trees e g the Sugar Maple Acer saccharum in eastern USA eastern Canada glucose can be transported upward in the xylem from the roots to the leaves and developing stems in the early Spring maple syrup is typically tapped in early Spring when the sap is moving upward from the roots to the developing leaves 33 Under conditions of high air humidity there are some tree species e g the coastal redwood and the Douglas fir that can absorb water from the air through stomata on the leaf surface and transport this fluid DOWN the tree in the xylem this is based on research done by Professor Todd Dawson in the Department of Integrative Biology at UC Berkeley 32 Brassinosteroid Hormones Support Growth of Xylem Tracheids Vessels 34 Xylem Cell Types Fig 35 10 35 11 35 14 35 17 20 35 22 Lab Man Fig 4 3 4 11 Tracheid Cells elongated water conducting cell that has gaps pits in its cell wall to allow water movement from one cell to the next pteridophytes gymnosperms and angiosperms 35 36 37 38 tcarlson berkeley edu 09 01 08 Xylem Cells Fig 35 10 35 11 35 14 35 …
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