The three plant tissue systems - dermal, ground, and vascular - each perform distinct and crucial functions for the plant's survival.
Dermal Tissue System
The dermal tissue system forms the outer protective layer of the plant. Its primary function is protection.
- Protection: It acts as a barrier against physical damage, pathogens, and excessive water loss. The epidermis, often covered in a waxy cuticle, helps prevent dehydration. Specialized cells like trichomes (leaf hairs) can deter herbivores or reflect sunlight.
- Gas Exchange: Stomata, pores in the epidermis surrounded by guard cells, regulate gas exchange (carbon dioxide intake for photosynthesis and oxygen release) and transpiration (water loss).
- Water and Nutrient Absorption (Roots): In roots, the epidermis has root hairs, which greatly increase the surface area for water and nutrient absorption from the soil.
Ground Tissue System
The ground tissue system makes up the bulk of the plant and performs various functions depending on the location and type of ground tissue cells.
- Photosynthesis: Parenchyma cells in the mesophyll of leaves are the primary site of photosynthesis. These cells contain chloroplasts, which capture sunlight and convert it into chemical energy.
- Storage: Ground tissue, particularly in roots and stems, can store carbohydrates (starch), water, and other nutrients. Parenchyma cells are often specialized for storage.
- Support: Collenchyma and sclerenchyma cells provide structural support to the plant. Collenchyma cells have thickened cell walls and are flexible, allowing the plant to bend without breaking. Sclerenchyma cells have very thick, rigid cell walls and provide strong support.
- Wound Repair: Parenchyma cells can divide and differentiate to repair wounds and regenerate damaged tissues.
Vascular Tissue System
The vascular tissue system transports water, minerals, and sugars throughout the plant. It consists of two main types of vascular tissues: xylem and phloem.
- Water and Mineral Transport (Xylem): Xylem transports water and dissolved minerals from the roots to the rest of the plant. The cells of xylem are dead at maturity, forming hollow tubes. Water moves through xylem via transpiration pull (evaporation from leaves) and cohesion-tension.
- Sugar Transport (Phloem): Phloem transports sugars (produced during photosynthesis) from source tissues (e.g., leaves) to sink tissues (e.g., roots, developing fruits) where they are used for growth and storage. The cells of phloem are alive at maturity, and sugars are transported via pressure flow.
In summary, the dermal tissue protects the plant, the ground tissue performs photosynthesis, storage, and support, and the vascular tissue transports water, minerals, and sugars.
