12.3 stems

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12.3 Stems. Pages 552-557. Canadian Economy. The forest sector’s contribution to the Canadian economy (GDP) was $23.5 billion, or 1.9 percent, in 2010. In 2010, Canada was the world’s second-largest forest product exporter (10.2 percent). Functions of Stems. Connect roots to leaves - PowerPoint PPT Presentation


12.3 Stems

12.3 StemsPages 552-557Canadian EconomyThe forest sectors contribution to the Canadian economy (GDP) was $23.5 billion, or 1.9 percent, in 2010.In 2010, Canada was the worlds second-largest forest product exporter (10.2 percent).

Functions of StemsConnect roots to leavesRaise leaves to the sun and flowers to pollinatorsStore water or carbohydratesPhotosynthesisProtectionTypes of stemsHerbaceous-do not contain wood

Vascular bundleLong continuous strand of vascular tissue (xylem and phloem)Herbaceous StemsEudicotMonocot

DifferenceIn monocots the vascular bundles are found throughout the ground tissue of the stem.In eudicots the vascular bundles are found in a ring around the stem.Eudicot-herbaceousXylem is closer to the centre and phloem is closer to the outside of the stem

Woody stemsContain wood and barkAll gymnosperms Most woody angiosperms are eudicotsMonocots do not produce wood

Cross-section of woody stem

Vascular cambiumWoody stems contain vascular cambium meristematic tissue.Divides to form new xylem tissue on the inside and new phloem tissue on the outside.WoodSapwood-young xylem transports water and mineralsHeartwood-cells fill up with resins and oils -provide rigidity and supportTypical Woody Stem

BarkTissues found outside the vascular cambium (phloem, cork cambium, and cork)Cork cambium-meristematic tissue produces cork

BarkProtects the tree from predators and firesGrowth ringsSpringrapid growth, large xylem cells, thin walls, lighter in colourSummerslow growth, smaller xylem cells, thick walls, darker in colour

Xylem cellsThick-walledDead at maturityCell walls with lignin for strengthTracheidsTracheids-long cylindrical cell with tapered ends with pits, holes that allow water to move to adjoining cells

Vessel ElementsShorter, wider, less taperedSides have pitsEnds have perforation plates

Phloem-living at maturity-contain cytoplasmTypes of phloemSieve cellsSieve tube elementsCompanion cellsPhloemSieve cells- pores, organelles Sieve tube elements have cytoplasm but lack a nucleus, ends are called sieve platesCompanion cells have nucleus and organelles associated with sieve tube element


Table 1. Xylem and phloem in gymnosperms and angiospermsPlant GroupXylem tissue cell typesPhloem tissue cell typesGymnosperms

TracheidsSieve cellsAngiosperms

TracheidsVessel elementsSieve tube elementsCompanion cellsUnderground StemsTubersCormsRhizomes

StolonsGrow along the soilFor example: strawberries, mint