Lecture Outline
Chapter 31: Plant Structure, Growth, and Differentiation

1. Plants exhibit similarity and diversity in structure and life span
   1. Roots, stems, leaves, flowers, and fruits make up the plant body
   2. The root system is typically below-ground, and the shoot system is the above-ground tissue, consisting of the stem, leaves, flowers, and fruits
      1. The root and shoot system is exposed to very different environmental conditions, but exists because plants require materials from both environments
2. The plant body is composed of cells and tissues
   1. Tissues of plants, like animal tissues, are composed of cells which form a structural unit
      1. Some tissues are simple (composed of only one type of cell), and others are complex (composed of more than one cell type)
      2. The three tissue systems of plants are the ground tissue system, the vascular tissue system (functions in conduction), and the dermal tissue system (functions in covering the body)
      3. Roots, stems, leaves, floral parts, and fruits are called organs as each is composed of different tissue types
      4. The tissue systems of the root and shoot systems are connected
   2. The ground tissue system is composed of three simple tissues
      1. The ground tissue system makes up the bulk of herbaceous plants
         1. Parenchyma, collenchyma, and sclerenchyma are differentiated based on their cell wall structure
         2. The primary cell is laid down first and it grows with the cell
         3. A secondary cell wall may be laid down internal to the primary cell wall
      2. Parenchyma cells have thin primary walls
         1. Parenchyma is a simple tissue composed of parenchyma cells
         2. The functions of parenchyma include storage, photosynthesis, and secretion
         3. Storage of starch, oil, water, and salts occurs in parenchyma
         4. Parenchyma cells are alive at maturity
      3. Collenchyma cells have unevenly thickened primary walls
         1. Collenchyma is also a simple tissue made of collenchyma cells
         2. Collenchyma provides support in soft plant organs
         3. Collenchyma cells are alive at maturity, and have uneven thickenings of the primary cell walls, particularly in the corners
      4. Sclerenchyma cells have both primary walls and thick secondary walls
         1. Sclerenchyma is a simple plant tissue composed of sclerenchyma cells specialized for support
         2. Sclerenchyma cells have secondary cell walls rich in lignin
         3. At maturity, sclerenchyma cells are often dead
         4. Sclerids are short, cubical cells found in nut shells and the pits of stone fruits
         5. Fibers are long cells found in clumps, common in the wood and bark of many angiosperms
   3. The vascular tissue system consists of two complex tissues
      1. The vascular tissue system is composed of xylem and phloem which are continuous in the root and shoot systems
      2. The conducting cells in xylem are tracheids and vessel elements
         1. Xylem conducts water and dissolved materials from the root to the shoot system and provides structural support
         2. In flowering plants, four types of cells make up the xylem
         3. Tracheids and vessel elements conduct fluid
            1. These cells are dead at maturity, and are hollow tubes
            2. Tracheids are the major components of xylem in gymnosperms
               1. Water passes from one tracheid to the next through pits in the cell walls
            3. Angiosperms have tracheids and vessel elements
               1. Vessel elements have a larger diameter and may be connected directly, end to end
               2. A stack of vessel elements is called a vessel
               3. Water may also pass laterally between vessel elements via pits
         4. Xylem also has fibers and parenchyma cells, which are not conducting cells
      3. Sieve tube members are the conducting cells of phloem
         1. Phloem conducts dissolved sugars throughout the plant, and provides support
         2. Phloem is a complex tissue composed of two types of conducting cells, plus fibers and parenchyma
         3. Dissolved sugars are conducted in sieve tube members
            1. Sieve tube members are stacked like vessel elements in tubes called sieve plates
            2. Sieve tube members have sieve plates
            3. Sieve tube members are alive at maturity, but most organelles have degenerated, including the nucleus
         4. Companion cells are adjacent to sieve tube members and direct the activities of both cells via cytoplasmic connections through plasmodesmata
   4. The dermal tissue system consists of two complex tissues
      1. The dermal tissue system is a single layer in herbaceous plants, and can be very thick in woody plants
      2. Epidermis is the outermost layer of cells of a herbaceous plant
         1. The epidermis is a complex tissue made of parenchyma cells with a small number of guard cells, and may contain outgrowths called trichomes
         2. The epidermis is typically one cell thick; the epidermal cells have thickened cell walls on the outer margin
         3. Epidermal cells are typically nonphotosynthetic, and are relatively transparent, allowing light to penetrate deeper tissues
         4. Epidermal tissue retards water loss with a waxy cuticle
         5. Stomata, surrounded by guard cells, allow diffusion of gases into and out of the leaf
         6. Trichomes are hairlike projections which function in increasing the effective surface area of the root (root hairs), salt excretion in halophytes, and may be protective in plants like nettles
      3. Epidermis is replaced by periderm in woody plants
         1. As a woody plant grows, the epidermis is lost and replaced by periderm
         2. Periderm is a complex tissue made of cork cells and cork parenchyma cells
         3. Cork cells are dead at maturity and function in waterproofing
         4. Cork parenchyma cells function in storage
3. Plants exhibit localized growth at meristems
   1. Growth includes mitosis, cell elongation, and cell differentiation
      1. Cell elongation occurs as the central vacuole fills with water
      2. Cell differentiation involves specialization into the different cell types
      3. Unlike animals, plants grow primarily in specialized areas known as meristems
         1. Cells in the meristems do not differentiate, and they retain the ability to divide
      4. Primary growth involves an increase in the length of a plant, and all plants grow this way
      5. Secondary growth involves an increase in the diameter of plant, and typically only gymnosperms and woody plants exhibit secondary growth
         1. Monocots lack true secondary growth
         2. Some herbaceous dicots exhibit secondary growth (such as the geranium)
   2. Primary growth takes place at apical meristems
      1. In the root of a plant, an apical meristem occurs just behind the root cap
         1. Behind the meristematic area, the area of cell elongation is marked by cells which are growing in size and beginning differentiation
      2. In the buds on the shoot system, a dome of meristematic cells forms an apical meristem
         1. Life primordia and bud primordia arise from this meristem
   3. Secondary growth takes place at lateral meristems
      1. Lateral meristems extend the length of stems and roots and have two meristematic areas
      2. The vascular cambium is a cylinder of meristematic cells between the wood and bark of a woody plant
         1. Cells of this cambium add to the wood (secondary xylem) and inner bark (secondary phloem)
      3. The cork cambium is a meristematic cylinder in the outer bark and cells produced here form the cork cells and cork parenchyma cells of the periderm
      4. Bark, therefore, can be defined as a living inner bark made of secondary phloem and a dead outer bark made of periderm