Plant Cells and Tissues: Structure and Function

The Cells and Tissues of Plants

Plant Cell: Plant cells have eukaryotic cell structures except for the animal centrosome and possess a cell wall surrounding the membrane. They have chloroplasts and vacuoles.

Cell Types

Parenchymal Cells: These cells secrete substances and store hormones. They can undergo differentiation to perform specific functions, such as tracheids, which die and become woody vessels to circulate crude sap.

Simple and Complex Tissues

Tissues are groups of cells that perform a specific activity. They are classified according to the number of cell types (one or more) into simple and complex tissues.

• Simple Tissues: Parenchyma, collenchyma, and sclerenchyma.
• Complex Tissues: Formed by different cell types performing various functions, such as xylem, phloem, epidermis, and periderm.

Meristematic Tissue

Responsible for the growth and development of plants. Formed by living cells with small nuclei, large vacuoles, and thin cell walls, which do not prevent their growth or division. There are three types:

• Embryonic Meristems: Found in seeds, they form the embryo cells and originate different adult tissues.
• Primary or Apical Meristems: Located at the tips of roots (cap) and stems (bud), causing growth in length.
• Lateral Meristems: Form concentric layers along stems and roots, increasing the plant's thickness.

• Cambium: Produces xylem (wood vessels) towards the inside and phloem (liberian vessels) towards the outside.
• Phellogen: Forms parenchyma inward and cortical suber outward.

Tissue Systems

Systems extend throughout the plant, forming roots, stems, and leaves.

There are three systems:

Dermal System

A protective cover formed by the epidermis, found in plant parts with primary growth (leaves, roots, and young stems). The periderm replaces the epidermis in older parts with secondary growth.

• Surface: In leaves, stems, and young roots, it protects the plant from desiccation, allows water and mineral absorption through root hairs, and acts as a defense by releasing toxic substances through glandular hairs. It is formed by living cells, flat and without chloroplasts (colorless), which secrete substances in fruits. In arid climates, it is covered with a cuticle to prevent water loss.
• Stomata: Located in the epidermis, they allow CO2 entry for photosynthesis and O2 release. They consist of two guard cells that leave a hole (ostiole) connecting to the substomatal chamber.
• Hairs or Trichomes: Unicellular or multicellular structures with protective functions against dryness, absorption (roots), and defense (nettles).

Periderm: Forms the outer bark of stems and roots, protecting the plant from water loss and extreme temperatures. It consists of several layers of dead cells with air and suberin. It allows air passage through lenticels.