Plants are complex organisms with specialized structures for growth and survival. Their organ systems and tissues work together to perform essential functions like photosynthesis, nutrient transport, and structural support.

From roots to shoots, plants have evolved unique adaptations to thrive in diverse environments. Understanding their internal organization reveals how these remarkable organisms capture sunlight, absorb water and nutrients, and respond to environmental challenges.

Plant Organ Systems and Tissues

Structure and functions of plant organs

• Shoot system consists of above-ground portions of the plant including stems, leaves, and reproductive structures
  • Performs photosynthesis to convert light energy into chemical energy (glucose)
  • Facilitates gas exchange (CO2 uptake and O2 release) through stomata in leaves
  • Enables reproduction through flowers, fruits, and seeds (angiosperms) or cones (gymnosperms)
• Root system comprises below-ground portions of the plant including primary and lateral roots
  • Anchors the plant in the soil providing stability and support
  • Absorbs water and minerals (nutrients) from the soil
  • Stores carbohydrates and other organic compounds
  • Conducts water and minerals to the shoot system through xylem tissue

Meristematic vs permanent tissues

• Meristematic tissues are composed of undifferentiated cells capable of active cell division
  • Located in regions of active growth such as apical meristems (shoot and root tips) and lateral meristems (cambium)
  • Responsible for primary growth (elongation) and secondary growth (thickening) of the plant body
• Permanent tissues are composed of differentiated cells that have lost the ability to divide
  • Derived from meristematic tissues and specialized for specific functions
  • Include parenchyma (photosynthesis, storage), collenchyma (support), sclerenchyma (mechanical strength), xylem (water transport), and phloem (sugar transport)

Primary regions of plant growth

• Apical meristems are located at the tips of shoots and roots
  • Responsible for primary growth resulting in elongation of stems and roots
• Lateral meristems are located parallel to the sides of stems and roots
  • Include vascular cambium (produces secondary xylem and phloem) and cork cambium (produces bark)
  • Responsible for secondary growth resulting in thickening of stems and roots
• Intercalary meristems are located between mature tissues in certain monocots (grasses)
  • Responsible for internode elongation allowing for rapid growth after grazing or mowing

Roles of plant tissue types

• Dermal tissue forms the outer protective covering of the plant body
  • Composed of epidermis (primary growth) and periderm (secondary growth)
  • Protects against water loss, physical damage, and pathogens
  • Regulates gas exchange and transpiration through stomata
• Vascular tissue is composed of xylem and phloem
  • Xylem transports water and minerals from roots to shoots
  • Phloem transports sugars and other organic compounds from leaves to the rest of the plant
  • Provides structural support and mechanical strength
  • Found in vascular plants, which have specialized tissues for transporting water and nutrients
• Ground tissue fills spaces between dermal and vascular tissues
  • Includes parenchyma (photosynthesis, storage), collenchyma (support), and sclerenchyma (mechanical strength)
  • Performs various functions such as photosynthesis, storage of starch and other organic compounds, and support

Simple vs complex plant tissues

• Simple tissues are composed of a single cell type
  • Parenchyma consists of living, thin-walled cells that perform photosynthesis, store starch, and secrete compounds
  • Collenchyma consists of living, elongated cells with unevenly thickened walls that provide structural support
  • Sclerenchyma consists of dead cells with thick, lignified secondary walls that provide mechanical strength (fibers and sclereids)
• Complex tissues are composed of more than one cell type
  • Xylem includes tracheids and vessel elements (water transport), fibers (support), and parenchyma (storage)
  • Phloem includes sieve elements and companion cells (sugar transport), fibers (support), and parenchyma (storage)

Plant Cell Structure and Function

• Plant cells have unique structures that distinguish them from animal cells:
  • Cell wall provides structural support and protection
  • Chloroplasts contain chlorophyll and are the site of photosynthesis
  • Large central vacuole maintains turgor pressure and stores nutrients
• These structures work together to support plant growth, photosynthesis, and water regulation (transpiration)

Plant Growth Regulation

• Plant hormones play a crucial role in coordinating growth and development
  • Examples include auxins (cell elongation), cytokinins (cell division), and gibberellins (stem elongation)
  • Hormones regulate processes such as root and shoot growth, fruit ripening, and responses to environmental stimuli