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Plant Structure & Growth. Chapter 35 35.1 & 35.2. Key differences between Monocots & Dicots. Dicots: Parts in 4’s or 5’s. Monocot: Parts in 3’s. Monocot vs. dicot flowers: left is spiderwort, a monocot; right is phlox. a dicot. .
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Plant Structure & Growth Chapter 35 35.1 & 35.2
Dicots: Parts in 4’s or 5’s Monocot: Parts in 3’s Monocot vs. dicot flowers: left is spiderwort, a monocot; right is phlox. a dicot.
Be able to draw and label a plan diagram showing the distribution of tissues in the stem & leaf of a dicotyledonous plant! Figure 35.17 Phloem Xylem Sclerenchyma(fiber cells) Ground tissue Ground tissueconnectingpith to cortex Pith Epidermis Keyto labels Epidermis Cortex Vascularbundles Vascularbundle Dermal 1 mm 1 mm Ground (b) (a) Cross section of stem withvascular bundles forming aring (typical of eudicots) Cross section of stem withscattered vascular bundles(typical of monocots) Vascular
Tissue Plan Diagram: Dicotyledon Stem A tissue plan diagram is simply a map of where the different types of tissue can be found. You don’t need to Draw each cell!
Figure 35.18 Guard cells Keyto labels Stomatalpore Dermal Ground Epidermalcell 50 m Vascular Sclerenchymafibers (b) Surface view ofa spiderwort(Tradescantia)leaf (LM) Cuticle Stoma Upperepidermis Palisademesophyll Spongymesophyll Bundle-sheathcell Lowerepidermis 100 m Xylem Cuticle Vein Guard cells Phloem Guardcells Air spaces Vein (c) Cross section of a lilac(Syringa) leaf (LM) (a) Cutaway drawing of leaf tissues
Storage/support tissue • Parenchyma (figure 25.5 page 442) • Thin walled • Stores food and water • In leaves, parenchyma contain the chloroplasts • Potato is mostly parenchyma Why thin walled and large spaces?
B. Collenchyma • Thicker cell walls • Primarily provide support • The stuff in celery that gets stuck in your teeth.
C. Sclerenchyma • Very thick walls • Only for support • Surrounds the veins of leaves, stems and roots
Relationship between distribution of tissues in a leaf & functions • Functions & Tissues: • Absorption of light: • Gas exchange: • Support: • Water conservation: • Transport of water & photosynthesis products • Xylem: • Phloem: • Both are in the spongy mesophyll Parenchyma cells in Mesophyll Stomata in the epidermis Collenchyma Cells in upper epidermis Stomata & guard cells conducts water & dissolved minerals • Transports sugars (products of photosyn.)
Functions of Roots, Stems, & Leaves • Basic function of roots: • Support & water update • Basic function of stems • Support & transport • Basic function leaves: • Gas exchange & photosynthesis
Interesting plant adaptations of roots, stems, & leaves • Can you name some?
Interesting plant adaptations of roots, stems, & leaves • Bulbs – collections of thick leaf bases (vertical underground shoots) that store food. Storage leaves Stem
Interesting plant adaptations of roots, stems, & leaves • Stem Tubers – enlarged ends of rhizomes or stolons specialized for storing food. Tubers
Interesting plant adaptations of roots, stems, & leaves • Storage Roots – food & water storage site. Storage Roots
Interesting plant adaptations of roots, stems, & leaves • Tendrils – modified leaves or stems that provide support. Tendrils
Growth Tissues • Plants only grow at the meristems. • Apical meristems – growth in length of roots & shoots • Where are they located? • What are they? • Located in tips of roots & shoots • Extra cells that enable growth in length (primary growth)
Apical bud Figure 35.12 Bud scale Axillary buds This year’s growth(one year old) Leafscar Node Budscar One-year-old sidebranch formedfrom axillary budnear shoot tip Internode Last year’s growth(two year old) Leaf scar Stem Bud scar Growth of twoyears ago(three years old) Leaf scar
Growth Tissues • Lateral meristems - Growth in thickness (secondary growth) by vascular & cork cambium • Cylinders of dividing cells extending along the length of roots and stems. • Vascular cambium - adds layers of secondary xylem (wood) & secondary phloem. These are the tree rings we see in cut longs. • Cork cambium – replaces epidermis with thicker tougher periderm. We call this bark.
Figure 35.11 Primary growth in stems Epidermis Cortex Primary phloem Shoot tip (shootapical meristemand young leaves) Primary xylem Pith Vascular cambium Secondary growth in stems Lateralmeristems Corkcambium Cork cambium Axillary budmeristem Cortex Periderm Primary phloem Secondary phloem Pith Root apicalmeristems Primaryxylem Vascular cambium Secondary xylem
Tropisms & Control of Plant Growth • Plant responses to directional external stimuli. • Plant responses can be either positive (toward stimuli) or negative (away from stimuli). • Phototropism is an example of positive stimuli – the plant will grow toward the light.
Tropisms lengthening cells. • Auxins promote growth by? • Auxins are produced in the coleoptile, a protective sheath around the emerging root or shoot. • Normally auxin is evenly distributed around the shoot causing vertical growth. Indole-3-acetic acid (IAA) is the most common, naturally-occurring, plant hormone of the auxin class.
Tropisms • If photoreceptors in the coleoptile detect a light stimulus from one direction, auxin is moved to the opposite direction of the growing shoot. • Uneven distribution of auxin caused increased bending toward the light.
