Plant Growth and Tissues

• Plants, or their shoots, exhibit upward growth, while roots grow downwards
• Plants start their life cycle by emerging from a seed
• The emergence of the first leaf or root marks an early stage of plant development
• A plant's length increases through primary growth
• A plant's width increases through secondary growth

Main Plant Tissues

• Dermal tissue forms the protective outer layer
• Vascular tissue contains several parts:
  • Epidermis as the outer layer
  • Mesophyll as the inner layer
  • Xylem and phloem
• Vascular tissue supports plant growth in stems and branches
• Ground tissue, which includes xylem and phloem, also serves as the skeleton of the plant
• Xylem transports water from the roots to the plant's upper parts
• Phloem transports food produced by photosynthesis to other areas.
• Ground tissue consists of epidermis, cortex, phloem, xylem, and pith in the inner center

Meristems

• Meristems are located at plant tips
• Primary or apical meristems include:
  • Shoot apex
  • Root apex
  • Procambium
  • Protoderm
  • Ground meristems
• Primary meristems facilitate length growth and produce emerging leaves/flowers in certain species
• Secondary/lateral meristems include:
  • Vascular cambium, which lies between procambium
  • Cork cambium, located between protoderm and ground meristem
• Secondary meristems enable width growth and active cell growth/division

Shoot Structure

• Lateral, apical, and ground meristems are part of the shoot structure

Root Structure

• Lateral, ground, and apical meristems are part of the root structure
• Root hairs and a root cap are also found in root structures
• The root cap protects the root
• The root cap is important because soil can be harsh and may damage roots
• The root cap is responsible for the roots' downward growth direction
• Without the root cap, roots may not grow correctly, growing sideways

Basic Plant Morphology

• Plants have two systems
  • The shoot system
  • The root system
• Plants have six organs:
  • Vegetative organs: root, stem, and leaf
  • Reproductive organs: flower, fruit, and seed

Plant Tissue Types

• Three basic tissue types:
  • Dermal (outer)
  • Ground (center)
  • Vascular (inner)
• Structure determines function

Simple Tissue

• Consists of one cell type
• Examples of simple tissue:
  • Dermal, which is made up of stomates/stomata and trichomes

Trichomes

• Trichomes are found in roots and stems
• Trichomes act as an extension of plants
• Trichomes help in efficiently capturing water and/or nutrients
• Some trichomes are visible to the naked eye
• Trichomes are "extra hands" for catching nutrients
  • Non-glandular trichomes
  • Glandular trichomes
• Root hairs help in capturing water and are found in roots only

Ground Tissue

• Parenchyma are thin-walled, alive at maturity, and multifaceted
• Parenchyma functions include:
  • Photosynthesis
  • Storage
  • Secretion (glands and trichomes)
  • Mitosis, which facilitates wound healing and cloning
  • Protection (epidermis)
• Collenchyma has unevenly thickened walls, with thickness variations
• Collenchyma is alive at maturity and mainly supports primary growth
• Sclerenchyma has evenly thickened cell walls and is dead at maturity
• Sclerenchyma provides strength, support, and protection
  • Fiber
  • Sclereid

Vascular Tissue

• Xylem mostly conducts water and nutrients
• Phloem mostly conducts sugars and amino acids or food

Complex Tissues

• Made up of more than one cell type
• Xylem comprises water-conducting tissue
  • Parenchyma
  • Vessels (big holes, where water goes in)
  • Tracheids (small holes, for efficient water transport)
  • Ray cells
• Phloems are food-conducting cells
  • Sieve-tube cells
  • Companion cells
  • Fibers
  • Parenchyma and ray cells
• Sieve-tube cells do not have a nucleus at maturity, but cytoplasm is present
• Periderm is a protective covering that is composed of cork and parenchyma
• Secretory structures produce and store latex, resin, nectar, and other substances in channels within the plant body

Vessel Member

• Vessel members are wider, shorter, thinner-walled, and less tapered
• Vessel members are aligned end-to-end, forming micropipes
• Vessel membranes have end walls with perforations

Tracheids

• Tracheids are long, thin cells with a tapered end
• The secondary wall of tracheids is hardened with lignin
• Water moves between cells through pits

Sieve-Tube Cell

• Consists of a sieve-tube member and companion cell
• A companion cell contains a nucleus because the sieve tube lacks its own nucleus
• Also contains a sieve plate