Plant Tissues and Organs: Structure and Function

Posted on Mar 12, 2025 in Forestry Engineering

1. Meristematic Tissue

MeriStar: Primary Meristem

Responsible for plant growth. Growth in length occurs in the terminal buds of the stem and root.

MeriStar Side: Secondary Meristem

Growth in thickness, arising from the first year of life. Two types:

  • Cambium: Internal, causes the conducting vessels.
  • Phellogen: External, originates suber or cork.

2. Adult Tissue

ECJ. Parenchymatous Tissue

Forms the major part of the plant; it is a tissue filler. Four types:

  • Parenchyma Chlorophyll: Cells have chlorophyll, enabling photosynthesis. Two types: Parenchyma Laguna (round) and Parenchyma Lattice (elongated).
  • Reserve Parenchyma: Stores substances (starch, fat, etc.).
  • Parenchyma Acuífero: Stores water (e.g., xerophytic cactus plants).
  • Parenchyma Aerífero: Stores air (e.g., aquatic plants).

ECJ. Supporting Tissue

Provides rigidity and strength.

  • Collenchyma: Formed by living cells, giving strength to growing parts.
  • Sclerenchyma: Formed by dead cells; their walls are thickened by lignin, providing resistance to parts that do not grow. Examples: fibers (long) and stone cells or scleroids (hard, found in fruit and peel).

ECJ. Conducting or Vascular Tissue

Transports sap from root to leaves and vice versa. Two types:

  • Woody Tissue or Xylem: Conducts crude sap from the root to the leaves. Elongated cells are arranged to form tubes. These are dead cells that circulate the crude sap; they have a substance called lignin that forms rings and hardens, these tubes are called tracheas or tracheids.
  • Liberian Tissue or Phloem: Conducts elaborated sap from the leaves throughout the plant. Sieve tubes consist of sieve cells, which are living cells without nuclei. The survival of these cells depends on the accompanying cells. The sieve cells are separated by sieve plates, which are walls with holes. In winter, a polysaccharide called callose obstructs these holes. In spring, the callose is reabsorbed, and sap circulation resumes.

ECJ. Protective Tissue

Protects the plant, located on the outside.

  • Epidermal Tissue: Living cells joined together without spaces. The outer layer is covered with a cuticle (+ cutin waxes) to waterproof the plant. The epidermis may have stomata for transpiration.
  • Suberous Tissue or Cork: Replaces the epidermis after a year. Covered with dead cells of a waterproofing substance called suberin. Has numerous holes (lenticels) that allow air into the plant.

ECJ. Secretory Tissue

Structures that secrete various substances, which may be waste or useful. Secretions include:

  • Flower nectar (sugary products of glandular hairs)
  • Gums and resins (from epidermal glands)
  • Scents (incense and myrrh)
  • Latex (milky, typical in the fig and from lactiferous pipes)
  • Scent on the skin of some fruits

3. Plant Organs

1. Root

(Primary structure in first-year plants) (Patterns: phloem, xylem, parenchyma cell, epidermis, endodermis, central parenchyma)