Overview
This lecture covers the major types of plant tissues, their structure, functions, and significance in plant growth and survival.
Introduction to Plant Tissues
- Plant tissues are groups of cells that perform specific functions within a plant.
- They enable growth, development, and survival, much like organs in animals.
Types of Plant Tissues
- There are two main categories: meristematic tissue and permanent tissue.
- Meristematic tissues consist of undifferentiated, actively dividing cells responsible for growth.
- Permanent tissues are mature, specialized, and usually lose the ability to divide.
Meristematic Tissue
- Apical meristems are located at the tips of roots and shoots and drive primary growth (length).
- Lateral meristems, such as vascular cambium and cork cambium, are found along stems and roots, enabling secondary growth (girth).
- Meristematic cells continuously divide by mitosis, producing new cells for the plant.
Permanent Tissue
- Simple permanent tissues contain one cell type: parenchyma, collenchyma, or sclerenchyma.
- Complex permanent tissues (xylem and phloem) contain multiple types of cells and enable transport.
Tissue Systems
- There are three main systems: dermal, ground, and vascular tissue systems.
- Dermal tissue includes the epidermis, cuticle, stomata, trichomes, and root hairs for protection and gas exchange.
- Ground tissue makes up most of the plant body, including parenchyma (storage, photosynthesis), collenchyma (flexible support), and sclerenchyma (rigid support).
- Vascular tissue consists of xylem (water/mineral transport) and phloem (sugar/organic compound transport).
Vascular Tissue: Xylem and Phloem
- Xylem cells (tracheids, vessel elements, fibers) are mainly dead and provide water/mineral transport and support.
- Phloem cells (sieve tubes, companion cells, fibers) are alive and transport sugars bidirectionally.
- Vascular bundles' arrangement differs between monocots (scattered) and dicots (ring).
- Secondary growth from the vascular cambium produces annual growth rings.
Adaptations
- Plants adapt tissue structure to their environment (e.g., thick cuticles in desert plants, air channels in aquatic plants).
- Specialized features like trichomes, root hairs, and storage tissues enhance survival.
Key Terms & Definitions
- Meristematic tissue — tissue with actively dividing cells for growth.
- Permanent tissue — mature cells with specialized functions.
- Parenchyma — versatile plant cells for storage, photosynthesis, and repair.
- Collenchyma — flexible supportive cells in young stems and leaves.
- Sclerenchyma — rigid supportive cells with thick lignin walls.
- Xylem — vascular tissue transporting water and minerals upward.
- Phloem — vascular tissue transporting sugars and nutrients.
- Epidermis — outermost cell layer providing protection.
- Cuticle — waxy layer preventing water loss.
- Stomata — pores for gas exchange.
- Trichomes — hair-like structures for protection and water retention.
Action Items / Next Steps
- Review diagrams of plant tissue structures and tissue systems.
- Compare functions and locations of xylem vs. phloem.
- Prepare examples of plant adaptations related to tissue structure for discussion.