9'4 Roots, Stems, Leaves

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9.4 - Roots, Stems, Leaves
Lithops fulviceps
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I. Plant Tissue Groups

• A. Ground Tissues
• Three Main Types of Cells (can also be associated
  with other tissues)
• 1. Parenchyma
• Generally unspecialized
• Thin walls
• Lots of functions (storage, photosynthesis, etc)
• 2. Collenchyma
• Thick yet flexible walls
• Primarily for support of new plant parts

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I. Plant Tissue Groups

• A. Ground Tissue (cont.)
• 3. Sclerenchyma
• Thicker than collenchyma
• Support
• Secondary wall with lignin
• May be dead
• B. Dermal Tissue
• Contains epidermis, guard cells, and specialized
  surface tissues (e.g. root hairs)
• Dermal tissue excretes cuticle

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I. Plant Tissue Groups

• C. Vascular Tissue
• Xylem and Phloem
• Occur in vascular bundles (including sclerenchyma
  cells)
• 1. Xylem
• Conduct water and minerals up plant
• Secondary cell wall provides strength
• Normally dead
• Two types of cells
• Tracheids - water passes through pits in
  secondary wall
• Vessel elements - holes go through both primary
  and secondary walls

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Xylem Structure
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I. Plant Tissue Groups

• C. Vascular Tissue (cont.)
• 2. Phloem
• Normally alive (still contains cytoplasm)
• Made up of sieve tubes (connected by sieve plates)

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II. Plant Growth Overview

• A. Life span
• Annual - born, live and love, die all in one year
  (whew!)
• Biennial - Two years
• Perennial - Just keep on livin

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II. Plant Growth Overview

• B. Meristems
• 1. Apical Meristem
• At tips
• Responsible for primary growth
• Growth through elongation
• 2. Lateral Meristems
• Lateral growth (makes you wider)
• Produces secondary growth
• Secondary tissue are thicker/tougher
• Wood is secondary xylem, bark is secondary dermal
  tissue

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III. Roots

• A. Organization
• Root cap protects the apical meristem
• Zone of cell division is where the apical
  meristem resides
• Zone of maturation forms root hairs
• Zone of elongation makes new root
• B. Cortex
• Main part of root
• Stores water, minerals, and starch

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III. Roots

• C. Endodermis
• Ring of cells that separate cortex from vascular
  tissue (or stele)
• Innermost layer of cortex
• D. Vascular Cylinder (Stele)
• Inside the endodermis
• Organization is different in monocots and dicots

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Root Structure
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IV. Stems

• Similar to roots, but lack an endodermis and
• A. Epidermis
• Cells secrete cuticle, do not make hairs
• B. Cortex
• More evenly distributed
• C. Vascular Bundles
• More spread out than the roots
• In dicots, vascular bundles are organized in ring
  (pith inside of the ring)
• In monocots, vascular bundles are randomly
  distributed

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Stem Structure (Primary)
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IV. Stems

• D. Secondary Growth
• Vascular cambium (lateral meristem) forms between
  xylem and phloem
• Form the wood of woody plants
• Growth goes both ways from cambium
• Outer part of cambium becomes bark (along with
  phloem)
• See why we can tap a maple tree for sugar

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Stem Structure (Secondary Growth)
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V. Leaves

• A. Epidermis
• Protective covering
• Make cuticle
• prevents transpiration
• Made of waxes and cutin
• Provide protection from microorganisms
• Lower epidermis has guard cells which surround
  stomata
• B. Palisades Layer
• Part of mesophyll
• Made up mostly of tightly packed parenchyma cells
  that undergo photosynthesis
• More pronounced in dicots

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V. Leaves

• C. Spongy Layer
• Made of loosely packed parenchyma cells
• Area of gas exchange
• D. Vascular Bundles
• Contain xylem and phloem
• Surrounded by bundle sheath cells
• Bundle sheath cells prevent gas bubble from
  blocking vascular tissue

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Leaf Structure
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Monocots Vs. Dicots