Plant Form

Plant Form Chapter 36 Plant Body Organization A vascular plant consists of: 1. Root system, which is underground -Anchors the plant, and is used to absorb water and minerals 2. Shoot system, which is above ground -Consists of supporting stems, photosynthetic leaves and reproductive flowers Each has an apex that extends growth Roots, shoots and leaves contain three basic tissue systems: -Dermal tissue – For protection (Wax and bark) -Ground tissue – For storage, photosynthesis and secretion -Vascular tissue – For conduction -Xylem – Water and dissolved minerals -Phloem – Nutrient-containing solution 2 Plant cell walls consist of cellulose -Primary cell wall -Found in all cells -Cellulose fibers parallel to microtubules -Secondary cell wall -Found in some cells -Additional layers of cellulose and lignin -Increase mechanical strength of wall Plant Cells 3 Plant Stem Cells Meristems are clumps of small cells with dense cytoplasm and large nuclei They act as stem cells do in animals -One cell divides producing a differentiating cell and another that remains meristematic 4 Apical meristems are located at the tips of stems and roots -Give rise to primary tissues which are collectively called the primary plant body The Primary Plant Body -Three primary meristems (that come from apical meristem) -Protoderm  Epidermis -Procambium  1o vascular tissue -Ground meristem  Ground tissue 5 Secondary Plant Body (increases girth) Lateral meristems are found in plants that exhibit secondary growth -Give rise to secondary tissues which are collectively called the secondary plant body -Woody plants have two types -Cork cambium  Outer bark -Vascular cambium  2o vascular tissue 6 Plant Tissues As mentioned earlier, plants contain three main types of tissue -Dermal -Ground -Vascular 7 *Forms the epidermis, which is usually one cell layer thick & is outer protective covering *Covered with a fatty cutin layer constituting the cuticle (prevents water loss) *Contains special cells, including guard cells, trichomes and root hairs Guard cells are paired sausage-shaped cells -Flank a stoma, which is the passageway for oxygen and carbon dioxide...and is the epidermal opening between 2 guard cells Dermal Tissue 8 Dermal Special Cells Continued Trichomes are cellular or multicellular hairlike outgrowths of the epidermis -Keep leaf surfaces cool and reduce evaporation by covering stomatal openings -Some are glandular, secreting substances that deter herbivory 9 Dermal Special Cells Continued Roots hairs are tubular extensions of individual epidermal cells in growing roots -Greatly increase the root’s surface area and efficiency of absorption...of water and minerals 10 Ground Tissue A tissue that functions in food, water storage, photosynthesis and secretion...Consist of 3 types of cells Collenchyma cells - support for organs, bend but don’t break Parenchyma cells - most common plant cell -storage,photosynthesis,secretion -chloroplasts-chlorenchyma Sclerenchyma cells - tough thick walls...usually have Secondary cell walls with lignin (polymer seen in 11 wood) Xylem -Constitutes the main water-and mineral-conducting tissue... Water goes in a stream from roots to shoots and out of the leaves via transpiration -Vessels: Continuous tubes of dead cylindrical cells arranged end-to-end -Tracheids: Dead cells that taper at the end and overlap one another -Vessels are shorter & wider than tracheids -And conduct water more efficiently Vascular Tissue 12 Vascular Tissue Xylem -Also conducts inorganic ions such as nitrates, and supports the plant body -Typically includes parenchyma cells in horizontal rows called rays -Function in lateral conduction and food storage Note: The diffusion of water vapor from a plant is termed transpiration 13 Phloem -Constitutes the main food-conducting tissue in vascular plants -Contains an elongated living cell with no nuclei called sieve tube members -Associated with companion cells nourishes sieve tube member cells Phloem transports sucrose, hormones, and amino acids Plants synthesize Amino Acids from Carbon and Oxygen obtained from air, Hydrogen from water in the soil. They form Carbon Hydrate via photosynthesis and combine it with Nitrogen obtained from the soil, leading to synthesis of amino acids Vascular Tissue 14 Roots Root cap -Contains two types of cells that are formed continuously by the root apical meristem -Columella cells: Inner -Root cap cells: Outer and lateral -Functions mainly in protection of the delicate tissues behind it -Also in the perception of gravity...columella cells have amyloplasts (plastids with starch grain) that collect on the side nearest the source of gravity...roots bend in that direction 15 Roots Zone of cell division -Contains mostly cuboidal cells, with small vacuoles and large central nuclei -Derived from rapid divisions of the root apical meristem -Quiescent center cells divide very infrequently -Apical meristem daughter cells soon subdivide into the three primary tissues Zone of elongation -Roots lengthen because cells become several times longer than wide 16 Cross Section of the Zone of Maturation Zone of maturation -The elongated cells become differentiated into specific cell types -Epidermal cells: Have very thin cuticle -Include root hair and nonhair cells -Cortex: Interior to the epidermis -Parenchyma cells used for storage Casparian strip (made of suberin) forces water through plasma membrane...membrane itself acts as a water filter 17 Modified Roots Prop roots Keep plant upright Aerial roots Obtain water from air Pneumatophores Oxygen uptake Water storage roots Weigh over 60 pounds Buttress roots Stability 18 Stems Like roots, stems contain the three types of plant tissue -Also undergo growth from cell division in apical and lateral stems Shoot apical meristem initiates stem tissue and intermittently produces primordia -Develop into leaves, other shoots and even flowers 19 Stems Leaves may be arranged in one of three ways 20 External Stem Structure 21 External Stem Structure Node = Point of attachment of leaf to stem Internode = Area of stem between two nodes Blade = Flattened part of leaf Petiole = Stalk of leaf Axil = Angle between petiole/blade and stem Axillary bud = Develops into branches with leaves or may form flowers Terminal bud = Extends the shoot system during the growing season 22 Internal Stem Structure Vascular tissue arrangement is directly related to the stem’s ability for secondary growth -In eudicots, a vascular cambium develops between the primary xylem and phloem -In monocots, there is no vascular cambium -Therefore, no secondary growth 23 Bulbous Underground stem with fleshy leaves Modified Stems Underground stems Grow along ground Swollen tip of rhizome Used for climbing Resemble leaves 24 Leaves Leaves are the main site of photosynthesis -They are determinate structures whose growth stops at maturity A leaf-blade has veins which consist of xylem and phloem -Microphyll Leaves= Have one vein -Megaphylls Leaves = Have many veins (most plants) -Monocot leaves have parallel veins -Eudicot leaves have netted or reticulate veins 25 Leaves Simple – undivided blades Pinnate - paired leaflets Palmate - center axis of leaflets 26 Basic Leaf Histology Epidermis has a waxy cuticle -The lower epidermis contains numerous mouth-shaped stomata flanked by guard cells The mesophyll is the tissue between the upper and lower epidermis 27