Lecture 1- Plant Anatomy

Plant Anatomy

Lecture Overview

  • Lecture 1, covering Chapter 35, Sections 1-3.

Tissue Systems in Plants

  • Three Main Tissue Systems in Plants:

    • Meristematic Tissue

    • Dermal Tissue (Epidermis)

    • Ground Tissue

    • Vascular Tissue

Cross Sections of Plant Tissues

  • Cross Sections Identify:

    • Epidermal Tissue

    • Ground Tissue

    • Vascular Tissue

Epidermal Tissue System

  • Epidermis

    • Also known as the dermal tissue system, it is the outer protective layer of a plant.

    • Key Components of the Epidermis:

    • Epidermal Cells: Basic unit of epidermis.

    • Stoma: Pore structures that regulate gas exchange.

    • Cuticle: A waxy layer covering the epidermis, reducing water loss.

Specialized Structures in the Epidermis

  • Trichomes:

    • Hair-like structures on the epidermis that can affect light penetration and prevent herbivory.

    • Size example: 200 μm in length.

  • Stomata:

    • Located in the epidermis, essential for regulating gas exchange (CO2 and water vapor).

    • Composed of Guard Cells that open and close the stomatal pore, regulating the exchange of gases.

    • Associated cells include:

    • Subsidiary Cells: Support guard cells.

    • Mesophyll Cells: Involved in photosynthesis.

    • Generates air spaces for gas exchange.

  • Root Hairs:

    • Extensions of epidermal cells that enhance water and nutrient absorption in roots.

Ground Tissue System

  • Functions of Ground Tissue:

    • Storage, photosynthesis, and structural support.

  • Cortex:

    • Located in the root, part of the ground tissue.

Vascular Tissue System

  • Composed of two main types:

    • Xylem:

    • Transport water and minerals.

    • Includes:

      • Tracheids: Spindle-shaped cells with pits for water transport.

      • Vessel Elements: Short, wide cells that have perforations for efficient water transport.

    • Phloem:

    • Transport sugars and nutrients.

    • Composed of:

      • Sieve-tube Members: Conduct sugars through sieve plates.

      • Companion Cells: Support sieve-tube members and are involved in transporting substances.

Plant Cell Anatomy

  • All plant cells have primary cell walls made of cellulose.

  • Secondary Cell Walls:

    • Present in some specialized cells provide additional strength.

    • Important for cells with lignified secondary walls, contributing to structural integrity.

Types of Plant Cells

  • Parenchyma:

    • Living cells with thin cell walls.

    • Functions:

    • Roots: Storage of carbohydrates.

    • Leaves: Photosynthesis and gas exchange (50 μm).

  • Collenchyma:

    • Living cells with irregular thickened cell walls.

    • Provides support and flexibility; often found in young stems and petioles (50 μm).

  • Sclerenchyma:

    • Composed of dead cells with very thick cell walls, providing structural support.

    • Includes:

    • Sclereids: Short and varied shapes. (10 μm)

    • Fibers: Long, slender, and provide tensile strength (10 μm).

Vascular Anatomy in Stems and Roots

  • Tissue Systems in Stems:

    • Epidermis, Vascular Bundles, Ground Tissue (Cortex, Pith).

    • Monocots have scattered vascular bundles; Eudicots have circular arrangements.

  • Root Anatomy:

    • Key Components:

    • Epidermis with root hairs.

    • Cortex for storage.

    • The Vascular Cylinder houses xylem and phloem.

    • Casparian Strip: A band of cell wall material deposited in the cell walls of the endodermis, regulates the flow of water and nutrients.

  • Endodermis: Innermost layer of the cortex in roots, regulates what enters the vascular tissue.

Tissue Systems in Leaves

  • Components of the Leaf Tissues:

    • Dermal: Provides protection, contains cuticle, guard cells, and stomata.

    • Ground: Contains mesophyll cells (palisade and spongy), involved in photosynthesis.

    • Vascular Bundle: Includes xylem and phloem, essential for transport of water and nutrients.

    • Key Structural Features:

    • Cuticle: Wax layer minimizing water loss

    • Upper and Lower Epidermis: Contain guard cells and stomata.

    • Palisade Mesophyll: Dense layer where most photosynthesis occurs.

    • Spongy Mesophyll: Looser arrangement for gas exchange.

Conclusion

  • Understanding plant anatomy is essential for studying plant biology, physiology, and ecology. Tissue systems are fundamental in the structure and function of plants, contributing to their survival and adaptability in various environments.