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Plant Body Organization

• A vascular plant consists of two main systems:

  • Root system

    • Located underground

    • Anchors the plant

    • Absorbs water and minerals

  • Shoot system

    • Located above ground

    • Composed of supporting stems, photosynthetic leaves, and reproductive flowers

    • Each system has an apex that extends growth

Structural Components of Plants

Shoot System Components

• Key components include:

  • Shoot apex

  • Flower

  • Stipule

  • Tendrils

  • Axillary buds

  • Leaves

  • Internodes

  • Nodes

    • Points where leaves attach to the stem

  • Veins in leaves (xylem and phloem arrangements)

Root System Components

• Key components include:

  • Primary root

  • Lateral roots

  • Root apex

Plant Cell Walls

• Composed primarily of cellulose:

  • Primary cell wall

    • Present in all plant cells

    • Cellulose fibers arranged parallel to microtubules

  • Secondary cell wall

    • Formed in some cells

    • Additional layers of cellulose and lignin for increased strength

Plant Tissue Systems

• Roots, shoots, and leaves contain three basic tissue systems:

  • Dermal tissue

    • Functions for protection (e.g. wax and bark)

  • Ground tissue

    • Functions for storage, photosynthesis, and secretion

  • Vascular tissue

    • Key for conduction, includes xylem and phloem

      • Xylem: Transports water and dissolved minerals

      • Phloem: Transports nutrient-containing solutions

Meristems

• Clumps of small cells with dense cytoplasm and large nuclei, acting as stem cells:

  • One cell divides producing a differentiating cell and one that remains meristematic

Types of Meristems

1. Apical meristems

• Located at tips of stems and roots, leading to primary tissue development

• Produce following primary meristems:

  • Protoderm -> Epidermis

  • Procambium -> Primary vascular tissue

  • Ground meristem -> Ground tissue

2. Lateral meristems

• Found in plants undergoing secondary growth

• Produce secondary tissues, leading to a secondary plant body

  • Types in woody plants:

    • Cork cambium -> Forms the outer bark

    • Vascular cambium -> Forms secondary vascular tissue

Distinction of Root Structure

• Roots display simpler organization than stems, typically with four regions:

  1. Root cap: Protects the root

  2. Zone of cell division: Contains rapidly dividing meristematic cells

  3. Zone of elongation: Cells lengthen, contributing to root growth

  4. Zone of maturation: Differentiation into specific cell types (epidermis, cortex, endodermis)

Endodermis and Casparian Strip

• The endodermis forms an inner boundary of the cortex

  • Contains Casparian strips that control water/mineral absorption into the vascular system

Plant Tissues Summary

Types of Tissues

• Plants have three main tissue types:

  1. Dermal tissue:

     • Forms epidermis, usually one cell layer thick, with a waxy cuticle and specialized cells such as guard cells and trichomes

  2. Ground tissue:

     • Composed of parenchyma (storage, photosynthesis), collenchyma (support), sclerenchyma (strength)

  3. Vascular tissue:

     • Comprised of xylem (water/minerals conduction) and phloem (food conduction)

Modified Roots

• Plants can develop modified roots for various functions:

  • Taproot system: A large primary root with smaller branches

  • Fibrous root system: Many thin roots of similar size

  • Adventitious roots: Arise from unusual places

  • Examples include prop roots, aerial roots, pneumatophores, and storage roots

Stems

• Like roots, stems consist of three tissue types and undergo growth via apical and lateral meristems:

  • The shoot apical meristem produces stem tissue and drives growth

External and Internal Structure

• Leaves can be arranged alternately, oppositely, or whorled

• Internal vascular bundles differ between monocots (scattered) and eudicots (arranged in a ring)

Leaves

• The main site for photosynthesis with various vein arrangements based on plant type

• Leaf structures include a waxy epidermis, stomata for gas exchange, and a mesophyll composed of palisade and spongy cells

Modified Leaves

• Can serve various purposes, including reproduction or adaptation to specific environments (e.g., insect-trapping, reducing water loss).