Plant Tissues - Lesson 1

• Cells are the fundamental units of life, arranged into tissues, and in plants, tissues are arranged into tissue systems
• Histology is the study of tissues
• Development of the plant body involves division, enlargement, differentiation of cells, and organization into specialized complexes like tissues and systems of tissues
• Growth in plants involves permanent or irreversible increase in number, size, and volume of cells, accompanied by cell differentiation, elongation, and development
• Cell differentiation is the process where cells undergo biochemical and structural changes for specialized functions
• Embryo of a seed plant has limited parts compared to the adult plant
• Primary growth is the initial growth of successively formed roots and vegetative and reproductive shoots, initiated by apical meristems
• Secondary growth involves an increase in stem and root thickness
• Diffuse secondary growth involves cells of the ground tissue not localized in a specific region or brought about by a special meristem
• Cambial secondary growth depends on the production of cells by a cambium, leading to an increase in stem and root diameter
• Periderm is a secondary tissue system assuming a protective function when the primary epidermal layer is disrupted during secondary increase in thickness
• Protective tissue covers the surface of leaves and living cells of roots and stems, with flattened cells parallel on top and bottom surfaces
• Epidermis is a single layer of closely packed cells that covers and protects the plant, secreting a cuticle to retain water
• Periderm/bark replaces the epidermis in plants undergoing secondary growth, consisting of cork cells to protect the plant
• Stomata are microscopic pores on plant surfaces surrounded by guard cells, regulating gas exchange
• Bulliform cells in grasses cause leaf rolling to conserve water in hot and dry conditions
• Trichomes are outgrowths of epidermal cells found in various plant parts, serving protective functions and nutrient absorption in carnivorous plants
• Root hairs are specialized for absorbing water and minerals from soil, increasing the absorptive surface of roots
• Meristems are tissues where cells are constantly dividing, producing new cells
• Apical meristems occur at the tips of roots and shoots, responsible for length-wise extension of the plant body through primary growth
• Primary meristems produce cells that form the primary tissues of a plant
• Types of Primary Meristems:

  • Protoderm: gives rise to the outer protective coating of the plant (dermal tissue system)
  • Procambium: gives rise to the vascular tissue system
  • Ground meristem: gives rise to the ground tissue system
• Origin of plant tissues:

  • Apical meristem
  • Protoderm
  • Ground meristem
  • Procambium
  • Epidermis
  • Cortex
  • Pith/Pith rays
  • Phloem
  • Xylem
• Lateral meristems are cylinders of meristematic cells in woody stems and roots, responsible for secondary growth and the increase in girth or diameter of plants
• Two types of cambia:

  • Vascular cambium: gives rise to secondary vascular tissue and produces wood
  • Cork cambium: found in woody plants, produces the outer bark
• Intercalary meristems are found in grasses and related plants, responsible for increases in length and the regrowth of cut grass
• Ground tissue synthesizes organic compounds, supports the plant, and provides storage; it includes parenchyma, collenchyma, and sclerenchyma cells
• Parenchyma cells are unspecialized, can photosynthesize or store starch, and are found in leaves, roots, and stems
• Collenchyma cells provide flexible support for organs like leaves and flower parts, and are living at maturity
• Sclerenchyma cells lack protoplasts at maturity, provide strength and support, and can occur as fibers or sclereids
• Xylem conducts water and minerals from roots to other plant organs, while phloem conducts metabolites, amino acids, and sugars from production sites to consumption sites
• Collenchyma cells are thick-walled, living cells that provide structural support and flexibility.
• Some plants have specialized epidermal structures such as trichomes (hairs) and stomata (pores).
• Some plants have specialized epidermal cells called guard cells that regulate gas exchange through stomata.
• Parenchyma cells are simple thin-walled cells that make up most of the plant body and perform photosynthesis, food storage, and secretion of substances.
• Epidermal cells are usually thin-walled, with no chloroplasts or other organelles associated with photosynthesis.
• The epidermis is the outermost layer of cells that covers all plant parts.
• Meristematic cells are undifferentiated cells that continuously divide to produce new cells for growth.
• Sclerenchyma cells have lignified cell walls and no protoplasm at maturity, providing rigidity and protection.
• Vascular tissues include xylem (water conduction) and phloem (nutrient transport).