Plant tissues

• The epidermis is the outermost layer of cells that covers all plant organs.
• Principal parts of a flowering plant:

  • Root: part of the plant axis found beneath the soil, absorbs water and minerals, stores, and anchors
  • Stem: conducts water and minerals, conducts food materials, supports leaves, stores food, may manufacture food
  • Leaf: outgrowth of the stem, flat and thin, green due to chlorophyll, functions closely with chlorophyll, stores food materials
  • Sexual Reproductive Structures: flowers and cones in more complex plants, continuation of the stem with specialized structures

  
• Trichomes are small, white bumps found on plants, serving functions like protecting from pests and diseases, and regulating the plant's temperature

  
• Factors influencing plant growth and development:

  • Water supply
  • Temperature
  • Minerals in the soil
  • Light
  • Oxygen and carbon dioxide supply
  • Presence of parasites or herbivores
• Meristematic tissue is responsible for plant growth, found in root tips, stem tips, and buds

  
• Meristematic tissues:

  • Actively dividing cells
  • Continually produce new cells
  • Consist of apical meristems, lateral meristem, and intercalary meristem
• Types of plant life spans:

  • Annuals: grow for one season only
  • Biennials: grow vegetatively for the first season, produce seeds in the second year
  • Perennials: grow for several to many years, producing seeds yearly after initial growth
• Apical meristems:

  • Located at the tips of roots and stems
  • Cells are isodiametric and cubical
  • Develop protoderm, ground meristem, and procambium
• Lateral meristem:

  • Increases plant girth or diameter
  • Includes vascular cambium and cork cambium
• Vascular cambium:

  • Located between bark and wood
  • Consists of fusiform and ray initials that produce new cells
• Cork cambium:

  • Develops protective cork layers if the plant is damaged
• Intercalary meristems:

  • Found at the base of each leaf in monocotyledon plants
  • Cause rapid elongation in plants like wheat and barley
• Permanent tissues:

  • Simple permanent tissues: composed of one kind of cell
  • Complex permanent tissues: composed of several types of cells working together
• Plant tissue systems include meristematic tissues and permanent tissues

  
• Root and shoot apical meristems are regions where new cells are produced

  
• Root apical meristem gives rise to the epidermis, cortex, endodermis, xylem, and phloem

  
• Simple permanent tissues are mostly composed of only one kind of cell, uniform in function and structure

  
• Parenchyma:

  • Most abundant cell type found in all major parts of plants
  • Cells are more or less spherical when newly produced, assuming various shapes when mature
  • Usually big and thin-walled with large vacuoles and air spaces in between
  • Known as aerenchyma if it has extensive connected air spaces, chlorenchyma if it contains numerous chloroplasts
  • Functions as food and waste storage, found in edible parts of most fruits and vegetables
• Collenchyma:

  • Composed of thick-walled cells of uneven thickness
  • Often occur just beneath the epidermis
  • Cells are longer than they are wide, pliable and strong
  • Usually smaller than parenchyma cells
• Sclerenchyma:

  • Cells are thick and tough-walled, usually impregnated with lignin
  • Functions as supporting tissues in plants
  • Two types: Sclereids (stone cells) and Fibers
• Epidermis:

  • Usually one cell in thickness, forms the surface layers of leaves, flowers, young stem, and roots
  • Outer walls are covered and impregnated with cutin, a fatty material
  • Contains stomata (stoma) for gas exchange and trichomes for protection
• Cork:

  • Composed of cells with walls impregnated with suberin, a fatty material
  • Forms a waterproof layer of tissue, found in outer layers of stems and roots of woody plants
  • Functions in water conservation and protection
• Secretory tissues:

  • Composed of cells that produce hormones or waste products
  • Examples include nectar in flowers, oil in citrus, menthol in mint leaves, latex, and resins in pine trees
• Complex permanent tissues occur in definite positions in a plant's body and are associated with specific functions
• Xylem:

  • Concerned with transporting water and minerals
  • Composed of 4 cell types: Xylem fibers, Xylem parenchyma, Vessels, and Tracheids
  • Tracheids and vessel elements make up the tracheary elements of xylem
• Phloem:

  • Responsible for transporting food manufactured by leaves to all plant parts
  • Composed of companion cells, Phloem fibers, Phloem parenchyma, and Sieve tube elements with sieve plates