Dr.A+-+Lecture+2-+%5Bcells%5D

I. Introduction

  • Growth, differentiation, and development of vascular plants.

II. Basic Morphology of Vascular Plants

  • Preparation for lab sessions.

Structures in Vascular Plants

  • Flower: Reproductive structure that produces seeds.

  • Terminal Bud: Shoot apex responsible for vertical growth.

  • Petiole: Stem attachment for the leaf blade.

  • Blade: Main part of the leaf.

  • Axillary Bud: Potential growth point at leaf attachment.

  • Internode: Space between nodes on stems.

  • Root Systems: Primary and lateral roots anchor the plant.

III. Plant Cell Basics

  • Differences from animal cells:

    • Cell walls, central vacuole, chloroplasts.

Cell Structures

  • Cell Wall: Provides structure and protection.

  • Central Vacuole: Maintains cell turgor, storage, and waste disposal.

  • Chloroplasts: Photosynthesis organelles.

General Definitions

  • Cytoplasm: Aqueous solution containing organelles.

  • Cytosol: Aqueous part of the cytoplasm.

  • Protoplast: Plasma membrane and contents.

  • Apoplast: Everything outside the plasma membrane.

IV. Cell Growth and Differentiation

  • Cell Cycle: Includes G-zero and terminal differentiation.

  • Cells can exit the cycle and re-enter in response to stimuli.

Cell Growth Processes

  1. Cell Division: Mitotic process leading to new cells.

  2. Cell Expansion: Increase in cell size following division.

  3. Cell Differentiation: Development of specific functions and structures.

V. Growth Zones in Plants

Zones of Growth

  • Division Zone: Area with meristematic cells that divide.

  • Elongation Zone: Cells expand and begin vacuole formation.

  • Differentiation Zone: Cells mature and differentiate into specific cell types.

Cell Appearances in Growth Stages

  1. Meristematic Cells: Small, dense, undifferentiated; akin to stem cells.

  2. Expanding Cells: Development of central vacuole, early differentiation.

  3. Differentiating Cells: Fully formed vacuole, establishing specialized types.

VI. Cell Wall Structure and Composition

Components of Cell Walls

  • Cellulose: Provides rigidity and strength through microfibril assembly.

  • Hemicellulose: Branching polysaccharides that link cellulose fibers.

  • Pectin: Gelling agent, adds flexibility to walls.

  • Proteins and Water: Modify properties and maintain plasticity.

Types of Cell Walls

  1. Primary Cell Walls: Flexible, found in all growing cells.

  2. Secondary Cell Walls: Thicker, formed post-expansion, mechanistically stronger due to lignin.

VII. Cell Wall Growth and Formation

New Cell Wall Creation

  • Formed during cytokinesis, expanding to contact parental wall.

Wall Growth Specialization

  • Cellulose Synthase: Enzymes that move along the plasma membrane, coordinate with microtubules.

VIII. Plasmodesmata

  • Function: Holes in cell walls facilitating intercellular communication.

  • Form a symplasmic network for nutrient and signal exchange.

IX. Secondary Wall Formation

  • Characteristics: Provides mechanical strength via lignin integration and adjustable microfibril orientation.

  • Lignin: Imparts hydrophobicity and increases structural support, especially in xylem tissue.

X. Primary vs. Secondary Cell Walls

Primary Cell Walls

  • Thin, flexible, and hydrophilic; present in all cells during growth.

Secondary Cell Walls

  • Thicker, more rigid, lignin present; significant in certain cell types post-expansion.