Chapter 33: Stems and Plant Transport Chapter 34: Roots

1. Chapter 33: Stems and Plant TransportChapter 34: Roots

2. Stem functions • Support – leaves and reproductive parts • Photosynthesis/access to pollination • Internal transport • Produce new living tissue • Other jobs • Asexual reproduction • Photosynthesis • Store starch

3. Herbaceous dicot stems • Epidermis – protection, cuticle (cutin) • Cortex – inside epidermis, ground tissue • Parenchyma – photosynthesis / storage • Collenchyma + sclerenchyma - support • Vascular bundles – conduction, support • Circle arrangement • Xylem (inner), phloem (outer) • Vascular cambium btw. Xylem and phloem

4. Pith – center of stem • Large parenchyma – storage • Because of arrangement of vascular tissues in bundles, there is no distinct separation of cortex + pith between vascular bundles • Arrangement of parenchyma btw. Bundles = pith rays

5. Fig. 35-17a Phloem Xylem Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Key to labels Cortex Epidermis Dermal Vascular bundle Ground Vascular 1 mm (a) Cross section of stem with vascular bundles forming a ring (typical of eudicots)

6. Monocot stems • Epidermis – cuticle • Vascular bundles – scattered • Xylem (inside), phloem (outside) • Bundle sheath - sclerenchyma • No distinct cortex or pith • Ground tissue – same functions as dicot stem • No lateral meristems • Primary growth only, no wood/bark

7. Fig. 35-17b Ground tissue Epidermis Key to labels Vascular bundles Dermal Ground Vascular 1 mm (b) Cross section of stem with scattered vascular bundles (typical of monocots)

8. Woody dicot + conifer stems • Secondary growth – 2 lateral meristems (replace primary tissues) • Pith in center • Vascular cambium • Secondary xylem – wood • Secondary phloem – inner bark • Cork cambium • Cork cells + cork parenchyma • Periderm (outer bark) = cork cambium, cork cells and cork parenchyma • Replaces epidermis

9. Woody stems starts with same primary tissues in vascular bundles • Secondary growth = many changes • Vascular cambium becomes continuous ring • Produce cells inside (sec. xylem), outside (sec. phloem) • Primary tissues become separated from each other • Sec. tissues take over functions of primary tissues (vertical movement of substances)

10. Fig. 35-11 Primary growth in stems Epidermis Cortex Shoot tip (shoot apical meristem and young leaves) Primary phloem Primary xylem Pith Lateral meristems: Vascular cambium Secondary growth in stems Cork cambium Periderm Axillary bud meristem Cork cambium Cortex Primary phloem Pith Primary xylem Secondary phloem Root apical meristems Secondary xylem Vascular cambium

11. Fig. 35-19a3 Pith (a) Primary and secondary growth in a two-year-old stem Primary xylem Vascular cambium Epidermis Primary phloem Cortex Cortex Primary phloem Epidermis Vascular cambium Growth Vascular ray Primary xylem Secondary xylem Pith Secondary phloem First cork cambium Cork Periderm (mainly cork cambia and cork) Most recent cork cambium Cork Bark Secondary phloem Layers of periderm Secondary xylem

12. Lateral movement through rays = chains of parenchyma that radiate out from center of woody stem or root • Formed by vascular cambium

13. Cork cambium – makes periderm (replaces epidermis) • Continuous ring or series of overlapping arcs • Different cork cambia + rates of division  different bark types • Lenticels for gas exchange • New tissues in 2 directions • Outside – cork cells; dead at maturity; protection • Inside – cork parenchyma; store water/starch

14. Wood terms • Sapwood – functional sec. xylem • Heartwood – older wood, center • Hardwood – flowering plants • Softwood – conifers, lack fibers, vessel elements • Knot – embedded dead branch • Annuals rings – concentric circles in cross section • Temperate zone only – age (spring and summer growth) • Spring wood – more water, larger cells • Summer wood – less water, narrow cells

15. Fig. 35-19b Secondary phloem Bark Vascular cambium Cork cambium Late wood Secondary xylem Periderm Early wood Cork 0.5 mm Vascular ray Growth ring (b) Cross section of a three-year- old Tilia (linden) stem (LM) 0.5 mm

16. Fig. 35-22 Growth ring Vascular ray Heartwood Secondary xylem Sapwood Vascular cambium Secondary phloem Bark Layers of periderm

18. Internal Transport • Xylem • Roots only upward to stems, leaves, flower, fruits, seeds • Water and dissolved nutrient minerals • Phloem • Leaves to parts throughout plant • Downward or upward • Sugar in solution

19. Xylem transport – xylem sap • No energy • Path of water • Soil  root tissues  root xylem  stem xylem  leaf xylem  leaf mesophyll  atmosphere • 2 mechanisms for upward flow: • Root pressure • Tension (transpiration) – cohesion model

20. Root pressure • Water – osmosis – soil to root • More water = more pressure at root • Water is pushed upward

21. Tension (transpiration)) – cohesion Model • Water is pulled up plant by tension (caused by transpiration pull) • Water column can’t be broken • Cohesion = water-water (H bonds) • Adhesion = water-xylem cells (H bonds)

22. Phloem Transport – phloem sap • Glucose  sucrose (glucose + fructose) in solution • Pressure – Flow Mechanisms • Source (excess sugar)  sink (area of storage-roots, fruits, seeds, apical meristems) • Pressure gradient • Sugar in leaf mesophyllcompanion cell  sieve tube member by active transport (ATP) • Then  water moves from xylem to sieve tubes by osmosis  increases pressure

23. At sink – sugar unloaded from sieve tube • Water follows • Decrease in pressure

24. Ch. 34 Roots • Functions • Anchor • Absorb water + dissolved nutrient minerals (nitrates, phosphates, sulfates) • storage

25. Herbaceous Dicot roots • Epidermis – no cuticle, has root hairs  increase absorption • Cortex – loose parenchyma • Storage • Spaces – water path, aeration • Endodermis – inner layer of cortex; regulates movement of minerals into xylem

26. Stele – center or dicot root; central cylinder of vascular tissues • Pericycle – outermost layer of stele, just inside endodermis; makes lateral roots • Xylem – centermost of stele; “xylem arms” • Phloem – between xylem arms

27. Fig. 35-14a1 Epidermis Key to labels Cortex Dermal Ground Endodermis Vascular Vascular cylinder Pericycle Xylem 100 µm Phloem (a) Root with xylem and phloem in the center (typical of eudicots)

28. Fig. 35-14a2 (a) Root with xylem and phloem in the center (typical of eudicots) Endodermis Key to labels Pericycle Dermal Ground Vascular Xylem Phloem 50 µm

29. Fig. 35-15-3 Epidermis 100 µm Emerging lateral root Lateral root Cortex 3 2 1 Vascular cylinder