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Plants Structure and Growth. 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.
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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
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
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
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
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...
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.
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
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.
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.
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.
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.
Vascular Tissue • Located in • Vascular cylindar in roots • Vascular bundles in stems • Veins in leaves • Two primary tissues • Xylem and Phloem
Vascular Tissue • Xylem • Water and minerals from roots to leaves • Two cell types, both non-living at maturity • Tracheids , Vessel elements Fig 9.6
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
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
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
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
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.
