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Plants Structure and Growth

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  1. PlantsStructure and Growth

  2. Fruit • an organ that contains seeds, protecting these as they develop and often aiding in their dispersal. • derived from ovaries, and other flower parts. • Ovary walls thicken to form pericarp • Can be composed of up to 3 layers • Exocarp • Mesocarp • Endocarp

  3. Types of Fruit • Simple fruits – form from a simple ovary of a single carpel, or from a compound ovary of several fused carpels • Dry fruits • Achenes – close fitting pericarp around single seed • Sunflowers • Grains – pericarp is fused to a single seed • Wheat, corn • Nuts - thick woody pericarp fused to a single seed • Walnuts, hazelnuts, acorns • Legumes - Pod that splits along two opposite sides • Beans, peas, peanuts

  4. Types of Fruit cont’d • Simple fruits – cont’d • Fleshy Fruits – mesocarp forms flesh • Drupes – 1 or 2 seeds, stony endocarp • Plum, peach • Berries – 1 to many seeds, no stony endocarp • Tomatoes,, grapes, all citrus

  5. Types of Fruit cont’d • Compound/Aggregate Fruits • Develop from several individual ovaries of one flower • Raspberries • Strawberries...the inside is not actually fruit, but flesh formed from the receptacle • Multiple fruits • Formed from the fusion of many carpels belonging to separate flowers • pineapple

  6. Fruit Structure and Function Fig 10.8

  7. Seeds and Young Shoots • Germination occurs when conditions are favorable • Need: water, warmth, and oxygen • Many seeds remain dormant until certain conditions are met • Inhibitors prevent germination, stimulators trigger it • High moisture levels, period of cold weather, fire etc...

  8. Seeds and Young Shoots • Initial leaves to appear are the cotyledons • In dicots the cotyledons provide initial nutrition in monocots endosperm fills this role • First root to appear is the radical.

  9. Fig. 10.9and 10.10

  10. Plants Structure • All plant tissue develops from meristems • Specialized regions where cell division occurs • Apical Meristems are responsible for increased length • Root Apical Meristem (RAM) • Shoot Apical Meristem (SAM) • Protoderm develops epidermal tissue • Ground Meristem produces ground tissue • Procambrium develops vascular tissue

  11. Fig. 9.11b

  12. Epidermal Tissue • Surrounds entire body of herbaceous and young woody plants • “Bark” develops after first year of growth • Bark is only a small portion of the new outer layer called periderm • Closely packed cells, designed to protect, and minimize water loss.

  13. Epidermal Tissue – cont`d Fig. 9.4a • Specialized epidermal cells: • Root Hairs – Long projections from epidermal cells to increase surface area • Trichomes – hairs on stems, leaves and reproductive organs to protect against moisture loss • Guard Cells – surround microscopic holes on underside of leaves, able to open and close for gas exchange.

  14. Ground Tissue • Forms the bulk of the plant • 3 main cell types • Parenchyma • Most abundant, look like ‘typical’ plant cell • Least specialized, often contain plastids that store products of photosynthesis.

  15. Ground Tissue cont’d • Collenchyma • Thickened cell wall, provide flexible support • Strands in celery • Sclerenchyma • Have thick secondary cell walls, mostly non-living, provide support and structure • Fibres – hemp, flax • Sclerids – stones in peaches, grittyness of pears.

  16. Ground Tissue cont’d

  17. Vascular Tissue • Located in • Vascular cylindar in roots • Vascular bundles in stems • Veins in leaves • Two primary tissues • Xylem and Phloem

  18. Vascular Tissue • Xylem • Water and minerals from roots to leaves • Two cell types, both non-living at maturity • Tracheids , Vessel elements Fig 9.6

  19. Vascular Tissue • Phloem • Sugar and other organic compounds, including - hormones, usually from leaves to roots • Two cell types • Sieve tube members – have holes between to form continuous tube, no nucleus • Companion cells have nucleus, controls and maintains life of both cells. Fig 9.7

  20. Leaves • Photosynthetic organs of plants • Structure generally a flattened blade and a petiole that attaches to stem • Simple leaves – single blade • Compound leaves – many blades on one petiole • Adaptations • Shade plants – broader leaves, darker in colour • Xerophytes – no moisture, small needle-like leaves • Tendrils to attach to objects • Catch insects

  21. Leaf StructureFig 9.8

  22. Leaf Structure • Cuticle (upper and lower) • Waxy layer prevents moisture loss • Epidermis (upper and lower) • Outer layer of cells, provides structural support, generally no chloroplasts

  23. LeafStructure cont’d • PallisadeMesophyll • Brick like cells, stacked on end • Primary site of photosynthesis • Spongy Mesophyll • Irregular cells, Loosely packed, lots of air space • Promotes gas exchange • Veins are held within this layer • Veins • Vascular tissue surrounded by bundle sheath cells

  24. Leaf Structure cont’d • Stomata • lower epidermis, regulates gas exchange and water levels • Opening surrounded on each side by two large guard cells. • Water levels control opening and closing • absorb water  swell  stomata opens. • lose water  relax  stomata close • During the heat of the day, water levels decrease, stoma stay closed • Helps to decrease water loss • At night, water levels are able to rise, stoma open allowing leaves to • release excess water, exchange Carbon Dioxide and Oxygen.

  25. Fig 9. 23