Plant Cells and Their Characteristics

Plant Cells

• Plant cells are eukaryotic, possessing a nucleus.
• They differ from prokaryotic cells, which lack a nucleus.
• Plant cells are characterized by membrane-bound organelles and a cell wall.
• Plant cells range from 10 to 100 micrometers in size.
• The higher the surface-to-volume ratio, the more efficient is the exchange of materials.
• Plant cell size impacts cellular communication efficiency.

Key Vocabulary

• Cell Wall: The rigid outer boundary surrounding the cell.
• Organelles: Membrane-bound structures within the cell.
• Plasma Membrane: The semi-permeable outer boundary of the cell.
• Cytoplasm: The fluid within the cell, containing organelles.
• Nucleus: The control center of the cell, containing DNA.
• Ribosomes: Structures involved in protein synthesis.

Eukaryotic vs Prokaryotic

• Eukaryotic cells contain a nucleus, while prokaryotic cells do not.
• Plant cells are eukaryotic.
• Animal cells are eukaryotic.
• Plant cells have a cell wall; animal cells do not.

Cell Components

• Plasma Membrane: The semi-permeable barrier, regulating the movement of substances.
• Composed of a phospholipid bilayer with proteins.
• Cytoplasm: Includes the cytosol and organelles.
• Nucleus: The control center, housing DNA, enclosed by a nuclear envelope with selective pores.
• Ribosomes: Involved in protein synthesis, found in various locations (rough ER, cytoplasm).

Plant Cell Components

• Cell Wall: Primarily composed of cellulose, providing structural support.
• Middle Lamella: Shared between adjacent cell walls.
• Plasmodesmata: Cytoplasmic strands enabling communication between adjacent cells.

Endoplasmic Reticulum (ER)

• Network of membranes, involved in synthesizing membranes and modifying proteins.
• Rough ER: Associated with protein synthesis (ribosomes).
• Smooth ER: Involved in lipid secretion.

Dictyosomes (Golgi Bodies)

• Modify carbohydrates and assemble polysaccharides.
• Package substances into vesicles.
• Vesicles may contain cell wall compounds or floral nectars.

Plastids

• Chloroplasts: Sites of photosynthesis, containing thylakoids and stroma.
• Contain pigments like carotenoids or starches.

Mitochondria

• Known as the "powerhouses" of the cell.
• Release energy from cellular respiration.
• Inner membrane forms cristae, increasing enzyme surface area.

Microbodies

• Specialized enzymes for processes like photorespiration.
• Maintain cell shape and facilitate movement with microtubules and microfilaments

Vacuoles

• Large organelles in plant cells (can occupy up to 90%).
• Store various substances.
• Regulate internal pressure.
• Contribute to pH maintenance.

Plant Cells vs Animal Cells

• Plant cells have cell walls and plastids, which animal cells lack.
• Animal cells have different division methods.
• Plant cells have unique components.

Plant Tissues

• Meristematic tissues: Responsible for plant growth and cell division.

  • Apical Meristems: Growth in length.
  • Lateral Meristems: Secondary growth (increase in girth).
  • Intercalary Meristems: Elongation (especially in grasses).

• Dermal Tissue: Protective layer.

  • Epidermis: Outermost layer.
  • Cuticle: Protective waxy layer.
  • Periderm: In woody plants, replaces epidermis.

• Ground Tissue: Fills spaces between dermal and vascular tissues.

  • Parenchyma Tissue: Living cells, often with large vacuoles.
  • Aerenchyma: Air spaces in aquatic plants.
  • Chlorenchyma: Photosynthesis.
  • Transfer Cells: Absorption and transport.
  • Collenchyma Tissue: Flexible support.

• Vascular Tissue: Transports substances throughout the plant.

  • Xylem Tissue: Transports water and minerals.
  • Vessels: Long tubes transporting water.
  • Tracheids: Transporting water and support.
  • Ray Parenchyma: Conducts water and stores food.
  • Phloem Tissue: Transports food produced by photosynthesis.
    • Sieve Tube Elements: Transporting food.
    • Companion Cells: Support sieve tube elements.
    • Phloem Fibers & Parenchyma: Provide support.

• Secretory Tissue: Produce and transport various substances to other parts of the plant.

  • Flower Nectar: Attracts pollinators
  • Citrus Oils: Flavor and aroma
  • Mucilage: Aids in water retention and seed germination
  • Latex: Defence against herbivores
  • Resins: Protection against pathogens

Root Modifications

• Food Storage Roots: Store starch and carbohydrates.
• Water Storage Roots: Store water in arid regions.
• Pneumatophores: Help aquatic plants obtain oxygen.
• Aerial Roots: Support climbing plants.
• Contractile Roots: Pull plants deeper into the soil.
• Buttress Roots: Provide stability to tropical trees.
• Mycorrhizae: Mutualistic associations enhancing nutrient and water uptake
• Root Nodules: Nitrogen-fixing bacteria.

Root Regions

• Root Cap: Protects the growing tip.
• Region of Cell Division: Responsible for new cell production (apical meristem).
  • Protoderm: Forms epidermis.
  • Ground Meristem: Forms cortex and pith.
  • Procambium: Develops into primary xylem & phloem
• Region of Elongation: Cell elongation for penetration into the soil.
• Region of Maturation: Cells mature into specialized cells, often developing root hairs.
• Internal Root Structure: Epidermis, cortex, endodermis, vascular cylinder, pericycle.