Plant Tissues and Their Functions
Introduction to Plant Organization
Organisms are structured hierarchically:
Cells form the basic units of life.
Tissues are groups of similar cells working together to perform specific functions.
Organs are composed of multiple tissues integrated to perform broader functions (e.g., leaves, stems, roots).
Plant Tissues: Overview
Meristems are specialized regions in plants where cell division is concentrated.
These regions are responsible for initiating growth and the subsequent differentiation of cells into various tissues.
Plants possess four primary tissue types:
Meristematic tissue
Ground tissue
Dermal tissue
Vascular tissue
Meristematic Tissue
Functional roles:
Responsible for the division of new cells, facilitating new growth (primary and secondary).
Also plays a crucial role in the repair of damaged plant parts.
Locations:
Apical meristem: Found at the tips of shoots (shoot apex) and roots (root apex or apices).
The shoot apex is visible in a longitudinal section of a shoot tip.
The root apex contains the apical meristem of the root, often protected by a rootcap.
Differentiation is the process by which cells produced by meristems mature and specialize into specific cell types and tissues.
Ground Tissue
Functional roles:
Storage: Stores water, nutrients, and carbohydrates.
Processing: Involved in metabolic processes such as photosynthesis.
Physical support: Provides structural integrity to the plant.
Locations (examples):
Makes up the bulk of the plant body, surrounding vascular tissues.
In stems, it includes the cortex (region outside the vascular bundles) and pith (central region of the stem).
Visible in longitudinal sections of the root apex, located between the dermal and vascular tissues.
Dermal Tissue
Functional roles:
Protection: Forms the outer protective layer of the plant, safeguarding against physical damage, pathogens, and water loss.
Nutrient absorption: In roots, dermal tissue (epidermis) is primarily responsible for absorbing water and minerals from the soil.
Location:
Epidermis: The outermost layer of cells covering leaves, stems, and roots.
Visible as the outermost layer in both root and shoot structures.
Vascular Tissue
Functional roles:
Movement of fluids/food: Responsible for the long-distance transport of water, minerals, and sugars throughout the plant.
Physical support: Also contributes to the structural support of the plant body.
Components:
Xylem: Primarily responsible for the transport of water and dissolved minerals from the roots to the rest of the plant.
Phloem: Primarily responsible for the transport of carbohydrates (sugars) produced during photosynthesis from leaves to other parts of the plant where they are needed for growth or storage.
Locations:
Organized into vascular bundles within stems and leaves.
Visible in stem cross-sections (transverse sections) as distinct bundles containing both xylem and phloem, often arranged circularly.
Examples of plants where vascular tissues are prominent include the Saguaro cactus.
Examples of Plant Structures and Tissue Identification
Shoot Apex: Contains the apical meristem, leaf primordia (developing leaves), and axillary bud primordia (developing side branches).
Root Apex: Features the apical meristem of the root and a protective rootcap.
Stem Cross-Section (Transverse Section): Reveals the arrangement of dermal (epidermis), ground (cortex, pith), and vascular tissues (vascular bundles containing xylem and phloem).
Examples include Nerium oleander L. (Apocynaceae) and Garrya ovata Benth. (Garryaceae).
Practical Activity: Celery Stalk Dissection
Objective: To identify various plant tissues using a common celery stalk.
Procedure:
Make a series of transverse sections (cross-sections) of a celery stalk.
Closely examine these sections.
Identify as many of the stem tissues (dermal, ground, vascular) as possible.
Discussion points:
Are meristematic tissues present in the celery sample? If so, where are they located?
Of the four tissue types, which one likely makes up the largest and smallest proportions of the mass of the celery sample? (Typically, ground tissue forms the largest proportion, and meristematic tissue forms the smallest in a mature stalk section.)