Overview
This lecture covers plant tissues, their types, how to identify them, their functions, and structural features relevant for exams.
Types of Plant Tissues
- Plant tissues are classified as meristematic (responsible for growth) or permanent (long-term function).
- Meristematic tissue is temporary and transforms into permanent tissue.
- Permanent tissues include parenchyma, collenchyma, sclerenchyma, and vascular tissues (xylem and phloem).
Meristematic Tissue
- Meristems are regions where plant growth occurs and cells differentiate.
- Apical meristems (at root and shoot tips) cause primary (length) growth.
- Lateral meristems (in the stem’s cambium) cause secondary (width) growth, producing thicker stems and bark.
Epidermal Tissue
- The epidermis forms the protective outer layer of plants.
- The cuticle (waxy, transparent layer) prevents water loss and allows light penetration.
- Specialized epidermal cells include stomata (pores for gas exchange, controlled by guard cells) and root hair cells (increase surface area for water/nutrient absorption).
Ground Tissues
Parenchyma
- Parenchyma cells have thin walls and intercellular airspaces; they provide storage, sponginess, and allow gaseous exchange.
- Chlorenchyma is parenchyma with chloroplasts for photosynthesis.
Collenchyma
- Collenchyma has unevenly thickened cell corners, providing flexible support and strength to young, green stems.
- Contain cellulose and pectin in thickened walls and may have chloroplasts.
Sclerenchyma
- Sclerenchyma has evenly thickened cell walls; provides rigidity and strength.
- Divided into fibers (in wood/bark) and sclereids (in nuts/stone fruit shells).
- Sclerenchyma cells are dead at maturity.
Vascular Tissues
Xylem
- Xylem transports water and minerals one way (roots to shoots).
- Consists of elongated, dead cells with thick lignified walls and large lumens.
- Contains pits for lateral water movement.
- Comes in vessel elements (cylindrical, end-to-end) and tracheids (spindle-shaped, overlapped).
Phloem
- Phloem transports sugars bidirectionally.
- Made of living sieve tube elements (stacked end-to-end) with sieve plates (filtering function).
- Companion cells provide metabolic support for sieve tubes.
Key Terms & Definitions
- Meristematic tissue — plant tissue responsible for growth and cell differentiation.
- Apical meristem — at root/shoot tip; causes lengthening.
- Lateral meristem — in cambium; causes thickening.
- Epidermis — protective plant outer layer.
- Cuticle — waxy, transparent layer reducing water loss.
- Stomata — small pores for gas exchange.
- Parenchyma — living cells for storage/gas exchange; thin walls, airspaces.
- Chlorenchyma — parenchyma with chloroplasts.
- Collenchyma — flexible, supportive cells with unevenly thickened walls.
- Sclerenchyma — rigid, dead support cells with thick, even walls.
- Xylem — vascular tissue transporting water/minerals up.
- Phloem — vascular tissue transporting sugars both ways.
- Sieve plate — porous end wall between phloem cells.
- Companion cell — supports phloem sieve tubes.
Action Items / Next Steps
- Study and practice drawing diagrams of plant tissues and label their parts.
- Review functions and identification features of each tissue for exams.
- Prepare for further lessons on plant organs.