Plants are complex organisms with specialized tissues and organs. This section explores the various types of plant tissues, including meristematic, ground, dermal, and vascular tissues, each serving unique functions in plant growth and development.

The chapter also examines plant organs like roots, stems, and leaves, as well as reproductive structures such as flowers, fruits, and seeds. Understanding these components is crucial for grasping plant structure and function.

Plant Tissues

Meristematic Tissue

• Meristematic tissue consists of actively dividing cells responsible for plant growth
• Located at the tips of roots and shoots (apical meristems) and along the sides of stems and roots (lateral meristems)
• Apical meristems enable primary growth, increasing plant length
• Lateral meristems, such as the vascular cambium and cork cambium, enable secondary growth, increasing plant girth
• Meristematic cells are unspecialized and have thin cell walls, dense cytoplasm, and prominent nuclei

Ground Tissue

• Ground tissue makes up the bulk of the plant body and includes parenchyma, collenchyma, and sclerenchyma cells
• Parenchyma cells are the most common type of plant cell and perform various functions such as photosynthesis, storage, and secretion
  • They have thin cell walls and are often loosely packed, allowing for gas exchange
• Collenchyma cells provide structural support, particularly in growing shoots and leaves
  • They have unevenly thickened cell walls and are elongated
• Sclerenchyma cells also provide support and have thick, lignified secondary cell walls
  • Two types of sclerenchyma cells: fibers (elongated) and sclereids (irregular shape)

Dermal and Vascular Tissue

• Dermal tissue covers the surface of the plant and includes the epidermis and periderm
  • Epidermis is a single layer of cells that protects the plant and regulates gas exchange and water loss through stomata (tiny pores)
  • Periderm replaces the epidermis in woody plants and consists of the cork cambium, cork cells, and phelloderm
• Vascular tissue transports water, nutrients, and sugars throughout the plant
  • Xylem conducts water and dissolved minerals from roots to leaves and provides structural support with tracheids and vessel elements
  • Phloem transports sugars and other organic compounds from leaves to other plant parts using sieve tube elements and companion cells

Plant Organs

Roots

• Roots anchor the plant, absorb water and nutrients, and store food
• Root systems can be taproot (single main root) or fibrous (many small roots)
• Root hairs, extensions of epidermal cells, increase the surface area for absorption
• Root caps protect the apical meristem as the root grows through the soil
• Roots exhibit primary and secondary growth, with secondary growth resulting in a thickened root (carrots, beets)

Stems

• Stems support leaves and reproductive structures, transport substances between roots and shoots, and store food
• Herbaceous stems are soft and flexible (most annual plants), while woody stems are hard and rigid (trees and shrubs)
• Nodes are points of leaf attachment, and internodes are stem regions between nodes
• Vascular bundles in stems contain xylem and phloem arranged in various patterns (scattered in monocots, ring in dicots)
• Lenticels in woody stems allow for gas exchange

Leaves

• Leaves are the main photosynthetic organs of plants
• Leaf structure includes the blade (flat, expanded portion), petiole (stalk connecting blade to stem), and stipules (small appendages at the base of the petiole)
• Leaf arrangement can be alternate, opposite, or whorled
• Leaf venation patterns include parallel (monocots) and reticulate (dicots)
• Leaf anatomy consists of the epidermis, mesophyll (palisade and spongy), and vascular bundles

Reproductive Structures

Flowers

• Flowers are the reproductive structures of angiosperms (flowering plants)
• Four main parts: sepals (protective), petals (attractive), stamens (male, produce pollen), and carpels (female, contain ovules)
• Complete flowers have all four parts; incomplete flowers lack one or more parts
• Perfect flowers have both stamens and carpels; imperfect flowers have only stamens or only carpels
• Flower arrangement can be solitary or in inflorescences (clusters)

Fruits and Seeds

• Fruits develop from the ovary after fertilization and protect and disperse the seeds
• Types of fruits include simple (from a single ovary), aggregate (from multiple ovaries of a single flower), and multiple (from multiple flowers)
• Examples of fruits: berries (tomatoes, grapes), drupes (peaches, cherries), pomes (apples, pears), and nuts (acorns, walnuts)
• Seeds contain an embryo, stored food, and a protective coat
• Monocot seeds have one cotyledon (corn, wheat); dicot seeds have two cotyledons (beans, peas)
• Seed dispersal methods include wind, water, animals, and explosive dehiscence