Plant Tissue Types

Overview

Plants consist of various tissue types that serve specific roles. Organized groups of cells work together structurally and functionally.

Main Tissue Systems

Dermal Tissue System

• Outer covering of the plant (protection).

• Interacts with the environment (light, gas exchange).

Ground Tissue System

• Responsible for photosynthesis, storage, and support.

• Occupies space between dermal and vascular tissues.

Vascular Tissue System

• Conducts water and solutes throughout the plant.

• Comprises xylem (water transport) and phloem (nutrient transport).

Dermal Tissue System

Acts as the skin layer of all plant organs. Functions include:

• Light passage

• Gas exchange

• Pathogen recognition

• Color display

Components of Dermal Tissue

• Guard Cells: Regulate the opening and closing of stomata.

• Stomata: Pores involved in gas exchange.

• Root Epidermal Cells: Enhance water absorption through root hairs.

Ground Tissue Systems

Occupies space between dermal and vascular tissues. Functions:

• Photosynthesis: Carried out in the mesophyll of leaves.

• Sugar and Starch Storage: Found mainly in roots.

Types of Ground Tissue

• Parenchyma: Alive at maturity, performs photosynthesis, and aids in healing. Thin primary cell walls; retains capacity to divide.

• Collenchyma: Provides support and flexibility. Unevenly thickened primary cell walls, found in young stems.

• Sclerenchyma: Function when dead, provides rigid support. Thickened secondary cell walls; may form fibers or sclerids (e.g., grit in pears).

Vascular Tissue Systems

Responsible for transporting food and water.

Components of Vascular Tissue

• Xylem: Conducts water and dissolved minerals. Supports plant structure. Contains tracheids and vessel members.

• Phloem: Conducts food and organic substances. Contains companion cells and sieve-tube elements.

Plant Cell Types

• Simple tissues are composed of one cell type.

• Complex tissues consist of multiple cell types.

Parenchyma Cells

• Alive when mature; most common cell type in young plants. Thin-walled; often have large central vacuoles.

Collenchyma Cells

• Support and flexibility; have thickened walls at corners. Usually elongated in shape, found in petioles and herbaceous stems.

Sclerenchyma Cells

• Dead at maturity; provide structural support. Thickened cell and secondary walls; includes fibers and sclerids.

Special Cork Tissue

• Cork Cambium: Produces cork.

• Cork contains suberin (a waterproofing fatty lipid). Forms the outer bark of the plant as epidermis dies and falls away. Some unsuberized tissue forms lenticels for gas exchange in bark.